No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Airborne observations of the tropospheric CO2 distribution and its controlling factors over the South Pacific Basin
Abstract
Highly precise measurements of CO2 mixing ratios were recorded aboard both the NASA DC-8 and P3-B aircraft during the Pacific Exploratory Mission-Tropics conducted in August-October 1996. Data were obtained at altitudes ranging from 0.1 to 12 km over a large portion of the South Pacific Basin representing the most geographically extensive CO2 data set recorded in this region. These data along with CO2 surface measurements from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) and the National Institute of Water and Atmospheric Research (NIWA) were examined to establish vertical and meridional gradients. The CO2 spatial distribution in the southern hemisphere appeared to be largely determined by interhemispheric transport as air masses with depleted CO2 levels characteristic of northern hemispheric air were frequently observed south of the Intertropical Convergence Zone. However, regional processes also played a role in modulating background concentrations. Comparisons of CO2 with other trace gases indicated that CO2 values were influenced by continental sources. Large scale plumes from biomass burning activities produced enhanced CO2 mixing ratios within the lower to midtroposphere over portions of the remote Pacific. An apparent CO2 source was observed in the NOAA/CMDL surface data between 15°N and 15°S and in the lower altitude flight data between 8°N and 8.5°S with a zone of intensity from 6.5°N to 1°S. Inferred from these data is the presence of a Southern Ocean sink from south of 15°S having two distinct zones seasonally out of phase with one another.
... Recently, spectroscopic techniques have become more robust and have started to be routinely deployed on airborne platforms due to their faster time response. These techniques include non-dispersive infrared absorption (NDIR), for the detection of CO 2 (Vay et al., 1999;Daube et al., 2002); and both direct laser absorption spectroscopy and cavity ring-down spectroscopy (CRDS, Chen et al., 2010) for the detection of CO 2 , CH 4 and other trace species. ...
... These could be determined by drying the air sample before it is analysed. Previously, this approach has been employed successfully for airborne measurements of CO 2 and CH 4 using a combination of a Nafion dryers and dry-ice traps (Vay et al., 1999;Daube et al., 2002;Peischl et al., 2010). However, we have found that even when using the Nafion dryer, measured water vapour levels in the air sample were not sufficiently low to remove the aforementioned effects. ...
... The performance of the system was found to be no worse when the dryer was used (11 July 2011-23 July 2011) compared to those flights when it was not (24 November 2011-3 May 2012). The lack of deviation between the measured target mixture and its calibration suggests that permeation of CO 2 and CH 4 through the membrane is small, which is in agreement with work by other groups (Vay et al., 1999). ...
High-resolution CH4 and CO2 measurements were made
on board the FAAM BAe-146 UK (Facility for Airborne Atmospheric
Measurements, British Aerospace-146) atmospheric research aircraft
during a number of field campaigns. The system was based on an infrared
spectrometer using the cavity-enhanced absorption spectroscopy
technique. Correction functions to convert the mole fractions retrieved
from the spectroscopy to dry-air mole fractions were derived using
laboratory experiments and over a 3 month period showed good stability.
Long-term performance of the system was monitored using WMO (World
Meteorological Office) traceable calibration gases. During the first
year of operation (29 flights) analysis of the system's in-flight
calibrations suggest that its measurements are accurate to 1.28 ppb
(1σ repeatability at 1 Hz = 2.48 ppb) for CH4 and 0.17
ppm (1σ repeatability at 1 Hz = 0.66 ppm) for CO2. The
system was found to be robust, no major motion or altitude dependency
could be detected in the measurements. An inter-comparison between
whole-air samples that were analysed post-flight for CH4 and
CO2 by cavity ring-down spectroscopy showed a mean difference
between the two techniques of -2.4 ppb (1σ = 2.3 ppb) for
CH4 and -0.22 ppm (1σ = 0.45 ppm) for CO2.
In September 2012, the system was used to sample biomass-burning plumes
in Brazil as part of the SAMBBA project (South AMerican Biomass Burning
Analysis). From these and simultaneous CO measurements, emission factors
for savannah fires were calculated. These were found to be 2.2 ±
0.2 g (kg dry matter)-1 for CH4 and 1710 ±
171 g (kg dry matter)-1 for CO2, which are in
excellent agreement with previous estimates in the literature.
... of the 20th century (Etheridge et al., 1998). In more recent times the growth rate 2 AMTD Abstract 10 AMTD 6, 1-41Abstract the membrane is small, which is in agreement with work by other groups (Vay et al., 1999). 18 AMTD 6, 1-41Abstract 25 CO 2 and CH 4 during the filling period and as a measure of the uncertainty during the sample period. ...
... These could be 13 Introduction determined by drying the air sample before it is analysed. Previously, this approach has been employed successfully for airborne measurements of CO 2 and CH 4 using a combination of a Nafion dryers and dry ice traps (Vay et al., 1999;Daube et al., 2002;Peischl et al., 2010). However, we have found that even when using the Nafion dryer, measured water vapour levels in the air sample were not sufficiently low to remove the 5 aforementioned effects. ...
High-resolution CH4 and CO2 measurements were made
onboard the FAAM BAe 146 UK atmospheric research aircraft during a
number of field campaigns. The system was based on an infrared
spectrometer using the cavity enhanced absorption spectroscopy
technique. Correction functions to convert the mole fractions retrieved
from the spectroscopy to dry air mole fractions were derived using
laboratory experiments and over a 3 month period showed good stability.
Long-term performance of the system was monitored using WMO traceable
calibration gases. During the first year of operation (29 flights)
analysis of the system's in-flight calibrations suggest that its
measurements are accurate to -0.07 ppbv (1 σ precision at 1 Hz =
2.48 ppbv) for CH4 and -0.06 ppmv (1 σ precision at 1
Hz = 0.66 ppmv) for CO2. The system was found to be very
robust, no major motion or altitude dependency could be detected in the
measurements. An inter-comparison between whole air samples that were
analysed post-flight for CH4 and CO2 by cavity
ring down spectroscopy showed a mean difference between the two
techniques of -2.4 ppbv (1 σ = 2.3 ppbv) for CH4 and
-0.22 ppmv (1 σ = 0.45 ppmv) for CO2. In September
2012, the system was used to sample biomass burning plumes in Brazil as
part of the SAMBBA project (South American biomass burning analysis).
From these and simultaneous CO measurements, emission factors for
savannah fires were calculated. These were found to be 2.2 ± 0.2
g (kg dry matter)-1 for CH4 and 1710 ± 171
g (kg dry matter)-1 for CO2, which are in
excellent agreement with previous estimates in the literature.
... Thouret et al. [6], have shown that there is a high probability of observing more than one layered structure above the boundary layer at any time. An example of the observations of several CO 2 layers using an in situ gas analyzer (LI-COR 6252, [7]) is given in across the US. The airborne in situ CO 2 measurements were made at several level altitude legs and during ascent and descent segments. ...
... TESTING AND VALIDATION After the DIAL system is integrated its performance will be tested by conducting comparisons with a well calibrated ground-based in situ gas analyzer (LI-COR 6252, [7]) at NASA Langley. A fully tested deployable system will be validated by conducting intensive comparisons using ground, tower and airborne LI-COR 7000 sensors at the ARM site in central Oklahoma, or a future NOAA-CMDL tall tower site. ...
Abstract-NASA ESTO’s Instrument Incubator Program has funded ,a 3 year program ,to develop ,a ground-based ,2- micron,Differential Absorption Lidar (DIAL) CO2 profiling system. This technology development program, towards the eventual development of a space-based DIAL system, involves the design, development, evaluation, and fielding of a ground- based CO2profiling system applicable to atmospheric boundary layer studies. This DIAL system ,leverages ,2-micron laser technology developed ,under a number ,of NASA programs ,to develop,new ,solid-state YLF laser technology ,that provides high pulse energy, tunable, wavelength-stabilized, and double- pulsed lasers that are operable over pre-selected temperature insensitive strong CO2absorption lines suitable for profiling of lower,tropospheric ,CO2. It also ,incorporates ,new ,high quantum efficiency, high gain, and high signal-to-noise ratio AlGaAsSb/InGaAsSb phototransistors, and a new receiver/signal processor ,system ,to cover ,a large ,signal dynamic,range with minimum,signal distortions to achieve high precision DIAL measurements. This CO2 profiling system can beused,as a ,validation tool of the ,OCO (Orbiting Carbon Observatory). In situ sensor system calibration is in progress at Pennsylvania State University for the evaluation of the ,DIAL
... Systematic measurement of the atmospheric CO 2 is one of the most promising methods for determining the distribution and magnitude of natural sources and sinks [e.g., Conway et al., 1994;Keeling et al., 1995;Francey et al., 1995;Nakazawa et al., 1997]. Most of the CO 2 monitoring has been conducted at the surface sites, but limited CO 2 measurements have been carried out in the free troposphere [Pearman and Beardsmore, 1984;Nakazawa et al., 1991Nakazawa et al., , 1993Matsueda and Inoue, 1996;Anderson et al., 1996;Francey et al., 1999;Vay et al., 1999]. ...
... The continuous CO 2 measurements carried out during the PEM-West A aircraft campaign in 1991 did not show a clear interhemispheric difference in the upper troposphere, even though they flew in September at similar longitudes [Anderson et al., 1996]. Aircraft measurements of CO 2 during the PEM-T campaign found that SPCZ acted as an effective barrier to meridional transport only at lower altitudes over the south Pacific, in August -October 1996 [Vay et al., 1999]. In the upper troposphere, they showed evidence of Northern Hemispheric air being transported to the Southern Hemisphere. ...
The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream-II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September–October 1998. The vertical distribution of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N–7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north-south boundary in the upper troposphere during BIBLE A was located around 2°N–7°N as the boundary is not necessary a permanent feature.
... In this paper, we describe the operation and calibration of the ER-2 and balloon CO 2 instruments and the modifications required for tropospheric sampling. We also present results from three intercomparison flights, when the ER-2 and balloon instruments were flown nearly simultaneously, and the results of an intercomparison flight between the ER-2 instrument and the NASA Langley Research Center (LaRC) CO 2 analyzer flown on the NASA DC-8 (Anderson et al. 1996;Vay et al. 1999). ...
... An independently developed in situ CO 2 analyzer from LaRC has been flown on the NASA DC-8 aircraft since 1991 (Anderson et al. 1996;Vay et al. 1999). An in-flight intercomparison between the DC-8 and ER-2 payloads during the ER-2 STRAT experiment and the DC-8 Vortex Ozone Transport Experiment indicated that the CO 2 instruments agreed to 0.14 ppmv on a flight leg at 10.7 km, but that there was a systematic difference of 0.44 ppmv on a second flight leg at 11.9 km with the ER-2 instrument reporting higher values (Weinheimer et al. 1998). ...
Two in situ CO2 analyzers have been developed for deployment on the NASA ER-2 aircraft and on stratospheric balloons. The ER-2 instrument has had more than 150 flights during 21 deployments from 1992 to 2000, resulting in a dataset with nearly pole-to-pole coverage that includes data from all seasons in both hemispheres except austral summer. In-flight calibrations show that the typical long-term (i.e., flight-to-flight) precision of the instruments is better than ±0.1 ppmv. The flight standards are traceable to standards held by the Scripps Institute of Oceanography and the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory. The balloon instrument has had eight balloon flights since September 1996, providing the first in situ observations of CO2 above ∼21 km. In addition, the balloon instrument has been flown on board a Cessna Citation II aircraft for sampling between the surface and 10 km. In this paper, the instrumentation and calibration procedures for both instruments are described in detail. An intercomparison of the two instruments during the Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) project showed that, on average, the instruments agreed to within 0.05 ppmv.
... These DIAL measurements are compared with in situ gas analyzer (LI-COR 6252, [10]) and are shown in Fig. 3. Offset between two caused by uncertainty in our knowledge of the spectroscopic constants. This problem is being addressed [10]. ...
... These DIAL measurements are compared with in situ gas analyzer (LI-COR 6252, [10]) and are shown in Fig. 3. Offset between two caused by uncertainty in our knowledge of the spectroscopic constants. This problem is being addressed [10]. The two sensors show the same trend and occurrence of CO 2 perturbations and DIAL data show excellent precision. ...
Technology developments are in progress towards the development of a Differential Absorption Lidar (DIAL) to measure range-resolved and column amounts of atmospheric CO2 . This system is also capable of providing high-resolution aerosol profiles and cloud distributions. It is being developed as part of the NASA ESTO Instrument Incubator Program (IIP). The long-term goal of this work is the development of a space-based DIAL system. The IIP effort involves the design, development, evaluation, and fielding of a ground-based CO2 profiling system. A successful outcome of this development will be an instrument capable of making measurements in the lower troposphere and boundary layer where the sources and sinks of CO2 are located. It will also be a valuable tool for contributing to the validation of space-based measurements of column CO2 from NASA's Orbiting Carbon Observatory (OCO) and for participation in the North American Carbon Program (NACP) regional intensive field campaigns. The system can also be used as a test-bed for the evaluation of lidar technologies for space-application. This DIAL system leverages 2-micron laser technology developed under a number of NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO2 absorption lines suitable for profiling of lower tropospheric CO2. It also incorporates new high quantum efficiency, high gain, and high signal-to- noise ratio phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. In situ sensor system calibration is in progress at Pennsylvania State University for field evaluation of the DIAL system in 2008. High-resolution laser spectroscopic measurements are being conducted at the Jet Propulsion Laboratory to characterize line parameters of the temperature insensitive line to be used for DIAL measurements. Atmospheric tests of the laser have been conducted by operating it locked to the CO2 absorption line center, with offset locking in the side-line mode, and in the off-line position. The reference laser is locked to center of absorption line within 390 kHz. This improves the level of stabilization improved by factor of 10 compared to earlier configuration. The detector has been characterized in the laboratory and has been evaluated by conducting atmospheric tests at NCAR, Boulder, Colorado. The receiver uses an F2.2 all aluminum 16" diameter telescope and optical design focuses light onto a 200-micron detector. Design, development, atmospheric testing, and performance evaluation associated with the development of this DIAL system are presented in this paper.
... All measurements employed in this study were acquired on the NASA DC-8 aircraft and include (1) fast (1-s) CH 2 O and ethane (C 2 H 6 ) measurements from the University of Colorado CAMS instrument (Richter et al., 2015), (2) University of California Irvine WAS measurements of 33 VOCs employing 2-L conditioned stainless steel electropolished canisters followed by laboratory multicolumn gas chromatography analysis employing various detectors (flame ionization detector, electron capture detector, and mass spectrometry; Simpson et al., 2020, and references therein), (3) California Institute of Technology CIMS measurements of AHNs (Teng et al., 2015), (4) University of Oslo proton transfer reaction time-of-flight mass spectrometric 1-s measurements (hereafter referred to as PTRMS) of benzene and toluene (Müller et al., 2004), (5) various tracer measurements to determine the planetary boundary layer (PBL) height, including differential absorption carbon monoxide (CO) measurements (DACOM) of CO and methane (Diskin et al., 2014), nondispersive infrared (IR) spectrometer measurements of CO 2 (Vay et al., 1999), diode laser hygrometer measurements of water vapor (Diskin et al., 2002), airborne differential absorption lidar/high spectral resolution lidar (HSRL) using aerosol backscatter (Hair et al., 2008), measurements of oxides of nitrogen (NO x ¼ NO 2 þNO) employing the National Center for Atmospheric Research (NCAR) four-channel chemiluminescence detector instrument (Weinheimer et al., 1994), Georgia Institute of Technology CIMS measurements of SO 2 (Huey et al., 2004), and various DC-8 aircraft parameter measurements. All measurements can be found at http:// doi.org/10.5067/Suborbital/KORUSAQ/DATA01, ...
