Grantee Research Project Results
Final Report: Southern Center For the Integrated Study of Secondary Air Pollutants (SCISSAP)
EPA Grant Number: R826372Title: Southern Center For the Integrated Study of Secondary Air Pollutants (SCISSAP)
Investigators: Chameides, William L. , Zika, Rod G. , McMurry, Peter H. , Russell, Armistead G.
Institution: Georgia Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 1998 through March 31, 2001
Project Amount: $3,000,000
RFA: Special Opportunity in Tropospheric Ozone (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The mission of the Southern Center for the Integrated Study of Secondary Air Pollutants (SCISSAP) is the development of the scientific understanding and analytical tools that underpin the design and implementation of an effective and integrated control strategy for secondary air pollutants, using the atmosphere of the Southern United States as a natural laboratory.
This mission is based on the premises that a basic understanding of the chemistry and physics of the atmosphere are a prerequisite for designing effective control strategies for secondary air pollutants, and that the concentration of secondary air pollutants in the atmosphere often is codependent because of interacting chemical reactions.
Over a 4-year period, beginning on April 1, 1998, SCISSAP was funded by the U.S. Environmental Protection Agency (EPA) National Center for Environmental Research's Science to Achieve Results (STAR) program to focus on an integrated study of ground-level ozone (O3) and particulate matter (PM) with diameters less than 2.5 µm (PM2.5) in the South. Specifically, four major and interrelated scientific questions were addressed:
Question 1. What is the composition and size distribution of fine particles in urban and rural locales in the Southern United States, and to what extent do temporal and spatial variations in these parameters correlate with those of ozone and its precursor compounds?
Question 2. What are the major precursor compounds and sources for fine particles in urban and rural locales in the Southern United States, and to what extent do these compounds and sources correspond to/correlate with the sources of natural and anthropogenic ozone precursors (i.e., volatile organic compounds [VOCs] and nitrogen oxides [NOx])?
Question 3. To what extent, if any, is the chemical composition and abundance of fine particles in urban and rural locales in the Southern United States affected by the concentration of natural and anthropogenic ozone precursors and/or ozone?
Question 4. To what extent is the concentration of ground-level ozone in urban and rural locales in the Southern United States affected by the concentration and composition of fine particles and/or the concentration of the precursors of fine particles?
To address these questions, the SCISSAP Science Team adopted two tangential and interrelated lines of investigation. One line of investigation focused first on the development and testing of a mobile capability to measure PM2.5, ozone, and their precusors, and then its subsequent application to large-scale, multi-investigator field experiments, as well as longer term regional monitoring in the Southeast. The other line of investigation focused on the development, evaluation, and application of a regional-scale air quality model for conducting integrated studies of ozone and PM: the "Urban-to-Regional, Multiscale Model: One Atmosphere" (URM-1ATM), with one atmosphere used to denote an integrated approach to treating the physics and chemistry of ozone, acid deposition, and PM simultaneously.
Summary/Accomplishments (Outputs/Outcomes):
During the past 4 years of the project, we have successfully developed a unique capability in the Southeastern United States: a facility for measuring PM2.5 concentrations and composition as well as ozone and ozone- and fine-particle/gaseous precursors. This facility played a central role in a number of major regional air quality field experiments, particularly in the 1999 Atlanta Supersite Experiment. The Science Team also was able to develop, evaluate, and apply a new multiscale, multipollutant regional modeling system. Both the measurement facility and modeling system continue to serve as a resource for the scientific and policymaking communities in the South and other regions of the United States.
Along with the accomplishments already mentioned, we also:
- Developed, field tested, intercompared, and implemented a Particle Composition Monitor (PCM) and related laboratory analytical techniques for measuring the mass and composition of PM2.5 and its precursor compounds using the filter-denuder technique.
- Developed, field tested, intercompared, and implemented a Differential Mobility Analyzer - Aerosol Particle Mass Analyzer (DMA-APM) for in situ measurements of particle mass as a function of mobility (i.e., size).
