No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Sulfur dioxide distribution over the Pacific Ocean 1991-1996
Abstract
In this study we combined the sulfur dioxide (SO2) data from the NASA Pacific Exploratory Missions (PEM) and the First Aerosol Characterization Experiment (ACE 1) to create a data set containing 4679 observations of SO2 in the troposphere of the Pacific Ocean during the period 1991-1996. These data have exceptionally high precision due to the use of isotopically labeled SO2 as an internal standard in each sample. The lower limit of detection was less than 2 pptv. The spatial extent of the data ranged from 60°N to 72°S, 110°E to 80°W, and from 50 m to 12 km above the ocean surface. A significant zonal gradient was observed between the northern and southern hemispheres. The western North Pacific was particularly well characterized during the NASA PEM-West A and B missions that focused on that region. Our data show that anthropogenic sources in eastern Asia dominated the sulfur chemistry in the lower troposphere of the western North Pacific eastward from the Asian continent for more than 1500 km and substantially farther in the mid and upper troposphere. The impact of Asian sources far from the continent was due primarily to transported SO2 with a substantially smaller impact from transported sulfate. Dimethyl sulfide was a significant source of SO2 only in the tropical boundary layer. In the southern hemisphere, anthropogenic sources had much less impact with very little SO2 detected in biomass burning plumes. Sulfur dioxide in the middle and upper troposphere of both hemispheres was strongly influenced by volcanic sources. Sulfur dioxide from the eruption of Mount Pinatubo dominated the SO2 distribution in the upper troposphere in the northern hemisphere in the second half of 1991. A significant fraction of the SO2 in the upper free troposphere in the northern hemisphere was attributed to SO2 transported from the stratosphere to the upper troposphere. Evidence for the transport of SO2 from the stratosphere to troposphere existed as far south as 30°N, but it was most intense at high latitudes. In the absence of major volcanic activity, such as the cataclysmic eruption of Mount Pinatubo, volcanic sources in East Asia contribute significant amounts of SO2 in the mid and upper troposphere of the northern hemisphere. In the southern hemisphere where anthropogenic sources are much weaker, volcanoes may contribute most of the SO2 found in the mid and upper troposphere. Deep convection by tropical and extratropical storms appeared to be a significant process contributing to long-range transport of volcanic SO2 for the southern hemisphere.
... In Fig. 7 we show a collection of published airborne measurements of SO 2 mainly observed before the year 2000 (Jaeschke et al., 1976;Inn and Vedder, 1981;Meixner, 1984;Möhler and Arnold, 1992;Reiner et al., 1998;Thornton et al., 1999;Jaeschke et al., 1999;Curtius et al., 2001). These are compared to MIPAS data of similar geographic range and season excluding periods of strong volcanic influence. ...
... In the northern high and mid-latitudes, e.g. in Meixner (1984), Möhler and Arnold (1992) and Reiner et al. (1998), the values increase with lower altitudes, which is re- flected in the MIPAS data set. At more remote regions like over the equatorial and southern Pacific Ocean, Thornton et al. (1999) observed in general lower SO 2 mixing ratios than in the Northern Hemisphere (bottom row in Fig. 7). This is reflected mainly by the MIPAS data which show a weaker vertical gradient compared to the observations in the north and are in magnitude similar to the Thornton et al. (1999) observations in the equatorial region. ...
... At more remote regions like over the equatorial and southern Pacific Ocean, Thornton et al. (1999) observed in general lower SO 2 mixing ratios than in the Northern Hemisphere (bottom row in Fig. 7). This is reflected mainly by the MIPAS data which show a weaker vertical gradient compared to the observations in the north and are in magnitude similar to the Thornton et al. (1999) observations in the equatorial region. However, at southern subtropical and mid-latitudes MIPAS values are higher than the in situ data by 20-30 pptv. ...
Vertically resolved distributions of sulfur dioxide (SO2) with global coverage in the height region from the upper troposphere to ~20 km altitude have been derived from observations by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat for the period July 2002 to April 2012. Retrieved volume mixing ratio profiles representing single measurements are characterized by typical errors in the range of 70–100 pptv and by a vertical resolution ranging from 3 to 5 km. Comparison with observations by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) revealed a slightly varying bias with altitude of −20 to 50 pptv for the MIPAS data set in case of volcanically enhanced concentrations. For background concentrations the comparison showed a systematic difference between the two major MIPAS observation periods. After debiasing, the difference could be reduced to biases within −10 to 20 pptv in the altitude range of 10–20 km with respect to ACE-FTS. Further comparisons of the debiased MIPAS data set with in situ measurements from various aircraft campaigns showed no obvious inconsistencies within a range of around ±50 pptv. The SO2 emissions of more than 30 volcanic eruptions could be identified in the upper troposphere and lower stratosphere (UTLS). Emitted SO2 masses and lifetimes within different altitude ranges in the UTLS have been derived for a large part of these eruptions. Masses are in most cases within estimations derived from other instruments. From three of the major eruptions within the MIPAS measurement period – Kasatochi in August 2008, Sarychev in June 2009 and Nabro in June 2011 – derived lifetimes of SO2 for the altitude ranges 10–14, 14–18 and 18–22 km are 13.3 ± 2.1, 23.6 ± 1.2 and 32.3 ± 5.5 days respectively. By omitting periods with obvious volcanic influence we have derived background mixing ratio distributions of SO2. At 10 km altitude these indicate an annual cycle at northern mid- and high latitudes with maximum values in summer and an amplitude of about 30 pptv. At higher altitudes of about 16–18 km, enhanced mixing ratios of SO2 can be found in the regions of the Asian and the North American monsoons in summer – a possible connection to an aerosol layer discovered by Vernier et al. (2011b) in that region.
... With increasing economic growth in the northern hemisphere, particularly in Asia, atmospheric SO 2 concentrations are rising in regions formerly considered pristine. The impact of anthropogenic activity in East Asia is clearly visible over the western Pacific [Blake et al., 1997;Gregory et al., 1996;Talbot et al., 1996;Thornton et al., 1999]. Recent measurements over the Indian Ocean revealed considerable impact from southern Asia [Lelieveld et al., 2001]. ...
... [3] Our previous measurements of SO 2 by GC/MS/ILS [Bandy et al., 1992[Bandy et al., , 1993Thornton et al., 1999] had a frequency of one sample every 3 to 3.5 min. The sample frequency was determined by the chromatographic retention time. ...
... [5] In the middle and upper free troposphere, anthropogenic SO 2 is often correlated with anthropogenic tracers such as O 3 , NO x , and hydrocarbons [Blake et al., 1997;Gregory et al., 1996;Talbot et al., 1996;Thornton et al., 1997Thornton et al., , 1999. Vertical profiles of SO 2 and O 3 with high spatial resolution are useful in determining the fate of SO 2 and its role in new particle production in the free troposphere. ...
[1] An atmospheric pressure ionization mass spectrometer (APIMS) was developed to determine atmospheric sulfur dioxide (SO2). High precision and immunity to sample loss, fluctuations in instrument sensitivity, etc., were achieved by adding isotopically labeled SO2 (34S16O2) continuously to the manifold as an internal standard. During the NASA Transport And Chemical Evolution Over The Pacific (TRACE P) program and the National Science Foundation (NSF) Passing Efficiency of the Low Turbulence Inlet (PELTI) program, 32S16O2 and 34S16O2 were each determined with integration times of 20 ms. From these data the ambient SO2 level was computed every 40 ms. In the PELTI studies at SO2 levels of approximately 60 parts per trillion by volume (pptv), vertical fluxes were determined with a precision better than 10%. When the data were averaged to 1 s, the lower limit of detection was
... rface aerosol concentrations are very well reproduced. Possible reasons for the overestimation of the ultrafine aerosol include overestimated SO 2 concentrations, underestimated loss rates onto aerosol and cloud particles, overestimated particle formation rates, and specifics of the M7 aerosol microphysics module, which we discuss in the following.Thornton et al., 1999) 1991-1996 geometric mean of 5° × 5° data (Thornton et al., 1999) bClarke and Kapustin, 2002 ). (b) Model SO2 number mixing ratio and observations from Thornton et al. (1999), grouped in the altitude bands 0–0.5 km, 0.5–4 km, 4–8 km, and 8–12 km, indicated by vertical bars, in blue (arithmetic mean) and red (geometric mean). (1999), gro ...
... Near-surface aerosol concentrations are very well reproduced. Possible reasons for the overestimation of the ultrafine aerosol include overestimated SO 2 concentrations, underestimated loss rates onto aerosol and cloud particles, overestimated particle formation rates, and specifics of the M7 aerosol microphysics module, which we discuss in the following.Thornton et al., 1999) 1991-1996 geometric mean of 5° × 5° data (Thornton et al., 1999) bClarke and Kapustin, 2002 ). (b) Model SO2 number mixing ratio and observations from Thornton et al. (1999), grouped in the altitude bands 0–0.5 km, 0.5–4 km, 4–8 km, and 8–12 km, indicated by vertical bars, in blue (arithmetic mean) and red (geometric mean). ...
... Possible reasons for the overestimation of the ultrafine aerosol include overestimated SO 2 concentrations, underestimated loss rates onto aerosol and cloud particles, overestimated particle formation rates, and specifics of the M7 aerosol microphysics module, which we discuss in the following.Thornton et al., 1999) 1991-1996 geometric mean of 5° × 5° data (Thornton et al., 1999) bClarke and Kapustin, 2002 ). (b) Model SO2 number mixing ratio and observations from Thornton et al. (1999), grouped in the altitude bands 0–0.5 km, 0.5–4 km, 4–8 km, and 8–12 km, indicated by vertical bars, in blue (arithmetic mean) and red (geometric mean). (1999), grouped in the altitude bands 0–0.5 km, 0.5–4 km, 4–8 km, and 8–12 km, indicated by vertical bars, in blue (arithmetic mean) and red (geometric mean). ...
Nucleation from the gas phase is an important source of aerosol particles in the Earth's atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosol-climate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth's radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are −1.15 W/m2 for charged H2SO4/H2O nucleation, −0.235 W/m2 for cluster activation, and −0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is −2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with −2.18 W/m2 to total absorbed solar short-wave radiation, compared to −0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth's radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.
... 10 Figure 4a shows latitudinal variation in SO 2 mixing ratios in the Pacific upper troposphere between 8 and 12 km from model calculations and PEM-TA, PEM-TB, and ACE-2 aircraft observations (Thornton et al., 1999). Our calculations are slightly lower than the observations, but generally within or close to the observed variability. ...
... (a) Calculated SO 2 concentration between 8-12 km at varying latitudes compared to an average of Pacific Exploratory Mission (PEM)-West A, PEM-West B, and Atmospheric Chemistry Experiment (ACE)-2 aircraft observations over the Pacific Ocean between 110 ? E and 80? W, binned into 10-degree segments with error bars representing plus/minus one standard deviation(Thornton et al., 1999). Model calculations are an annual average in the same longitude and altitude region. ...
Using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA), we studied aerosol formation and microphysics in the tropical upper troposphere and lower stratosphere (UTLS) based on three nucleation schemes (two binary homogeneous schemes and an ion-mediated scheme). Simulations suggest that ion-mediated nucleation rates in the UTLS are 25% higher than binary rates, but that the rates predicted by the two binary schemes vary by two orders of magnitude. However, it is found that coagulation, not nucleation, controls number concentration at sizes greater than approximately 10 nm. Therefore, based on this study, atmospherically relevant processes in the UTLS are not sensitive to the choice of nucleation schemes. The dominance of coagulation over other microphysical processes is consistent with other recent work using microphysical models. Simulations using all three nucleation schemes compare reasonably well to observations of size distributions, number concentration across latitude, and vertical profiles of particle mixing ratio in the UTLS. Interestingly, we find we need to include Van der Waals forces in our coagulation scheme to match the UTLS aerosol concentrations. We conclude that this model can accurately represent sulfate microphysical processes in the UTLS, and that the properties of particles at atmospherically relevant sizes are not sensitive to the details of the nucleation scheme. We also suggest that micrometeorites, which are not included in this model, dominate the aerosol properties in the upper stratosphere above about 30 km.
... The most likely sources of these plumes were ships, which were occasionally observed visually. While RICO was considered " clean " for aerosol concentrations compared to continental or near shore conditions, the SO 2 concentrations were much higher than those encountered in the central Pacific CBL (Thornton et al., 1999; Bandy et al., 1996). The SO 2 plumes in the CBL during the early part of RF14 were remarkable in their magnitude and areal extent for a region expected to be clean with a long fetch of TW. ...
... The cold pools are marked by decreases in equivalent potential temperature ( e ) and decreases in turbulence compared to the warmer CBL air. RF14 was similar to many RICO flights in the CBL with SO 2 concentrations typical of northern hemisphere marine CBL (Thornton et al., 1993; Tu, 2004 ) but atypical of a remote TW CBL in the Pacific (Thornton et al., 1999 ). Although the region appeared free of the impacts of continental sources, numerous ships transited the area (Capaldo et al., 1999 ) as well as the presence of the R/V Seward Johnson , which provided a platform for a cloud radar and a wind profiler. ...
During the Rain in (shallow) Cumulus over the Ocean (RICO) project simultaneous high rate sulfur dioxide (SO<sub>2</sub>) measurements and cloud condensation nuclei (CCN) spectra were made for the first time. For research flight 14 (14 January 2005) the convective boundary layer was impacted by precipitation and ship plumes for much of the midday period but not in the late afternoon. Number densities of accumulation mode aerosols (0.14 to 0.2 μm diameter) were a factor of two greater in the later period while CCN were 35% to 80% greater for aerosols that activate at supersaturations >0.1%. Linear correlations of SO<sub>2</sub> and CCN were found for SO<sub>2</sub> concentrations ranging from 20 to 600 parts-per-trillion (pptv). The greatest sensitivities were for SO<sub>2</sub> and CCN that activate at supersaturations >0.1% for both clean and polluted air. In a region unaffected by pollution SO<sub>2</sub> was linearly correlated only with CCN at >0.2% supersaturation. These correlations imply that the smallest CCN may be activated by SO<sub>2</sub> through heterogeneous conversion. Evidence for entrainment of CCN from the cloud layer into the CBL was found.