Environmental Research embarked on the Korea-United States Air Quality (KORUS-AQ) study to address air quality issues over the Korean peninsula. Underestimation of volatile organic compound (VOC) emissions from various large facilities on South Korea's northwest coast may contribute to this problem, and this study focuses on quantifying top-down emissions of formaldehyde (CH 2 O) and VOCs from the largest of these facilities, the Daesan petrochemical complex, and comparisons with the latest emission inventories.To accomplish this and additional goals discussed herein, this study employed a number of measurements acquired during KORUS-AQ onboard the NASA DC-8 aircraft during three Daesan overflights on June 2, 3, and 5, 2016, in conjunction with a mass balance approach. The measurements included fast airborne measurements of CH 2 O and ethane from an infrared spectrometer, additional fast measurements from other instruments, and a suite of 33 VOC measurements acquired by the whole air sampler. The mass balance approach resulted in consistent top-down yearly Daesan VOC emission flux estimates, which averaged (61 + 14) Â 10 3 MT/year for the 33 VOC compounds, a factor of 2.9 + 0.6 (+1.0) higher than the bottom-up inventory value. The top-down Daesan emission estimate for CH 2 O and its four primary precursors averaged a factor of 4.3 + 1.5 (+ 1.9) times higher than the bottom-up inventory value. The uncertainty values in parentheses reflect upper limits for total uncertainty estimates. The resulting averaged top-down Daesan emission estimate for sulfur dioxide (SO 2) yielded a ratio of 0.81-1.0 times
... All measurements employed in this study were acquired on the NASA DC-8 aircraft and include (1) fast (1-s) CH 2 O and ethane (C 2 H 6 ) measurements from the University of Colorado CAMS instrument (Richter et al., 2015), (2) University of California Irvine WAS measurements of 33 VOCs employing 2-L conditioned stainless steel electropolished canisters followed by laboratory multicolumn gas chromatography analysis employing various detectors (flame ionization detector, electron capture detector, and mass spectrometry; Simpson et al., 2020, and references therein), (3) California Institute of Technology CIMS measurements of AHNs (Teng et al., 2015), (4) University of Oslo proton transfer reaction time-of-flight mass spectrometric 1-s measurements (hereafter referred to as PTRMS) of benzene and toluene (Müller et al., 2004), (5) various tracer measurements to determine the planetary boundary layer (PBL) height, including differential absorption carbon monoxide (CO) measurements (DACOM) of CO and methane (Diskin et al., 2014), nondispersive infrared (IR) spectrometer measurements of CO 2 (Vay et al., 1999), diode laser hygrometer measurements of water vapor (Diskin et al., 2002), airborne differential absorption lidar/high spectral resolution lidar (HSRL) using aerosol backscatter (Hair et al., 2008), measurements of oxides of nitrogen (NO x ¼ NO 2 þNO) employing the National Center for Atmospheric Research (NCAR) four-channel chemiluminescence detector instrument (Weinheimer et al., 1994), Georgia Institute of Technology CIMS measurements of SO 2 (Huey et al., 2004), and various DC-8 aircraft parameter measurements. All measurements can be found at http:// doi.org/10.5067/Suborbital/KORUSAQ/DATA01, ...
The U.S. National Aeronautics and Space Administration in partnership with Korea’s National Institute of Environmental Research embarked on the Korea-United States Air Quality (KORUS-AQ) study to address air quality issues over the Korean peninsula. Underestimation of volatile organic compound (VOC) emissions from various large facilities on South Korea’s northwest coast may contribute to this problem, and this study focuses on quantifying top-down emissions of formaldehyde (CH2O) and VOCs from the largest of these facilities, the Daesan petrochemical complex, and comparisons with the latest emission inventories. To accomplish this and additional goals discussed herein, this study employed a number of measurements acquired during KORUS-AQ onboard the NASA DC-8 aircraft during three Daesan overflights on June 2, 3, and 5, 2016, in conjunction with a mass balance approach. The measurements included fast airborne measurements of CH2O and ethane from an infrared spectrometer, additional fast measurements from other instruments, and a suite of 33 VOC measurements acquired by the whole air sampler. The mass balance approach resulted in consistent top-down yearly Daesan VOC emission flux estimates, which averaged (61 ± 14) × 103 MT/year for the 33 VOC compounds, a factor of 2.9 ± 0.6 (±1.0) higher than the bottom-up inventory value. The top-down Daesan emission estimate for CH2O and its four primary precursors averaged a factor of 4.3 ± 1.5 (± 1.9) times higher than the bottom-up inventory value. The uncertainty values in parentheses reflect upper limits for total uncertainty estimates. The resulting averaged top-down Daesan emission estimate for sulfur dioxide (SO2) yielded a ratio of 0.81–1.0 times the bottom-up SO2 inventory, and this provides an important cross-check on the accuracy of our mass balance analysis.
... [18] The observed vertical distribution of CO 2 is an important indicator of the coupling between flux and transport processes influencing the CO 2 concentration field as much pollution transport takes place in the free troposphere [Vay et al., 1999[Vay et al., , 2003Choi et al., 2008] at heights typically unattainable by the surface monitoring network. Vertical profiling by aircraft aids the interpretation of surface observations by linking the surface with the boundary layer and free troposphere. ...
High-resolution in situ CO_2 measurements were conducted aboard the NASA DC-8 aircraft during the ARCTAS/POLARCAT field campaign, a component of the wider 2007–2008 International Polar Year activities. Data were recorded during large-scale surveys spanning the North American sub‐Arctic to the North Pole from 0.04 to 12 km altitude
in spring and summer of 2008. Influences on the observed CO_2 concentrations were investigated using coincident CO, black carbon, CH_3CN, HCN, O_3, C_2Cl_4, and Δ^(14)CO_2 data, and the FLEXPART model. In spring, the CO_2 spatial distribution from 55°N to 90°N was largely determined by the long-range transport of air masses laden with Asian
anthropogenic pollution intermingled with Eurasian fire emissions evidenced by the greater variability in the mid-to-upper troposphere. At the receptor site, the enhancement ratios of CO_2 to CO in pollution plumes ranged from 27 to 80 ppmv ppmv^(−1) with the highest anthropogenic content registered in plumes sampled poleward of 80°N. In summer, the CO_2 signal largely reflected emissions from lightning-ignited wildfires within the boreal forests of
northern Saskatchewan juxtaposed with uptake by the terrestrial biosphere. Measurements within fresh fire plumes yielded CO_2 to CO emission ratios of 4 to 16 ppmv ppmv^(−1) and a mean CO_2 emission factor of 1698 ± 280 g kg^(−1) dry matter. From the ^(14)C in CO_2 content of 48 whole air samples, mean spring (46.6 ± 4.4‰) and summer (51.5 ± 5‰) Δ^(14)CO_2 values indicate a 5‰ seasonal difference. Although the northern midlatitudes were identified as the emissions source regions for the majority of the spring samples, depleted Δ^(14)CO_2 values were observed in <1% of the data set. Rather, ARCTAS Δ^(14)CO_2 observations (54%) revealed predominately a pattern of positive disequilibrium (1–7‰) with respect to background regardless of season owing to both heterotrophic respiration and fire-induced combustion of biomass. Anomalously enriched Δ^(14)CO_2 values (101–262‰) measured
in emissions from Lake Athabasca and Eurasian fires speak to biomass burning as an increasingly important contributor to the mass excess in Δ^(14)CO_2 observations in a warming
Arctic, representing an additional source of uncertainty in the quantification of fossil fuel CO_2.
... The WMO has recommended that measurements of CO 2 and CH 4 at 1 Hz frequency should be within (1 σ) 0.66 ppmv for CO 2 and (1 σ) 2.48 ppbv CH 4 (WMO 2009;WDCGG 2013), with the WMO/GAW Central Calibration Laboratories (CCL) providing calibration gases for CO 2 and CH 4 at NOAA-ESRL to facilitate such highly precise observations. Advancements in instrument technology involving techniques, like non-dispersive infrared absorption for detecting CO 2 (NDIR, Vay et al. 1999) and cavity ring-down spectroscopy (CRDS) for the detection of CO 2 and CH 4 (Chen et al. 2010;Tuzson et al. 2010), have certainly improved the accuracy of measurements. ...
An enhanced performance model of the greenhouse gas analyser (GGA) instrument from Los Gatos Research (LGR), which uses off-axis integrated cavity output spectroscopy (OA-ICOS) technology to obtain highly precise and accurate measurements, has been installed at the National Remote Sensing Center (NRSC), Shadnagar with the objective of generating a long-term record of measurements conforming to standards set by the World Meteorological Organisation (WMO). A calibration procedure to ensure the precision and accuracy of measurements was formulated using National Oceanic and Atmospheric Administration-Earth System Research Laboratory (NOAA-ESRL) calibration gases bearing WMO certification. The 10 s (1 σ) average precision of carbon dioxide (CO2) and (methane (CH4)) measurements by the GGA was 101 parts per billion volume (0.30 ppbv) and accuracy 78 ppbv (0.24 ppbv), respectively. The 5 s average of 1 Hz measurements was used to compute precision, which varied from 92.52 to 116.36 ppbv (1σ, 1 Hz = 0.66 parts per million volume (ppmv), WMO-2009)) for CO2 and CH4 0.45 ppbv to 0.55 ppbv (1 σ, 1 Hz = 2.48 ppbv, WMO-2009) respectively. Diurnal variation of greenhouse gas concentrations, temperature, and pressure, showed high fluctuations when cavity pressure and temperature varied from the standard values. The residuals of dry mixing ratios with respect to (w.r.t.) the NOAA span gases varied from +30 to −60 ppbv for CO2 and ±0.35 ppbv for CH4. A case study using the corrected observations over 1 year revealed the role of wind velocity and anthropogenic emissions, as well as the seasonal variations in the ambient concentrations of CO2 and CH4 gases near the surface.
... Interhemispheric transport is a key process aecting the accuracy of source quanti®cation for species such as methane by inverse modelling (Houweling et al., 1999), and is a source of dierence among global threedimensional chemistry transport models (CTMs) (Denning et al., 1999). Vay et al. (1999) showed that the CO 2 distribution in the Southern Hemisphere appeared to be largely determined by the interhemispheric transport as air masses with depleted CO 2 levels characteristic of the Northern Hemisphere were frequently observed south of the Intertropical Convergence Zone (ITCZ). Quay et al. (1999) observed that a high d 13 C value in the Southern Hemisphere compared with the Northern Hemisphere was a result of interhemispheric transport. ...
... Airborne profiles of CO 2 have previously been measured on the NASA DC-8 [4], [27] and by others [11], [24], [29]. Measurements reported here are among the first to be specifically focused on validating the orbital satellite measurements of XCO 2 and XCH 4 being made from space by GOSAT. ...
In this paper, we report the vertical profiles of $hbox{CO}_{2}$ and $hbox{CH}_{4}$ measured with a cavity ring-down spectrometer (CRDS) on a research aircraft from near-ground level to 8 km above mean sea level. The airborne platform employed in this paper is an Alpha Jet aircraft operated from NASA's Ames Research Center. Flights were undertaken to Railroad Valley, NV, USA, to coincide with overpasses of the Greenhouse Gases Observing Satellite (GOSAT). Ground-based $hbox{CO}_{2}$ and $hbox{CH}_{4}$ were simultaneously measured using CRDS, at the time and location of the airborne and satellite measurements. Results of three GOSAT coordinated aircraft profiles and ground-based measurements in June 2011 are presented and discussed in this paper. The accuracy of the $hbox{CO}_{2}$ and $hbox{CH}_{4}$ measurements has been determined based upon laboratory calibrations (World Meteorological Organisation traceable standard) and pressure/temperature flight simulations in a test chamber. The overall uncertainty for the airborne measurements ranged from 0.31 to 0.39 ppm for $hbox{CO}_{2}$ and from 3.5 to 5.6 ppb for $hbox{CH}_{4}$. Our column-averaged $hbox{CO}_{2}$ and $hbox{CH}_{4}$ measurements, which include about 61% of the total atmospheric mass, are extrapolated, using- different techniques, to include the remainder of the tropospheric and stratospheric $hbox{CO}_{2}$ and $hbox{CH}_{4}$. The $hbox{CO}_{2}$ data are then analyzed using the Atmospheric $hbox{CO}_{2}$ Observations from Space 2.9 and 3.3 algorithms. For methane data, the RemoTeC v2.1 algorithm was used in its full physics setup. Column-averaged $hbox{CO}_{2}$ and $hbox{XCO}_{2}$, measured by GOSAT and analyzed from our data, ranged from 388.1 to 396.4 ppm, and $hbox{XCH}_{4}$ ranged from 1.743 to 1.822 ppm. The agreement of the satellite and aircraft $hbox{CO}_{2}$ mixing ratios, as well as ground measurements, falls within the uncertainties of the methods employed to acquire these numbers.
... Airborne profiles of CO 2 have previously been carried out on the NASA DC-8 (Vay et al., 1999) and by others (Chen et al., 2010). Measurements reported here are among the first ones to be specifically focused on validating the orbital satellite measurements of XCO 2 being made from space by GOSAT. ...
In this paper we report vertical profiles of CO2 measured
with a cavity ring-down spectrometer (CRDS, Picarro, Inc., 2301-m) on a
research aircraft from near ground level to 8 km above mean sea level
(a.m.s.l.). The airborne platform employed in this study is an Alpha Jet
aircraft operated from NASA Ames Research Center. Flights were
undertaken to Railroad Valley, Nevada, USA, to coincide with overpasses
of the Greenhouse Gases Observing Satellite (GOSAT). Ground based
CO2 was simultaneously measured using CRDS, also at the time
and location of the airborne and satellite measurements. Results of
three GOSAT coordinated aircraft profiles and ground based measurements
in June 2011 are presented and discussed in this paper. The accuracy of
the CO2 measurements has been determined based upon
laboratory calibrations (WMO traceable standard) and
pressure/temperature flight simulations in a test chamber. The 2-σ
error bars for the CO2 data presented here are ± 0.4
ppm. Our column CO2 measurements, which include about 85% of
the tropospheric mass, are extrapolated, using two different techniques,
to include the remainder of the tropospheric and stratospheric
CO2. The data are then analyzed using the ACOS (Atmospheric
CO2 observations from space; JPL algorithm used to analyze
XCO2 from GOSAT data) averaging kernels. ACOS version 2.9 is
used to interpret the GOSAT data in a collaborative effort between JPL
and the GOSAT team. Column averaged CO2, XCO2,
measured by GOSAT and analyzed from our data ranged from 388.1 to 390.5
ppm. Values of XCO2 determined from our Alpha Jet
measurements and from the GOSAT on three overflight days agree within 1
ppm or better (<0.3%).
... Greater than expected values of biomass burning indicator species were found over the Pacific during the PEM-Tropics A period. Analyses of carbon dioxide, ozone, acidic species, non-methane hydrocarbons (NMHC's) and halocarbons indicated the residuals of biomass burning from upstream sources [Vay et al., 1999;Schultz et al., 1999;Talbot et al., 1999;Blake et al., 1999]. Dibb et al. [1999] used the radioactive tracer Pb-210 to derive transit times between 5-14 days for most plumes over the Pacific. ...
During the austral spring months of September and October when biomass burning is prevalent in the Southern Hemisphere, long-range transport can move the biomass burning byproducts from southern Africa to the Pacific Basin. Meteorological data from September 1996 were used to examine the transport from Africa using forward trajectories. Long-range transport is defined as trajectories that extend from Africa eastward to at least 110°E within 10 days. Five categories were found from trajectory analysis to constitute the major long-range transport pathways: zonal flow (35%) and four anticyclonic flows over Australia (5%), the western Pacific (5%), Easter Island (0.8%) and South America (0.9%). Chemical data collected during NASA’s Pacific Exploratory Mission-Tropics, Phase A (PEM-Tropics A) and Transport and Atmospheric Chemistry near the Equator- Atlantic (TRACE-A) missions were studied to determine the chemical evolution of burning byproducts during the long-range transport. Photochemical decay and physical mixing with background air were both found to be important dilution processes, with estimates of physical mixing lifetimes shorter than photochemical decay lifetimes. Greater values of pollution were detected at mid-tropospheric altitudes over the Pacific Basin, suggesting that more pollution is transported to mid-levels at long ranges.
... The retrieved latitudinal gradient then decreases and reaches about À1.5 ppmv in September. These values are coherent with several studies made on latitudinal variation of CO 2 [Machida et al., 2003;Vay et al., 1999]. In October, the concentration is minimal in the Pacific, particularly in its Eastern part. ...