- Developed, field tested, and implemented a system for quantifying in situ concentrations of oxygenated volatile organic compounds (OVOCs).
- Participated in the 1999 Southern Oxidants Study Nashville/Middle Tennessee Ozone Study and carried out first measurements of PM2.5 vertical gradient within the boundary layer.
- Hosted and provided analytical laboratory and meeting facilities for the 1999 Atlanta Supersite Experiment and participated in the experiment.
- Participated in the 2000 Texas Air Quality Study.
- Operated urban and rural PM2.5 monitoring sites in Tennessee and Georgia.
- Developed an ongoing regional center for air quality field measurements with a mobile measurement capability in the Southeastern United States; this capability has played a key role in the state of Georgia supported Fall-line Air Quality Study, and a locally supported field experiment in Pensacola, FL, during the summer of 2002.
- Helped develop and evaluate a regional-scale air quality model (URM-1ATM).
- Used the URM-1ATM in the Southern Appalachians Mountains Initiative (SAMI) to address specific policy questions and migrated many of the critical components of URM-1ATM to EPA's Models 3.
Findings From the Experimental Programs
In addition to developing and evaluating new and improved instrumentation and analytical techniques for characterizing air pollutant concentrations and characteristics, SCISSAP endeavored to use this technology in field experiments to test various hypotheses with regard to the characteristics and processes that control the characteristics of PM2.5 in the Southeast. Specific findings and their policy-relevant implications are outlined below.
Finding 1. PM2.5 composition (at the 24-hour integrated sampling time used in the study) was found to show little variability across the sites operated from Nashville, TN, to Atlanta, GA, to Houston, TX. In virtually all cases, more than 60 percent of the PM2.5 mass was found to arise from sulfate (and the ammonium associated with it) and organic carbon (and the other organic elements assumed to be associated with the organic carbon).
Finding 2. PM2.5 mass, sulfate, nitrate, and ammonium concentrations were found to have a positive vertical gradient between 4 and 42 m altitude at a suburban site in Tennessee.
Finding 3. The daily variations in the chemical components of PM2.5 exhibited little or no correlation with their gaseous precursors, and PM2.5 mass was not well correlated with local ozone concentrations.
Finding 4. PM2.5 mass concentrations showed only moderate increases from rural, to suburban, to urban locales.
Finding 5. Different instrumentation designed to measure the mass and composition of PM2.5 with 12- or 24-hour integrated sampling generally will yield comparable results with each other and with more sophisticated continuous and semicontinuous methodologies.
Finding 6. Under highly humid conditions (e.g., Atlanta in the summer), significant artifacts in the measurement of PM2.5 mass using the filter technique can arise from the presence of solid hydrates on the filter.
Finding 7. Negative artifacts in the measurement of particulate organic carbon (OC) using EPA's Federal Reference Method (FRM) filter-denuder technique can arise as a result of the liberation of semivolatile organics from the filter during sampling.
Finding 8. Atmospheric particles of 100 nm and 300 nm in Atlanta at approximately 3-6 percent relative humidity typically had two distinct densities: 1.6±0.1 g cm-3 and 0.45±0.20 g cm-3.
Finding 9. Effective densities of diesel exhaust particles decrease with increasing size. At 50 nm, densities are about 1.1±0.1 g cm-3, while at 300 nm, densities are about 0.3±0.05 g cm-3.
Finding 10. The DMA-APM technique can measure the mass and density of spherical particles to within 5 percent.
Finding 11. The DMA-APM technique can measure the mass and "effective densities" of non-spherical particles.
Finding 12. Diagnostic analysis of measurements of PM2.5 composition and related gas-phase concentrations in Atlanta tend to support the notion that the amount of ammonium nitrate found in PM2.5 is controlled by thermodynamic equilibrium between the PM2.5 and gas-phase ammonia and nitric acid.
Finding 13. PM2.5 in the Southeast generally is slightly acidic with relatively small amounts of nitrate.