... Comparisons of modeled SO 2 to observations are provided in Figure and Atmospheric Chemistry Experiment (ACE)-2 aircraft observations [Thornton et al., 1999]. ...
... The model calculations are slightly lower than the observations, but generally within or close to the observed variability. , and ACE-2 aircraft observations over the Pacific Ocean between 110°E and 80°W, binned into 10-degree segments with error bars representing plus/minus one standard deviation [Thornton et al., 1999]. Model calculations are an annual average in the same longitude and altitude region. ...
Stratospheric aerosols can influence radiative forcing and atmospheric
chemistry, yet much remains to be learned about their sources and
evolution. To improve understanding of these processes, a sulfate
aerosol microphysical sectional model coupled to a climate model
(WACCM/CARMA) has been developed. This model includes sulfur emissions,
a 63-species chemistry module, and aerosol microphysics (nucleation,
coagulation, growth, and deposition). This model was utilized to study
stratospheric aerosol under ambient conditions as well as from large
volcanic eruptions and hypothetical climate engineering scenarios.
Simulations of ambient aerosol using three nucleation schemes reveal
that one theory for ion-induced nucleation from galactic cosmic rays
predicts 25% higher nucleation rates in the upper troposphere and lower
stratosphere (UTLS) than its related binary homogeneous nucleation
scheme, but that the rates predicted by two binary schemes vary by two
orders of magnitude. None of the nucleation schemes are superior at
matching the limited observations available at the smallest sizes. It is
found that coagulation, not nucleation, controls number concentration at
sizes greater than approximately 10 nm, suggesting that processes
relevant to atmospheric chemistry and radiative forcing in the UTLS are
not sensitive to the choice of nucleation schemes. Simulations using all
three nucleation schemes compare reasonably well to observations of
aerosol size distributions, number concentrations, and mass in the UTLS.
The inclusion of van der Waals forces in the coagulation scheme improves
comparison to observations in the UTLS. Simulations of the Mount
Pinatubo eruption find stratospheric aerosol mass and aerosol optical
depth (AOD) to increase by two orders of magnitude, in agreement with
observations, highlighting the eruption's significant impact on
stratospheric aerosol. The model predicts effective radius to triple six
months after the eruption and 525 nm AOD to increase to 0.45 three
months after the eruption in the tropics, in agreement with
observations. In the mid- and highlatitude Southern Hemisphere, the
simulated 525 nm AOD is about one-third that of observations 3 months
after the eruption, which may be due to the August eruption of Cerro
Hudson in Chile, which is not included in the model. Simulated 525 nm
AOD spans a narrower range than observations, tapers more quickly, and
peaks at 5°N while the data peaks at 5°S. Possible explanations
for these differences include the lack of ash, aerosol heating or the
Cerro Hudson eruption in the model, unmatched winds for the year 1991,
or biases in the data. Simulations of stratospheric sulfur injection
scenarios reveal numerous insights into the efficacy and consequences of
hypothetical geoengineering scenarios. Continuous SO2 injection in a
narrow region at the equator is found to have limited efficacy at higher
injection rates, while broadening the injection region or injecting SO4
particles instead of SO 2 gas can increase sulfate burden, in agreement
with previous work. Injection of H2SO4 gas does not increase burdens
compared to SO2, in disagreement with previous work using a plume model.
It is suggested that the results found in the plume model were not due
to injecting H2SO4, but rather to converting gases to particles.
Considerably more research is needed on plumes to test assumptions made
during modeling studies. Additionally, stratospheric geoengineering
significantly perturbs tropospheric aerosol mass burden, number, and
size distributions at much greater levels than simulated for the
eruption of Mount Pinatubo. Tropospheric burdens increase by a factor of
two or three, with the majority of the increases occurring at all
latitudes in the 100 hPa thick layer just below the tropopause, as well
as most of the troposphere at high latitudes. These perturbations could
impact upper tropospheric radiative forcing or chemistry, highlighting
the need to further study the efficacy and consequences of
geoengineering before its employment is seriously considered.
... [3] The average mixing ratio of SO 2 in the free troposphere away from polluted regions is estimated at 15-100 ppt [Thornton et al., 1997[Thornton et al., , 1999. Continental concentrations in the planetary boundary layer (PBL) depend mainly on anthropogenic emissions and range from 20 ppt to hundreds of ppb [Seinfeld and Pandis, 1998]. ...
... The resulting SCD REF was 0.115 DU ± 100%. This value is within the range of reported concentrations for clean continental area [Thornton et al., 1999;U. S. EPA, 2008]. ...
The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA Aura satellite measures a suite of trace gases including SO2. Since its launch in July 2004, OMI has made many measurements of SO2 including natural sources such as explosive and effusive volcanic eruptions and volcanic passive degassing, and human sources such as coal power plants, metal smelters, and oil refineries. Validation of these measurements is very difficult because of OMI reduced sensitivity to SO2 in the planetary boundary layer and the transient nature of volcanic plumes. The recent eruption of the Okmok volcano in the Aleutian islands provided a unique opportunity for high quality validation because the plume spent several days moving over a research-grade ground-based spectrometer located in Washington state, the multi-function differential absorption spectroscopy (MFDOAS) instrument. This instrument provided accurate determinations of column abundance of SO2 in the Okmok plume using the direct sun as a source with an estimated accuracy less than 0.2 DU, which is an order of magnitude better than data from the operational Brewer spectrophotometer network. We discuss our instrumentation, data reduction technique and SO2 time series results during 2 days of observations of the Okmok plume over Pullman, WA. Measured SO2 column amount ranged from 0.5 DU to 5DU ( 1 DU, Dobson Unit =2.69*10**16 molecules/cm**2) due to inhomogeneity of the plume. Direct overpass comparison with OMI shows good qualitative agreement with OMI operational low stratospheric SO2 data. Corrections for the OMI field of view, SO2 plume height, and temperature improve agreement further as well as comparisons with the off-line Iterative Spectral Fit (ISF) algorithm. This case study provides critical validation of the volcanic OMI SO2 measurements.
... A peak occurs in the tropics above 25 km where OCS is converted into SO 2 , and SO 2 increases again in the upper stratospheric due to photolytic conversion of H 2 SO 4 back to SO 2 (Mills et al., 2005). Figure 4a shows latitudinal variation in SO 2 mixing ratios in the Pacific upper troposphere between 8 and 12 km from model calculations and PEM-TA, PEM-TB, and ACE-2 aircraft observations (Thornton et al., 1999). Our calculations are slightly lower than the observations, but generally within or close to the observed variability. ...
... H 2 SO 4 also has a local maximum in the Northern Hemisphere subtropical upper troposphere due to availability of SO 2 and OH for chemical conversion. As Fig. 5b shows, calculated H 2 SO 4 mixing ratios are generally within the standard deviation of PEM-TA aircraft observations (Lucas and Prinn, and Atmospheric Chemistry Experiment (ACE)-2 aircraft observations over the Pacific Ocean between 110 • E and 80 • W, binned into 10-degree segments with error bars representing plus/minus one standard deviation (Thornton et al., 1999). Model calculations are an annual average in the same longitude and altitude region. ...
Using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA), we studied aerosol formation and microphysics in the upper troposphere and lower stratosphere (UTLS) as well as the middle and upper stratosphere based on three nucleation schemes (two binary homogeneous schemes and an ion-mediated scheme related to one of the binary schemes). Simulations suggest that ion-mediated nucleation rates in the UTLS are 25 % higher than its related binary scheme, but that the rates predicted by the two binary schemes vary by two orders of magnitude. None of the nucleation schemes is superior at matching the limited observations available at the smallest sizes. However, it is found that coagulation, not nucleation, controls number concentration at sizes greater than approximately 10 nm. Therefore, based on this study, processes relevant to atmospheric chemistry and radiative forcing in the UTLS are not sensitive to the choice of nucleation schemes. The dominance of coagulation over other microphysical processes in the UTLS is consistent with other recent work using microphysical models. Simulations using all three nucleation schemes compare reasonably well to observations of size distributions, number concentration across latitude, and vertical profiles of particle mixing ratio in the UTLS. Interestingly, we find that we need to include Van der Waals forces in our coagulation scheme to match the UTLS aerosol concentrations. We conclude that this model can reasonably represent sulfate microphysical processes in the UTLS, and that the properties of particles at atmospherically relevant sizes appear to be insensitive to the details of the nucleation scheme. We also suggest that micrometeorites, which are not included in this model, dominate the aerosol properties in the upper stratosphere above about 30 km.
... The most likely sources of these plumes were ships, which were occasionally observed visually. While RICO was considered " clean " for aerosol concentrations compared to continental or near shore conditions, the SO 2 concentrations were much higher than those encountered in the central Pacific CBL (Thornton et al., 1999; Bandy et al., 1996). The SO 2 plumes in the CBL during the early part of RF14 were remarkable in their magnitude and areal extent for a region expected to be clean with a long fetch of TW. ...
... The cold pools are marked by decreases in equivalent potential temperature ( e ) and decreases in turbulence compared to the warmer CBL air. RF14 was similar to many RICO flights in the CBL with SO 2 concentrations typical of northern hemisphere marine CBL (Thornton et al., 1993; Tu, 2004 ) but atypical of a remote TW CBL in the Pacific (Thornton et al., 1999 ). Although the region appeared free of the impacts of continental sources, numerous ships transited the area (Capaldo et al., 1999 ) as well as the presence of the R/V Seward Johnson , which provided a platform for a cloud radar and a wind profiler. ...
During the Rain in (shallow) Cumulus over the Ocean (RICO) project simultaneous measurements of high rate sulfur dioxide (SO2) measurements and cloud condensation nuclei (CCN) spectra were made for the first time. During research flight 14 (14 January 2005) the convective boundary layer was impacted by precipitation and ship plumes in midday but not in the late afternoon. Accumulation mode aerosols (0.14 to 0.2 mum diameter) were a factor of two greater in the latter period while CCN were 30 % to 65 % greater for aerosols that activate at supersaturations >0.1 %. Linear correlations of SO2 and CCN were found for SO2 concentrations ranging from 20 to 600 parts-per-trillion (pptv). The greatest sensitivities were for SO2 and CCN that activate at supersaturations >0.1 % for both clean and polluted air. In a region affected by a cold pool event SO2 was only linearly correlated with CCN at >0.2 % S.
... Three-dimensional modeling studies have demonstrated that convective upward transport of SO 2 is efficient particularly over the tropics[Takigawa et al., 2002]and midlatitudes during summertime[Pitari et al., 2002]. Flight campaign data have also confirmed a significant gradient of SO 2 between the NH and SH in the troposphere[Thornton et al., 1999]. These modeled and observed results suggest that strong convection in local summer can cause vertical transport of large amounts of SO 2 and sulfate particles in the NH during boreal summer and small amounts in the SH in austral summer, thus creating the seasonal difference in the stratospheric entry value.[31]The ...
... The larger seasonal amplitude of E 0.525 in the NH and the seasonal evolution similar to those of q w (Figures 3 and 7) suggest a similar transport mechanism to that of q w because of the long chemical lifetime at these altitudes. Furthermore, aircraft observations of SO 2 in the upper troposphere have indicated a hemispheric difference in the amount of SO 2 , with larger values in the NH [Thornton et al., 1999], suggesting that tropospheric SO 2 and sulfate particles with high concentrations in the NH might enter the stratosphere from the NH monsoon regions (20 – 40°N) during boreal summer. This may be one reason for the asymmetry in E 0.525 , which shows higher values of >0.16 in the area of 10– 40°N at 16– 19 km in September (Figure 5d). ...
Extinction data from the Stratospheric Aerosol and Gas Experiment (SAGE) II in the lower stratosphere were analyzed for seasonal cycles in the near-background levels of stratospheric aerosol. The data analyzed were the extinction coefficient at 0.525 mum (beta 0.525) and the extinction ratio at 0.525 mum (E 0.525) on the basis of climatological zonal monthly mean for the years 1998-2004. Distinct seasonal cycles were found for beta 0.525 at 35-15°S above 28 km (region A) and at 20°S-30°N from 16 to 20.5 km (region B). In the A region, the seasonal cycle of E 0.525 was characterized by a maximum in local fall and can be explained by the ascent of mean meridional circulation in local summer and descent in local winter. In the B region, the seasonal cycles of E 0.525 were characterized by a maximum in October-January, which can be interpreted by meridional transport and mixing. The amplitude of the seasonal cycles for E 0.525 exhibited asymmetry between the Northern Hemisphere (NH) and the Southern Hemisphere (SH); the amplitudes at latitudes of 20-30° were larger in the SH than in the NH above 29 km, whereas they were larger in the NH than in the SH below 18 km. Comparison of the distribution of E 0.525 with that of SAGE II water vapor suggested that the E 0.525 distribution is controlled by the stratospheric circulation and troposphere-originated gases. One difference between E 0.525 and water vapor was found in the E 0.525 maximum that appears over the winter subtropics. The E 0.525 maximum can be attributed to the dominance of temperature and microphysical effects compared to transport effects, whereas the water vapor distribution can be attributed to transport effects. Another difference is that an upward propagation of the seasonal cycle of E 0.525 at 5°S-30°N disappeared near 23 km. This difference is explained by the fact that the chemical and microphysical processes of aerosol formation become significant above 23 km.