Midtropospheric carbon dioxide (CO2) concentration is retrieved in the tropics [20S:20N], over sea, at night, for the period April to October 2003 from the Atmospheric Infrared Sounder (AIRS) observations. The method relies on a non-linear regression inference scheme using neural networks. A rough estimate of the mean precision of the method is about 2.5 ppmv (0.7%). The retrieved seasonal cycle and its latitudinal dependence agree well with aircraft CO2 in situ measurements made at the same altitude range. Maps produced on a monthly basis at a resolution of 15° × 15°, although not yet fully understood, show good agreement with known characteristics of CO2 distribution reflecting both atmospheric transport and surface fluxes (fossil fuel emissions, biomass burning, air-surface gas exchanges).
... The retrieved latitudinal gradient then decreases and reaches about À1.5 ppmv in September. These values are coherent with several studies made on latitudinal variation of CO 2 [Machida et al., 2003;Vay et al., 1999]. In October, the concentration is minimal in the Pacific, particularly in its Eastern part. ...
Launched in May 2002 on board the NASA Aqua platform, the high spectral resolution 2378-channel Atmospheric Infrared Sounder (AIRS) is used to retrieve mean concentration of midtropospheric carbon dioxide (CO_2) concentration. The retrieval procedure, first applied to the TIROS-N Operational Vertical Sounder (TOVS) onboard the NOAA polar satellites, is based on a neural network non-linear inversion scheme. Use is made of a restricted set of AIRS channels selected for their high sensitivity to CO_2 variations in the mid-troposphere (500 hPa to the tropopause) and their low sensitivity to other atmospheric thermodynamic variables. The simultaneous use of these infrared measurements, sensitive to both temperature and CO_2 variations, and of microwave measurements from the Advanced Microwave Sounding Unit (AMSU) also flying on board Aqua, only sensitive to temperature, allows separating the two effects. A detection of clear fields of view is performed through thresholds tests based on AIRS and AMSU observations. From April 2003 to now, maps of monthly CO_2 concentration are obtained in the topical zone [20N; 20S] at a resolution of 15° × 15°, so far over sea and at night. A rough estimate of the precision of the method is about 2.5 ppmv (about 0.7 %). A comparison of the satellite retrieved monthly mean CO_2 concentration seasonal cycle with commercial airliners CO_2 in situ measurements made at the same altitude range shows very good agreement. These retrievals should help constraining carbon flux inversion models, with large potential benefits for global carbon cycle research, especially in the tropics where the flask network is less efficient and where strong convective vertical mixing rapidly transmits surface CO_2 variations to that part of the atmosphere seen by AIRS.
... The measurement precision and accuracy of these compounds are given 25 in Spectrometer (GT-CIMS) instrument, which uses SF − 6 ion chemistry to selectively ionize SO 2 (Kim et al., 2007). Carbon dioxide CO 2 was measured using the NASA Langley Atmospheric Vertical Observations of CO 2 in the Earth's Troposphere (AVOCET) instrument, which uses a modified Li-Cor model 6252 differential, non-dispersive infrared (NDIR) gas analyzer at the 4.26 µm CO 2 absorption band (Vay et al., 1999(Vay et al., , 2003. Methane and CO were measured by the NASA Langley Differential Absorption CO Measurement (DACOM) instrument, which uses two tunable diode lasers in the infrared spectral region to simultaneously measure the absorption of light by CH 4 (3.3 µm) and CO (4.7 µm) (Fried et al., 2008). ...
Oil sands comprise 30% of the world's oil reserves and
the crude oil reserves in Canada's oil sands deposits are second only to
Saudi Arabia. The extraction and processing of oil sands is much more
challenging than for light sweet crude oils because of the high viscosity of
the bitumen contained within the oil sands and because the bitumen is mixed
with sand and contains chemical impurities such as sulphur. Despite these
challenges, the importance of oil sands is increasing in the energy market.
To our best knowledge this is the first peer-reviewed study to characterize
volatile organic compounds (VOCs) emitted from Alberta's oil sands mining
sites. We present high-precision gas chromatography measurements of 76
speciated C2–C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes,
aromatics, monoterpenes, oxygenated hydrocarbons, halocarbons and sulphur
compounds) in 17 boundary layer air samples collected over surface mining
operations in northeast Alberta on 10 July 2008, using the NASA DC-8
airborne laboratory as a research platform. In addition to the VOCs, we
present simultaneous measurements of CO2, CH4, CO, NO, NO2,
NOy, O3 and SO2, which were measured in situ aboard the DC-8.
Carbon dioxide, CH4, CO, NO, NO2, NOy, SO2 and 53 VOCs
(e.g., non-methane hydrocarbons, halocarbons, sulphur species) showed clear
statistical enhancements (1.1–397×) over the oil sands compared to
local background values and, with the exception of CO, were greater over the
oil sands than at any other time during the flight. Twenty halocarbons
(e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or
were minimally enhanced (
... The latitudinal gradient found in April is 6 ppmv from southern to northern tropics and goes down to -1.5 ppmv in September. These values are coherent with several studies made on latitudinal variation of CO 2 (Machida et al. 2003, Vay et al. 1999). From July to September, a maximum of CO 2 concentration is found east of Africa in the equatorial region. ...
The new 2378 channel high spectral resolution NASA/Aqua/Atmospheric Infrared Sounder (AIRS) launched in May 2002 is used to retrieve mean concentration of atmospheric carbon dioxide (CO2). A reduced set of AIRS channels, presenting a high sensitivity to variations of the atmospheric CO2 and reduced sensitivities to variations of other atmospheric components, and well covering the mid- troposphere (from 700 hPa to the tropopause), is first selected using the Optimum Sensitivity Profile (OSP) method. A cloud elimination procedure based on AIRS and Atmospheric Microwave Sounding Unit (AMSU) observations is then performed to detect clear fields of view. The resulting AIRS and AMSU measurements, the latter being not sensitive to CO2 variations, are used in a neural network inference procedure. This non-linear regression scheme has already proven its efficiency in the retrieval of mid-tropospheric CO2 from NOAA polar satellites. The first results obtained with AIRS give hope to improve the accuracy of the retrieval. Maps of monthly mean mid-tropospheric CO2 concentration are obtained for a few months in the tropics (20S;20N). The retrievals show good agreements with aircraft observations.
... [18] The observed vertical distribution of CO 2 is an important indicator of the coupling between flux and transport processes influencing the CO 2 concentration field as much pollution transport takes place in the free troposphere [Vay et al., 1999[Vay et al., , 2003Choi et al., 2008] at heights typically unattainable by the surface monitoring network. Vertical profiling by aircraft aids the interpretation of surface observations by linking the surface with the boundary layer and free troposphere. ...
LRT of CO2 emissions to North PoleEnriched 14CO2 from fires offsetting ff CO2CO2 Emission Factor 1634 g per kg DM
... Carbon dioxide measurements were made using the same fast-response, differential absorption CO 2 instrument deployed during SOLVE, which was a modified LI-COR model 6252 having a response time of Ͻ1 s with a corresponding precision of ϳ50 ppbv. A detailed description of the CO 2 measurement system and its operation can be found in Anderson et al. (1996) and Vay et al. (1999). Since CO 2 is not easily lost to tubing or inlet walls, samples can be siphoned from ports at any point along the airframe and brought to a conveniently located instrument rack for CO 2 assay. ...
Results are reported from an experiment conducted aboard the NASA DC-8 research aircraft to determine whether cabin air vented upstream of investigator's inlets had potentially contaminated ambient air samples obtained aboard the aircraft during previous airborne scientific expeditions. For the study, three multiport inlet rakes were mounted in windows downstream of an exhaust vent in locations forward, above, and aft of the right wing. These were used to make impact pressure measurements for determining boundary layer thickness (delta) as well as to collect ambient air samples at various distances outward from the airframe. The fraction of cabin air in the samples was determined by doping the vent air with a metered amount of CO2, then monitoring air at the inlet ports for differential CO2 enhancements. Data were collected at altitudes ranging from the surface to 12 km, at various indicated airspeeds, pitch and yaw angles, and during vertical ascents and descents. Results indicate that delta varies from about 13 to 37 cm and depends on inlet position, as well as the aircraft velocity, altitude, and pitch angle. The CO2-doped vent air was observed to mix throughout the depth of the boundary layer, but to be confined vertically to a narrow stream so that its interception by any particular inlet probe was highly dependent upon the aircraft-indicated airspeed and pitch angle. The inlet located forward of the wing was the most highly impacted, as samples collected there contained up to 0.8% cabin air at cruise altitudes under typical aircraft operating conditions. The implications of these findings on previous datasets are discussed, and a modified formula for calculating delta values appropriate for the DC-8 is proposed.
... This causes mean concentrations of CO and CH 4 to be significantly greater in the NH than in the SH. CO2 has a pronounced seasonal cycle [Vay et al., 1999] because of a wide variety of biological sources and sinks, most notably photosynthesis. During PTB, CO2 concentrations were greater in the NH than the SH because photosynthesis rates were reduced during the NH winter and because there was an increase in the combustion of fossil fuels used during the NH winter for heating. ...
We examine interhemispheric transport processes that occurred over the central Pacific during the PEM-Tropics B mission (PTB) in March-April 1999 by correlating the observed distribution of chemical tracers with the prevailing and anomalous windfields. The Intertropical Convergence Zone (ITCZ) had a double structure during PTB, and interhemispheric mixing occurred in the equatorial region between ITCZ branches. The anomalously strong tropical easterly surface wind had a large northerly component across the equator in the central Pacific, causing transport of aged, polluted air into the Southern Hemisphere (SH) at altitudes below 4 km. Elevated concentrations of chemical tracers from the Northern Hemisphere (NH) measured south of the equator in the central Pacific during PTB may represent an upper limit because the coincidence of seasonal and cold phase ENSO conditions are optimum for this transport. Stronger and more consistent surface convergence between the northeasterly and southeasterly trade winds in the Southern Hemisphere (SH) resulted in more total convective activity in the SH branch of the ITCZ, at about 6øS. The middle troposphere between 4-7 km was a complex shear zone between prevailing northeasterly winds at low altitudes and southwesterly winds at higher altitudes. Persistent anomalous streamline patterns and the chemical tracer distribution show that during PTB most transport in the central Pacific was from SH to NH across the equator in the upper troposphere. Seasonal differences in source strength caused larger interhemispheric gradients of chemical tracers during PTB than during the complementary PEM-Tropics A mission in September-October 1996.
... The LI-COR-based CO 2 sampling system was operated at constant 7216 pressure (250 torr) and had a precision of ±0.1 ppm (1 σ) and accuracy of ±0.25 ppm. Experimental procedures are described in detail by Anderson et al. (1996) and Vay et al. (1999Vay et al. ( , 2003. The MILAGRO/INTEX-B in situ CO 2 data are archived at 1 s resolution and are publically available via http://www-air.larc.nasa.gov. ...
Radiocarbon samples taken over Mexico City and the surrounding region
during the MILAGRO field campaign in March 2006 exhibited an unexpected
distribution: (1) relatively few samples (23%) were below the North
American free tropospheric background value (57‰) despite the
fossil fuel emissions from one of the world's most highly polluted
environments; and (2) frequent enrichment well above the background
value was observed. Correlate source tracer species and air transport
characteristics were examined to elucidate influences on the radiocarbon
distribution. Our analysis suggests that a combination of radiocarbon
sources biased the "regional radiocarbon background" above the North
American value thereby decreasing the apparent fossil fuel signature.
These sources included the release of bomb or "hot" radiocarbon
sequestered in plant carbon pools via the ubiquitous biomass burning in
the region as well as the direct release of radiocarbon as
CO2. Plausible large local perturbations include the burning
of hazardous waste in cement kilns; medical waste incineration; and
emissions from the Laguna Verde Nuclear Power Plant. These observations
provide insight into the use of Δ14CO2 to
constrain fossil fuel emissions in the megacity environment, indicating
that underestimation of the fossil fuel contribution to the
CO2 flux is likely wherever biomass burning coexists with
urban emissions. Our findings increase the complexity required to
quantify fossil fuel-derived CO2 in source-rich environments
characteristic of megacities, and have implications for the use of
Δ14CO2 observations in evaluating bottoms-up
emission inventories and their reliability as a tool for validating
national emission claims of CO2 within the framework of the
Kyoto Protocol.
... This causes mean concentrations of CO and CH 4 to be significantly greater in the NH than in the SH. CO2 has a pronounced seasonal cycle [Vay et al., 1999] because of a wide variety of biological sources and sinks, most notably photosynthesis. During PTB, CO2 concentrations were greater in the NH than the SH because photosynthesis rates were reduced during the NH winter and because there was an increase in the combustion of fossil fuels used during the NH winter for heating. ...
During the recent NASA Tropical Composition, Cloud and Climate Coupling
Experiment (TC4) in the summer of 2007, much effort was directed towards
locating and sampling fresh convective outflow in the ITCZ region near
Central America, coordinating observations from a variety of suborbital
and satellite platforms. One of the fundamental TC4 science questions
to be answered concerns the processes responsible for ozone distribution
in the climate-critical upper troposphere and lowermost stratosphere.
Seven flight days during the TC4 mission contain significant in situ
upper tropospheric sampling between 8.5 and 12 km (330 — 200 hPa,
338 — 350 K) during coordinated aircraft "racetrack" patterns,
near or in active convection. Preliminary results from NASA DC-8 in
situ data show an approximately 20 ppbv difference between ozone
measured inside and outside of active convective clouds. Using this
information as a starting place, we "zoom out" to include combined
observations of aerosols and ozone from the DIAL lidar on the DC- 8,
ozone and relative humidity from sondes, clouds from CPL lidar on the
NASA ER-2, and ozone and aerosols from MLS, TES and CALIPSO on the
"A-Train". We will test the simple hypothesis that the in cloud/out of
cloud difference in ozone measured during vigorous convection provides
useful information about the convective vertical redistribution of
ozone, as well as informing the lower boundary condition for the
tropical transition layer.
... Relationships Schultz et al., 1999; Vay et al., 1999] [Pickering et al., 1990 [Pickering et al., , 1991 [1996, 1999] and Talbot et al. [1994, 1996a, b, 19971. ...
Ten-day backward trajectories are used to determine the origins of air parcels arriving at airborne DC-8 chemical measurement sites during NASA's Pacific Exploratory Mission-Tropics A (PEM-T) that was conducted during August-October 1996. Those sites at which the air had a common geographical origin and transport history are grouped together, and statistical measures of chemical characteristics are computed. Temporal changes in potential temperature are used to determine whether trajectories experience a significant convective influence during the 10-day period. Those trajectories that do not experience a significant convective influence are divided into four geographical categories depending on their origins and paths. Air parcels originating over Africa and South America are characterized by enhanced mixing ratios of 03, CO, HNO3, and PAN. The backward trajectories travel at high altitudes (-- • 10-11 km), covering long distances due to strong upper-tropospheric westerly winds. The observed enhancement of combustion-related species is attributed to biomass burning from distant sources to the west, extending even to South America. The relatively large value of Be-7 probably is due either to less efficient removal of aerosols from upper tropospheric air or to small stratospheric contributions. Aged marine parcels are found to have relatively small concentrations of burning-related species. Although these trajectories arrive at a wide range of aircraft altitudes, they do not pass over a land mass during the preceding 10-day period. Air passing over Australia but no other land mass exhibits a combustion signature; however, photochemical product species such as 03 and PAN are less enhanced than in the long-range transport category. These trajectories travel shorter distances and are at lower altitudes (-- • 5-8 km) than those reaching Africa and/or South America. The combustion influence on these parcels is attributed to biomass burning emissions injected over Australia. That burning is less widespread than in Africa and South America. Finally, trajectories originating over Southeast Asia appear to receive a weak combustion influence. However, compared to Africa and South America, Southeast Asia has a relatively small incidence of biomass burning. There is little combustion input from Australia due to the high transport altitudes compared to the lower heights of the convection. The Southeast Asian parcels exhibit the greatest NO x to • NO/ratio of any category, perhaps due to lightning. Parcels experiencing a significant convective influence also are examined. Most of these parcels pass through widespread, persistent convection along either the South Pacific Convergence Zone or Intertropical Convergence Zone approximately 5 days prior to arriving at the aircraft locations. Thus the category mostly represents marine convection. Mixing ratios of peroxides and acids in the convective category are found to be smaller than in parcels not experiencing convection. Small mixing ratios of Be-7 and Pb-210 suggest particle removal by precipitation.
