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Introduction to the A&WMA 2002 Critical Review Visibility: Science and Regulation
... Ultrafine (<100 nm) and fine (<2.5 m) suspended particulate matter (PM) fractions affect human health ( Mauderly & Chow, 2008; Pope & Dockery, 2006), visibility (Chow et al., 2002; Watson, 2002), and the earth's radiation balance (MacCracken, 2008; Princiotta, 2009). Because ultrafine particles contribute little to aerosol mass, PM 2.5 and PM 10 (particles with aerodynamic diameters less than 2.5 and 10 m, respectively) may not be appropriate indices for evaluating the effects of aerosols on human health (Biswas & Wu, 2005; Chow, Watson, Savage, et al., 2005; Seigneur, 2009). ...
Size distributions of ambient aerosols at the Fresno Supersite were measured with four commerciallyavailable scanning mobility particle sizers (SMPS). TSI nano, TSI standard, Grimm, and MSP instrumentswere collocated at the Fresno Supersite and particle size distributions were measured continuously fromAugust 18 through September 18, 2005. For particles with diameters between 10 and 200 nm, differencesamong hourly-average ambient particle concentrations ranged from 0% between the TSI nano and Grimmin the 30-50nm size range to 39% between the Grimm and MSP in the 10-30nm size range. MSP concentrationswere 10-33% lower than those measured with the TSI standard for particles smaller than 200 nm.The TSI nano and TSI standard agreed to within 5% in their overlapping size range (10-84 nm). The TSInano and Grimm agreed to within 40% for 5-10nm particles.
... Atmospheric haze is common in the region. Visible plumes from industrial stacks, diesel trucks, twostroke motorcycles, smoke-belching cars, coal-burning, fire-places and stoves reveal many of the sources that cause regional haze (Chow et al., 2002; Watson 2002a, b). For example, the annual emissions of PM 10 , NO x , and SO 2 were as high as 258, 564 and 596 kt, respectively, in 1997 in PRDR (Hong Kong Environmental Protection Department, 2002). ...
The concentrations of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were investigated at eight sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of the Pearl River Delta Region (PRDR), China, during winter and summer 2002. The comparison of summer and winter results was made in order to investigate spatial and seasonal variations. PM2.5 and PM10 samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed by the thermal optical reflectance (TOR) method following the Interagency Monitoring of PROtected Visual Environments (IMPROVE) protocol. During summer, the average OC and EC concentrations in PM2.5 were 9.2 and 4.1 μg m–3, while those in PM10 were 12.3 and 5.2 μg m–3. Carbonaceous aerosol accounted for 38.0% of the PM2.5 and 32.9% of the PM10. The daily average OC, EC, PM2.5 and PM10 concentrations in PRDR were higher in winter than in summer. The average OC/EC ratio was 2.5 for PM2.5 and PM10, suggesting the presence of secondary organic aerosols. The estimated secondary organic carbons in PM2.5 and PM10 were 4.1 and 5.6 μg m–3, respectively. The OC and EC were found to be correlated in winter (correlation coefficient r=0.82) and summer (r=0.64), which implied that motor vehicle sources contributed to the ambient carbonaceous particles. The distribution of eight carbon fractions in OC and EC at eight sites was first reported in ambient samples in Asia, which also indicated that motor vehicle exhaust was the dominant contributor to carbonaceous particles.
... Source samples were taken from 09/23/99, through 02/25/00, to represent: (1) Texas fugitive dust (e.g., paved roads, unpaved roads, and soil) (termed geological material), (2) motor vehicle exhaust from gasoline-and diesel-fueled vehicles operated in Texas and Mexico, (3) wildfires simulated by controlled burns of wood and grass typical of Big Bend National Park, (4) coal-fired power station effluent and coal fly ash, (5) a refinery fluidized bed catalyst cracker, (6) cement kilns fired by coal, coke, scrap tires, and used oil filters, and (7) residential meat cooking. Hot stack, dilution stack, airborne plume, groundbased source-dominated, and grab/resuspension sampling methods have been applied to source profile characterization (Gordon et al., 1984; Chow et al., 1988; Hildemann et al., 1989; Houck, 1991; Watson and Chow, 2001; Watson et al., 2001a, 2002). Dilution stack, ground-based source-dominated, and grab/resuspension methods were used for these profiles. ...