... [3] The average mixing ratio of SO 2 in the free troposphere away from polluted regions is estimated at 15-100 ppt [Thornton et al., 1997[Thornton et al., , 1999. Continental concentrations in the planetary boundary layer (PBL) depend mainly on anthropogenic emissions and range from 20 ppt to hundreds of ppb [Seinfeld and Pandis, 1998]. ...
... The resulting SCD REF was 0.115 DU ± 100%. This value is within the range of reported concentrations for clean continental area [Thornton et al., 1999;U. S. EPA, 2008]. ...
The ozone monitoring instrument (OMI), launched on the EOS/Aura satellite in July 2004, makes daily global observations of natural and anthropogenic SO2 emissions with unprecedented spatial resolution. Here we present the first robust comparison of OMI volcanic SO2 retrievals with ground−based instrumentation, using direct Sun observations of the Okmok volcanic cloud from Washington State University (WSU) in Pullman, WA on 18–20 July 2008. These measurements were made by the multifunction differential optical absorption spectroscopy (MFDOAS) instrument developed at WSU, as the Okmok cloud drifted over Pullman in the upper troposphere and lower stratosphere (UTLS). Observation conditions were favorable with cloud-free skies and a relatively homogeneous volcanic cloud distribution on OMI ground pixel scales (∼20–50 km). Movement of the Okmok cloud north and south of Pullman over a period of several days permitted comparison with three OMI overpasses with SO2 column amounts above the SO2 background level. The total SO2 columns measured by MFDOAS during OMI overpasses were 3.11 ± 0.23 Dobson units (DU), 1.75 ± 0.16 DU and 1.22 ± 0.18 DU (1 DU = 2.69 × 1016 molecules/cm2 = 0.029 g/m2). Comparison of ground-based direct Sun and operational and off-line OMI retrievals show an excellent agreement, providing the first validation of OMI measurements of volcanic SO2 in the UTLS.
... Transport during the MT season showed similarly distinct composition profiles depending on air mass origin. Air from EA exhibited higher concentrations of SO 2− 4 , O 3 , CH 4 , and NH + 4 , owing to urban emissions in continental outflow (Chuang et al., 2014;Talbot et al., 1997;Thornton et al., 1999;Umezawa et al., 2014;Wang et al., 2007) and extensive secondary aerosol formation (Hatakeyama et al., , 2004(Hatakeyama et al., , 2011Krupa and Manning, 1988;Matsui et al., 2014). In contrast, WP air is characterized as pure marine due to Figure 7. Linear regressions of (a) CO 2 / CO, (b) CH 4 / CO, (c) OA/ CO, (d) SO 2− 4 / CO, and (e) BC/ CO for the Maritime Continent (MC; red) and East Asia (EA; purple). ...
The tropical Northwest Pacific (TNWP) is a receptor for pollution sources throughout Asia and is highly susceptible to climate change, making it imperative to understand long-range transport in this complex aerosol-meteorological environment. Measurements from the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex; 24 August to 5 October 2019) and back trajectories from the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) were used to examine transport into the TNWP from the Maritime Continent (MC), peninsular Southeast Asia (PSEA), East Asia (EA), and the West Pacific (WP). A mid-campaign monsoon shift on 20 September 2019 led to distinct transport patterns between the southwest monsoon (SWM; before 20 September) and monsoon transition (MT; after 20 September). During the SWM, long-range transport was a function of southwesterly winds and cyclones over the South China Sea. Low- (high-) altitude air generally came from MC (PSEA), implying distinct aerosol processing related to convection and perhaps wind shear. The MT saw transport from EA and WP, driven by Pacific northeasterly winds, continental anticyclones, and cyclones over the East China Sea. Composition of transported air differed by emission source and accumulated precipitation along trajectories (APT). MC air was characterized by biomass burning tracers while major components of EA air pointed to Asian outflow and secondary formation. Convective scavenging of PSEA air was evidenced by considerable vertical differences between aerosol species but not trace gases, as well as notably higher APT and smaller particles than other regions. Finally, we observed a possible wet scavenging mechanism acting on MC air aloft that was not strictly linked to precipitation. These results are important for understanding the transport and processing of air masses with further implications for modeling aerosol lifecycles and guiding international policymaking to public health and climate, particularly during the SWM and MT.
... 375 Transport during the MT season showed similarly distinct composition profiles depending on air mass origin. Air from EA exhibited higher concentrations of SO4 2-, O3, CH4, and NH4 + , owing to urban emissions in continental outflow (Chuang et al., 2014;Talbot et al., 1997;Thornton et al., 1999;Umezawa et al., 2014;Wang et al., 2007) and extensive secondary aerosol formation (Hatakeyama et al., , 2004(Hatakeyama et al., , 2011Krupa and Manning, 1988;Matsui et al., 2014). In contrast, WP air is characterized as pure marine due to composition similar to those previously reported in Pacific 380 marine environments (Davis et al., 1996;Matsumoto et al., 1998;Talbot et al., 1997). ...
The tropical Western North Pacific (TWNP) is a receptor for pollution sources throughout Asia and is highly susceptible to climate change, making it imperative to understand long-range transport in this complex aerosol-meteorological environment. Measurements from the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex; 24 Aug to 5 Oct 2019) and back trajectories from the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) were used to examine transport into the TWNP from the Maritime Continent (MC), Peninsular Southeast Asia (PSEA), East Asia (EA), and West Pacific (WP). A mid-campaign monsoon shift on 20 Sep 2019 led to distinct transport patterns between the southwest monsoon (before 20 Sep) and monsoon transition (after 20 Sep). During the southwest monsoon, long-range transport was a function of southwesterly winds and cyclones over the South China Sea. Low (high) altitude air generally came from MC (PSEA), implying distinct aerosol processing related to convection and perhaps wind shear. The monsoon transition saw transport from EA and WP, driven by Pacific northeasterly winds, continental anticyclones, and cyclones over the East China Sea. Composition of transported air differed by emission source and accumulated precipitation along trajectories (APT) as an indicator of convection. MC air was characterized by biomass burning tracers while major components of EA air pointed to Asian outflow and secondary formation. Convective scavenging of PSEA air was evidenced by considerable vertical differences between aerosol species but not trace gases, as well as notably higher APT and smaller particles than other regions. Finally, we observed a possible wet scavenging mechanism acting on MC air aloft that was not strictly linked to precipitation. These results are important for understanding the transport and processing of air masses with further implications for modeling aerosol lifecycles and guiding international policymaking on public health and climate.
... Fig. 4. The nuclei number concentration that is required to make the timescales τ G,scoa and τ R,coag equal to each other. below 0.1 ppb in marine areas, between about 0.1 and 5 ppb in rural areas and between about 1 and 50 ppb in urban areas (Sickles, 1999;Thornton et al., 1999;Redington and Derwent, 2002). By noting that daytime OH radical concentrations vary in the range (1-5)× 10 6 molecules cm −3 over mid latitudes (Spivakovski et al., 2000), we estimate that typical daytime production rates for gaseous sulfuric acid are well below 10 4 molecules cm −3 s −1 in marine areas, between about 2 × 10 3 and 6 × 10 5 molecules cm −3 s −1 in rural areas and between about 2 × 10 4 and × 10 6 molecules cm −3 s −1 for urban areas. ...
A theoretical framework was constructed by which one can estimate the relative role of different processes in thedynamics of atmospheric nucleation mode particles. The framework relies on 14 timescales that describe (1) changes inthe total nuclei number concentration, (2) changes in the mean diameter of the nucleation mode and (3) concentrationsof low-volatile vapours responsible for the growth of nuclei. The magnitude of the derived timescales can be calculatedrelatively easily from the available measurement or modelling data. Application to the lower-troposphere revealed thatunder most conditions removal of nuclei is dominated by their coagulation with larger background particles and thatthis process competes very strongly with growth of nuclei to sizes relevant to atmospheric chemistry and physics.Withsome exceptions, self-coagulation of nuclei was shown to be of marginal importance compared with their growth bycondensation and their removal by coagulation. Finally, by comparing predictions based on relevant timescales withthose obtained from detailed numerical simulations, quantitative criteria were derived concerning (1) when one mayneglect self-coagulation of nuclei when looking at nucleation mode dynamics and (2) when the whole nucleation modecan be neglected because of its eventual removal. These criteria are extremely useful for atmospheric modellers whoneed to simplify their models as much as possible. From the modelling point of view, other processes requiring furtherattention are the introduction of new nuclei into the system and decrease in nuclei number concentration due to dilutionof the air. DOI: 10.1111/j.1600-0889.2004.00095.x
... Furthermore additional small fluxes of other short-lived gases such as CS 2 and H 2 S were included. This seems at odds with measured SO 2 mixing ratios in the background upper troposphere, which are generally below 10-20 ppt (Thornton et al., 1999). In fact, upward transport through the tropical tropopause layer (12-18 km altitude) is very slow and the air mass residence time is several months. ...
Globally, carbonyl sulphide (COS) is the most abundant sulphur gas in the atmosphere. Our chemistry-climate model (CCM) of the lower and middle atmosphere with aerosol module realistically simulates the background stratospheric sulphur cycle, as observed by satellites in volcanically quiescent periods. The model results indicate that upward transport of COS from the troposphere largely controls the sulphur budget and the aerosol loading of the background stratosphere. This differs from most previous studies which indicated that short-lived sulphur gases are also important. The model realistically simulates the modulation of the particulate and gaseous sulphur abundance in the stratosphere by the quasi-biennial oscillation (QBO). In the lowermost stratosphere organic carbon aerosol contributes significantly to extinction. Further, using a chemical radiative convective model and recent spectra, we compute that the direct radiative forcing efficiency by 1 kg of COS is 724 times that of 1 kg CO<sub>2</sub>. Considering an anthropogenic fraction of 30% (derived from ice core data), this translates into an overall direct radiative forcing by COS of 0.003 W m<sup>−2</sup>. The direct global warming potentials of COS over time horizons of 20 and 100 yr are GWP(20 yr) = 97 and GWP(100 yr) = 27, respectively (by mass). Furthermore, stratospheric aerosol particles produced by the photolysis of COS (chemical feedback) contribute to a negative direct solar radiative forcing, which in the CCM amounts to −0.007 W m<sup>−2</sup> at the top of the atmosphere for the anthropogenic fraction, more than two times the direct warming forcing of COS. Considering that the lifetime of COS is twice that of stratospheric aerosols the warming and cooling tendencies approximately cancel.
... California and Alaska range between 36 and 50 ppt at altitudes between 15.2 and 20.3 km. Airborne in situ measurements of SO 2 in the altitude range from 8 to 15 km were summarized for USA campaigns by Thornton et al. [1999]. The in situ SO 2 measurements for the European campaigns were compared with MIPAS observations, and reasonable agreement between both data sets was found . ...
Interest in stratospheric aerosol and its role in climate has increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space-based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any non-volcanically driven change, making them difficult to understand. While the role of carbonyl sulfide (OCS) as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide (SO2) emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of non-sulfate matter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes.
... Observation of SO 2 presented the hemispheric difference in the amount of SO 2 in summer midlatitudes with larger values in NH [Thornton et al., 1999]. This hemispheric difference of summer SO 2 agrees with the hemispheric difference of E 0.452 in summer. ...
Extinction data observed with Stratospheric Aerosol and Gas Experiment (SAGE) II in the upper stratosphere and lower stratosphere (UT/LS) during the period of the background level of stratospheric aerosol (1998–2004) are examined for seasonal cycle. For the data analysis, the extinction coefficient at 0.452, 0.525, and 1.02 µm, and the effective radius are used. The analyzed quantities show large seasonal amplitude in 45 • S–40 • N above 26 km, and in 15 • S-30 • N at 14–21 km. Intriguingly, the seasonal amplitude exhibits asymmetry in the distribution between the Northern Hemisphere (NH) and Southern Hemisphere (SH). That is, the amplitude of seasonal cycle at latitudes of 20–40 • is smaller in NH than that in SH above 26 km, while it is larger in NH than that in SH between 14 and 18 km. The extinction ratio peak is at around 28–30 km over the tropics. Very small values of extinction ratio at latitudes of 20–30 • at 10–15 km, and a steep gradient of extinction ratio and of effective radius at latitudes of 20–30 • in the lower stratosphere are observed. The two regions are considered to correspond to the outflow from the tropical convection, and to the subtropical barriers in the lower stratosphere, respectively. These features are compared and discussed with the distribution of water vapor.
... There are large terrestrial sources of sulfur dioxide (SO 2 ) to the atmosphere whereby it is oxidized to sulfuric acid (H 2 SO 4 ) and subsequently affects the Earth's radiative balance via the formation of non-sea-salt sulfate aerosol. Marine boundary layer SO 2 concentrations are typically around 25 ppt above the Pacific Ocean , although concentrations increase with proximity to coastal regions due to terrestrial influences (Thornton et al., 1999;Yang et al., 2011). Like ozone, SO 2 is subject to deposition into the oceans, with no reemission. ...