... OCS was always present above its detection limit. High precision in situ measurements of carbon dioxide (CO 2 ) were made on the DC-8 by a modified Li-COR model 6252 infrared gas analyzer having an accuracy and precision of 0.25 ppmv and 0.07 ppmv, respectively [Vay et al., 1999]. ...
Short Title: North American OCS sink Index Terms: 0322 Constituent sources and sinks, 0345 Pollution--urban and regional, 0365 Troposphere--composition and chemistry, 0368 Troposphere--constituent transport and chemistry Key Words: Carbonyl sulfide (OCS), Carbon Dioxide (CO 2), terrestrial sink, sources. 2 Abstract: An extensive set of carbonyl sulfide (OCS) observations were made as part of the NASA Intercontinental Chemical Transport Experiment -North America (INTEX-NA) study, flown from 1 July to 18 August 2004 mostly over the eastern United States and Canada. We use these data to show that summertime OCS mixing ratios at low altitude were dominated by a surface sink, and were highly correlated with CO 2 . In marked contrast to the 2001 early springtime Transport and Chemical Evolution over the Pacific (TRACE-P) experiment, which sampled Asian outflow, anthropogenic OCS emissions were dominated by this draw-down, although evidence for local emissions were observed on some low altitude flight legs. The INTEX-NA observations are combined with the STEM regional atmospheric chemistry model for a top down validation of bottom up OCS surface fluxes. In preparation for 4 dimensional variational inversion, this manuscript summarizes INTEX-NA observations. The STEM model is applied to simulate OCS using the best available surface fluxes (1 degree, monthly, 8 sectors), fixed boundary conditions, and no chemical reactions. Initial STEM results suggest a 200% underestimation of the OCS sink.
... es an eective interhemispheric transport in redistributing species. Interhemispheric transport is a key process aecting the accuracy of source quanti®cation for species such as methane by inverse modelling (Houweling et al., 1999), and is a source of dierence among global threedimensional chemistry transport models (CTMs) (Denning et al., 1999). Vay et al. (1999) showed that the CO 2 distribution in the Southern Hemisphere appeared to be largely determined by the interhemispheric transport as air masses with depleted CO 2 levels characteristic of the Northern Hemisphere were frequently observed south of the Intertropical Convergence Zone (ITCZ). Quay et al. (1999) observed that a high d 13 C val ...
Interhemispheric transport is a key process
affecting the accuracy of source quantification for species such as methane by
inverse modelling, and is a source of difference among global three-dimensional
chemistry transport models (CTMs). Here we use long-term observations of the
atmospheric concentration of long-lived species such as CH3CCl3
and CFCl3 for testing three-dimensional chemistry transport models (CTMs);
notably their ability to model the interhemispheric transport, distribution,
trend, and variability of trace gases in the troposphere. The very striking
contrast between the inhomogeneous source distribution and the nearly
homogeneous trend, observed in the global ALE/GAGE experiments for both CH3CCl3
and CFCl3 illustrates an efficient interhemispheric transport of
atmospherically long-lived chemical species. Analysis of the modelling data at
two tropical stations, Barbados (13° N, 59° W) and Samoa
(14° S, 124° W), show the close relationship between
inter-hemispheric transport and cross-equator Hadley circulations. We found that
cross-equator Hadley circulations play a key role in producing the globally
homogeneous observed trends. Chemically, the most rapid interaction between CH3CCl3
and OH occurs in the northern summer troposphere; while the most rapid
photolysis of CH3CCl3 and CFCl3, and the
chemical reactions between CFCl3 and O(1D), take place in
the southern summer stratosphere. Therefore, the cross-equator Hadley
circulation plays a key role which regulates the southward flux of chemical
species. The regulation by the Hadley circulations hence determines the amount
of air to be processed by OH, O(1D), and ultraviolet photolysis, in
both hemispheres. In summary, the dynamic regulation of the Hadley circulations,
and the chemical processing (which crucially depends on the concentration of OH,
O(1D), and on the intensity of solar insolation) of the air
contribute to the seasonal variability and homogeneous growth rate of observed
CH3CCl3 and CFCl3.Key words: Atmospheric composition and structure
(middle atmosphere - composition and chemistry; pollution - urban and regional)
- Meteorology and atmospheric dynamics (convective processes)
... More quantitative CO2 measurements in the atmosphere were made in March, 2007 in the boundary layer using the Ho:Tm:LuLiF laser and the existing heterodyne detection system. These DIAL measurements were compared with in situ gas analyzer (LI-COR 6252, [10]) and initial results indicate that the two sensors show the same trend and occurrence of CO2 [11]. The advantages of the phototransistor include high gain (> 3000), lower NEP, and higher quantum efficiency ( 70°/O) compared to the traditional extended wavelength PIN photodiodes. ...
A ground-based Differential Absorption Lidar (DIAL) is being developed with the capability to measure range-resolved and column amounts of atmospheric CO<sub>2</sub>. This system is also capable of providing high-resolution aerosol profiles and cloud distributions. It is being developed as part of the NASA Earth Science Technology Office's Instrument Incubator Program. This three year program involves the design, development, evaluation, and fielding of a ground-based CO<sub>2</sub> profiling system. At the end of a three-year development this instrument is expected to be capable of making measurements in the lower troposphere and boundary layer where the sources and sinks of CO<sub>2</sub> are located. It will be a valuable tool in the validation of NASA Orbiting Carbon Observatory (OCO) measurements of column CO<sub>2</sub> and suitable for deployment in the North American Carbon Program (NACP) regional intensive field campaigns. The system can also be used as a test-bed for the evaluation of lidar technologies for space- application. This DIAL system leverages 2-mum laser technology developed under a number of NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO<sub>2</sub> absorption lines suitable for profiling of lower tropospheric CO<sub>2</sub>. It also incorporates new high quantum efficiency, high gain, and relatively low noise phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. Atmospheric tests of the laser have been conducted by operating it locked to the CO<sub>2</sub> absorption line center, with off-set locking in the side-line mode, and in the off-line position. The reference laser is locked to center of absorption line within 390 kHz. This improves the level of stabilization by factor of 10 compared to earlier configuration. The det-
ector has been characterized in the laboratory and by conducting atmospheric tests at The National Center of Atmospheric Research (NCAR), Boulder, Colorado. The receiver uses an F2.2 all aluminum 40 cm diameter telescope and the system is designed to focus light onto a 200 mum size detector. Subsystem level integration and testing has been completed in the second year. System level testing is planned in the third year along with validation in the late spring of 2008 that involves comparisons with ground-based and aircraft in situ CO<sub>2</sub> sensors.
... The measurement precision and accuracy of these compounds are given 25 in Spectrometer (GT-CIMS) instrument, which uses SF − 6 ion chemistry to selectively ionize SO 2 (Kim et al., 2007). Carbon dioxide CO 2 was measured using the NASA Langley Atmospheric Vertical Observations of CO 2 in the Earth's Troposphere (AVOCET) instrument, which uses a modified Li-Cor model 6252 differential, non-dispersive infrared (NDIR) gas analyzer at the 4.26 µm CO 2 absorption band (Vay et al., 1999(Vay et al., , 2003. Methane and CO were measured by the NASA Langley Differential Absorption CO Measurement (DACOM) instrument, which uses two tunable diode lasers in the infrared spectral region to simultaneously measure the absorption of light by CH 4 (3.3 µm) and CO (4.7 µm) (Fried et al., 2008). ...
Oil sands comprise 30% of the world's oil reserves and the crude oil reserves in Canada's oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen contained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is increasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta's oil sands mining sites. We present high-precision gas chromatography measurements of 76 speciated C2–C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenates, halocarbons, and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measurements of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8. Methane, CO, CO2, NO, NO2, NOy, SO2 and 53 VOCs (e.g., halocarbons, sulphur species, NMHCs) showed clear statistical enhancements (up to 1.1–397×) over the oil sands compared to local background values and, with the exception of CO, were higher over the oil sands than at any other time during the flight. Twenty halocarbons (e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or were minimally enhanced (
Recognizing the role of Carbon dioxide (CO 2 ) in altering climate research and air pollution, direct measurements carried out over a coastal urban station using Li-COR CO ² /H 2 O analyser. The objective of the present study is to examine CO 2 variability during December-March. Day-to-day variability of CO 2 ranges from 380-550 ppm with a mean (423.1) and standard deviation (29.2). Monthly mean diurnal variability of CO 2 is maximum during midnight to early morning hours and minimum during afternoon. Overall diurnal variation is similar during the entire months. The link between CO 2 concentrations with Wind speed (WS), Atmospheric temperature (T) is examined. Wind speed varies inversely with CO 2 . Atmospheric temperature shows an exponentially decaying relation with CO 2 . The diurnal CO 2 variability is associated with the competing source/sink mechanisms. The CO 2 forcing is estimated and varies from 0.75 to 3.5 Wm ⁻² with temperature change from 0.75 to 2.0 ⁰ C.
In support of future satellite missions that aim to address the current shortcomings in measuring air quality from space, NASA's DISCOVER-AQ field campaign was designed to enable exploration of relationships between column measurements of trace species relevant to air quality at high spatial and temporal resolution. In the DISCOVER-AQ dataset, a modest correlation (r2 = 0.45) between ozone (O3) and formaldehyde (CH2O) column densities was observed. Further analysis revealed regional variability in the O3-CH2O relationship, with Maryland having a strong relationship when data were viewed temporally, and Houston having a strong relationship when data were viewed spatially. These differences in regional behavior are attributed to differences in VOC emissions. In Maryland, biogenic VOCs were responsible for ~28% of CH2O formation within the boundary layer column, causing CH2O to, in general, increase monotonically throughout the day. In Houston, persistent anthropogenic emissions dominated the local hydrocarbon environment, and no discernable diurnal trend in CH2O was observed. Box model simulations suggested that ambient CH2O mixing ratios have a weak diurnal trend (±20% throughout the day) due to photochemical effects, and that larger diurnal trends are associated with changes in hydrocarbon precursors. Finally, mathematical relationships were developed from first principles and were able to replicate the different behaviors seen in Maryland and Houston. While studies would be necessary to validate these results and determine the regional applicability of the O3-CH2O relationship, the results presented here provide compelling insight into the ability of future satellite missions to aid in monitoring near-surface air quality.
We report here airborne measurements of atmospheric CO2 over
the western North Pacific during the March-April 2001 Transport and
Chemical Evolution over the Pacific (TRACE-P) mission. The CO2
spatial distributions were notably influenced by
cyclogenesis-triggered transport of regionally polluted continental air
masses. Examination of the CO2 to
C2H2/CO ratio indicated rapid outflow of
combustion-related emissions in the free troposphere below 8 km.
Although the highest CO2 mixing ratios were measured within
the Pacific Rim region, enhancements were also observed further east
over the open ocean at locations far removed from surface sources. Near
the Asian continent, discrete plumes encountered within the planetary
boundary layer contained up to 393 ppmv of CO2. Coincident
enhancements in the mixing ratios of C2Cl4,
C2H2, and C2H4 measured
concurrently revealed combustion and industrial sources. To elucidate
the source distributions of CO2, an emissions database for
Asia was examined in conjunction with the chemistry and 5-day backward
trajectories that revealed the WNW/W sector of northeast Asia was a
major contributor to these pollution events. Comparisons of NOAA/CMDL
and JMA surface data with measurements obtained aloft showed a strong
latitudinal gradient that peaked between 35° and 40°N. We
estimated a net CO2 flux from the Asian continent of
approximately 13.93 Tg C day-1 for late winter/early spring
with the majority of the export (79%) occurring in the lower free
troposphere (2-8 km). The apportionment of the flux between
anthropogenic and biospheric sources was estimated at 6.37 Tg C
day-1 and 7.56 Tg C day-1, respectively.
We present observations of methane (CH4) mixing ratio and
13C/12C isotopic ratios in CH4
(δ13C) data from a collaborative shipboard project
using bulk carrier ships sailing between Nelson, New Zealand, and Osaka,
Japan, in the western Pacific Ocean. Measurements of the CH4
mixing ratio and δ13C in CH4were obtained
from large clean-air samples collected in each 2.5° to 5° of
latitude between 30°S and 30°N on eight voyages from 2004 to
2007. The data show large variations in CH4 mixing ratio in
the tropical western Pacific, and data analysis suggests that these
large variations are related to the positions and strengths of the South
Pacific Convergence Zone and the Intertropical Convergence Zone, with
variability in the sources playing a much smaller role. These
measurements are compared with results from a modified version of the
Unified Model (UMeth) general circulation model along two transects, one
similar to the ship transects and another 18.75° to the east.
Although UMeth was run to a steady state with the same sources and sinks
each year, the gradient structures varied considerably from year to
year, supporting our conclusion that variability in transport is a major
driver for the observed variations in CH4. Simulations forced
with an idealized representation of the El Niño-Southern
Oscillation (ENSO) suggest that a large component of the observed
variability in latitudinal gradients of CH4 and its
δ13C arises from intrinsic variability in the climate
system that does not occur on ENSO time scales.
The NASA Pacific Exploratory Mission to the Pacific tropics (PEM-Tropics) is the third major field campaign of NASA's Global Tropospheric Experiment (GTE) to study the impact of human and natural processes on the chemistry of the troposphere over the Pacific basin. The first two campaigns, PEM-West A and B were conducted over the northwestern regions of the Pacific and focused on the impact of emissions from the Asian continent. The broad objectives of PEM-Tropics included improving our understanding of the oxidizing power of the tropical atmosphere as well as investigating oceanic sulfur compounds and their conversion to aerosols. Phase A of the PEM-Tropics program, conducted between August-September 1996, involved the NASA DC-8 and P-3B aircraft. Phase B of this program is scheduled for March/April 1999. During PEM-Tropics A, the flight tracks of the two aircraft extended zonally across the entire Pacific Basin and meridionally from Hawaii to south of New Zealand. Both aircraft were instrumented for airborne measurements of trace gases and aerosols and meteorological parameters. The DC-8, given its long-range and high-altitude capabilities coupled with the lidar instrument in its payload, focused on transport issues and ozone photochemistry, while the P-3B, with its sulfur-oriented instrument payload and more limited range, focused on detailed sulfur process studies. Among its accomplishments, the PEM-Tropics A field campaign has provided a unique set of atmospheric measurements in a heretofore data sparse region; demonstrated the capability of several new or improved instruments for measuring OH, H2SO4, NO, NO2, and actinic fluxes; and conducted experiments which tested our understanding of HOx and NOx photochemistry, as well as sulfur oxidation and aerosol formation processes. In addition, PEM-Tropics A documented for the first time the considerable and widespread influence of biomass burning pollution over the South Pacific, and identified the South Pacific Convergence Zone as a major barrier for atmospheric transport in the southern hemisphere.