Finding 14. A positive correlation was found between simultaneously measured OVOC concentrations and speciated, size-segregated particulate OC abundances in Atlanta. Calculation of the hourly new particle production potential from hourly OVOC measurements suggest that gas to particle conversion is a significant source of new organic aerosols. This calculation of new particle production predicts approximately one-half of the measured PM2.5 total organic carbon observed.
Findings from the Modeling Program-Addressing Overarching Questions
In addition to addressing the scientific and policy-relevant issues outlined above, the data gathered by SCISSAP and related programs were used to evaluate the URM-1ATM being developed by the SCISSAP Modeling Team. Once successfully evaluated, the model was used to comprehensively address the four major scientific questions SCISSAP set out to answer in its original proposal. Our findings are summarized below.
Question 1. What is the concentration and composition of PM2.5 in urban and rural locales in the South, and to what extent do temporal and spatial variations in these parameters correlate with those of O3 and its precursor compounds?
Finding 15. Although ozone and elemental carbon exhibit significant variations between urban and rural regions, most of the other components of PM2.5 have relatively uniform concentrations between urban and rural areas, though certain regions have higher sulfate than others. On the other hand, on urban scales there is a tendency for ozone and PM to be highest in or just down wind of urban areas.
Question 2. What are the major precursor compounds and sources for PM2.5 in urban and rural locales in the South, and to what extent do these compounds and sources correspond to or correlate with the sources of natural and anthropogenic O3 precursors (i.e., VOC and NOx)?
Finding 16. The major precursors for PM2.5 in the Southeast are SO2 (largely from coal-fired power plants) and organic carbon, from a myriad of sources including biogenic (e.g., biomass burning and secondary conversion of higher organics) and anthropogenic (automobiles, cooking, etc.). Nitrate plays less of a role at present because the aerosol is so acidic that much of the ammonia necessary for ammonium nitrate formation is tied up as ammonium sulfate. Ammonia, largely from animal waste and fertilizer use, acts to form a fraction of the PM mass, but is important as it is the primary neutralizing agent. For ozone, the two primary precursors are NOx and, again, organics. Automobiles appear to play a major role, followed by electrical generating units in terms of ozone formation because of NOx emissions. Automotive (in urban areas) and biogenic (most everywhere else) sources, as well as solvent usage, have the most impact on forming ozone from the VOC perspective.
Finding 17. Sensitivity maps show that both ozone and sulfate have similar source-impact patterns. Thus, one would expect that controls for precursors of both pollutants would have benefits over the same general area.
Finding 18. Inverse modeling suggests that the inventory of anthropogenic VOC emissions in the Eastern United States is too low by a factor of approximately 2.
Question 3. How are the formation rates and concentrations of O3 and PM2.5, as well as the PM2.5 composition, affected by the relative emissions and concentrations of NOx, SOx, NH3, and VOC species, and what are the mechanisms responsible for these relationships?
Finding 19. Over most of the domain, ozone formation is NOx-limited, though not always in urban areas where there can be a greater sensitivity to VOC emissions. Outside of primary emissions of particulate matter, SOx appears to be the most sensitive precursor for PM formation because it also captures ammonia and water. Sulfate appears to be formed primarily via gas phase oxidation, though aqueous phase reactions are important. Organic PM appears to be split between primary emissions and oxidation of biogenic emissions. Nitrate is formed from oxidation of NO2, which takes place both during the day and at night, followed by reaction with ammonia. Ammonia acts as a neutralizing agent for sulfate and nitrate. The nitrate is highest, at least during the summer, in the early morning hours, when the air is cooler and more humid, promoting condensation.
Finding 20. We do find that elevated NOx sources are less efficient at forming ozone than ground level sources, as has been found from aircraft studies as well. Increased emissions, while increasing ozone, can decrease the "ozone production efficiency" (OPE). We see a much more linear response in SO2 emissions.