The annual gross and net primary productivity of the surface oceans is similar in size to that on land (IPCC, 2001). Marine productivity drives the cycling of gases such as oxygen (O2), dimethyl sulfide (DMS), carbon monoxide (CO), carbon dioxide (CO2), and methyl iodide (CH3I) which are of fundamental importance in studies of marine productivity, biogeochemical cycles, atmospheric chemistry, climate, and human health, respectively. For example, ˜30% of the world's population (1,570 million) is thought to be at risk of iodine-deficiency disorders that impair mental development (WHO, 1996). The main source of iodine to land is the supply of volatile iodine compounds produced in the ocean and then transferred to the atmosphere via the air-surface interface. The flux of these marine iodine species to the atmosphere is also thought to be important in the oxidation capacity of the troposphere by the production of the iodine oxide radical ( Alicke et al., 1999). A further example is that the net flux of CO2 from the atmosphere to the ocean, ˜1.7±0.5 Gt C yr-1, represents ˜30% of the annual release of anthropogenic CO2 to the atmosphere (IPCC, 2001). This net flux is superimposed on a huge annual flux (90 Gt C yr-1) of CO2 that is cycled "naturally" between the ocean and the atmosphere. The long-term sink for anthropogenic CO2 is recognized as transfer to the ocean from the atmosphere. A final example is the emission of volatile sulfur, in the form of DMS, from the oceans. Not only is an oceanic flux from the oceans needed to balance the loss of sulfur (a bioessential element) from the land via weathering, it has also been proposed as having a major control on climate due to the formation of cloud condensation nuclei (Charlson et al., 1987). Indeed, the existence of DMS and CH3I has been used as evidence in support of the Gaia hypothesis (Lovelock, 1979).There are at least four main processes that affect the concentration of gases in the water column: biological production and consumption, photochemistry, air-sea exchange, and vertical mixing. We will not discuss the effect of vertical mixing on gases in seawater and instead refer the reader to Chapter 6.08. Nor will we consider the deeper oceans as this region is discussed in chapters on benthic fluxes and early diagenesis (Chapter 6.11), the biological pump (Chapter 6.04), and the oceanic calcium carbonate cycle (Chapter 6.19) all in this volume. We will discuss the cycling of gases in surface oceans, including the thermocline, and in particular concentrate on the exchange of various volatile compounds across the air-sea interface.As we will show, while much is known about the cycling of gases such as CO2 and DMS in the water column, frustratingly little is known about many of the chemical species for which the ocean is believed to be a significant source to the atmosphere. We suspect the passage of time will reveal that the cycling of volatile compounds containing selenium and iodine may well prove as complex as that of DMS. Early studies of DMS assumed that it was produced from a precursor compound, dimethylsulfoniopropionate (DMSP), known to be present in some species of phytoplankton, and that the main sink in the water column was exchange across the air-sea interface. We now know that DMSP and DMS are both rapidly cycled in water column by a complex interaction between phytoplankton, microzooplankton, bacteria, and viruses (see Figure 1). Some detailed process experiments have revealed that only ˜10% of the total DMS produced (and less than 1.3% of the DMSP produced) is transferred to the atmosphere, with the bulk of the DMS and DMSP, either being recycled in the water column or photo-oxidized (Archer et al., 2002b).
... Typical values of these parameters inside clouds are of the order [OH] = 10 6 cm À3 , k = 10 À12 cm 3 s À1 and CS = 0.1-1 s À1 . The concentration of SO 2 is more difficult to estimate, since it depends on the initial concentration of SO 2 in the boundary layer which varies a lot both spatially and temporally [Thornton et al., 1999;Carmichael et al., 2003], as well as on the depletion of SO 2 from the rising air parcel by detrainment and in-cloud oxidation [Mari et al., 2000]. A reasonable range for SO 2 concentration is 10 8 -10 10 cm À3 , on the basis of which the concentration of sulfuric acid would be in the range 10 2 -10 5 cm À3 inside a cloud. ...
Deep convection associated with thunderstorms and sometimes with frontal systems is an effective way to transport material from the planetary boundary layer to the upper troposphere and even to the lower stratosphere. Aerosol particles observed in clouds and in cloud outflows suggest that deep convection is an important source of particles in the upper troposphere. However, the detailed pathways by which the observed small particles could have been formed inside the clouds are unknown. In this paper we propose a hypothesis, where water insoluble trace gases that can survive the deep convective updraft are producing new particles at low temperatures near the tropopause. In order to be able to verify this new mechanism, laboratory experiments were designed to simulate this process. It was found that ambient water insoluble trace gases were indeed able to produce new aerosol particles by homogeneous nucleation under cloud like conditions. Therefore it seems that our hypothesis gives a plausible explanation for new particle production inside cloud anvils and cloud outflows.
... Due to strong westerlies in winter and spring, pollutants from the continent are usually dispersed eastward to downwind areas. It has been evident that the input of continental pollutants into the downwind marine atmosphere can cause significant changes in the chemistry associated with sulfur dioxide, nitrogen oxides and even chloride (Savoie and Prospero, 1989; Prospero and Savoie, 1989; Parungo et al., 1994; Thornton et al., 1999; Andreae et al., 2000;). However, few in situ observational data on clouds whose gaseous and particulate precursors were influenced by the input are available. ...
Aerosol particles were collected with an aircraft-borne sampler above, within and below a stratocumulus over the Sea of Japan on December 3, 2000, when continental influence was expected. Particles in the range of 0.3–7 μm and cloud droplets in the range of 0.3–10 μm were captured and they were identified individually upon their elemental composition and morphologies from the analyses by using electron microscopes and an energy dispersive X-ray spectrometer. Interstitial particles and droplets coexisted in the cloud and their number ratio was about 3:2 in the detected ranges. Spherical particles that were inferred to be mainly composed of sulfate, nitrate and ammonium occupied more than 95% of the interstitial particles. Similar particles were also majorities in the above- and below-cloud air, where their percents to total particles were 93% and 74%, respectively. Acidic sulfate particles were rarely found in the below-, in- and even above-cloud air. The nuclei of 90% cloud droplets had similar composition and size distribution to the spherical particles in the scope of our analysis. These results suggest that the continentally influenced stratocumulus was characterized by neutralized nuclei and interstitial particles. Sea-salt particles were detected mainly in the below-cloud air. A few droplets with sea-salt nuclei were detected there and in the cloud. Such droplets were usually larger than those with spherical nuclei but their number fraction to total droplets in the cloud (about 8%) was much smaller than the spherical nuclei to total droplet fraction, indicating that sea-salt particles produced larger droplets but they constituted only a small number fraction of droplets in the cloud.
... [2] Volcanic emissions are an important source of atmospheric gases and aerosols, including various sulfur and halogen compounds. They play important roles in the Earth's radiation budget [e.g., Robock, 2000;Graf and Timmreck, 2001], in tropospheric and stratospheric chemistry and dynamics [e.g., Tabazadeh and Turco, 1993;Chin and Jacob, 1996;Graf et al., 1998;Thornton et al., 1999], and can impact terrestrial ecosystems and human health over local to regional scales [e.g., Sutton and Elias, 1993;Mannino et al., 1996;Thordarson et al., 1996;Raga et al., 1999;Johnston et al., 2000]. Despite a rather good understanding of the chemistry of volcanic volatiles in the strato-sphere [e.g., Coffey, 1996], relatively little is known about the chemistry of, and deposition from, tropospheric volcanic plumes [e.g., Cadle et al., 1979;Lazrus et al., 1979;Delmelle et al., 2001]. ...
[1] Existing studies of the composition of volcanic plumes generally interpret the presence of sulfate aerosol as the result of comparatively slow oxidation of gaseous SO2. We report here new observations from Masaya Volcano, Nicaragua, which demonstrate that sulfate aerosol may also be emitted directly from volcanic vents. Simultaneous aerosol and gaseous S, Cl, and F compounds were collected at the rim of the passively degassing crater in May 2001. Mean concentrations of SO42−, Cl−, and F− within the plume were 83, 1.2, and 0.37 μg m−3, respectively (fine aerosol fraction 2.5 μm). The aerosols were highly acidic, with estimated pH of
... For the calculation of the H 2 SO 4 production rate, OH and SO 2 concentrations need to be specified. We assume SO 2 volume mixing ratios between 10 and 200 ppt, with a median near 40 ppt based on observations in the Pacific upper troposphere north of 20 • (Thornton et al., 1999). Upper tropospheric OH mixing ratios at northern mid-latitudes range up to 0.4 ppt (Jaeglé et al., 2000). ...
The recent observation of ultrafine aerosol particles in cirrus clouds has raised the question whether aerosol formation within cirrus clouds is possible, and if so, what mechanisms are involved. We have developed an aerosol parcel model of neutral and charged H2SO4/H2O aerosol processes, including nucleation from the gas phase and loss onto cirrus ice particles. Laboratory thermodynamic data for sulfuric acid uptake and loss by small neutral and charged clusters are used, allowing for a reliable description of both neutral and charged nucleation down to the very low temperatures occurring in the upper troposphere and lower stratosphere. The model implements a first order scheme for resolving the aerosol size distribution within its geometric size sections, which efficiently suppresses numerical diffusion. We operate the model offline on trajectories generated with a detailed 1D cirrus model which describes ice crystal nucleation, deposition growth, vertical advection of ice crystals and water vapor, and ice crystal sedimentation. In this paper we explore the possibility of aerosol formation within non-convective cirrus clouds and draw conclusions for aerosol formation in anvil cirrus. We find that sulfate aerosol formation within cirrus clouds can proceed even at high ice surface area concentrations, and depends strongly on the size of the cirrus ice crystals and on the surface area concentration of preexisting aerosol particles.
The kinetics of the reaction OH/OD(?=1,2,3) + SO2 have been studied using a photolysis / laser induced fluorescence technique. The rate coefficients OH/OD(v=1,2,3) + SO2, k1, over the temperature range 295 - 810 K were used to determine the limiting high pressure limit, k1(?). This method is usually applicable if the reaction samples the potential well of the adduct, HOSO2, and if intramolecular vibrational relaxation is fast. In the present case, however, the rate coefficients showed an additional fast removal contribution as evidenced by the increase in k1 with vibrational level; this behaviour together with its temperature dependence is consistent with the existence of a weakly bound complex on the potential energy surface prior to adduct formation. The data were analysed using a composite mechanism that incoporates energy transfer mechanisms via both the adduct and the complex, and yielded a value of k1(?)(295 K) equal to (7.2 ? 3.3) ? 10(-13) cm(3) molecule(-1) s(-1), (errors at 1?) a factor of between two to three smaller than the current recommended IUPAC and JPL values of (2.0) and (1.6 ? 0.4) ? 10(-12) cm(3) molecule(-1) s(-1) at 298 K, respectively, although the error bars do overlap. k1(?) was observed to only depend weakly on temperature. Further evidence for a smaller k1(?) is presented in the companion paper.
We present a climatology of monthly and 10° zonal mean profiles of sulfur dioxide (SO2) volume mixing ratios (vmr) derived from MIPAS/Envisat measurements in the altitude range 15–45 km from July 2002 until April 2012. The vertical resolution varies from 3.5–4 km in the lower stratosphere up to 6–10 km at the upper end of the profiles with estimated total errors of 5–20 pptv for single profiles of SO2. Comparisons with few available observations of SO2 up to high altitudes from ATMOS, for a volcanically perturbed situations from ACE-FTS and, at the lowest altitudes, with stratospheric in-situ observations reveal general consistency of the datasets. The observations are the first empirical confirmation of features of the stratospheric SO2 distribution which have only been shown by models up to now: (1) the local maximum of SO2 at around 25–30 km altitude which is explained by the conversion of carbonyl sulfide (COS) as the precursor of the Junge layer, and (2) the downwelling of SO2 rich air to altitudes of 25–30 km at high latitudes during winter and its subsequent depletion on availability of sunlight. This has been proposed as the reason for the sudden appearance of enhanced concentrations of condensation nuclei during Arctic and Antarctic spring. Further, the strong increase of SO2 to values of 80–100 pptv in the upper stratosphere through photolysis of H2SO4 has been confirmed. Lower stratospheric variability of SO2 could mainly be explained by volcanic activity and no hint for a strong anthropogenic influence has been found. Regression analysis revealed a QBO (quasi-biennial oscillation) signal of the SO2 time series in the tropics at about 30–35 km, a SAO (semi-annual oscillation) signal at tropical and subtropical latitudes above 32 km and annual periodics predominantly at high latitudes. Further, the analysis indicates a correlation with the solar cycle in the tropics and southern subtropics above 30 km. Significant negative linear trends are found in the tropical lower stratosphere, probably due to reduced tropical volcanic activity and at southern mid-latitudes above 35 km. A positive trend is visible in the lower and middle stratosphere at polar to subtropical southern latitudes.
Many of the reactive trace gases detected in the atmosphere are both emitted from and deposited to the global oceans via exchange across the air-sea interface. The resistance to transfer through both air and water phases is highly sensitive to physical drivers (waves, bubbles, films, etc.), which can either enhance or suppress the rate of diffusion. In addition to outlining the fundamental processes controlling the air-sea gas exchange, the authors discuss these drivers, describe the existing parameterizations used to predict transfer velocities, and summarize the novel techniques for measuring in situ exchange rates. They review trace gases that influence climate via radiative forcing (greenhouse gases), those that can alter the oxidative capacity of the atmosphere (nitrogen- and sulfur-containing gases), and those that impact ozone levels (organohalogens), both in the troposphere and stratosphere. They review the known biological and chemical routes of production and destruction within the water column for these gases, whether the ocean acts as a source or sink, and whether temporal and spatial variations in saturation anomalies are observed. A current estimate of the marine contribution to the total atmospheric flux of these gases, which often highlights the significance of the oceans in biogeochemical cycling of trace gases, is provided, and how air-sea gas fluxes may change in the future is briefly assessed.