This paper describes the large-scale distributions of HNO3, HCOOH, and CH3COOH over the central and South Pacific basins during the Pacific Exploratory Mission-Tropics (PEM-Tropics) in austral springtime. Because of the remoteness of this region from continental areas, low part per trillion by volume (pptv) mixing ratios of acidic gases were anticipated to be pervasive over the South Pacific basin. However, at altitudes of 2-12 km over the South Pacific, air parcels were encountered frequently with significantly enhanced mixing ratios (up to 1200 pptv) of acidic gases. Most of these air parcels were centered in the 3-7 km altitude range and occurred within the 15°-65°S latitudinal band. The acidic gases exhibited an overall general correlation with CH3Cl, PAN, and O3, suggestive of photochemical and biomass burning sources. There was no correlation or trend of acidic gases with common industrial tracer compounds (e.g., C2Cl4 or CH3CCl3). The combustion emissions sampled over the South Pacific basin were relatively aged exhibiting C2H2/CO ratios in the range of 0.2-2.2 pptv/ppbv. The relationships between acidic gases and this ratio were similar to what was observed in aged air parcels (i.e., >3-5 days since they were over a continental area) over the western North Pacific during the Pacific Exploratory Mission-West Phases A and B (PEM-West A and B). In the South pacific marine boundary layer a median C2H2/CO ratio of 0.6 suggested that this region was generally not influenced by direct inputs of biomass combustion emissions. Here we observed the lowest mixing ratios of acidic gases, with median values of 14 pptv for HNO3, 19 pptv for HCOOH, and 18 pptv for CH3COOH. These values were coincident with low mixing ratios of NOx (
In order to examine distribution of atmospheric CO2 concentration over the central and western Pacific Ocean and elucidate factors governing the distribution, shipboard measurements were made between 1992 and 1996. Large variations in the concentration were observed in the northernmost and the tropical regions during the cruises. Also, year-to-year differences in the latitudinal CO2 distribution were detected. To interpret these variations, analyses were performed in terms of atmospheric transport from various source regions using meteorological and climatological data. The following results were obtained: (1) Episodic large CO2 variations appeared north of 30°N over the central and western Pacific during the periods of ship cruises. These variations were related with exchanges of continental and marine air masses associated with movements of weather systems. (2) Discontinuous changes of CO2 concentration were observed in the equatorial region during spring cruises, reflecting suppression of interhemispheric air mixing. However, the magnitude, the sharpness, and the location of these discontinuous changes were associated with variations in the strength of air convergence and the movement of enhanced convective areas, and were quite variable. (3) Differences in the latitudinal CO2 gradient from northern low latitudes to southern low latitudes were found between each spring cruise. Comparison with climatological data suggests that the difference in the CO2 gradient is related to variation in the anomaly of meridional wind component distribution over the central and western Pacific at low latitudes.
Radiocarbon samples taken over Mexico City and the surrounding region during the MILAGRO field campaign in March 2006 exhibited an unexpected distribution: (1) relatively few samples (23%) were below the North American free tropospheric background value (57 +/- 2aEuro degrees) despite the fossil fuel emissions from one of the world's most highly polluted environments; and (2) frequent enrichment well above the background value was observed. Correlate source tracer species and air transport characteristics were examined to elucidate influences on the radiocarbon distribution. Our analysis suggests that a combination of radiocarbon sources biased the 'regional radiocarbon background' above the North American value thereby decreasing the apparent fossil fuel signature. Likely sources include the release of C-14-enhanced carbon from bomb C-14 sequestered in plant carbon pools via the ubiquitous biomass burning in the region as well as the direct release of radiocarbon as CO2 from other 'hot' sources. Plausible perturbations from local point 'hot' sources include the burning of hazardous waste in cement kilns; medical waste incineration; and emissions from the Laguna Verde Nuclear Power Plant. These observations provide insight into the use of delta(CO2)-C-14 to constrain fossil fuel emissions in the megacity environment, indicating that underestimation of the fossil fuel contribution to the CO2 flux is likely wherever biomass burning coexists with urban emissions and is unaccounted for as a source of the elevated CO2 observed above local background. Our findings increase the complexity required to quantify fossil fuel-derived CO2 in source-rich environments characteristic of megacities, and have implications for the use of delta(CO2)-C-14 observations in evaluating bottom-up emission inventories and their reliability as a tool for validating national emission claims of CO2 within the framework of the Kyoto Protocol.
Measurements of gaseous and particulate reactive nitrogen and sulfur species, as well as other chemical species, were made using the P-3B and DC-8 aircraft over the western Pacific during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) experiment, conducted between February and April 2001. These measurements provide a good opportunity to study the extent to which anthropogenic NOx and SO2 emitted over the East Asian countries remain as NOy and SOx (=SO2 + nssSO42-) in the form of gas or fine particles when an air mass is transported into the western Pacific region. In this paper a method to estimate transport efficiencies, ε(NOy) and ε(SOx), in an air mass that has experienced multiple injection, mixing, and loss processes is described. In this analysis, CO and CO2 are used as passive tracers of transport, and the emission inventories of CO, CO2, NOx, and SO2 over the East Asia region are used. Results from the P-3B presented in this study indicate that 20-40% and 15% of NOx emitted over the northeastern part of China remained as NOy over the western Pacific in the boundary layer (BL) and free troposphere (FT), respectively. In the FT, PAN is found to have been the dominant form of NOy, while only 0.5% of emitted NOx remained as NOx. The transport efficiency of SOx is estimated to have been 25-45% and 15-20% in the BL and FT, respectively. Median values of the nssSO42-/SOx ratio are 0.4-0.6 both in the BL and FT, however large variability is found in the FT. These results are generally consistent with those derived using DC-8 data. The results obtained in this study indicate that more than half of NOy and SOx were lost over the continent and that the vertical transport from the BL to FT further reduced their amounts by a factor of 2, likely due to wet removal. Budgets of NOy and SOx were also studied for air masses, which we sampled during TRACE-P and the flux out from the continent in these cases is estimated to be 20% of the emissions. Flux in the BL and FT is found to have a similar contribution.
Measurements of carbon monoxide, methane, and their isotopic composition are presented for samples collected on six ship voyages across the Pacific between New Zealand and the United States between 1996 and 1998. The data cover a latitude range from approximately 40°S to 40°N and clearly define significant latitudinal gradients in mixing ratios and isotopic composition and their seasonal variations. Observational data are compared with recent three-dimensional inverse modeling studies of the global CO and CH4 distributions (Bergamaschi et al., 2000a, b, c) constrained by CO and CH4 mixing ratio data from the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory network and additional isotope measurements from a set of five globally distributed stations. Thus the shipboard measurements represent a unique opportunity for independent validation of the inverse models. In general, we see a very good agreement between measurements and model results, both for CO and CH4 mixing ratios and their stable isotopic composition (delta13CO,deltaC18O,delta13CH4). This is in particular true for the simulation of mean latitudinal gradients of these quantities. For some voyages, however, significant deviations in the ``fine structure'' of the latitudinal profiles are apparent and are attributed to synoptic scale variations that are not captured by the model (for which a standard meteorology is applied). In most cases, deviations between observations and model results exhibit similar patterns for CH4 and CO, and the deviations in mixing ratios are linked with corresponding deviations in the isotopic signature. Furthermore, a clear correlation between CO and ethane mixing ratios is visible. Observations of 14CO show a general minimum around the equator and cycles of opposite phase in each hemisphere. Virtually identical 14CO minima were observed in both hemispheres in 1997, indicating similar OH levels. We also show model results for deltaCH3D and the mass-independent isotope fraction in C17O (despite the absence of observational data for the ship voyages) in our discussion to illustrate the potential of these isotopic signatures for the understanding of the global cycles of CH4 and CO, respectively.
In situ and laser remote measurements of gases and aerosols were made
with airborne instrumentation to establish a baseline chemical signature
of the atmosphere above the South Pacific Ocean during the NASA Global
Tropospheric Experiment (GTE)/Pacific Exploratory Mission-Tropics A
(PEM-Tropics A) conducted in August-October 1996. This paper discusses
general characteristics of the air masses encountered during this
experiment using an airborne lidar system for measurements of the
large-scale variations in ozone (O3) and aerosol
distributions across the troposphere, calculated potential vorticity
(PV) from the European Centre for Medium-Range Weather Forecasting
(ECMWF), and in situ measurements for comprehensive air mass
composition. Between 8°S and 52°S, biomass burning plumes
containing elevated levels of O3, over 100 ppbv, were
frequently encountered by the aircraft at altitudes ranging from 2 to 9
km. Air with elevated O3 was also observed remotely up to the
tropopause, and these air masses were observed to have no enhanced
aerosol loading. Frequently, these air masses had some enhanced PV
associated with them, but not enough to explain the observed
O3 levels. A relationship between PV and O3 was
developed from cases of clearly defined O3 from stratospheric
origin, and this relationship was used to estimate the stratospheric
contribution to the air masses containing elevated O3 in the
troposphere. The frequency of observation of the different air mass
types and their average chemical composition is discussed in this paper.
A compact, diode laser-based sensor has been developed for meteorological balloons to measure atmospheric carbon dioxide profiles. The sensor achieves a precision of better than 1 ppmv using a novel pressure/temperature compensating reference cell. This device weighs less than 1 kg and uses less than 4 Watts of battery electrical power. Turnkey operation is achieved by a digital signal processor. A full description of the sensor and a discussion of its performance are provided.
Significant technology developments are progressing in the areas of lasers, detectors, and receiver systems to enable tropospheric CO2 profiling capability needed to understand global carbon cycle processes. High precision measurements are required to understand the variability of atmospheric CO 2 and to evaluate the influence of sources and sinks of CO 2. A review of recent technology developments is presented including new developments in lasers and new high efficiency, relatively low noise detectors at 2 μm wavelength region. A ground-based heterodyne differential absorption lidar (DIAL) was used to observe the diurnal variability of CO 2 in the lower troposphere. In situ CO2 measurements via a Li-Cor NDIR spectrometer were compared with the observations of the ground-based DIAL system to evaluate its sensitivity. A measurement precision of 1.5% standard deviation was estimated for the DIAL measurements of the ground-based DIAL system. Capability of a shot-noise limited ground-based direct detection DIAL system using a novel 2 μm phototransitor and a large collection area receiver for tropospheric profiling of CO2 is investigated.
In this study, we focus on the spatial variations in CO2 and related meteorological parameters quantified in the planetary boundary layer (PBL) from airborne measurements over Illinois, Ohio and Nebraska, USA during the INTEX-NA campaign, July 8th, 2004. The airborne measurements were conducted during morning hours (8:47 a.m) in Nebraska whereas mostly during afternoon hours (1:00 pm and 1:50 pm) in Illinois and Ohio respectively. We perform wavelet analysis using a continuous wavelet transform and wavelet coherence functions for the CO2 data and underlying meteorological variables to interpret the airborne observations. In addition, we also used LANDSAT derived land use/cover information to relate to CO2 variations observed in the PBL. Maximum CO2 mixing ratios were observed over Nebraska and the lowest CO2 mixing ratios over Illinois followed by Ohio. Spectral decomposition of the CO2 data using scalograms revealed lower frequency signals of shorter duration over Illinois compared to Ohio and Nebraska. Further, the high frequency CO2 data for Illinois showed good cyclicity. The high frequency data in Illinois corresponded to low CO2 values of less than 354ppm, and the time localization of these frequencies closely matched with corn/soybeans mixed agricultural land use suggesting significant CO2 uptake. Results from the wavelet coherence analysis between the CO2 time series and meteorological parameters (potential temperature, relative humidity, water vapor partial pressure, water vapor mixing ratio, wind speed and infrared surface temperature) revealed significant differences in coherences as a function of sampling time. The scale and time dependent wavelet coherence variations observed for CO2 and meteorological data over three different states were attributed to mesoscale variability including variations in the type of vegetation, topography, land-vegetation contrast, cloud cover, and overall landscape heterogeneity.
We use historical and new atmospheric trace gas observations to refine the estimated source of methane (CH(4)) emitted into California's South Coast Air Basin (the larger Los Angeles metropolitan region). Referenced to the California Air Resources Board (CARB) CO emissions inventory, total CH(4) emissions are 0.44 ± 0.15 Tg each year. To investigate the possible contribution of fossil fuel emissions, we use ambient air observations of methane (CH(4)), ethane (C(2)H(6)), and carbon monoxide (CO), together with measured C(2)H(6) to CH(4) enhancement ratios in the Los Angeles natural gas supply. The observed atmospheric C(2)H(6) to CH(4) ratio during the ARCTAS (2008) and CalNex (2010) aircraft campaigns is similar to the ratio of these gases in the natural gas supplied to the basin during both these campaigns. Thus, at the upper limit (assuming that the only major source of atmospheric C(2)H(6) is fugitive emissions from the natural gas infrastructure) these data are consistent with the attribution of most (0.39 ± 0.15 Tg yr(-1)) of the excess CH(4) in the basin to uncombusted losses from the natural gas system (approximately 2.5-6% of natural gas delivered to basin customers). However, there are other sources of C(2)H(6) in the region. In particular, emissions of C(2)H(6) (and CH(4)) from natural gas seeps as well as those associated with petroleum production, both of which are poorly known, will reduce the inferred contribution of the natural gas infrastructure to the total CH(4) emissions, potentially significantly. This study highlights both the value and challenges associated with the use of ethane as a tracer for fugitive emissions from the natural gas production and distribution system.
An extensive set of carbonyl sulfide (OCS) and carbon disulfide
(CS2) observations were made as part of the NASA Transport
and Chemical Evolution over the Pacific (TRACE-P) project, which took
place in the early spring 2001. TRACE-P sampling focused on the western
Pacific region but in total included the geographic region 110°E to
290°E longitude, 5°N to 50°N latitude, and 0-12 km altitude.
Substantial OCS and CS2 enhancements were observed for a
great many air masses of Chinese and Japanese origin during TRACE-P.
Over the western Pacific, mean mixing ratios of long-lived OCS and
shorter-lived CS2 showed a gradual decrease by about 10% and
a factor of 5-10, respectively, from the surface to 8-10 km altitude,
presumably because land-based sources dominated their distribution
during February through April 2001. The highest mean OCS and
CS2 levels (580 and 20 pptv, respectively, based on 2.5°
× 2.5° latitude bins) were observed below 2 km near the coast
of Asia, at latitudes between 25°N and 35°N, where urban Asian
outflow was strongest. Ratios of OCS versus CO for continental SE Asia
were much lower compared to Chinese and Japanese signatures and were
strongly associated with biomass burning/biofuel emissions. We present a
new inventory of anthropogenic Asian emissions (including biomass
burning) for OCS and CS2 and compare it to emission estimates
based on regional relationships of OCS and CS2 to CO and
CO2. The OCS and CS2 results for the two methods
compare well for continental SE Asia and Japan plus Korea and also for
Chinese CS2 emissions. However, it appears that the inventory
underestimates Chinese emissions of OCS by about 30-100%. This
difference may be related to the fact that we did not include natural
sources such as wetland emissions in our inventory, although the
contributions from such sources are believed to be at a seasonal low
during the study period. Uncertainties in OCS emissions from Chinese
coal burning, which are poorly characterized, likely contribute to the
discrepancy.
The Pacific Exploratory Mission (PEM)-Tropics provided extensive aircraft data to study the atmospheric chemistry of tropospheric air in Pacific Ocean regions, extending from Hawaii to New Zealand and from Fiji to east of Easter Island. This region, especially the tropics, includes some of the cleanest tropospheric air of the world and, as such, is important for studying atmospheric chemical budgets and cycles. The region also provides a sensitive indicator of the global-scale impact of human activity on the chemistry of the troposphere, and includes such important features as the Pacific "warm pool," the Intertropical Convergence Zone (ITCZ), the South Pacific Convergence Zone (SPCZ), and Walker Cell circulations. PEM-Tropics was conducted from August to October 1996. The ITCZ and SPCZ are major upwelling regions within the South Pacific and, as such, create boundaries to exchange of tropospheric air between regions to the north and south. Chemical data obtained in the near vicinity of the ITCZ and the SPCZ are examined. Data measured within the convergent zones themselves are not considered. The analyses show that air north and south of the convergent zones have different chemical signatures, and the signatures are reflective of the source regions and transport histories of the air. Air north of the ITCZ shows a modest urban/industrialized signature compared to air south of the ITCZ. The chemical signature of air south of the SPCZ is dominated by combustion emissions from biomass burning, while air north of the SPCZ is relatively clean and of similar composition to ITCZ south air. Chemical signature differences of air north and south of the zones are most pronounced at altitudes below 5 km, and, as such, show that the ITCZ and SPCZ are effective low-altitude barriers to the transport of tropospheric air. At altitudes of 8 to 10 km, chemical signatures are less dissimilar, and air backward trajectories (to 10 days) show cross-convergent-zone flow. At altitudes below about 5 km, little cross-zonal flow is observed. Chemical signatures presented include over 30 trace chemical species including ultrafine, fine, and heated-fine (250øC) aerosol.