Question 4. To what extent do the mechanisms elucidated above affect the formulation of an integrated control strategy for O3 and PM2.5? Do our findings suggest an "optimum" strategy for addressing both pollutants?
Finding 21. Strategies to reduce NOx and SO2 simultaneously will be effective in reducing ozone and PM at the same time. For example, using new, combined cycle gas turbines (or coal gasification), could lower both pollutants effectively. On the other hand, one could envision controls that only go after one of the precursors alone. We did not do an economic optimization to find which would be best. Also of importance, both ozone and PM share a largely uncontrollable source, biogenics such as trees, which will limit the effectiveness of controls. For example, there will be a limit on how low PM levels can go because the biogenic fraction appears to be substantial on stagnant and hot days. Further, in the Southeast, VOC controls primarily will be effective only in and around urban areas, at least on high ozone days.
Finding 22. Our model results show (and as indicated by the measurements) that, at times, reducing SO2 emissions, and hence PM sulfate, can be offset by increased nitrate aerosol as ammonium is no longer tied up neutralizing the sulfuric acid. The extent of this was quite varied over the region. In some cases, this led to a very small impact, though at other times and locations, upwards of about 50 percent of the reduction in sulfate could be lost by an increase in ammonium nitrate. It also was found that this result will change in the future, as SO2 emissions are reduced because of acid rain controls and ammonia emissions may increase because of increased agricultural operations. In such cases, the effect of reduced sulfate leading to increased nitrate becomes more significant. We also found that there is a seasonal dependence. As part of a separate project, using URM-1ATM, we found that over a synthetic year, the replacement phenomena led to a relatively small reduction in the overall benefits of SO2 control, on the order of 10 percent.
Policy-Relevant Implications of Scientific Findings
Emission Control Strategies
- As is the case for ground level ozone pollution, PM2.5 pollution in the Southeastern United States is regional in extent. The fine particle sources appear to be regionally distributed with perhaps direct emissions of PM2.5 and its precursors and/or secondary formation of PM2.5 occurring aloft as opposed to at the surface.
- Mitigation of PM2.5 pollution in the Southeastern United States likely will require the development and implementation of regional-, as opposed to urban-scale emission control and pollution prevention strategies.
- PM2.5 mass in the Southeastern United States is dominated by OC and sulfate, and so, control strategies that aim to reduce total fine particle mass concentrations will require emission reductions in organic carbon and sulfur oxides (SOx).
- In the Southeast, there generally is an inadequate amount of ammonia to neutralize sulfate and hence PM2.5 is slightly acidic. This in turn limits the amount of particulate nitrate that can form. Thus, PM2.5 mitigation efforts based on reducing particulate sulfate by decreasing SO2 emissions may be offset, to some extent, by a concomitant increase in particulate nitrate.
- It would be prudent to consider implementation of controls on NOx and NH3 emissions at the same time that SOx controls are implemented. Controls on NOx emission will have the added benefit of mitigating regional ground-level ozone pollution.
- Controls on the gaseous emissions of OVOC and their precursors could have a significant impact on reducing PM2.5 mass concentrations in Atlanta.
- Controls on particulate emissions from diesel engines may lead to the elimination of a unique class of "low density" particles that were observed in the Atlanta atmosphere.
Fine Particle Monitoring
- Although the EPA-approved filter-denuder technique can yield reasonably robust measurements of PM2.5 mass and composition, the method is subject to artifacts and thus, thorough quality-assurance/quality-control (QA/QC) procedures and self-consistency checks must be adopted with this technique. For example, accurate estimates of total organic mass require development and application of methods for quantifying and correcting for artifacts arising from liberation of semi-volatile organics.
- The DMA-APM provides a precise and accurate technique for measuring particle density, thereby enabling a determination of the definitive relationships between aerodynamic and mobility equivalent diameters. This relationship helps to reconcile measurements based on different physical principles.
- In situ techniques for semi-continuous, direct measurement of mass size distributions and concentrations can provide insights into the accuracy of filter-based measurements of mass concentrations, such as are used in EPA's Federal Reference Method (FRM) network, as well as the health impacts of short-term variations in fine particle mass and composition.