This work deals with a study of stratospheric aerosols and transport processes responsible for their time evolution from the first two years observations of the CALIOP lidar carried on the French-US CALIPSO satellite launched in May 2006. After adaptation of the retrieval algorithms to the faint Mie scattering signal and calibration correction required by the presence of aerosols at altitude levels of standard calibration, it is shown that zonal mean scattering ratios of 2% precision could be obtained. After applying those corrections as well as a cloud mask based on the depolarization of the lidar signal, the time evolution of the aerosols between 15-40 km altitude from July 2006 to September 2008, leads to the following conclusions: i) a significant contribution, often ignored, of volcanic eruptions of medium 3-4 explosivity index resulting in plumes injected at around 19-20 km altitude, then slowly lifted by the Brewer-Dobson circulation until 25 km within one year; and ii) the decoupling between, the mid- and lower stratosphere separated by a region of small or zero vertical velocity at around 20 km. In agreement with generally accepted ideas, the tropical midstratosphere displays a slow upwelling at an average of 300 m/month within the "tropical pipe", and meridional exchange intensity modulated by the quasi-biennial oscillation. In contrast and in contradiction with the currently accepted scheme of slow ascent by radiative heating of air above the top altitude of convective outflow around 14 km, the region below 20 km is found to be the location of frequent injections of clean air, likely washed-out from the troposphere, and particularly intense at equatorial latitudes during austral summer. Since the TTL, the Tropical Tropopause Layer, is defined as the region of the stratosphere under influence of the troposphere, those observations suggest a top of this layer at around 20 km. A consequence of the mixing with injected clean air is the fast cleansing of volcanic aerosols occasionally present in the TTL. Finally, another unexpected feature reported by the lidar is the presence of additional seasonal aerosols between 15-18 km, above West Africa and South Asia during their respective monsoon season, which could be small mineral dust lifted by convection from neighbouring desert areas.
Significance
Ammonites went extinct at the time of the end-Cretaceous asteroid impact, as did more than 90% of species of calcium carbonate-shelled plankton (coccolithophores and foraminifera). Comparable groups not possessing calcium carbonate shells were less severely affected, raising the possibility that ocean acidification, as a side effect of the collision, might have been responsible for the apparent selectivity of the extinctions. We investigated whether ocean acidification could have caused the disappearance of the calcifying organisms. In a first detailed modelling study we simulated several possible mechanisms from impact to seawater acidification. Our results suggest that acidification was most probably not the cause of the extinctions.
The TwO-Moment Aerosol Sectional (TOMAS) microphysics model has been integrated into the state-of-the-art general circulation model, GISS ModelE2. This paper provides a detailed description of the ModelE2-TOMAS model and evaluates the model against various observations including aerosol precursor gas concentrations, aerosol mass and number concentrations, and aerosol optical depths. Additionally, global budgets in ModelE2-TOMAS are compared with those of other global aerosol models, and the ModelE2-TOMAS model is compared to the default aerosol model in ModelE2, which is a one-moment aerosol (OMA) model (i.e. no aerosol microphysics). Overall, the ModelE2-TOMAS predictions are within the range of other global aerosol model predictions, and the model has a reasonable agreement (mostly within a factor of 2) with observations of sulfur species and other aerosol components as well as aerosol optical depth. However, ModelE2-TOMAS (as well as ModelE2-OMA) cannot capture the observed vertical distribution of sulfur dioxide over the Pacific Ocean, possibly due to overly strong convective transport and overpredicted precipitation. The ModelE2-TOMAS model simulates observed aerosol number concentrations and cloud condensation nuclei concentrations roughly within a factor of 2. Anthropogenic aerosol burdens in ModelE2-OMA differ from ModelE2-TOMAS by a few percent to a factor of 2 regionally, mainly due to differences in aerosol processes including deposition, cloud processing, and emission parameterizations. We observed larger differences for naturally emitted aerosols such as sea salt and mineral dust, as those emission rates are quite different due to different upper size cutoff assumptions.
The study of atmospheric trace gases is increasing over the years. One of these gases is sulfur dioxide (SO 2), which is found in the troposphere and stratosphere, as a result of both natural and anthropogenic emissions. A campaign was made in Cubatao-SP, from 04/12/2007 to 08/07/2007, to measure the total column of this gas with a Brewer Spectrophotometer. With this instrument the total column of SO 2 was calculated. Since this region is highly industrialized, high total columns of SO 2 were expected, which indeed occurred, with a daily average of 6.4 DU during the whole period. Palavras-chave: dióxido de enxofre, Espectrofotômetro Brewer, poluição 1-INTRODUÇÃO Um dos poluentes mais estudados tanto em áreas remotas e urbanas é o dióxido de enxofre (SO 2). Estudar as mudanças no SO 2 atmosférico é importante para compreender seus efeitos sobre a química atmosférica e o campo de radiação, além das consequências sobre o clima. O SO 2 é emitido para a atmosfera como resultado tanto dos fenômenos naturais quanto atividades antrópicas, por exemplo, a queima de combustíveis fósseis, a oxidação da matéria orgânica do solo, erupções vulcânicas e queima de biomassa. A maior parte do SO 2 emitido por fontes naturais é produzida por vulcões e pela oxidação de gases de enxofre originados da decomposição de plantas. A maior fonte antropogênica de SO 2 é a combustão do carvão, o que corresponde cerca de 50% das emissões anuais, bem como a queima de óleo de 25 a 30% (Baird, 2002). O SO 2 de atividades antrópicas foi reconhecido como sendo a principal fonte de ácido sulfúrico e aerossóis de sulfato sobre os continentes (Thornton et al., 1999). O tempo de permanência de SO 2 na atmosfera varia de 1-4 dias (Rocha et al., 2004). De acordo com Georgoulias et al. (2009), quando próximo ao solo em altas concentrações, esse gás tem um efeito direto sobre a saúde humana, provocando doenças respiratórias, mortes prematuras em casos extremos, e inibem o crescimento das plantas. O SO 2 também é precursor de ácido sulfúrico (H 2 SO 4), sendo depositado como chuva ácida. O gás também tem um papel significativo na física de formação de nuvens, levando a nuvens de alta refletividade. Na estratosfera, o SO 2 é oxidado e combina-se com água para formar aerossóis de sulfato (Bekki, 1995). Estes aerossóis dispersam a radiação solar e absorvem a radiação de onda longa, que aquece a região estratosférica e provoca resfriamento na superfície da Terra (Georgoulias et al., 2009). A cidade de Cubatão, localizada no estado de São Paulo (figura 1), é conhecida por seu complexo industrial, com muitas fábricas de produtos químicos, ferro/siderurgia, petroquímicas e fertilizantes. A localização da cidade possui características que não favorecem a dispersão de poluentes atmosféricos. As condições meteorológicas sobre Cubatão incluem períodos de estagnação de massas de ar sobre a área, associada com inversões de temperatura, circulação de brisa marítima, sistemas frontais e sistemas convectivos isolados (Gonçalves et al., 2000).
The collection of rainwater samples was made at Jeju area during 2009~2010, and the major ionic species were analyzed. In the comparison of ion balance, conductivity, and acid fraction for the validation of analytical data, the correlation coefficients showed a good linear relationship within the range of 0.966~0.990. The volume-weighted mean pH and electric conductivity were 4.9 and , respectively, at the Jeju area. The volume-weighted mean concentrations of ionic species in rainwater were in the order of > > > > > > > > > > > > > > > . The ionic strength of rainwater was mM during the study period. The composition ratios of ionic species were such as 50.1% for the marine sources (, , ), 30.9% for the anthropogenic sources (, , ), and 4.7% for the soil source (), and 3.1% for organic acids (, ). From the seasonal comparison, the concentrations of , , and increased in winter and spring seasons, indicating a reasonable possibility of long range transport from Asia continent. Especially, the acidifying contributions by major inorganic acids ( and ) and organic acids ( and ) were 87.6% and 12.4%, respectively. In comparison by sectional inflow pathway of air mass during the rainy sampling days, the concentrations of and were relatively high when the air mass was moved from the China continent into Jeju area.
This study was carried out to understand long-range transport of using aircraft measurements for the identification of it's horizontal and vertical concentration and distribution pattern. Thirteen missions of aircraft measurements have been done around 3700'/12430' from October 1997 to November 2001. Concentrations of was 1.5~2.0 ppb in the below mixing layer, 0.6~1.1 ppb in the above mixing layer. was found to be relatively higher than marine background level, 0.08~0.2ppb, indicating the western coast being influenced by long-range transport except for the summer season. The vertical distribution of was classified into 3 groups using its vertical sounding and meteorology pattern; the first is linear decay pattern, the second is exponential decay pattern, and the last is gaussian distribution pattern in the below mixing layer, 2 patterns of linear decay and gaussian distribution patterns in the upper layer. It is founded that vertical distribution pattern is strongly dependent on meteorological condition, for example atmospheric stability and predominant air flow.
We present a climatology of monthly and 10° zonal mean profiles of sulfur dioxide (SO2) volume mixing ratios (vmr) derived from MIPAS/Envisat measurements in the altitude range 15–45 km from July 2002 until April 2012. The vertical resolution varies from 3.5–4 km in the lower stratosphere up to 6–10 km at the upper end of the profiles, with estimated total errors of 5–20 pptv for single profiles of SO2. Comparisons with the few available observations of SO2 up to high altitudes from ATMOS for a volcanically perturbed situation from ACE-FTS and, at the lowest altitudes, with stratospheric in situ observations reveal general consistency of the datasets. The observations are the first empirical confirmation of features of the stratospheric SO2 distribution, which have only been shown by models up to now: (1) the local maximum of SO2 at around 25–30 km altitude, which is explained by the conversion of carbonyl sulfide (COS) as the precursor of the Junge layer; and (2) the downwelling of SO2-rich air to altitudes of 25–30 km at high latitudes during winter and its subsequent depletion on availability of sunlight. This has been proposed as the reason for the sudden appearance of enhanced concentrations of condensation nuclei during Arctic and Antarctic spring. Further, the strong increase of SO2 to values of 80–100 \unit{pptv} in the upper stratosphere through photolysis of H2SO4 has been confirmed. Lower stratospheric variability of SO2 could mainly be explained by volcanic activity, and no hints of a strong anthropogenic influence have been found. Regression analysis revealed a QBO (quasi-biennial oscillation) signal of the SO2 time series in the tropics at about 30–35 km, an SAO (semi-annual oscillation) signal at tropical and subtropical latitudes above 32 km and annual periodics predominantly at high latitudes. Further, the analysis indicates a correlation with the solar cycle in the tropics and southern subtropics above 30 km. Significant negative linear trends are found in the tropical lower stratosphere, probably due to reduced tropical volcanic activity and at southern mid-latitudes above 35 km. A positive trend is visible in the lower and middle stratosphere at polar to subtropical southern latitudes.
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.
The Pacific Exploratory Mission Tropics (PEMT) A (1996) and B (1999) field campaigns occurred over a large area of the Pacific Basin and revealed the presence of ``rivers'' of continental outflow propagating into the remote marine atmosphere that were also supported by remote sensing and modeling efforts. Airborne measurements of both the coarse and fine mode aerosol during these campaigns provided assessment of the spatial variability in aerosol parameters (including optical properties and degree of internal versus external mixing) in continental plumes encountered over the Pacific Ocean. Large perturbations to the ``pristine'' marine atmosphere were observed. Most plumes were encountered in the Southern Hemisphere during PEMT A, while the opposite was observed during PEMT B. A variety of anthropogenic and natural sources for these continental plumes are suggested by the data, including biomass burning, urban/industrial emissions, and in the case of Asian outflow, dust storms. Aerosol size distributions (particularly for the refractory component) varied from one plume to another and most combustion-derived aerosol appeared to be an internal mix of a refractory soot-like constituent in a volatile matrix. Within the sampled plumes, size-resolved volatility suggested that this volatile matrix was relatively well neutralized, implying the presence of ammonia in the particle phase. The radiatively important single scatter albedo (omega) obtained from measured ``dry'' scattering and absorption coefficients ranged from approximately 0.88 (pollution with no coarse particles) to 0.94 (pollution and dust) in the free troposphere (FT) to 0.98 (pollution and sea salt) within the marine boundary layer (MBL). Vertical profiles often revealed more concentrated plumes aloft, typically situated in dry air with ambient relative humidity (RH)
The gas-phase products of dimethylsulfide (DMS) oxidation are simulated in the global D Model of Atmospheric Transport and Chemistry (MATCH). The focus is on the sensitivities to the assumed mechanisms of DMS oxidation chemistry in large-scale models, and hence volcanic and anthropogenic sources of SO2 are ignored. Four representations of DMS chemistry are considered, including two comprehensive mechanisms (about 50 reactions) and two parameterized schemes (four and five reactions). The gas-phase yields of DMS, SO2, methanesulfonic acid (MSA) and H2SO4 are compared between these four cases as a measure of the sensitivity to uncertain DMS chemistry. Among the four cases, DMS is largely invariant, while SO2 using parameterized chemistry is three times higher than its levels using comprehensive chemistry in the tropical upper troposphere. For MSA and H2SO4, there are order-of-magnitude inter-mechanistic differences at high and low altitudes in the extratropics, respectively. The differences are attributed to fixed branching yields and the absence of important intermediate species and pathways in the parameterized mechanisms. Regional budgets are also analyzed within the remote Southern Ocean and central tropical Pacific. While the DMS budget varies primarily between the regions, the SO2, MSA and H2SO4 budgets vary strongly between the regions and mechanisms. The DMS oxidation products, therefore, are as sensitive to the assumed mechanisms as to the external conditions between the tropics and extratropics. To distinguish between the mechanism cases, the MATCH simulations are also compared to campaign measurements. The simulated values of DMS and SO2 are found to approximate the observations, but do not provide mechanism differentiation. The gas-phase H2SO4 and MSA simulations differ more extensively from the observations, yet the comprehensive chemistry cases give a better fit to the MSA measurements. Better fits to the MSA observations are also achieved for the two mechanisms that consider dimethylsulfoxide (DMSO) as an MSA precursor.