NASA's Pacific Exploratory Mission-Tropics (PEM-T) experiment investigated the atmospheric chemistry of a large portion of the tropical and subtropical Pacific Basin during August to October 1996. This paper summarizes meteorological conditions over the PEM-T domain. Mean flow patterns during PEM-T are described. Important circulation systems near the surface include subtropical anticyclones, the South Pacific Convergence Zone (SPCZ), the Intertropical Convergence Zone (1TCZ), and middle latitude transient cyclones. The SPCZ and ITCZ are areas of widespread ascent and deep convection; however, there is relatively little light-ning in these oceanic regions. A large area of subsidence is associated with the subtropical anticy-clone centered near Easter Island. PEM-T occurred during a period of near normal sea surface temperatures. When compared to an 11 year climatology (1986-1996), relatively minor circula-tion anomalies are observed during PEM-T. Some of these circulation anomalies are consistent with much stronger anomalies observed during previous La Nina events. In general, however, the 1996 PEM-T period appears to be climatologically representative. Meteorological conditions for specific flights from each major operations area are summarized. The vertical distribution of ozone along selected DC-8 flights is described using the DIAL remote sensing system. These ozone distributions are related to thermodynamic soundings obtained during aircraft maneuvers and to backward trajectories that arrived at locations along the flight tracks. Most locations in the deep tropics are found to have relatively small values of tropospheric ozone. Backward trajecto-ries calculated from global gridded analyses show that much of this air originates from the east and has not passed over land within 10 days. The deep convection associated with the ITCZ and SPCZ also influences the atmospheric chemistry of these regions. Flights over portions of the subtropics and middle latitudes document layers of greatly enhanced tropospheric ozone, some-times exceeding 80 ppbv. In situ carbon monoxide in these layers often exceeds 90 ppbv. These regions are located near, and especially south of Tahiti, Easter Island, and Fiji. The layers of enhanced ozone usually correspond to layers of dry air, associated with widespread subsiding air. The backward trajectories show that air parcels arriving in these regions originate from the west, passing over Australia and even extending back to southern Africa. These are regions of biomass burning. The in situ chemical measurements support the trajectory-derived origins of these ozone plumes. Thus the enhanced tropospheric ozone over the central Pacific Basin may be due to biomass burning many thousands of kilometers away. Middle-latitude portions of the PEM-T area are influenced by transient cyclones, and the DC-8 traversed tropopause folds during several flights. The flight area just west of Ecuador experiences outflow from South America. Thus the biomass burning that is prevalent over portions of Brazil influences this area.
High resolution in situ measurements of atmospheric CO2 were made from the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment - North America (INTEX-NA) campaign, part of the wider International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). During the summer of 2004, eighteen flights comprising 160h of measurements were conducted within a region bounded by 27 to 53°N and 36 to 139°W over an altitude range of 0.15 to 12 km. These large-scale surveys provided the opportunity to examine the characteristics of the atmospheric CO2 signal over sparsely sampled areas of North America and adjacent ocean basins. The observations showed a high degree of variability (≤ 18%) due to the myriad source and sink processes influencing the air masses intercepted over the INTEX-NA sampling domain. Surface fluxes had strong effects on continental scale concentration gradients. Clear signatures of CO2 uptake were seen east of the Mississippi River, notably a persistent CO2 deficit in the lowest 2-3 km. When combining the airborne CO2 measurements with LANDSAT and MODIS data products, the lowest CO2 mixing ratios observed during the campaign (337 ppm) were tied to mid-continental agricultural fields planted in corn and soybeans. We used simultaneous measurements of CO, O3, C2Cl4, C2H6, C2H2 and other unique chemical tracers to differentiate air mass types. Coupling these distinct air mass chemical signatures with transport history permitted identification of convection, stratosphere-troposphere exchange, long-range transport from Eastern Asia, boreal wildfires, and continental outflow as competing processes at multiple scales influencing the observed concentrations. Our results suggest these are important factors contributing to the large-scale distribution in CO2 Mixing ratios thus these observations offer new constraints in the computation of the North American carbon budget.
The three-dimensional (3-D) distribution of carbon monoxide (CO) over
the southern Pacific during the NASA Global Tropospheric Experiment
Pacific Exploratory Mission-Tropics (PEM-T) (August-October 1996) has
been analyzed in comparison to other CO measurements. The following data
sets have been used in the study: National Oceanic and Atmospheric
Administration Climate Monitoring and Diagnostic Laboratory surface
level sampling; Commonwealth Scientific and Industrial Research
Organization aircraft measurements over Cape Grim, Tasmania; solar
spectroscopic measurements at Lauder, New Zealand; and data from two
spaceborne Measurement of Air Pollution From Satellite experiments. For
the PEM-T mission back trajectories analysis and 3-D modeling of the CO
transport have been performed. It has been demonstrated that CO
measurements obtained by different in situ and remote techniques can be
used to build the picture of the CO climatology over the large
geographical area. The structure of the CO distribution over the western
part of the southern Pacific during the austral spring is mainly
controlled by emission from biomass burning in Australia and Africa and
subsequent long-range transport. The prevailing westerly transport
occurs in the middle and upper troposphere, whereas the marine boundary
layer remains relatively clean and uniform. Barriers in the form of the
Intertropical Convergence Zone and South Pacific Convergence Zone
protect the equatorial area (equator to 10°S) from direct impact of
biomass burning plumes from north and southwest. Consistency between the
measurements taken in different years and modeling results indicates
that the observed feature is a stable phenomenon. Outside the equatorial
area the CO vertical distribution has a broad distinctive maximum at the
altitude range 5-8 km and latitudes between 20°S and 30°S. This
maximum is a stable feature, and its location indicates the area where
the most intensive westerly transport occurs.
Of late years there has been much interest in the effect of human activities on the natural circulation of carbon. This demands a knowledge of the amount of CO2 in atmosphere both now and in the immediate past. Here the average amount obtained by 30 of the most extensive series of observations between 1866 and 1956 is presented, and the reliability of the 19th century measurements discussed. A base value of 290 p.p.m. is proposed for the year 1900. Since then the observations show a rising trend which is similar in amount to the addition from fuel combustion. This result is not in accordance with recent radio carbon data, but the reasons for the discrepancy are obscure, and it is concluded that much further observational data is required to clarify this problem. Some old values, showing a remarkable fall of CO2 in high southern latitudes, are assembled for comparison with the anticipated new measurements, to be taken in this zone during the Geophysical Year.
Using delta C-13 measurements in atmospheric CO2 from a cooperative global air sampling network, we determined the partitioning of the net uptake of CO2 between ocean and land as a function of latitude and time. The majority of delta C-13 measurements were made at the Institute of Arctic and Alpine Research (INSTAAR) of the University of Colorado. We perform an inverse deconvolution of both CO2 and delta C-13 observations, using a two-dimensional model of atmospheric transport. Also, the discrimination against C-13 by plant photosynthesis, as a function of latitude and time, is calculated from global runs of the simple biosphere (SiB) model. Uncertainty due to the longitudinal structure of the data, which is not represented by the model, is studied through a bootstrap analysis by adding and omitting measurement sites. The resulting error estimates for our inferred sources and sinks are of the order of 1 GTC (1 GTC = 10(exp 15) gC). Such error bars do not reflect potential systematic errors arising from our estimates of the isotopic disequilibria between the atmosphere and the oceans and biosphere, which are estimated in a separate sensitivity analysis. With respect to global totals for 1992 we found that 3.2 GTC of carbon dissolved into the ocean and that 1.5 GTC were sequestered by land ecosystems. Northern hemisphere ocean gyres north of 15 deg N absorbed 2.7 GTC. The equatorial oceans between 10 deg S and 10 deg N were a net source to the atmosphere of 0.9 GTC.
The NASA Pacific Exploratory Mission to the Pacific tropics (PEM-Tropics) is the third major field campaign of NASA's Global Tropospheric Experiment (GTE) to study the impact of human and natural processes on the chemistry of the troposphere over the Pacific basin. The first two campaigns, PEM-West A and B were conducted over the northwestern regions of the Pacific and focused on the impact of emissions from the Asian continent. The broad objectives of PEM-Tropics included improving our understanding of the oxidizing power of the tropical atmosphere as well as investigating oceanic sulfur compounds and their conversion to aerosols. Phase A of the PEM-Tropics program, conducted between August-September 1996, involved the NASA DC-8 and P-3B aircraft. Phase B of this program is scheduled for March/April 1999. During PEM-Tropics A, the flight tracks of the two aircraft extended zonally across the entire Pacific Basin and meridionally from Hawaii to south of New Zealand. Both aircraft were instrumented for airborne measurements of trace gases and aerosols and meteorological parameters. The DC-8, given its long-range and high-altitude capabilities coupled with the lidar instrument in its payload, focused on transport issues and ozone photochemistry, while the P-3B, with its sulfur-oriented instrument payload and more limited range, focused on detailed sulfur process studies. Among its accomplishments, the PEM-Tropics A field campaign has provided a unique set of atmospheric measurements in a heretofore data sparse region; demonstrated the capability of several new or improved instruments for measuring OH, H2SO4, NO, NO2, and actinic fluxes; and conducted experiments which tested our understanding of HOx and NOx photochemistry, as well as sulfur oxidation and aerosol formation processes. In addition, PEM-Tropics A documented for the first time the considerable and widespread influence of biomass burning pollution over the South Pacific, and identified the South Pacific Convergence Zone as a major barrier for atmospheric transport in the southern hemisphere.
Several recent studies have compared observed changes in near-surface temperature with patterns of temperature change predicted by climate models in response to combined forcing by carbon dioxide and anthropogenic sulphate aerosols. These results suggest that a combined carbon dioxide + sulphate aerosol signal is easier to identify in the observations than a pattern of temperature change due to carbon dioxide alone. This work compares modelled and observed patterns of vertical temperature change in the atmosphere. Results show that the observed and model-predicted changes in the mid- to low troposphere are in better accord with greenhouse warming predictions when the likely effects of anthropogenic sulphate aerosols and stratospheric ozone reduction are incorporated in model calculations, and that the level of agreement increases with time. This improved correspondence is primarily due to hemispheric-scale temperature contrasts. If current model-based estimates of natural internal variability are realistic, it is likely that the level of time-increasing similarity between modelled and predicted patterns of vertical temperature change is partially due to human activities.
NASA's Pacific Exploratory Mission-Tropics (PEM-T) experiment investigated the atmospheric chemistry of a large portion of the tropical and subtropical Pacific Basin during August to October 1996. This paper summarizes meteorological conditions over the PEM-T domain. Mean flow patterns during PEM-T are described. Important circulation systems near the surface include subtropical anticyclones, the South Pacific Convergence Zone (SPCZ), the Intertropical Convergence Zone (1TCZ), and middle latitude transient cyclones. The SPCZ and ITCZ are areas of widespread ascent and deep convection; however, there is relatively little light-ning in these oceanic regions. A large area of subsidence is associated with the subtropical anticy-clone centered near Easter Island. PEM-T occurred during a period of near normal sea surface temperatures. When compared to an 11 year climatology (1986-1996), relatively minor circula-tion anomalies are observed during PEM-T. Some of these circulation anomalies are consistent with much stronger anomalies observed during previous La Nina events. In general, however, the 1996 PEM-T period appears to be climatologically representative. Meteorological conditions for specific flights from each major operations area are summarized. The vertical distribution of ozone along selected DC-8 flights is described using the DIAL remote sensing system. These ozone distributions are related to thermodynamic soundings obtained during aircraft maneuvers and to backward trajectories that arrived at locations along the flight tracks. Most locations in the deep tropics are found to have relatively small values of tropospheric ozone. Backward trajecto-ries calculated from global gridded analyses show that much of this air originates from the east and has not passed over land within 10 days. The deep convection associated with the ITCZ and SPCZ also influences the atmospheric chemistry of these regions. Flights over portions of the subtropics and middle latitudes document layers of greatly enhanced tropospheric ozone, some-times exceeding 80 ppbv. In situ carbon monoxide in these layers often exceeds 90 ppbv. These regions are located near, and especially south of Tahiti, Easter Island, and Fiji. The layers of enhanced ozone usually correspond to layers of dry air, associated with widespread subsiding air. The backward trajectories show that air parcels arriving in these regions originate from the west, passing over Australia and even extending back to southern Africa. These are regions of biomass burning. The in situ chemical measurements support the trajectory-derived origins of these ozone plumes. Thus the enhanced tropospheric ozone over the central Pacific Basin may be due to biomass burning many thousands of kilometers away. Middle-latitude portions of the PEM-T area are influenced by transient cyclones, and the DC-8 traversed tropopause folds during several flights. The flight area just west of Ecuador experiences outflow from South America. Thus the biomass burning that is prevalent over portions of Brazil influences this area.
Observed atmospheric concentrations of CO2 and data on the partial pressures of CO2 in surface ocean waters are combined to identify globally significant sources and sinks of CO2. The atmospheric data are compared with boundary layer concentrations calculated with the transport fields generated by a
general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric
concentration gradient can be maintained only if sinks for CO2 are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO2 in the surface waters of the Northern Hemisphere and the atmosphere are too small for the oceans to be the major sink of
fossil fuel CO2. Therefore, a large amount of the CO2 is apparently absorbed on the continents by terrestrial ecosystems.
The observed spatial patterns of temperature change in the free
atmosphere from 1963 to 1987 are similar to those predicted by
state-of-the-art climate models incorporating various combinations of
changes in carbon dioxide, anthropogenic sulphate aerosol and
stratospheric ozone concentrations. The degree of pattern similarity
between models and observations increases through this period. It is
likely that this trend is partially due to human activities, although
many uncertainties remain, particularly relating to estimates of natural
variability.
The model transport parameters were previously derived from a three-dimensional general circulation model. It is found that the southern oceans are a sink of carbon of 0.8-1.5 Gt yr-1 (1 Gt equals 1015g) and that the equatorial areas are a source to the atmosphere of 1.4-2.8 Gt yr1. Tropical deforestation as a major source of CO2 must be smaller than that because the oceans account for a significant part of the equatorial flux. There seems to be significant seasonality in the sources and sinks of CO2, both in the tropics and in the southern oceans. The seasonal net ecosystem production north of 25°N is found to be 6.2-8.2 Gt of carbon, but these estimates are probably somewhat too low. -from Authors
Partition des flux de CO2 entre l'ocean et la biosphère terrestre pour les années 1990, 1991, 1992 à l'aide d'un modèle d'inversion 2D par bandes de latituide contraint par des mesures de CO2 et par des mesures de C13 du reseau NOAA/CMDL.