Representative PM2.5 and PM10 source emissions were sampled in Texas during the Big Bend Regional Aerosol Visibility and Observa (BRAVO) study. Chemical source profiles for elements, ions, and carbon fractions of 145 samples are reported for paved and unpaved road dust, soil dust, motor vehicle exhaust, vegetative burning, four coal-fired power stations, an oil refinery catalytic cracker, two cement kilns, and residential meat cooking. Several samples were taken from each emitter and source type, and these were averaged by source type, and in source subgroups based on commonality of chemical composition. The standard deviation represents the variability of the chemical mass fractions. BRAVO profiles differed in some respects from profiles measured elsewhere. High calcium abundances in geological dust, high selenium abundances in coal-fired power stations, and high antimony abundances in oil refinery catalytic cracker emissions were found. Abundances of eight thermally evolved carbon fractions [Atmos. Environ. 28 (15) (1994) 2493] differ among combustion sources, and a Monte Carlo simulation demonstrates that these differences are sufficient to differentiate among several carbon-emitters.
To prevent spreads of Coronavirus disease-2019 (COVID-19), China adopted the lockdown measures in late January 2020, providing a platform to study the response of air quality and atmospheric chemical and physical properties to strict reduced emissions. In this study, the continuous measurements of aerosol light absorption were conducted in Nanjing, east China, from January 3 to March 31, 2020. Our results showed that the contribution of black carbon (BC) to light absorption at the different wavelengths was more than 75 % and the rest light absorption was contributed by brown carbon (BrC), which was mainly originated from primary emissions. Secondary BrC absorption, which was produced by photochemical oxidation, constituted a minor fraction (2-7 %) of the total absorption. Compared with the sampling in the pre-lockdown, the significant decreases of BC (43 %) and secondary BrC absorption (31 %) were found during the lockdown period, resulting in a substantial decrease of solar energy absorbance by 36 % on a local scale. The control measures also changed the diurnal variations of light absorption. Due to the reduced emissions, the relative fraction of fossil fuel to BC also dropped from 78 % in the pre-lockdown to 71 % in the lockdown. The concentrations of BC, PM2.5 and NO2 decreased 1.1 μg m⁻³, 33 μg m⁻³ and 9.1 ppb whereas O3 concentration increased 9.0 ppb during the COVID-19 lockdown period. The decreased concentrations of BC, PM2.5 and NO2 were mainly contributed by both emission reduction (51 - 64 %) and meteorological conditions (36 - 49 %). Our results highlighted that the balance of control measures in alleviation of particulate matter (PM) and O3 pollution, and meteorology should be seriously considered for improvement of air quality in this urban city of China.
The spatiotemporal distribution and chemical composition of atmospheric fine particles in areas around the Taiwan Strait were firstly investigated. Fine particles (PM2.5) were simultaneously collected at two sites on the west-side, one site at an offshore island, and three sites on the east-side of the Taiwan Strait in 2013–2014. Field sampling results indicated that the average PM2.5 concentrations at the west-side sampling sites were generally higher than those at the east-side sampling sites. In terms of chemical composition, the most abundant water-soluble ionic species of PM2.5 were SO42−, NO3−, and NH4+, while natural crustal elements dominated the metallic content of PM2.5, and the most abundant anthropogenic metals of PM2.5 were Pb, Ni and Zn. Moreover, high OC/EC ratios of PM2.5 were commonly observed at the west-side sampling sites, which are located at the downwind of major stationary sources. Results from CMB receptor modeling showed that the major sources of PM2.5 were anthropogenic sources and secondary aerosols at the both sides, and natural sources dominated PM2.5 at the offshore site. A consistent decrease of secondary sulfate and nitrate contribution to PM2.5 suggested the transportation of aged particles from the west-side to the east-side of the Taiwan Strait.