Conclusions:
As a result of the EPA funding SCISSAP, a new scientific and technical capability for air quality research, management, and policy formulation has been developed in the Southeastern United States. This new capability encompasses a state-of-the-science mobile facility for measuring gaseous and particulate pollutants, as well as a state-of-the-science multiscale, multipollutant air quality modeling system.
During the course of the project, the tools described above were used to address a number of policy-relevant scientific issues related to: (1) understanding causes and remedies to fine particle and ground-level ozone pollution in the Southeastern United States; and (2) the monitoring of fine particles in the atmosphere. With regard to the mitigation of fine particle pollution in the South, our studies confirmed the importance of organic carbon and sulfur oxide emissions and the need to control these emissions on regional rather than urban scales. However, because of thermodynamic interactions between sulfate, ammonium, and nitrate, our studies also suggest that control of nitrogen oxide and ammonium emissions may be desirable at the same time that organic carbon and sulfur oxide emission controls are implemented.
With regard to instrumentation for measuring particulates, our studies suggest that the EPA FRM, using the filter-denuder technique, can yield accurate data on the mass and overall composition of fine particles. However, the possibility of artifacts, especially for organic carbon, persists. Further work and development of denuders, filters, and extraction techniques probably is needed. Our studies also suggest that a wealth of additional information on particulate composition, density, and short-term variability can be obtained with the use of a new and emerging class of semicontinuous particulate monitors. The information and data that can be generated by these new monitors may prove to be especially useful in epidemiological and medical effects research aimed at uncovering the specific components of fine particles that are responsible for the adverse health effects in humans.
The new capabilities developed in SCISSAP now are being used within the region to support both air quality research and management. The mobile monitoring facility is playing a central role in a variety of local and regional air quality studies funded by local and state agencies, as well as the EPA. Most notable among these studies is the Georgia Fall Line Air Quality Study (FAQS), which seeks to identify the sources of pollutants and pollutant precursors, and recommends solutions to realized and potential poor air quality in the Augusta, Macon, and Columbus metropolitan areas of Georgia (see http://cure.eas.gatech.edu/faqs/ Exit ). We envision that the mobile facility will continue to represent a valuable resource for the region in the coming years.
The URM-1ATM modeling system developed SCISSAP has made contributions beyond SCISSAP. The modeling system was used in the Southern Appalachian Mountain Initiative to assess the air quality benefits of various possible pollution control scenarios, and now is being migrated to EPA's Models 3.
Journal Articles on this Report : 31 Displayed | Download in RIS Format
Other project views: | All 54 publications | 33 publications in selected types | All 31 journal articles |
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Baumann K, Ift F, Zhao JZ, Chameides WL. Discrete measurements of reactive gases and fine particle mass and composition during the 1999 Atlanta Supersite Experiment. Journal of Geophysical Research–Atmospheres 2003;108(D7):SOS 4-1-SOS 4-20. |
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Biswas J, Hogrefe C, Rao ST, Hao W, Sistla G. Evaluating the performance of regional-scale photochemical modeling systems. Part III-Precursor predictions. Atmospheric Environment 2001;35(35):6129-6149. |
R826372 (Final) R825260 (Final) |
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Boylan JW, Odman MT, Wilkinson JG, Russell AG, Doty KG, Norris WB, McNider RT. Development of a comprehensive, multiscale "one atmosphere" modeling system:application to the Southern Appalachian Mountains. Atmospheric Environment 2002;36(23):3721-3734. |
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Capaldo KP, Kasibhatla P, Pandis SN. Is aerosol production within the remote marine boundary layer sufficient to maintain observed concentrations? Journal of Geophysical Research–Atmospheres 1999;104(D3):3483-3500. |