9 stations et 2 bateaux en 90 et 91. Flux de 1992 plus 'complets' que ceux de 90 et 91 par l'ajout de 19 stations et d'un bateau soit 25 stations et 3 bateaux à partir de 1992.
modèle d'inversion : Run standart : 1992, tous les sites disponibles, CO2 et C13 traités indépendamment -----> flux S (CO2) et S13 (13CO2).
méthode isotopique : calcul des flux océanique (So) et terrestre (Sb) à partir de S, S13, des flux de déséquilibre isotopique et des fractionnements isotopiques air/mer et air/biosphère terrestre.
conclusions majeures : puit biosphérique terrestre boréal = -3.5 +- 1.8 GT
puit océanique boreal(15N-90N) = -2.7 +- 1.8 GT
source artic ecosystems (>65N) = 1+- 1.2 GT
puit biosphérique léger tropique sud = -0.3 +- 1.8 GT
source océan équatorial = 0.9 +- 1.8 GT
+ émission forte pendant la saison sèche en Afrique (feux de savanne)
+ pompage rapide de l'océan au printemps (bloom)
Description du modèle de transport TM1
Validation par des traceurs
The distribution and variations of atmospheric CO2 from 1981 to 1992 were determined by measuring CO2 mixing ratios in samples collected weekly at a cooperative global air sampling network. Analysis of the data reveals that the global CO2 growth rate has declined from a peak of ~2.5 ppm yr⁻¹ in 1987-1988 to ~0.6 ppm yr⁻¹ in 1992. The north pole-south pole CO2 difference increased from ~3 ppm during 1981-1987 to ~4 ppm during 1988-1991. In 1992 the difference was again ~3 ppm. At two-dimensional model analysis of the data indicates that the low CO2 growth rate in 1992 is mainly due to an increase in the Northern Hemisphere CO2 sink from 3.9 Gt C yr⁻¹ in 1991 to 5.0 Gt C yr⁻¹ in 1992. The increase in the north pole-south pole CO2 difference appears to result from an increase in the Southern Hemisphere CO2 sink from ~0.5 to ~1.5 Gt C yr⁻¹. -Authors
The Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) experiment, sponsored by the NASA GTE program, was a multinational field mission that took place simultaneously in Brazil, Africa, and the South Atlantic region, between the African and the Brazilian coasts. The general objective of the field mission was to investigate the tropospheric minor constituent composition, known to be disturbed by biomass burning practices. This report describes ozone measurements that were made by the Brazilian component. Two field missions in central Brazil were made with the objective of investigating ozone concentrations in the biomass burning source region: one smaller mission in the wet season period, April, and a major mission in the dry season, September/October 1992. The main field expedition during the dry season obtained data over a period of about 20 days in September and a few days in October 1992, in a savanna environment of central Brazil. Simultaneous surface ozone and ozone soundings were made. In the wet season the observation site was Goiânia (16°S, 49°W) and in the dry season, two other sites were added: Cuiabá (16°S, 56°W) and Porto Nacional (11°S, 48°W). In addition, measurements were also made at an Atlantic coast site, Natal (6°S, 35°W), outside of the savanna region, and not affected directly by the biomass burning source areas, used as a control site. The average behavior of the ozone concentrations at the different sites suggests that surface ozone concentrations tend to be rather uniform, despite different precipitation rates, but slightly larger at the drier sites. However, other factors, such as burning fuel, for example, or cloudiness, may be also important to determine ozone concentrations. This is reflected by large day-to-day variabilities that are common in the source region. The diurnal variation of the surface ozone concentrations maximize around 1600 LT. Hourly averages in September, at this time, amount to 47 parts per billion by volume (ppbv) at Porto Nacional and 40 ppbv at Cuiabá. For this station the values are lower than those of previous years (55 ppbv in 1991 and 48 ppbv in 1990). Only small differences, of the order of 5 ppbv, are observed between the source (burning) sites and Natal (the control site) in the wet season. In April, only 16 ppbv are observed at Natal. Much larger concentrations may be observed occasionally in the source areas, in the dry season. For example, at Porto Nacional, 80 ppbv have been measured at the surface and in the lower troposphere. In comparison with the coastal site, near the surface, large scatter in concentration values at Porto Nacional (20-80 ppbv) contrast with the smaller concentration range seen at Natal (20-40 ppbv). In addition, at Natal the ozone mixing ratios below about 600 hPa are distributed around a vertical gradient in which the mixing ratios increase with height, whereas at Porto Nacional in the same height region, larger concentrations and a large scatter of the data are apparent. In the upper troposphere, perhaps surprisingly, the ozone concentrations at Natal and Porto Nacional are about equal, 70 ppbv at 10 km (with larger scatter at Natal than at Porto Nacional), probably reflecting a net production of ozone along the pathways from the source regions, coupled with its longer lifetime at the higher altitudes. This data set is consistent with the hypothesis that tropical ozone in the troposphere is produced photochemically from biomass burning products in the dry season. These products are exported from the source regions to the upper atmospheric levels by dry and wet convection and once in the upper atmospheric levels are taken eastward to the South Atlantic by the prevailing winds, where they contribute to local ozone formation. The air masses at Natal, Brazil, in the lower atmospheric levels, i.e., below about 500 hPa, originate from the South Atlantic. This
Since 1978, variations in the C-13/C-12 ratio of atmospheric CO2 have been studied at a series of land stations between 33 deg N and the South Pole. In 1979 and 1980 these measurements were supplemented by sampling oceanic air from ships passing in the vicinity of three of these land stations, including Mauna Loa Observatory and Cape Kumukahi, Hawaii, and Fanning Island in the Line Island group south of Hawaii. As the new shipboard data provide additional insight into the causes of variations at the involved land stations, the present investigation is concerned with a reexamination of major aspects of the carbon isotopic distribution of atmospheric CO2 based on the land data also. The oceanic expedition involved was organized by the Global Atmospheric Research Program (GARP) to obtain meteorological data during the time from Jan. 1, 1979 to July 1, 1980. Attention is given to the analysis of the C-13/C-12 data, the identification of sources and sinks of atmospheric CO2, and aspects of oxygen isotopic variation.
Representative data on the variations of carbon dioxide in the atmosphere are presented. The data reveal a presumably natural source in the tropical oceanic areas and the industrial source of midlatitudes. Using a simple model of large-scale exchange, the meridional eddy exchange coefficient is computed to be about 3×1010 cm2 sec−1, and the meridional transport from tropical to north polar areas is computed to be about 2×1010 metric tons of carbon dioxide per year. An analysis of the seasonal variation shows that land vegetation north of 45°N is responsible for a net consumption of carbon dioxide of about 1.5×1010 tons during the vegetation period in summer. It is concluded that carbon dioxide is an excellent tracer for the study of atmospheric mixing processes. More data are needed, however, to make full use of it.
Fast response (5-s resolution) CO2 measurements were recorded
on two recent NASA-sponsored airborne atmospheric chemical survey
missions: the summer/fall 1991 Pacific Exploratory Mission-West A
(PEM-West A) and the winter 1992 Airborne Arctic Stratospheric
Expedition II (AASE II). Both missions were conducted aboard the NASA
Ames Research Center DC-8 aircraft and included sampling between the
surface and 12-km altitudes over a wide range of latitudes and
longitudes. In the following text, these data, along with simultaneous
surface measurements from the NOAA flask sampling network, are examined
to establish the vertical distribution and variability of CO2
as a function of location and season. Results indicate that middle to
upper tropospheric (>5 km altitude) CO2 concentrations
often differ considerably (>5 parts per million by volume in some
cases) from values recorded at surface stations within the same
geographic region. These differences are particularly notable at middle
to high northern latitudes where midtropospheric concentration changes
and seasonal cycles are generally delayed in time and highly damped in
amplitude relative to surface observations.
This paper evaluates the potential sources of the enhanced levels of NO that were observed throughout the upper troposphere over the equatorial and tropical South Atlantic. During September/October 1992 NOx (NO+ NO:) mixing ratios in the 8-to 13- km region averaged 150 parts per trillion by volume (pptv) and were greatly affected by what appeared as spatially large "plumes" (100 to 1000 km) with NO enhancements of over 800 parts per trillion by volume. Other trace gases were also enhanced within these plumes (e.g., CO, CO:, CH4, CH3CI, C:H:, C:H, C3H8, and PAN). However, for these tracers of surface emissions, inconsistent patterns of enhancement were found with respect to one another and to NO. We analyzed these plumes for indications of coherent relationships between the enhanced levels of NO and the enhanced levels of biogenic and combustion-related This analysis indicated that the tracer relationships were primarily produced by their common injection via deep convection into the upper troposphere. A corollary analysis using a combustion tracer reference frame in combination with meteorological analysis indicates a longer than expected lifetime of NOx in the upper troposphere. This analysis also suggests that an efficient mechanism may exist in the upper troposphere for recycling HNO3 back into NOx with a rate comparable to that predicted for the HNO3 formation. During the Transport and Atmospheric Chemistry Near the Equator Atlantic study period this in-situ formation of NOx is estimated to provide the equivalent of approximately 0.7 TgN/yr of NOx within the South Atlantic basin's upper troposphere. This magnitude of local in situ source is estimated to be comparable to the combined inputs from lightning and biomass burning, which are both injected via deep convection. Our analysis also suggests that lightning can contribute as much as half of the external input of NOx into this region of the upper troposphere with biomass burning possibly representing the remainder.
The NASA TRACE A experiment (September- October 1992) investigated effects of dry season biomass burning emissions from both South America and southern Africa on the tropical South Atlantic troposphere. Whole air canister samples were collected aboard the NASA DC-8 aircraft and analyzed for a wide range of nonmethane hydrocarbons (NMHCs) and halocarbons. Fast response in situ quantification of CH4, CO, and CO2 were also performed on the DC-8. Sampling took place over Brazilian agricultural areas and southern African savanna where there was active biomass burning. The vertical distribution of the measured gases revealed that the concentrations of most hydrocarbons, methyl halides, CH4, CO, and CO2, were enhanced in the boundary layer of these regions principally as a result of biomass fires. Brazilian and African biomass burning emission ratios were calculated for CH3Br, CH3C1, CH3I, and NMHCs relative to CO and CO2. Although both fire regions were dominated by efficient (flaming) combustion (CO/CO2 ratios
A total of 1667 whole air samples were collected onboard the NASA DC-8 aircraft during the 6-week Pacific Exploratory Mission over the western Pacific (PEM-West A) in September and October 1991. The samples were assayed for 15 C2-C7 hydrocarbons and six halocarbons. Latitudinal (0.5øS to 59.5øN) and longitudinal (114øE to 122øW) profiles were obtained from samples collected between ground level and 12.7 km. Thirteen of the 18 missions exhibited at least one vertical profile where the hydrocarbon mixing ratios increased with altitude. Longitude-latitude color patch plots at three altitude levels and three-dimensional color latitude- altitude and longitude-altitude contour plots exhibit a significant number of middle-upper tropospheric pollution events. These and several lower tropospheric pollution plumes were characterized by comparison with urban data from Tokyo and Hong Kong, as well as with natural gas and the products from incomplete combustion. Elevated levels of nonmethane hydrocarbons (NMHC) and other trace gases in the upper-middle free troposphere were attributed to deep convection over the Asian continent and to typhoon-driven convection near the western Pacific coast of Asia. In addition, NMHCs and CH3CC13 were found to be useful tracers with which to distinguish hydrocarbon and halocarbon augmented plumes emiued from coastal Asian cities into the northwestern Pacific.
The distribution and variations of atmospheric CO2 from 1981 to 1992 were determined by measuring CO2 mixing ratios in samples collected weekly at a cooperative global air sampling network. The results constitute the most geographically extensive, carefully calibrated, internally consistent CO2 data set available. Analysis of the data reveals that the global CO2 growth rate has declined from a peak of ~2.5 ppm yr-1 in 1987-1988 to ~0.6 ppm yr-1 in 1992. In 1992 we find no increase in atmospheric CO2 from 30° to 90°N. Variations in fossil fuel CO2 emissions cannot explain this result. The north pole-south pole CO2 difference increased from ~3 ppm during 1981-1987 to ~4 ppm during 1988-1991. In 1992 the difference was again ~3 ppm. A two-dimensional model analysis of the data indicates that the low CO2 growth rate in 1992 is mainly due to an increase in the northern hemisphere CO2 sink from 3.0 Gt C yr-1 in 1991 to 5.0 Gt C yr-1 in 1992. The increase in the north pole-south pole CO2 difference appears to result from an increase in the southern hemisphere CO2 sink from ~0.5 to ~1.5 Gt C yr-1.
Determination of the present global budget of atmospheric carbon dioxide (CO2) from the small and persistent concentration gradients that exist in the atmosphere is discussed. The CO2 concentration at any site results from a combination of two factors: local sources or sinks and long-range transport. To separate these two effects, an atmospheric transport model is needed. The extensive sets of global CO2 measurements of the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Monitoring for Climatic Change (GMCC) division and of the Upper Atmosphere and Space Research Laboratory of Tohoku University are combined with a two-dimensional transport model to derive, in an ``inverse'' calculation, the latitudinal and seasonal distributions of sources and sinks of CO2 necessary to reproduce the observed concentrations. The model transport parameters were previously derived from a three-dimensional general circulation model. It is found that the southern oceans are a sink of carbon of 0.8-1.5 Gt yr-1 (1 Gt equals 1015g) and that the equatorial areas are a source to the atmosphere of 1.4-2.8 Gt yr-1. Tropical deforestation as a major source of CO2 must be smaller than that because the oceans account for a significant part of the equatorial flux. There seems to be significant seasonality in the sources and sinks of CO2, both in the tropics and in the southern oceans.The seasonal net ecosystem production north of 25°N is found to be 6.2-8.2 Gt of carbon, but these estimates are probably somewhat too low. The source deduction problem is difficult to solve, especially for the middle and high latitudes in the northern hemisphere. This is due to a lack of observations over the continents, which occupy more than half of the global area at these latitudes and are the regions where the sources and sinks are most intense. Evidence is found in the results obtained for GMCC and Tohoku data that the longitudinal variability of the data is large enough, even in equatorial and southern latitudes, to prevent a two-dimehsional model from calculating a fully credible source/sink field. The longitudinal variations in the observations have to be accounted for with a three-dimensional transport model.
An extensive set of atmospheric CO2 observations were obtained during the First Global Geophysical Experiment (FGGE) Hawaii to Tahiti Shuttle expediation of 1979-1980. These data have been examined using a one-dimensional meridional diffusive transport model of the atmospheric circulation. The observed CO2 concentration field was first decomposed into three parts: a seasonal component consisting of two harmonic functions of time, with periods of 1 year and 6 months; a mean annual north-south concentration profile; and a linear trend with time, independent of latitude. In the first of two papers interpreting these data, we consider which features of the north-south eddy transport are revealed by the seasonal component of the CO2 concentration field. We assume that the FGGE data represent a zonally and vertically uniform CO2 field, and we restrict our analysis to the latitude belt between 14.5°N and 14.5°S, where seasonal sources and sinks of CO2 have minimal influence on the atmosphereic CO2 concentration. The strongest feature of the CO2 data for calibrating the model is the steadily diminishing amplitude of the annual harmonic from north to south. We show that in the absence of sources and sinks the magnitude of the eddy diffusion coefficient as a function of latitude can be perscribed from this amplitude, provided that two additional quantities are specified at a single reference location.These additional quantities are the amplitude of the first hamonic of the seasonal flux and the phase difference between that harmonic and the first harmonic of the local concentration signal. Selecting 14.5°S for this reference location, we find through comparisons of the model prediction with the FGGE CO2 data that the diffusion coefficient depends primarily on the selected amplitude of the seasonal flux and is practically independent of the phase difference. On the basis of the goodness of fit of the model predictions to the CO2 data, we set a lower limit on this flux amplitude, corresponding to an average eddy diffusion coefficient of 4.6 × 109 cm 2s-1. This is equivalent to an upper limit of 1.4 years on the interhemispheric exhange time for CO2. We are unable to set an upper limit on the diffusion coefficient because the phasing of the first harmonic inthe FGGE data shifts so slightly with latitude that even very large diffusion coefficients yield satisfactory model predictions of the seasonal CO2, concentration field. The relative variation in the diffusion coefficient withlatitude, which is derived sloely from the amplitude of the first harmonic of the CO2 data, reveals two zones of resistance to interhemispheric CO2 exchange.One, near 8°N, corresponds to the well-known intertropical convergence zone of the wind field which exists around the entire earth. The second, near 8°S, correlates with a weaker wind convergence zone in the central Pacific. This regional feature evidently affects the CO2 concentration field in the vicinity of the FGGE data set, but it may not represent a global feature.
Observations of atmospheric CO2 concentrations at Mauna Loa, Hawaii, and at the South Pole over the past four decades show an approximate proportionality between the rising atmospheric concentrations and industrial CO2 emissions. This proportionality, which is most apparent during the first 20 years of the records, was disturbed in the 1980s by a disproportionately high rate of rise of atmospheric CO2, followed after 1988 by a pronounced slowing down of the growth rate. To probe the causes of these changes, we examine here the changes expected from the variations in the rates of industrial CO2 emissions over this time, and also from influences of climate such as El Niño events. We use the 13C/12C ratio of atmospheric CO2 to distinguish the effects of interannual variations in biospheric and oceanic sources and sinks of carbon. We propose that the recent disproportionate rise and fall in CO2 growth rate were caused mainly by interannual variations in global air temperature (which altered both the terrestrial biospheric and the oceanic carbon sinks), and possibly also by precipitation. We suggest that the anomalous climate-induced rise in CO2 was partially masked by a slowing down in the growth rate of fossil-fuel combustion, and that the latter then exaggerated the subsequent climate-induced fall.
Atmospheric CO2 measurements from the NOAA Geophysical Monitoring for Climatic Change program at the Mauna Loa Observatory are presented for the period 1974-1985. Hourly and daily variations in CO2 concentration due to local sources and sinks and the long-term increase in CO2 are examined. IT is shown that the seasonal cycle was increasing at a rate of 0.05 + or - 0.02 ppm/yr. The average CO2 growth rate for the period is 1.42 + or - 0.02 ppm/yr. The fraction of CO2 remaining in the atmosphere from fossil fuel combustion is found to be 59 percent.