The aim of the present work is a detailed analysis of aerosol columnar optical depth as a tool to determine near-surface aerosol extinction in Reno, Nevada, USA during the summer of 2012. Ground and columnar aerosol optical properties were obtained by use of in situ Photoacoustic and Integrated Nephelometer (PIN) and Cimel CE-318 sunphotometer instruments, respectively. Both techniques showed that seasonal weather changes and fire plumes had enormous influence on local aerosol optics. The Apparent Optical Height (AOH) followed the shape but not magnitude of the development of the Convective Boundary Layer (CBL) when fire conditions were not present. Back trajectory analysis demonstrated that a local flow known as the Washoe Zephyr circulation often induced aerosol transport from Northern California over the Sierra Nevada Mountains that increased the Aerosol Optical Depth at 500 nm during afternoons when compared with mornings. Aerosol fine-mode fraction indicated that afternoon aerosols in June and July and fire plumes in August were dominated by submicron particles, suggesting upwind urban plume biogenically enhanced evolution toward substantial secondary aerosol formation. This fine particle optical depth was inferred to be beyond the surface, thereby complicating use of remote sensing measurements for near-ground aerosol extinction measurements. It is likely that coarse mode depletes fine mode aerosol near the surface by coagulation and condensation of precursor gases.
The calibration of photoacoustic aerosol optical absorption measurements through simultaneous photoacoustic spectroscopy of the oxygen A-band absorption is demonstrated. While aerosol absorption shows no sharp spectral structures for size-distributed aerosols, the molecular oxygen A-band has sharp absorption lines in the near-infrared (i.e., 760–770 nm) spectral region. Line-strength, shape, and broadening of these lines are well known and molecular oxygen is ubiquitous with a constant concentration in the troposphere. Simultaneous photoacoustic spectroscopy of aerosol and molecular oxygen A-band absorption with a tunable, external cavity diode laser yields a convenient calibration for the photoacoustic measurement of aerosol absorption coefficients without the need for pressurized and potentially toxic calibration gases.
The goal of this project is to identify and fill knowledge gaps concerning emission testing methods, emission factors and rates, and activities that create emissions for non-road military diesel engines. This requires the development of new measurement methods that quantify a larger number of chemical compounds and particle sizes, at concentration levels much less than the certification requirements, and for fuels and operating cycles that are not well represented by engine certification tests. Specific project objectives are: 1. Develop, test, and apply new methods for quantifying non-road emissions that more efficiently and realistically represent actual operations than engine dynamometer certification tests. 2. Develop source-, activity-, and fuel-specific emission rate estimates for representative Department of Defense (DoD) mobile and stationary diesel equipment, most of which is not used on public roadways. Emitted pollutants include carbon monoxide (CO), oxides of nitrogen (NOX), volatile organic compounds (VOC), particulate matter (PM, including PM2.5 [particles < 2.5 um aerodynamic diameter], and ultrafine particles [UP, particles less than 0.1 um aerodynamic diameter]), sulfur dioxide, (SO2), and ammonia (NH3). Chemical source profiles for PM2.5 are also quantified. 3. Determine how non-road emissions can be integrated with emissions modeling databases and software that estimate total diesel emissions.
A resurgence of interest has arisen lately in the use of reciprocal nephelometers in aerosol instrumentation that also measures other optical properties such as extinction by the cavity ringdown method and absorption by the photoacoustic method. This paper provides fresh insight into these nephelometers from perspectives of instrument component evaluation, intra-instrument comparison and basic calibration. In particular, a 4° truncation angle reciprocal integrating nephelometer (IN) is described and demonstrated. An experimental setup for the measurement of the IN sensor cosine response is developed and described. To calibrate the IN, the sampling volume can be filled with an aerosol with negligible light absorption (e.g., ammonium sulfate), and scattering and extinction coefficients are monitored simultaneously. The performance of the IN is evaluated, at a wavelength of 532 nm, through extensive comparison with a 1° truncation angle integrating sphere integrating nephelometer (ISIN) that operates at the same wavelength. The intercomparison included measurements of ambient aerosol, kerosene soot, ammonium sulfate aerosol, NaCl aerosol and CO2 gas. Results of a linear regression analysis indicate an agreement between the IN and the ISIN within ±8%. The main advantages of the IN over the ISIN are its fast time response, relatively large signal-to-noise (S/N) ratio and design simplicity.