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Carrico CM, Bergin MH, Xu J, Baumann K, Maring H. Urban aerosol radiative properties:measurements during the 1999 Atlanta Supersite Experiment. Journal of Geophysical Research–Atmospheres 2003;108(D7):8422. |
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Hogrefe C, Rao ST, Kasibhatla P, Kallos G, Tremback CJ, Hao W, Olerud D, Xiu A, McHenry J, Alapaty K. Evaluating the performance of regional-scale photochemical modeling systems: Part I--meteorological predictions. Atmospheric Environment 2001;35(24):4159-4174. |
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Hogrefe C, Rao ST, Kasibhatla P, Hao W, Sistla G, Mathur R, McHenry J. Evaluating the performance of regional-scale photochemical modeling systems: Part II--ozone predictions. Atmospheric Environment 2001;35(24):4175-4188. |
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Kasibhatla P, Chameides WL. Seasonal modeling of regional ozone pollution in the eastern United States. Geophysical Research Letters 2000;27(9):1415-1418. |
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McMurry PH, Wang X, Park K, Ehara K. The relationship between mass and mobility for atmospheric particles:a new technique for measuring particle density. Aerosol Science and Technology 2002;36(2):227-238. |
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Mendoza-Dominguez A, Russell AG. Iterative inverse modeling and direct sensitivity analysis of a photochemical air quality model. Environmental Science & Technology 2000;34(23):4974-4981. |
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Mendoza-Dominguez A, Wilkinson JG, Yang YJ, Russell AG. Modeling and direct sensitivity analysis of biogenic emissions impacts on regional ozone formation in the Mexico-U.S. border area. Journal of the Air & Waste Management Association 2000;50(1):21-31. |
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Mendoza-Dominguez A, Russell AG. Estimation of emission adjustments from the application of four-dimensional data assimilation to photochemical air quality modeling. Atmospheric Environment 2001;35(16):2879-2894. |
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Mendoza-Dominguez A, Russell AG. Emission strength validation using four-dimensional data assimilation:application to primary aerosol and precursors to ozone and secondary aerosol. Journal of the Air & Waste Management Association 2001;51(11):1538-1550. |
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Orsini DA, Ma Y, Sullivan A, Sierau B, Baumann K, Weber RJ. Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition. Atmospheric Environment 2003;37(9-10):1243-1259. |
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Park K, Cao F, Kittelson DB, McMurry PH. Relationship between particle mass and mobility for diesel exhaust particles. Environmental Science & Technology 2003;37(3):577-583. |
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Park K, Kittelson DB, McMurry PH. A closure study of aerosol mass concentration measurements:comparison of values obtained with filters and by direct measurements of mass distributions. Atmospheric Environment 2003;37(9-10):1223-1230. |
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Park K, Kittelson DB, Zachariah MR, McMurry PH. Measurement of inherent material density of nanoparticle agglomerates. Journal of Nanoparticle Research 2004;6(2):267-272. |
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Park K, Kittelson DB, McMurry PH. Structural properties of diesel exhaust particles measured by transmission electron microscopy (TEM): Relationships to particle mass and mobility. Aerosol Science and Technology 2004;38(9):881-889. |
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Sakurai H, Park K, McMurry PH, Zarling DD, Kittelson DB, Ziemann PJ. Size-dependent mixing characteristics of volatile and nonvolatile components in diesel exhaust aerosols. Environmental Science & Technology 2003;37(24):5487-5495. |
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Sakurai H, Tobias HJ, Park K, Zarling D, Docherty KS, Kittelson DB, McMurry PH, Ziemann PJ. On-line measurements of diesel nanoparticle composition and volatility. Atmospheric Environment 2003;37(9-10):1199-1210. |