A semiautomatic nondispersive infrared analyzer apparatus has been developed for analysis of up to 50 COâ air samples per day. The samples are collected in 500-ml glass flasks and are transferred to the analyzer with a novel, free-floating piston pump. Sample and calibration gas transfer operations are controlled by a microprocessor, and data are recorded, analyzed, and output by a Hewlett-Packard 9845A/S desktop computer. The apparatus is described, including operating and test modes, and performance characteristics determined from 2 years of operation are given. 7 references, 5 figures, 5 tables.
This document describes the compilation, content, and format of the most comprehensive C0{sub 2}-emissions database currently available. The database includes global, regional, and national annual estimates of C0{sub 2} emissions resulting from fossil-fuel burning, cement manufacturing, and gas flaring in oil fields for 1950--92 as well as the energy production, consumption, and trade data used for these estimates. The methods of Marland and Rotty (1983) are used to calculate these emission estimates. For the first time, the methods and data used to calculate CO, emissions from gas flaring are presented. This C0{sub 2}-emissions database is useful for carbon-cycle research, provides estimates of the rate at which fossil-fuel combustion has released C0{sub 2} to the atmosphere, and offers baseline estimates for those countries compiling 1990 C0{sub 2}-emissions inventories.
In the second of two papers interpreting atmospheric CO2 observations obtained during the First Global Geophysical Experiment (FGGE) Hawaii to Tahiti Shuttle expedition of 1979-1980, we consider features of the atmospheric CO2 cycle revealed by the mean annual component of the CO2 concentration field. For this purpose the FGGE data, after decomposition into seasonal, secular, and north-south varying components, were extended to 71°N and to the south pole by included smoothed mean annual data based on CO2 observations at seven land stations. The resulting mean annual north-south profile was referred to a datum of January 1, 1980. An additional profile for January 1, 1962, was derived from observations at five land stations, at an Arctic ice floe station, and from ships, during the period 1960-1963. Both profiles have been examined using a one-dimensional meridional diffusive transport model of the atmospheric circulation in which the latitudinal dependence of the eddy diffusion coefficient between 14.5°N and 14.5°S has been determined from seasonal variations in atmospheric CO2, and its mean value estimated from halocarbon and 85Kr data. The difference between the two CO2 concentration profiles is explained as being due almost entirely to the combustion of fossil fuels, which caused 2.7 × 1015 g more carbon to be injected into the air in 1980 than in 1962, predominantly north of 14.5°N. A residual profile was obtained by subtracting the predicted effect of the injection of fossil fuel CO2 from the 1980 profile. This residual profile has a peak concentration near the equator which, according to the model, is a result of the release of 5.0 × 1015 g yr-1 of carbon to the atmosphere between 14.5°N and 14.5°S, balanced by an equal removal from the atmosphere poleward of these latitudes.The source-sink couple inferred to produce this CO2 exchange is consistent with the distribution of CO2 partial pressure in the equatorial ocean surface water, as observed on the FGGE Shuttle Expedition, provided that the air-sea exchange rate of CO2 there is 30 mol m-2 yr-1. This exaggerated rate probably reflects the lack of vertical resolution in the model, such that the CO2 concentration near the sea surface is assumed to apply to the entire air column. The residual profile also shows a higher average concentration in the southern hemisphere than in the northern. The cause of this difference, of the order of 1 ppm, could not be resolved by the model owing to lack of information on the character of sources and sinks and transport behavior poleward of 14.5°N and 14.5°S it may be owing to either oceanic or land biospheric CO2 exchange with the air or even to time dependent atmospheric transport.
The North-South gradient of atmospheric CO2 is commonly used to infer the latitudinal distribution of sources and sinks at the earth surface. Here we analyze the East–West and vertical gradients occurring at regional scale over the subtropical/subantarctic ocean (around 30°S−45°S), which is known to be the major sink of the southern hemisphere. Using French and Australian inter calibrated datasets, we find a significant depletion of atmospheric CO2 near Tasmania (Cape Grim, 40°41′S, 144°41′E, CGO) compared to the open Indian Ocean (Amsterdam Is., 37°48′S, 77°32′E, AMS). This depletion was about − 0.4 ± 0.2 ppmv for the 1988–1992 period. For the same period, CGO values were also depleted by − 0.85 ± 0.25 ppmv and − 1.1 ± 0.4 ppmv relative to the mid- and high-troposphere. Using a 3-D atmospheric transport model based on meteorological analysis, and a diagnostic CO2 flux scenario updated for the year 1990, we investigate the respective role of industrial, oceanic and biospheric fluxes. The main component which can explain such longitudinal and vertical oceanic sink appears to be the subtropical/subantarctic oceanic sink and its regional patterns. Using the oceanographic datasets in the Atlantic, Pacific, and West Indian oceans, we can reconstruct more than half of vertical gradient observed over CGO, but not the CGO depletion relative to AMS. Finally, we discuss the hypothesis of an extra oceanic CO2 sink south of the Australian mainland.
Systematic collection of air samples over the Pacific Ocean was begun in March 1982 on board a container ship sailing between Japan and Australia. A current picture of seasonal and meridional variations of lower tropospheric CO2 was derived from the measurement of these samples and supplementary information from several other observational programs. It was concluded that: (1) the amplitude of the seasonal variation was about 15 ppmv in high and mid-latitudes of the northern hemisphere and decreased southward to low values of about 1 ppmv in the southern hemisphere; (2) the maximum and minimum concentrations of the seasonal variation in the mid-latitudes of the northern hemisphere appeared early in April and in mid-August, respectively, and their occurrences were delayed gradually southward and northward from that latitude; (3) the annual mean CO2 concentration was high in the mid-northern hemisphere, decreased gradually southward to low values in the mid-southern hemisphere and increased slightly again in the Antarctic region, the concentration difference between the mid-northern hemisphere and the Antarctic region being about 3 ppmv; (4) the year-to-year changes of annual mean CO2 concentrations in all latitudes covered by this measurement were 1.3 and 1.7 ppmv yr−1, for 1982–1983 and 1983–1984, respectively.
The Pacific Exploratory Mission (PEM)-Tropics provided extensive aircraft data to study the atmospheric chemistry of tropospheric air in Pacific Ocean regions, extending from Hawaii to New Zealand and from Fiji to east of Easter Island. This region, especially the tropics, includes some of the cleanest tropospheric air of the world and, as such, is important for studying atmospheric chemical budgets and cycles. The region also provides a sensitive indicator of the global-scale impact of human activity on the chemistry of the troposphere, and includes such important features as the Pacific "warm pool," the Intertropical Convergence Zone (ITCZ), the South Pacific Convergence Zone (SPCZ), and Walker Cell circulations. PEM-Tropics was conducted from August to October 1996. The ITCZ and SPCZ are major upwelling regions within the South Pacific and, as such, create boundaries to exchange of tropospheric air between regions to the north and south. Chemical data obtained in the near vicinity of the ITCZ and the SPCZ are examined. Data measured within the convergent zones themselves are not considered. The analyses show that air north and south of the convergent zones have different chemical signatures, and the signatures are reflective of the source regions and transport histories of the air. Air north of the ITCZ shows a modest urban/industrialized signature compared to air south of the ITCZ. The chemical signature of air south of the SPCZ is dominated by combustion emissions from biomass burning, while air north of the SPCZ is relatively clean and of similar composition to ITCZ south air. Chemical signature differences of air north and south of the zones are most pronounced at altitudes below 5 km, and, as such, show that the ITCZ and SPCZ are effective low-altitude barriers to the transport of tropospheric air. At altitudes of 8 to 10 km, chemical signatures are less dissimilar, and air backward trajectories (to 10 days) show cross-convergent-zone flow. At altitudes below about 5 km, little cross-zonal flow is observed. Chemical signatures presented include over 30 trace chemical species including ultrafine, fine, and heated-fine (250øC) aerosol.
Of late years there has been much interest in the effect of human activities on the natural circulation of carbon. This demands a knowledge of the amount of CO2 in atmosphere both now and in the immediate past. Here the average amount obtained by 30 of the most extensive series of observations between 1866 and 1956 is presented, and the reliability of the 19th century measurements discussed. A base value of 290 p.p.m. is proposed for the year 1900. Since then the observations show a rising trend which is similar in amount to the addition from fuel combustion. This result is not in accordance with recent radio carbon data, but the reasons for the discrepancy are obscure, and it is concluded that much further observational data is required to clarify this problem. Some old values, showing a remarkable fall of CO2 in high southern latitudes, are assembled for comparison with the anticipated new measurements, to be taken in this zone during the Geophysical Year.
Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO2) and methane (CH4). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH4/ppm CO2, a standard error of 0.6, and a correlation coefficient (r2) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.
A new automatic flask sampling system for the Boeing 747 commercial airliner was developed to observe CO2 and CH4 mixing ratios in the upper atmosphere at altitudes of 9–13 km. It was confirmed by a test flight that sample air collected using our system was useful for precise measurements of the trace gases in the upper atmosphere. Monthly air sampling was performed over the western Pacific between Narita in Japan and Cairns in Australia during 1993–1994. Measurements of both CO2 and CH4 in the Northern Hemisphere showed a clear seasonal cycle that was largely influenced by the seasonal variation in the lower troposphere. A significant decrease of mixing ratio during the winter season was observed in the CH4 variation, suggesting the intrusion of lower stratospheric air into the upper troposphere. The seasonal variation of both the gases gradually decayed toward the equator, but a different seasonal cycle appeared in the Southern Hemisphere. This change indicated the significance of meridional transport of both gases through the upper troposphere into the Southern Hemisphere. The mixing ratio level of both gases showed a recent increase in the upper troposphere.
During the Amazon Boundary Layer Experiment, approximately 100 hours of in situ carbon monoxide measurements were obtained using a tunable diode laser sensor that provided continuous, fast-response (about 1 s) measurements. This data set, taken on board the NASA Electra between July 12 and August 12, 1985, characterizes the temporal and spatial changes in the CO distribution over the Amazon Basin as meteorological conditions progressed from the early to middle phases of the 1985 day season. Early dry-season CO values of 75-95 ppbv were generally observed in the PBL. As the dry season became well established, biomass burning and a persistent capping inversion at about 3 km profoundly altered the CO distribution, with PBL values typically reaching 150-275 ppbv. Concentrations as high as 800 ppbv were measured within identifiable haze layers. An analysis of satellite imagery shows that biomass burning was occurring along the Amazon River system and in savannah areas located more than 1000 km south of the region sampled.
Approximately 250,000 measurements made for the pCO2 difference between surface water and the marine atmosphere, DeltapCO2, have been assembled for the global oceans. Observations made in the equatorial Pacific during El Nino events have been excluded from the data set. These observations are mapped on the global 4 degrees x 5 degrees grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Nino year. Monthly global distributions of DeltapCO2 have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using DeltapCO2 distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-Cyr-1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. These estimates are subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of DeltapCO2 over the global oceans. Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.
A synthesis of the global methane cycle is presented to attempt to generate an accurate global methane budget. Methane-flux measurements, energy data, and agricultural statistics are merged with databases of land-surface characteristics and anthropogenic activities. The sources and sinks of methane are estimated based on atmospheric methane composition and variations, and a global 3D transport model simulates the corresponding atmospheric responses. The geographic and seasonal variations of candidate budgets are compared with observational data, and the available observations are used to constrain the plausible methane budgets. The preferred budget includes annual destruction rates and annual emissions for various sources. The lack of direct flux measurements in the regions of many of these fluxes makes the unique determination of each term impossible. OH oxidation is found to be the largest single term, although more measurements of this and other terms are recommended.
Science Applications International Corporation, 1 Enterprise Parkway
- D J Westberg
D. J. Westberg, Science Applications International Corporation, 1 Enterprise Parkway, Suite 300, Hampton, VA 23666. (Received October 10, 1997; revised April 20, 1998; accepted April 22, 1998.)
CO 2 emissions-modern record, in Trends 1991: A Compendium f Data on Global Change
- G Marland
- T A Boden
Marland, G., and T. A. Boden, CO 2 emissions-modern record, in Trends 1991: A Compendium f Data on Global Change, edited by T. A. Boden, R. J. Sepanski, and F. W. Stoss, 665 pp., Carbon Dioxide Inf. Anal. Cent., Oak Ridge Nat. Lab., Oak Ridge, Tenn., 1991.
Global, regional, and national CO 2 emission estimates from fossil fuel burning, cement production, and gas flaring: 1950-1994, NDP-O30/R7, Carbon Dioxide Inf
- G Marland
- R J An&es
- T A Boden
Marland, G., R. J. An&es, and T. A. Boden, Global, regional, and national CO 2 emission estimates from fossil fuel burning, cement production, and gas flaring: 1950-1994, NDP-O30/R7, Carbon Dioxide Inf. Anal. Cent. (CDIAC) Oak Ridge, Tenn., spring 1997.
A mete-orological overview of the PEM-Tropics period
- H E Fuelberg
- R E Newell
- S P Longmore
- Y Zhu
- D J Westberg
- E V Browell
- D R Blake
- G R Gregory
- G W Sachse
Fuelberg, H. E., R. E. Newell, S. P. Longmore, Y. Zhu, D. J. Westberg, E. V. Browell, D. R. Blake, G. R. Gregory, and G. W. Sachse, A mete-orological overview of the PEM-Tropics period, J. Geophys. Res., this issue.
The Pacific Exploratory Mission in the tropical Pacific: PEM-Tropics A this issue. Intergovernmental Panel on Climate Change, Climate Change: The IPCC Scientific Assessment Intergovernmental Panel on Climate Change, Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment
- R J Fuelberg
- I Mcneal
- R J Raper
- J T Bendura
- G J Houghton
- J J Jenkins
- Ephraums
Fuelberg, R. J. McNeal, I. Raper, and R. J. Bendura, The Pacific Exploratory Mission in the tropical Pacific: PEM-Tropics A, August-September 1996, J. Geophys. Res., this issue. Intergovernmental Panel on Climate Change, Climate Change: The IPCC Scientific Assessment, edited by J. T. Houghton, G. J. Jenkins, and J. J. Ephraums, 365 pp., Cambridge U@BULLETfiv. Press, New York, 1990. Intergovernmental Panel on Climate Change, Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment, edited by J.T. Houghton, B. A. Callarider, and S. K. Varney, 200 pp., Cambridge Univ. Press; New York, 1992. Jaffe, B., in New Worm of Chemistry, p. 358, Silver Burdett, New York, 1942.
Temporal and spa-tial variations of upper tropospheric and lower stratospheric carbon dioxide Longitudinally different variations of lower tropospheric carbon diox-ide concentrations over the North Pacific Ocean
- V W J H Kirchhoff
- J R Alves
- F R Silva
- J Fishman
- K Miyashita
- S Aoki
- M Tanaka
- T Nakazawa
- S Murayama
- K Miyashita
- S Aoki
- M Tanaka
Kirchhoff, V.W.J.H., J. R. Alves, F. R. da Silva, and J. Fishman, Observations of ozone concentrations in the Brazilian Cerrado during Nakazawa, T., K. Miyashita, S. Aoki, and M. Tanaka, Temporal and spa-tial variations of upper tropospheric and lower stratospheric carbon dioxide, Tellus, Ser. B, 43, 106-111, 1991. Nakazawa, T., S. Murayama, K. Miyashita, S. Aoki, and M. Tanaka, Longitudinally different variations of lower tropospheric carbon diox-ide concentrations over the North Pacific Ocean, Tellus, Ser. B, 44, 161-172, 1992.
Three-month tracer diffusion experiments and their seasonal difference in interhemispheric mass exchange in the troposphere Research Activities in Atmospheric and Oceans ModellingRep
- Y Nikaidou
Nikaidou, Y., Three-month tracer diffusion experiments and their seasonal difference in interhemispheric mass exchange in the troposphere, in Research Activities in Atmospheric and Oceans Modelling, Rep. 13, WMO/TD, 332, pp. 7.21-7.22, World Meteorol. Org., Geneva, 1989.