Aircraft observations were performed over the sea near the southwest islands of Japan under Asian Atmospheric Particulate Environmental Change Experiment 2/Asian Pacific Regional Aerosol Characterization Experiment (APEX-E2/ACE-Asia) project during the period of 16–28 April 2001. The polluted air mass from east Asia was associated with very high concentrations of SO2 (1–10 ppb) and aerosol particles (3000–5000 cm−3) in the marine boundary layer. The cloud condensation nuclei (CCN) concentration at 0.3% supersaturation was as high as 800–2000 cm−3 during the penetrations of air pollutants from east Asia. The correlation coefficient between SO2 and aerosol particles was significant in such polluted atmosphere. Concentration of CCN (NCCN) was linearly related to concentration of aerosol particles (NAP) according to NCCN ∼ 0.75NAP. The ratio of CCN to aerosol condensation nuclei particle concentrations was lower than 0.3 in the relatively clean maritime atmosphere, but it was as high as ∼0.5 in the continentally influenced atmosphere in the boundary layer. These results indicated that the influence of anthropogenic pollutants from east Asia increased the contribution percentage of aerosol particles to CCN in the polluted atmosphere over the observation area. The observational results also indicated that a mean cloud droplet concentration (NC) in the continentally influenced clouds was ∼2 times as much as NC in the relatively clean maritime clouds. The slope of log-log relationship between NC and NCCN was ∼0.39. This study strongly suggests that high CCN concentration formed many cloud droplets and decreased their effective radius at similar liquid water content under the outflow of air pollutants from east Asia.
We examine the budget and export of anthropogenic SOx (SO2 and sulfate aerosol) emitted from East Asia during the late winter/early spring when continental outflow conditions dominate. Our study is based on simulations using a modified version of the China-MAP coupled regional climate/chemical transport model of Qian and Giorgi [1999]. The modification involves the addition of algorithms to treat the vertical transport and removal of SOx by convective clouds. Model-calculated anthropogenic SO2 concentrations peaked at values greater than 20 ppbv at the surface in the urban source regions of China and Korea, but averaged only about 5 pbbv in the rural areas. Midtropospheric SO2 concentrations were more than an order of magnitude less, with peak values of around 0.1–0.15 ppbv overlying the urban source regions. The model-calculated sulfate aerosol distribution is more disperse, with peak surface concentrations of 5–10 ppbv in urban source regions, and concentrations of about 3 ppbv or less in rural areas and 1 ppbv or less in the midtroposphere. The model-calculated SOx concentrations are generally within a factor of 2 of the relevant observed concentrations at nonurban sites. The calculations indicate that during the late winter/early spring period, about 50% of the anthropogenic SOx emitted over East Asia is removed from the continental source regions. Roughly 30% is wet and dry deposited onto the neighboring oceans, and the remaining 20% is exported out of the model domain. The vast majority of the exported SOx is in the form of sulfate aerosol and is transported into the midtroposphere overlying the North Pacific Ocean. The rate of SOx export, about 0.2 Tg S per month, is significant when compared to natural S sources to the North Pacific Ocean, suggesting that the export of anthropogenic SOx from East Asia is perturbing sulfate aerosol concentrations over the North Pacific Ocean during the late winter and early spring. On an intraregional basis we find that China is the largest contributor to the emission and export of SOx from East Asia. However, all the nations/continental subregions of East Asia appear to be net exporters of SOx, even those downwind of China.
Fast time resolution (>1 Hz) sulfur dioxide (SO2) measurements were obtained using an atmospheric pressure ionization mass spectrometer with isotopically labeled internal standard on the NASA Wallops P-3B during the NASA Transport and Chemical Evolution Over the Pacific (TRACE-P) field experiment. The high time resolution for SO2 allowed a view into the dynamics of SO2 transport, including the effects of clouds. Two missions along 124.5°E from the vicinity of Taiwan to the northern Yellow Sea near the Korean peninsula were flown on consecutive days with quite different weather conditions. Although the winds on both flights were westerly to northwesterly, the SO2 concentrations were markedly different in vertical and horizontal distributions. Together with turbulence measurements and other high rate data on the P-3B, we have assessed how cloud processing and atmospheric dynamics may have caused the differences in the SO2 distributions. Below 2 km, SO2 layers of a few hundred meters depth were often isolated from the mixed layer. The relatively slow process of entrainment limited loss of SO2 to the marine mixed layer. When compared to 3-D model results of SO2 along the flight track, the in situ SO2 data showed that the model poorly represented the SO2 distribution along the flight track for the cloudy day, while the model gave a reasonably good representation of the in situ data during the clear air flight. On the clear air flight day, the model achieved a closer representation of the SO2 distribution, but it overestimated the SO2 concentrations just above the well-mixed boundary layer. The deviations between the observations and the model appear to be related the treatment of the boundary layer dynamics.
Distributions of volatile sulfur compounds (carbonyl sulfide (COS), carbon disulfide (CS2), hydrogen sulfide (H2S), dimethyl sulfide (DMS)) in surface seawater and overlying atmosphere were measured in the northwestern Pacific, eastern Indian, and Southern Oceans (40°N-66°S, 40°E-140°E) in November-December 1996 during the 38th Japanese Antarctic Research Expedition cruise. Seawater measurements revealed that DMS was the dominant sulfur compound, with concentrations of 0.5-15.8 nM. High values were found in the Southern Ocean's marginal ice zone (84°E-63°E, 59°S-63°S), suggesting that the area during the bloom acts as an important source of atmospheric DMS. Atmospheric concentrations were 456-471 pptv for OCS, n.d. (not detected level) -13 pptv for CS2, n.d. -17 pptv for H2S, and n.d. -755 pptv for DMS. Concentrations of OCS were nearly constant. Concentrations of CS2 and H2S were high in terrigenic air masses and low in those of oceanic origin. Comparison of atmospheric DMS data and a steady state box model using sea-to-air fluxes of DMS and assumed OH radical concentrations revealed that atmospheric DMS concentrations in the equatorial region and most of the Southern Ocean were balanced with local oceanic emission residues and photochemical oxidation. Simultaneous measurements in the atmosphere showed DMS was the dominant sulfur gas that was oxidized rapidly to sulfate aerosols in the marine atmosphere.
Sulfur isotope measurements were performed on size-segregated aerosols collected during the Albatross oceanographic campaign from 61°N to 35°S above the Atlantic Ocean in October and November 1996. Results obviously showed the dependence of the sulfur isotope ratio upon particle size, the finest particles being depleted in 34S compared to coarse particles, suggesting a heavier continental influence in the fine mode. In the coarse mode, 50-90% of the excess sulfate in both hemispheres was found to be of biogenic origin. In the fine mode a different picture was obtained. In the Northern Hemisphere the contribution of biogenic sulfur was found to be less than 35% of the excess sulfur even in relatively clean air masses. On the other hand, in the Southern Hemisphere the participation of biogenic sulfur was about 60% of the excess sulfur in purely marine air. The contribution of continental sulfur to the fine fraction in the Southern Hemisphere was up to 40+/-25% even under pure oceanic conditions and far more in the Northern Hemisphere. These results attest to the possible importance of long-range transport of fine sulfate particles or SO2, possibly through the free troposphere, or the importance of anthropogenic emissions due to shipping.
Observations over the tropical Pacific during the Pacific Exploratory Mission (PEM)-Tropics B experiment (March-April 1999) are analyzed. Concentrations of CO and long-lived nonmethane hydrocarbons in the region are significantly enhanced due to transport of pollutants from northern industrial continents. This pollutant import also enhances moderately O3 concentrations but not NOx concentrations. It therefore tends to depress OH concentrations over the tropical Pacific. These effects contrast to the large enhancements of O3 and NOx concentrations and the moderate increase of OH concentrations due to biomass burning outflow during the PEM-Tropics A experiment (September-October 1996). Observed CH3I concentrations, as in PEM-Tropics A, indicate that convective mass outflux in the middle and upper troposphere is largely independent of altitude over the tropical Pacific. Constraining a one-dimensional model with CH3I observations yields a 10-day timescale for convective turnover of the free troposphere, a factor of 2 faster than during PEM-Tropics A. Model simulated HO2, CH2O, H2O2, and CH3OOH concentrations are generally in agreement with observations. However, simulated OH concentrations are lower (~25%) than observations above 6 km. Whereas models tend to overestimate previous field measurements, simulated HNO3 concentrations during PEM-Tropics B are too low (a factor of 2-4 below 6 km) compared to observations. Budget analyses indicate that chemical production of O3 accounts for only 50% of chemical loss; significant transport of O3 into the region appears to take place within the tropics. Convective transport of CH3OOH enhances the production of HOx and O3 in the upper troposphere, but this effect is offset by HOx loss due to the scavenging of H2O2. Convective transport and scavenging of reactive nitrogen species imply a necessary source of 0.4-1 Tg yr-1 of NOx in the free troposphere (above 4 km) over the tropics. A large fraction of the source could be from marine lightning. Oxidation of DMS transported by convection from the boundary layer could explain the observed free tropospheric SO2 concentrations over the tropical Pacific. This source of DMS due to convection, however, would imply in the model free tropospheric concentrations much higher than observed. The model overestimate cannot be reconciled using recent kinetics measurements of the DMS-OH adduct reaction at low pressures and temperatures and may reflect enhanced OH oxidation of DMS during convection.
We present a detailed evaluation of the atmospheric sulfur cycle simulated in the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. The model simulations of SO2, sulfate, dimethyl-sulfide (DMS), and methanesulfonic acid (MSA) are compared with observations from different regions on various timescales. The model agrees within 30% with the regionally averaged sulfate concentrations measured over North America and Europe but overestimates the SO2 concentrations by more than a factor of 2 there. This suggests that either the emission rates are too high, or an additional loss of SO2 which does not lead to a significant sulfate production is needed. The average wintertime sulfate concentrations over Europe in the model are nearly a factor of 2 lower than measured values, a discrepancy which may be attributed largely to the sea-salt sulfate collected in the data. The model reproduces the sulfur distributions observed over the oceans in both long-term surface measurements and short-term aircraft campaigns. Regional budget analyses show that sulfate production from SO2 oxidation is 2 to 3 times more efficient and the lifetimes of SO2 and sulfate are nearly a factor of 2 longer over the ocean than over the land. This is due to a larger free tropospheric fraction of SO2 column over the ocean than over the land, hence less loss to the surface. The North Atlantic and northwestern Pacific regions are heavily influenced by anthropogenic activities, with more than 60% of the total SO2 originating from anthropogenic sources. The average production efficiency of SO2 from DMS oxidation is estimated at 0.87 to 0.91 in most oceanic regions.
Recent studies suggest that the environmental effects of volcanic gas emissions in the lower troposphere have been underestimated. This chapter first briefly summarizes the techniques available for characterizing tropospheric volcanic gas plumes, including the composition and fluxes of emitted gases and aerosols, as well as their atmospheric dispersion. The second part documents the contribution of gas emissions from degassing craters to the composition of the atmosphere, including effects from dry and wet deposition chemistry. The third section deals with the detrimental impacts on vegetation, soils, and groundwater in relation to passive degassing activity. Improved understanding of the impacts of volcanic degassing on the atmospheric and terrestrial environment will require: (1) systematic two-dimensional and three-dimensional measurements of tropospheric volcanic plumes, (2) development of general physical and chemical models to describe the fate of volcanic gases and aerosols during transport in the troposphere, and (3) investigation of the response of diverse ecosystems to volcanogenic air pollution.
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.
Globally, carbonyl sulphide (COS) is the most abundant sulphur gas in
the atmosphere. Our chemistry-climate model of the lower and middle
atmosphere with aerosol module realistically simulates the background
stratospheric sulphur cycle, as observed by satellites in volcanically
quiescent periods. The model results indicate that upward transport of
COS from the troposphere largely controls the sulphur budget and the
aerosol loading of the background stratosphere. This differs from most
previous studies which indicated that short-lived sulphur gases are also
important. The model realistically simulates the modulation of the
particulate and gaseous sulphur abundance in the stratosphere by the
quasi-biennial oscillation (QBO). In the lowermost stratosphere organic
carbon aerosol contributes significantly to extinction. Further, we
compute that the radiative forcing efficiency by 1 kg of COS is 724
times that of 1 kg CO2, which translates into an overall
radiative forcing by anthropogenic COS of 0.003 W m-2. The
global warming potentials of COS over time horizons of 20 and 100 yr are
GWP(20 yr) = 97 and GWP(100 yr) = 27, respectively (by mass).
Furthermore, stratospheric aerosol particles produced by the photolysis
of COS contribute to a negative radiative forcing, which amounts to
-0.007 W m-2 at the top of the atmosphere for the
anthropogenic fraction, more than two times the warming forcing of COS.
Considering that the lifetime of COS is twice that of stratospheric
aerosols the warming and cooling tendencies approximately cancel. If the
forcing of the troposphere near the tropopause is considered, the
cooling dominates.
1] The Pacific Exploratory Mission Tropics (PEMT) A (1996) and B (1999) field campaigns occurred over a large area of the Pacific Basin and revealed the presence of ''rivers'' of continental outflow propagating into the remote marine atmosphere that were also supported by remote sensing and modeling efforts. Airborne measurements of both the coarse and fine mode aerosol during these campaigns provided assessment of the spatial variability in aerosol parameters (including optical properties and degree of internal versus external mixing) in continental plumes encountered over the Pacific Ocean. Large perturbations to the ''pristine'' marine atmosphere were observed. Most plumes were encountered in the Southern Hemisphere during PEMT A, while the opposite was observed during PEMT B. A variety of anthropogenic and natural sources for these continental plumes are suggested by the data, including biomass burning, urban/industrial emissions, and in the case of Asian outflow, dust storms. Aerosol size distributions (particularly for the refractory component) varied from one plume to another and most combustion-derived aerosol appeared to be an internal mix of a refractory soot-like constituent in a volatile matrix. Within the sampled plumes, size-resolved volatility suggested that this volatile matrix was relatively well neutralized, implying the presence of ammonia in the particle phase. The radiatively important single scatter albedo (w) obtained from measured ''dry'' scattering and absorption coefficients ranged from approximately 0.88 (pollution with no coarse particles) to 0.94 (pollution and dust) in the free troposphere (FT) to 0.98 (pollution and sea salt) within the marine boundary layer (MBL). Vertical profiles often revealed more concentrated plumes aloft, typically situated in dry air with ambient relative humidity (RH) <40%, and much lower values of w than in the underlying MBL.