An instrument employing cavity ring-down (CRD) and cavity-enhanced detection (CED) for the local measurement of aerosol extinction is described and demonstrated. CRD measures the life-time of photons in a high-quality optical cavity and thereby deter-mines the sum of sample extinction between the cavity mirrors and that due to mirror losses. CRD systems can be calibrated with a single gas for the determination of extinction. A green laser emit-ting subnanosecond pulses is used as a light source, facilitating measurements free from optical interference in the cavity. The ad-dition of a low-frequency chopper allows for the determination of extinction coefficients with simple linear fitting procedures and also facilitates CED measurements by providing laser power mod-ulation for phase-sensitive detection. CED measures the average power transmitted by the optical cavity. After calibration with two gases, CED allows for the independent measurement of extinction with very high dynamic range and for an independent compari-son with CRD measurements, thereby increasing confidence in the measurements. INTRODUCTION The atmospheric extinction of electromagnetic waves in the visible and near-visible spectral regions influences the earth's climate by changing short-wave radiative forcing (Jain et al. 2000; Reddy and Venkataraman 2000) and influences optical remote sensing by ground-based, airborne, and satellite systems (Schott 1997), including visual perception by humans (Chow of Nevada. It is a pleasure to thank all participants in the Reno Aerosol Optics Study (RAOS) and the Combustion Aerosol Optics Study (CAOS) in Missoula for their support with these experiments.
Using a novel morphology segregation technique, we observed minority populations ( approximately 3%) of submicron-sized, cluster-dilute fractal-like aggregates, formed in the soot-formation window (fuel-to-air equivalence ratio of 2.0-3.5) of a premixed flame, to have mass fractal dimensions between 1.2 and 1.51. Our observations disagree with previous observations of a universal mass fractal dimension of approximately 1.8 for fractal-like aerosol aggregates formed in the dilute-limit via three-dimensional diffusion-limited cluster aggregation processes. A hypothesis is presented to explain this observation. Subject to verification of this hypothesis, it may be possible to control the fractal dimension and associated properties of aggregates in the cluster-dilute limit through application of a static electric field during the aggregation process.
The 1999 Regional Haze Rule provides a context for this review of visibility, the science that describes it, and the use of that science in regulatory guidance. The scientific basis for the 1999 regulation is adequate. The deciview metric that tracks progress is an imperfect but objective measure of what people see near the prevailing visual range. The definition of natural visibility conditions is adequate for current planning, but it will need to be refined as visibility improves. Emissions from other countries will set achievable levels above those produced by natural sources. Some natural events, notably dust storms and wildfires, are episodic and cannot be represented by annual average background values or emission estimates. Sulfur dioxide (SO2) emission reductions correspond with lower sulfate (SO4(2-)) concentrations and visibility improvements in the regions where these have occurred. Non-road emissions have been growing more rapidly than emissions from other sources, which have remained stable or decreased since 1970. Simpler models representing transport, limiting precursor pollutants, and gas-to-particle equilibrium should be used to understand where and when emission reductions will be effective, rather than large complex models that have insufficient input and validation measurements. Examples of model-based source attribution show large differences among estimates from various modeling systems and with ambient measurements.
The Integrating Sphere Integrating Nephelometer is a novel and unique reciprocal nephelometer that uses an integrating sphere with attached truncation-reduction tubes to contain the sample volume and to integrate the scattered light. Its main advantage compared with current integrating nephelometers is a sevenfold reduction in truncation angle, which reduces errors in measured scattering from large particles. Additional features include improved sampling efficiency for large particles and a well-defined operating wavelength.
This study compares the optical coefficients of size-selected soot particles measured at a wavelength of 870 nm with those predicted by three theories, namely, Rayleigh-Debye-Gans (RDG) approximation, volume-equivalent Mie theory, and integral equation formulation for scattering (IEFS). Soot particles, produced by a premixed ethene flame, were size-selected using two differential mobility analyzers in series, and their scattering and absorption coefficients were measured with nephelometry and photoacoustic spectroscopy. Scanning electron microscopy and image processing techniques were used for the parameterization of the structural properties of the fractal-like soot aggregates. The aggregate structural parameters were used to evaluate the predictions of the optical coefficients based on the three light-scattering and absorption theories. Our results show that the RDG approximation agrees within 10% with the experimental results and the exact electromagnetic calculations of the IEFS theory. Volume-equivalent Mie theory overpredicts the experimental scattering coefficient by a factor of approximately 3.2. The optical coefficients predicted by the RDG approximation showed pronounced sensitivity to changes in monomer mean diameter, the count median diameter of the aggregates, and the geometric standard deviation of the aggregate number size distribution.
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