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Solomon P, Baumann K, Edgerton E, Tanner R, Eatough D, Modey W, Marin H, Savoie D, Natarajan S, Meyer MB, Norris G. Comparison of integrated samplers for mass and composition during the 1999 Atlanta Supersites project. Journal of Geophysical Research–Atmospheres 2003;108(D7):8423. |
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Solomon PA, Chameides W, Weber R, Middlebrook A, Kiang CS, Russell AG, Butler A, Turpin B, Mikel D, Scheffe R, Cowling E, Edgerton E, St. John J, Jansen J, McMurry P, Hering S, Bahadori T. Overview of the 1999 Atlanta Supersite project. Journal of Geophysical Research–Atmospheres 2003;108(D7):SOS 1-1--SOS 1-24. |
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Weber RJ, Orsini D, Daun YN, Klotz PJ, Brechtel F. A particle-into-liquid collector for rapid measurement of aerosol bulk chemical composition. Aerosol Science and Technology 2001;35(3):718-727. |
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Weber RJ, Bergin M, Kiang CS, Chameides W, Orsini D, St JJ, Chang M, Bergin M, Carrico C, Lee YN, Dasgupta P, Slanina J, Turpin B, Edgerton E, Hering S, Allen G, Solomon P. Short-term temporal variation in PM2.5 mass and chemical composition during the Atlanta Supersite Experiment, 1999. Journal of the Air & Waste Management Association 2003;53(1):84-91. |
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Weber R, Orsini D, Duan Y, Baumann K, Kiang CS, Chameides W, Lee YN, Brechtel F, Klotz P, Jongejan P, ten Brink H, Slanina J, Boring CB, Genfa Z, Dasgupta P, Hering S, Stolzenburg M, Dutcher DD, Edgerton E, Hartsell B, Solomon P, Tanner R. Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite. Journal of Geophysical Research–Atmospheres 2003;108(D7):SOS 9-1--SOS 9-13. |
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Wright DL, Kasibhatla PS, McGraw R, Schwartz SE. Description and evaluation of a six-moment aerosol microphysical module for use in atmospheric chemical transport models. Journal of Geophysical Research--Atmospheres 2001;106(D17):20275-20291. |
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Wright DL, Yu S, Kasibhatla PS, McGraw R, Schwartz SE, Saxena VK, Yue GK. Retrieval of aerosol properties from moments of the particle size distribution for kernels involving the step function: cloud droplet activation. Journal of Aerosol Science 2002;33(2):319-337. |
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Yu S, Zender CS, Saxena VK. Direct radiative forcing and atmospheric absorption by boundary layer aerosols in the southeastern US:model estimates on the basis of new observations. Atmospheric Environment 2001;35(23):3967-3977. |
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Yu S, Saxena VK, Zhao Z. A comparison of signals of regional aerosol induced forcing in eastern China and the southeastern United States. Geophysical Research Letters 2001;28(4):713-716. |
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Yu S, Kasibhatla PS, Wright DL, Schwartz SE, McGraw R, Deng A. Moment-based simulation of microphysical properties of sulfate aerosols in the eastern United States:Model description, evaluation, and regional analysis. Journal of Geophysical Research--Atmospheres 2003;108(D12):4353. |
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Zhang J, Chameides WL, Weber R, Cass G, Orsini D, Edgerton E, Jongejan P, Slanina J. An evaluation of the thermodynamic equilibrium assumption for fine particulate composition: nitrate and ammonium during the 1999 Atlanta Supersite Experiment. Journal of Geophysical Research–Atmospheres 2002;108(D7):SOS 2-1--SOS 2-11. |
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Supplemental Keywords:
air, ambient air, atmosphere, ozone, exposure, environmental chemistry, modeling, monitoring, measurement methods, southeast, EPA Region 4., RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Analytical Chemistry, tropospheric ozone, Atmospheric Sciences, environmental monitoring, ambient ozone data, ozone occurrence, precursor compounds, fine particles, VOCs, air pollution models, air quality data, chemical composition, chemical transport model, atmospheric chemical cycles, chemical kinetics, atmospheric monitoring, Center for Study of Secondary Air Pollutants, field measurements, secondary air pollutants, fine particulate formation, ambient aerosol particlesRelevant Websites:
Southern Center for Integrated Study of Secondary Air Pollutants (SCISSAP) Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.