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.
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.
Reported here are results from an airborne photochemical/sulfur field study in the equatorial Pacific. This study was part of NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM) Tropics A program. The focus of this paper is on data gathered during an airborne mission (P-3B flight 7) near the Pacific site of Christmas Island. Using a Lagrangian-type sampling configuration, this sortie was initiated under pre-sunrise conditions and terminated in early afternoon with both boundary layer (BL) as well as buffer layer (BuL) sampling being completed. Chemical species sampled included the gas phase sulfur species dimethyl sulfide (DMS), sulfur dioxide (SO2), methane sulfonic acid (MSA)g, and sulfuric acid (H2SO4)g. Bulk aerosol samples were collected and analyzed for methane sulfonate (MS), non-sea-salt sulfate (NSS), Na+, Cl-, and NH4+. Critical non-sulfur parameters included real-time sampling of the hydroxyl radical (OH) and particle size/number distributions. These data showed pre-sunrise minima in the mixing ratios for OH, SO2, and H2SO4 and post-sunrise maxima in the levels of DMS, OH, and H2SO4. Thus, unlike several previous studies involving coincidence DMS and SO2 measurements, the Christmas Island data revealed that DMS and SO2 were strongly anticorrelated. Our ``best estimate'' of the overall efficiency for the conversion of DMS to SO2 is 72+/-22%. These results clearly demonstrate that DMS was the dominant source of SO2 in the marine BL. Using as model input measured values for SO2 and OH, the level of agreement between observed and simulated BL H2SO4(g) profiles was shown to be excellent. This finding, together with supporting correlation analyses, suggests that the dominant sulfur precursor for formation of H2SO4 is SO2 rather than the more speculative sulfur species, SO3. Optimization of the fit between the calculated and observed H2SO4 values was achieved using a H2SO4 first-order loss rate of 1.3×10-3s-1. On the basis of an estimated total ``wet'' aerosol surface area of 75 mum2/cm3, a H2SO4 sticking coefficient of 0.6 was evaluated at a relative humidity of ~=95%, in excellent agreement with recent laboratory measurements. The Christmas Island data suggest that over half of the photochemically generated SO2 forms NSS, but that both BL NSS and MS levels are predominantly controlled by heterogeneous processes involving aerosols. In the case of MS, the precursors species most likely responsible are the unmeasured oxidation products dimethyl sulfoxide (DMSO) and methane sulfinic acid (MSIA). Gas phase production of MSA was shown to account for only 1% of the observed MS; whereas gas phase produced H2SO4 accounted for ~20% of the NSS. These results are of particular significance in that BL-measured values of the ratio MS/NSS have often been used to estimate the fraction of NSS derived from biogenic DMS and to infer the temperature environment where DMS oxidation occurred. If our conclusions are correct and both products are predominantly formed from complex and still poorly characterized heterogeneous processes, it would suggest that for some environmental settings a simple interpretation of this ratio might be subject to considerable error.
New particle formation in a tropical marine boundary layer setting was characterized during NASA's Pacific Exploratory Mission–Tropics
A program. It represents the clearest demonstration to date of aerosol nucleation and growth being linked to the natural marine
sulfur cycle. This conclusion was based on real-time observations of dimethylsulfide, sulfur dioxide, sulfuric acid (gas),
hydroxide, ozone, temperature, relative humidity, aerosol size and number distribution, and total aerosol surface area. Classic
binary nucleation theory predicts no nucleation under the observed marine boundary layer conditions.
Remote and in situ measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases and aerosols over the western Pacific during NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission-West A (PEM-West A) conducted in September-October 1991. This paper discusses the 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 and airborne in situ instrumentation for comprehensive measurements of air mass composition. In low latitudes of the western Pacific the airflow was generally from the east, and under these conditions the air was observed to have low aerosol loading and low ozone levels throughout the troposphere. Ozone was found to be below 10 parts per billion volume (ppbv) near the surface to 40-50 ppbv in the middle to upper troposphere. In the middle and high latitudes the airflow was mostly westerly, and the background O3 was generally less than 55 ppbv. On 60% of the PEM-West A flights, O3 was observed to exceed these levels in regions that were determined to be associated with stratospheric intrusions. In convective outflows from typhoons, near-surface air with low ozone (10 km). Several cases of continental plumes from Asia were observed over the Pacific during westerly flow conditions. These plumes were found in the lower troposphere with ozone levels in the 60-80 ppbv range and enhanced aerosol scattering. At low latitudes over the central Pacific the troposphere primarily contained air with background or low ozone levels; however, stratospherically influenced air with enhanced ozone (40-60 ppbv) was observed several times in the lower troposphere. The frequency of observation of the air masses and their average chemical composition are also discussed in this paper.
Seven techniques for the field measurement of trace atmospheric SO2 were compared simultaneously over 1 month in 1994 using samples produced in situ by dynamic dilution. Samples included SO2 in dry air, in humid air, and in air with potentially interfering gases added. In addition, 2 days of comparison using diluted ambient air were conducted. Six of the seven techniques compared well, with good linear response and no serious interferences but with a range of calibration differences of about 50%.
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.
Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially
to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both
the direct scattering of shortwavelength solar radiation and the modification of the shortwave reflective properties of clouds
by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate
forcing due to anthropogenic sulfate is estimated to be –1 to –2 watts per square meter, globally averaged. This perturbation
is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing
has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions
of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic
influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse
gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical
distribution of aerosol climate forcing and on the controlling chemical and physical processes.
The subject of long range transport (LRT) of pollutants is in the early stages of study in Asia (Merrill et al., 1985; Kotamarthi and Carmichael, 1990; Arndt et al., 1996). The results from the PEM West A & B experiments have shown the widespread impact that long range transport of materials from the continental regions of east Asia has on the chemical composition of the troposphere over the western Pacific (Hoell et al., 1996). The projected growth in emissions for the region suggests that the long range transport of pollutants in east Asia will grow in importance over the next several decades.
As part of the NASA Tropospheric Chemistry Program, a series of field intercomparisons have been conducted to evaluate the state-of-the art for measuring key tropospheric species. One of the objectives of the third intercomparison campaign in this series, Chemical Instrumentation Test and Evaluation 3 (CITE 3), was to evaluate instrumentation for making reliable tropospheric aircraft measurements of sulfur dioxide, dimethyl sulfide, hydrogen sulfide, carbon disulfide, and carbonyl sulfide. This paper reports the results of the intercomparisons of five sulfur dioxide measurement methods ranging from filter techniques, in which samples collected in flight are returned to the laboratory for analyses (chemiluminescent or ion chromatographic), to near real-time, in-flight measurements via gas chromatographic, mass spectrometric, and chemiluminescent techniques. All techniques showed some tendency to track sizeable changes in ambient SO2 such as those associated with altitude changes. For SO2 mixing ratios in the range of 200 pptv to a few ppbv, agreement among the techniques varies from about 30% to several orders of magnitude, depending upon the pair of measurements intercompared. For SO2 mixing ratios less than 200 pptv, measurements from the techniques are uncorrelated. In general, observed differences in the measurement of standards do not account for the flight results. The CITE 3 results do not unambiguously identify one or more of the measurement techniques as providing valid or invalid SO2 measurements, but identify the range of `potential` uncertainty in SO2 measurements reported by currently available instrumentation and as measured under realistic aircraft environments.
A gas chromatograph/mass spectrometer is described for determining atmospheric sulfur dioxide, carbon disulfide, dimethyl sulfide, and carbonyl sulfide from aircraft and ship platforms. Isotopically labelled variants of each analyte were used as internal standards to achieve high precision. The lower limit of detection for each species for an integration time of 3 min was 1 pptv for sulfur dioxide and dimethyl sulfide and 0.2 pptv for carbon disulfide and carbonyl sulfide. All four species were simultaneously determined with a sample frequency of one sample per 6 min or greater. When only one or two species were determined, a frequency of one sample per 4 min was achieved. Because a calibration is included in each sample, no separate calibration sequence was needed. Instrument warmup was only a few minutes. The instrument was very robust in field deployments, requiring little maintenance.
The NASA Pacific Exploratory Mission-West A (PEM-West A) experiment in 1991 covered large portions of the northwestern Pacific Ocean troposphere and a transect of the subtropical troposphere of the North Pacific Ocean. Sulfur dioxide consistently increased with altitude from the surface to 11 km except for a few cases of anthropogenic inputs con- freed to the planetary boundary layer. Using the PEM West A data set for SO2, sulfate, and calculated OH over the central Pacific Ocean, we have estimated the impacts of the SO2 on the formation of condensation nuclei and the lifetimes of SO2 and sulfate for this region.
Sulfur dioxide and dimethyl sulfide were determined in the marine boundary layer of the northeast Pacific Ocean west of Seattle, Washington. The mean DMS and SO2 concentrations were 75 and 28 pptv, respectively. During periods of high DMS levels (180 pptv) we found thta SO2 levels remained low (25 pptv) and statistically the same as periods of low DMS. Sulfur dioxide showed no observable diurnal variation indicating that nonphotochemically driven losses to aerosol and other surfaces cannot explain the low SO2 levels observed. We conclude that a low efficiency of conversion of DMS to SO2 is the most likely explanation for the low SO2 levels. Implications of the low yield of SO2 in terms of the kinetics of oxidation of DMS are discussed.
Measurements of seawater dimethylsulfide (DMS), atmospheric dimethylsulfide, and sulfur dioxide (SO2) were made on board the R/V Discoverer in the Southern Ocean, southeast of Australia, as part of the First Aerosol Characterization Experiment (ACE 1). The measurements covered a latitude range of 40°S-55°S during November-December 1995. Seawater DMS concentrations ranged from 0.4 to 6.8 nM, with a mean of 1.7+/-1.1nM(1sigma). The highest DMS concentrations were found in subtropical convergence zone waters north of 44°S, and the lowest were found in polar waters south of 49°S. In general, seawater DMS concentrations increased during the course of the study, presumably due to the onset of austral spring warming. Atmospheric DMS concentrations ranged from 24 to 350 parts per trillion by volume (pptv), with a mean of 112+/-61pptv(1sigma). Atmospheric SO2 was predominantly of marine origin with occasional anthropogenic input, as evidenced by correlation with elevated 222Rn and air mass trajectories. Concentrations ranged from 3 to 1000 pptv with a mean of 48.8+/-149pptv(1sigma) and a median 15.8 pptv. The mean SO2 concentration observed in undisturbed marine air was 11.9+/-7.6pptv(1sigma), and the mean DMS to SO2 ratio in these conditions was 13+/-9(1sigma). Diurnal variations in SO2 were observed, with a daytime maximum and early morning minimum in agreement with model simulations of DMS oxidation in the marine boundary layer. Steady state calculations and photochemical box model simulations suggest that the DMS to SO2 conversion efficiency in this region is 30-50%. Comparison of these results with results from warmer regions suggests that the DMS to SO2 conversion efficiency has a positive temperature dependence.
A field study of the chemistry of dimethyl sulfide (DMS) was conducted on the island of Kiritimati (Christmas Island) during July and August, 1994. This island is located at 2°N, 157°W approximately 2000 km south of Hawaii. We obtained a very repeatable diurnal variation for both DMS and sulfur dioxide (SO2) during two 5-day and one 2-day experiments. Near sunrise DMS was about 200 pptv. It decreased to about 120 pptv by late afternoon. During the daytime SO2 increased from about 20 pptv to about 75 pptv. At night DMS increased and SO2 decreased almost linearly. About 62% of the DMS was converted to SO2. DMS was emitted from the ocean at an average flux of 3.7 × 1013 molecules m−2 s−1. The average dry deposition velocity of SO2 was 6.8 mm sec−1. Most of the SO2 appeared to be lost to the ocean although a comparable but not significantly larger flux to aerosol cannot be ruled out. Dimethyl sulfoxide was in the range 10 to 50 pptv with a mean of about 25 pptv. Dimethyl sulfone was in the range 0 to 15 pptv with a mean of about 3 pptv. There was no diurnal trend in either species. A much smaller fraction of the DMS was converted to dimethyl sulfone than dimethyl sulfoxide.
The NASA Pacific Exploratory Mission over the Western Pacific Ocean (PEM-West B) field experiment provided an opportunity to study sulfur dioxide (SO2) in the troposphere over the western Pacific Ocean from the tropics to 60øN during February-March 1993. The large suite of chemical and physical measurements yielded a complex matrix in which to understand the distribution of sulfur dioxide over the western Pacific region. In contrast to the late summer period of Pacific Exploratory Mission-West A (PEM-West A) (1991) over this same area, SO2 showed little increase with altitude, and concentrations were much lower in the free troposphere than during the PEM-West B period. Volcanic impacts on the upper troposphere were again found as a result of deep convection in the tropics. Extensive emission of SO2 from the Pacific Rim land masses were primarily observed in the lower well-mixed part of the boundary layer but also in the upper part of the boundary layer. Analyses of the SO2 data with aerosol sulfate, beryllium-7, and lead-210 indicated that SO2 contributed to half or more of the observed total oxidized sulfur (SO2 plus aerosol sulfate) in free tropospheric air. The combined data set suggests that SO2 above 8.5 km is transported from the surface but with aerosol sulfate being removed more effectively than SO2. Cloud processing and rain appeared to be responsible for lower SO2 levels between 3 and 8.5 km than above or below this region.
An updated, new version (3.0) of the Generic Mapping Tools (GMT) has just been released. GMT is a public domain collection of UNIX tools that contains programs to manipulate (x,y) and (x,y,z) data and to generate PostScript illustrations, including simple x-y diagrams, contour maps, color images, and artificially illuminated, perspective, shaded-relief plots using a variety of map projections [Wessel and Smith, 1991]. GMT has been installed on super computers, workstations and personal computers, all running some flavor of UNIX. We estimate that approximately 5000 scientists worldwide are currently using GMT in their work.
The atmospheric chemistry. of sulfur dioxide over the tropical South Pacific Ocean is investigated by using results from field measurements and numerical models. Simultaneous real time measurements of sulfur dioxide and its biogenic precursor dimethylsulfide were made at 12øS, 135øW for a 6-day period from March 3 through March 9, 1992. The mean SO2 and DMS mole fractions were 71 _+ 56 pmol mol 4 (lc0 and 453 _+ 93 pmol mo1-1 (lc 0 respectively. These concentrations are compared to those predicted by a time-dependent photochemical box model of the marine boundary layer. Model estimates of the yield of SO2 from DMS oxidation range from 27% to 54%. Even with low yields, DMS is the dominant source of SOin this region. Estimates of vertical entrainment velocities based on the tropospheric ozone budget suggest that vertical entrainment is a minor source of SO:. The relative rates of various loss mechanisms for SO: are dry deposition to the sea surface (58%), in-cloud oxidation (9%), OH oxidation (5%), and uptake by sea-salt aerosols (28%).
The transport of SO2 and sulfate in East Asia (including eastern China, Korea, and Japan) during the period of March 1 through March 14, 1994, is studied using a three-dimensional regional-scale atmospheric chemistry model. This period corresponds to that in which the Pacific Exploratory Mission in the Western Pacific Ocean (PEM-West B) was being conducted around Japan. During this period, characterized by the passage of cold fronts and relatively dry conditions, the anthropogenic sulfur emitted from the source regions in East Asia is transported out into the central Pacific Ocean. The sulfur transport is largely limited to the lower 4 km of the atmosphere, with the maximum flux occurring in the 30° to 40°N latitude band containing the bulk of the anthropogenic emissions. The interactions between the sulfur cycle and mineral aerosol are also included in the analysis. It is found that the chemical conversion of SO2 to sulfate in the presence of mineral aerosol may be a significant process during this time period, and may contribute from 20% to 40% of the total sulfate production. Sulfur dioxide arising from volcanic sources in Japan is also discussed.
During the Soviet/American Gases and Aerosols (SAGA 3) program in February and March 1991 we measured a wide variety of sulfur compounds simultaneously in the equatorial Pacific marine boundary layer. We made measuremetns of atmospheric dimethyl sulfide (DMS), sulfur dioxide (SO2), and size-resolve aerosol non-sea-salt sulfate (NSS), and methane sulfonate (MSA). Some of our observed ratios contradict commonly held views of the marine sulfur cycle: the large DMS/NSS ratio implies that NSS may not be the primary product of DMS oxidation under some conditions. We also found much more DMS than SO2, which may suggest that SO2 is not always an intermediate in DMS oxidation. The small SO2/NSS ratio also supports the idea that most NSS was not formed from SO2. Although our measured ratios of MSA/NSS were similar to previous observations in this region, much of the MSA was contained on supermicron particles, in contrast to both the NSS and the earlier MSA observations at higher latitudes. This implies that MSA/NSS ratios in ice cores may not accurately reflect the MSA/NSS ratios in their source areas.
The atmospheric chemistry of sulfur dioxide over the tropical South Pacific Ocean is investigated by using results from field measurements and numerical models. Simultaneous real time measurements of sulfur dioxide and its biogenic precursor dimethylsulfide were made at 12°S, 135°W for a 6-day period from March 3 through March 9, 1992. The mean SO2 and DMS mole fractions were 71+/-56 pmolmol-1 (1sigma) and 453+/-93 pmolmol-1 (1sigma) respectively. These concentrations are compared to those predicted by a time-dependent photochemical box model of the marine boundary layer. Model estimates of the yield of SO2 from DMS oxidation range from 27% to 54%. Even with low yields, DMS is the dominant source of SO2 in this region. Estimates of vertical entrainment velocities based on the tropospheric ozone budget suggest that vertical entrainment is a minor source of SO2. The relative rates of various loss mechanisms for SO2 are dry deposition to the sea surface (58%), in-cloud oxidation (9%), OH oxidation (5%), and uptake by sea-salt aerosols (28%).
On the 1978 Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases (Gametag) flights, 201 measurements of the tropospheric concentration of SO2 were made over a latitude range 57°S to 70°N. The area sampled included the central and the southern Pacific Ocean and the western section of the United States and Canada. Sulfur dioxide levels averaged 89+/-69 pptv in the boundary layer and 122+/-85 pptv in the free troposphere in the northern hemisphere. In the southern hemisphere, SO2 concentrations averaged 57+/-18 pptv in the boundary layer and 90+/-21 pptv in the free troposphere. The mean concentration of the continental data was 112+/-79 pptv in the boundary layer and 160+/-100 pptv in the free troposphere. The SO2 marine values were 54+/-19 pptv in the boundary layer and 85+/-28 pptv in the free troposphere. From a simple chemical model we conclude that a significant amount of background SO2 may originate from the oxidation of OCS.
The NASA Pacific Exploratory Mission-West experiment in 1991 and 1994 covered large portions of the western Pacific Ocean troposphere and transects of the troposphere of the equatorial and subtropical North Pacific Ocean. Sulfur dioxide and dimethyl sulfide were con- currently measured from the surface to 12 km. In 1991, sulfur dioxide had significant anthropo- genic and volcanic sources. In 1994, sulfur dioxide aloft was significantly lower than in 1991. During both periods, deep convection was responsible for the distribution of sulfur dioxide and dimethyl sulfide. An assessment is made of the proportion of sulfur dioxide that could be made from dimethyl sulfide convected to high altitude. The subsequent formation of new aerosol par- ticles from sulfur dioxide at high altitude is evaluated.
Boundary-layer and free-troposphere measurements of sulfur dioxide, dimethyl sulfide, and carbon disulfide were made during transits of the central and southern Pacific Ocean between Hawaii and Australia. Sulfur dioxide was generally less than 100 pptv and highly variable with no correlation with respect to geographic location or altitude. Dimethyl sulfide in the boundary layer had a concentration range of 2, DMS, and CS2. In 1989, additional SO2 measurements were made between Hawaii and the equator and to the west of Hawaii downwind of the Kilauea volcano plumes.
Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO2 are used as internal standards. Spiked air samples are dried to a dew point of <−60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO2 and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO2 and 42% for DMS at concentrations from 5–15 pptv.
Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (3750 S–7730 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within 30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%.
The major source of cloud-condensation nuclei (CCN) over the oceans
appears to be dimethylsulphide, which is produced by planktonic algae in
sea water and oxidizes in the atmosphere to form a sulphate aerosol.
Because the reflectance (albedo) of clouds (and thus the earth's
radiation budget) is sensitive to CCN density, biological regulation of
the climate is possible through the effects of temperature and sunlight
on phytoplankton population and dimethylsulphide production. To
counteract the warming due to doubling of atmospheric CO2, an
approximate doubling of CCN would be needed.
Dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO42−), sodium (Na+), ammonium (NH4+), and nitrate (NO3−) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m−3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m−3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.
The atmospheric SO2 concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m−3 (STP). The nonsea-salt sulfate (ns-SO42−) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO2 and nss-SO42− from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a ‘sea-salt inversion layer’ was reflected in the profiles of those aerosol components, e.g., Na+ and NO3−, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently ‘remote’ northern hemispheric regions.
The usability and reliability of potential vorticity as a meteorological stratospheric tracer are evaluated. The concept of potential vorticity conservation during transport in which stratospheric and tropospheric air are mixing is tested. Aircraft data collected on April 20, 1984 in the western and southwestern U.S. are analyzed in order to derive potential vorticity data; vertical cross sections of constant-pressure data and temperature and wind speed gradients are examined. The tropopause fold observed during the April 20, 1984 aircraft flights is described. The potential vorticity, ozone mixing ratio, and carbon monoxide mixing ratio are compared; a positive correlation between potential vorticity and the ozone mixing ratio and a negative correlation between the potential vorticity and the carbon monoxide mixing ratio are detected. The data support the concepts of the conservation of potential vorticity, the entrainment and mixing of tropospheric air across the boundaries of the fold, and the applicability of potential vorticity as a stratospheric tracer.
Seawater concentrations of dimethylsulfide (DMS) and atmospheric concentrations of DMS, sulfur dioxide, methanesulfonate (MSA), and non-sea-salt (nss) sulfate were measured over the eastern Pacific Ocean between 105 deg and 110 deg W from 20 deg N to 60 deg S during February and March 1989. Although the samples collected in the Southern Hemisphere appear to be of marine origin, no significant correlation was found between the latitudinal distributions of DMS, SO2, MSA, and nss SO4(2-). However, an inverse correlation was found between atmospheric temperature and the MSA to nss SO4(2-) molar ratio in submicrometer aerosol particles with a decrease in temperature corresponding to an increase in the molar ratio. Although this trend is consistent with laboratory results indicating the favored production of MSA at lower temperatures, it is contrary to Southern Hemisphere baseline station data. This suggests either a decrease in the supply of DMS relative to nonmarine sources of nss SO4(2-) at the baseline stations in winter or additional mechanisms that affect the relative production of MSA and nss SO4(2-).
Key sulfur-containing compounds in the atmosphere and ocean: Determination by gas chromatography-mass spectrometry and isotopically labeled internal standards, inIsotope Effects in Gas-Phase Chemistry
- A R Bandy
- D C Thornton
- R G Ridgeway
- W Jr
- Blomquist
- A R Bandy
- D C Thornton
- R G Ridgeway
- W Jr
- Blomquist
Vertical distribution of dimethylsulfide, sulfur di-oxide, aerosol ions, and radon over the northeast Pacific Ocean Sulfur Dioxide and dimethyl sulfide in marine air at Cape Grim
- H Berresheim
- T W Andreae
- M A Kritz
- T S Bates
- J T Merrill
- S M Blomquist
- D C Chen
Sulfur dioxide concentrations and smnple locations for all altitudes over the Pacific basin for the period 1991-1996. References Andreae, M. O., H. Berresheim, T. W. Andreae, M. A. Kritz, T. S. Bates, and J. T. Merrill, Vertical distribution of dimethylsulfide, sulfur di-oxide, aerosol ions, and radon over the northeast Pacific Ocean, J. Atmos. Chem., 6, 149-173, 1988. Ayers, G. P., J. M. Cainey, R. W. Gillett, E. S. Saltzman and M. Hooper, Sulfur Dioxide and dimethyl sulfide in marine air at Cape Grim, Tasmania, Tellus, 49R, 292-299, 1997. Bandy, A. R., D. L. Scott, B. W. Blomquist, S. M. Chen, and D.C.
A meteoro-logical overview of the PEM-Tropics period
- H E Fuelberg
- R E Newell
- S Longmore
- Y Zhu
- D Westberg
- E V Browell
- D R Blake
- G R Gregory
- G W Sachse
Fuelberg, H.E., R.E. Newell, S. Longmore, Y. Zhu, D. Westberg, E. V. Browell, D. R. Blake, G. R. Gregory, and G. W. Sachse, A meteoro-logical overview of the PEM-Tropics period, J. Geophys. Res., this is-sue.
Seasonal variations of atmospheric sulfur dioxide and dimethyl sulfide concentrations at Amsterdam Island in the southern Indian Ocean Results of the Gas-Phase-Sulfur Intercomparison Experiment (GASIE): Overview of experimental setup, results, and general conclusions
- J P Putaud
- N Mihalopolous
- B C Nguyen
- J M Campin
- S Stecher
- H A Iii
Putaud, J.P., N. Mihalopolous, B.C. Nguyen, J.M. Campin, and S. Bel-viso, Seasonal variations of atmospheric sulfur dioxide and dimethyl sulfide concentrations at Amsterdam Island in the southern Indian Ocean, J. Atmos. Chem., 15, 117-131, 1992. Stecher, H. A., III, et al., Results of the Gas-Phase-Sulfur Intercomparison Experiment (GASIE): Overview of experimental setup, results, and general conclusions, J. Geophys. Res., 102, 16,219-16,236, 1997.
Shipboard measurements of DMS and SO2 southwest of Tasmania during ACE 1
- W J Debruyn
- T S Bates
- J M Cainey
- E S Saltzman
DeBruyn, W. J., T. S. Bates, J. M. Cainey, and E. S. Saltzman, Shipboard measurements of DMS and SO2 southwest of Tasmania during ACE 1, J. Geophys. Res., I03, 16,703-16,711, 1998.
Pacific Exploratory Mission in the tropical Pacific: PEM-Tropics A this issue Observations of the at-toospheric sulfur cycle on SAGA-3
- J Hoell
Hoell, J. et al., Pacific Exploratory Mission in the tropical Pacific: PEM-Tropics A, August-September 1996, J. Geophys. Res., this issue. Huebert B. J.; S. Howell, P. Laj, J. E. Johnson, T. S. Bates, P. K. Quinn, V. Yegorov, A.D. Clarke, and J. N. Porter, Observations of the at-toospheric sulfur cycle on SAGA-3, J. Geophys. Res., 101, 6911-6918, 1996.
Shipboard measurements of DMS and SO2 southwest of Tasmania during ACE 1
- DeBruyn