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Final Report: Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Carnegie Mellon Report
EPA Grant Number: R826371C005Subproject: this is subproject number 005 , established and managed by the Center Director under grant R826371
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States
Center Director: Seinfeld, John
Title: Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Carnegie Mellon Report
Investigators: Pandis, Spyros N.
Institution:
EPA Project Officer: Shapiro, Paul
Project Period: April 15, 1998 through April 14, 2003
RFA: Special Opportunity in Tropospheric Ozone (1997)
Research Category: Air Quality and Air Toxics
Description:
Objective:The objective of this research project was directed toward improving the microphysical treatment of aerosols in atmospheric models.
Summary/Accomplishments (Outputs/Outcomes):Inorganic Aerosol Modeling. Four inorganic aerosol thermodynamics models were evaluated for use in atmospheric particulate matter (PM) models. Three of them (ISORROPIA, SCAPE2, and SEQUILIB) are computationally efficient, while the fourth (GFEMN) is used as a benchmark. The predictions of the models were intercompared for the full composition/temperature/relative humidity space and also against measurements from Southern California. ISORROPIA was determined to combine accuracy with computational speed and is the recommended model of choice for use in large-scale air quality models (Ansari and Pandis, 1999).
At RH below 70 percent atmospheric aerosols may exist as either solid particles or as highly concentrated aqueous solutions. For a range of atmospheric conditions, both states are thermodynamically possible. The importance of the existence of metastable equilibrium states on the partitioning of nitrate between the gas and aerosol phases was investigated (Ansari and Pandis, 2000a). The potential existence of metastable aerosols in Southern California, where pollutant levels are high, appears to have a small effect on total nitrate partitioning. However, for areas characterized by moderate-to-low pollutant levels, such as the Northeastern United States, a significant effect is predicted.
A novel approach to the modeling of the mass transfer of semivolatile species was developed (Capaldo, et al., 2000). The hybrid method utilizes equilibrium assumptions for the fine aerosol mode (particles with diameter less than 1 µm), and the dynamic approach for the coarse aerosol mode. The hybrid method maintains most of the predictive ability of the dynamic approach and is 50 times more computationally efficient.
The partitioning of nitrate and ammonium between the gas and particulate phases was studied combining the models developed in this project and measurements taken in Mexico City during the 1997 IMADA-AVER field campaign (Moya, et al., 2001). Atmospheric equilibrium models predict daily average PM2.5 nitrate concentrations within 20 percent of the IMADA-AVER measurements. Six-hour average PM2.5 nitrate concentrations are predicted within 30-50 percent on average, except for the afternoon sampling periods (12:00-18:00). Investigating the possible sources of these discrepancies, it appears that a dynamic rather than an equilibrium approach is more suitable in reproducing aerosol behavior during these afternoon periods in Mexico City.
A size-resolved equilibrium model, SELIQUID, was developed and used to simulate the size-composition distribution of semivolatile inorganic aerosol in an urban environment (Moya, et al., 2002). Predictions of SELIQUID were compared against size-resolved composition measurements at different locations during the Southern California Air Quality Study. Based on the modeling results, the size distribution of submicrometer nitrate and ammonium can be determined by thermodynamic equilibrium only when the RH exceeds 60 percent. On the other hand, the equilibrium assumption, in some cases at least, introduces errors in the calculation of the coarse nitrate and ammonium that increase with particle size.
The Trajectory-Grid approach of Chock and Winkler was modified and implemented in the Hybrid and Dynamic module (Gaydos, et al., 2003). The modules were incorporated into PMCAMx (a 3D chemical transport module) and evaluated against measurements collected in Southern California during 1987 and 1995. The improved modules were approximately 10 times more computationally efficient than their older versions. The model predictions agreed with measured concentrations of the major aerosol components within 30 percent.
Organic-Inorganic Aerosol Modeling. An integrated modeling approach was developed combining available secondary organic aerosols (SOA) and inorganic aerosol models to predict overall aerosol behavior (Ansari and Pandis, 2000b). The effect of SOA on water absorption and nitrate partitioning between the gas and aerosol phases was determined. On average, it appears that SOA accounts for approximately 7 percent of total aerosol water and increases aerosol nitrate concentrations by approximately 10 percent. At high relative humidity (>85 percent) and low SOA mass fractions (<20 percent of total PM2.5), the role of SOA in nitrate partitioning and its contribution to total aerosol water is negligible. At low relative humidity (~50 percent) and high SOA mass fraction concentrations (~30 percent of total PM2.5), SOA is predicted to account for approximately 20 percent of total aerosol water and a 50 percent increase in aerosol nitrate concentrations.
A series of modeling approaches for the description of the dynamic behavior of SOA and its interactions with the inorganic components was investigated (Koo, et al., 2003). The models employ a lumped species approach based on available smog chamber studies and the UNIFAC group contribution method. The SOA size distribution predicted by the traditional bulk equilibrium approach is biased towards smaller sizes compared with that of a fully dynamic model. An improved weighting scheme for the bulk equilibrium approach is proposed in this work and is shown to minimize this discrepancy.
Aqueous Phase Chemistry Modeling. Given that bulk aqueous-phase chemistry models are less computationally intensive than corresponding size-resolved models, a model equipped to combine the accuracy of the size-resolved code with the efficiency of the bulk method has been developed. Bulk and two-section size-resolved approaches are combined into a single variable size-resolution model (VSRM) to combine both accuracy and computational speed (Fahey and Pandis, 2001). Depending on initial system conditions, bulk or size-resolved calculations are executed based on a set of semi-empirical rules. For the conditions examined, on average, the VSRM sulfate predictions are within 3 percent of a six-section size-resolved model, but the VSRM is 15 times faster.
Journal Articles on this Report: 10 Displayed | Download in RIS Format
| Other subproject views: | All 10 publications | 10 publications in selected types | All 10 journal articles |
| Other center views: | All 47 publications | 45 publications in selected types | All 45 journal articles |
| Type | Citation | ||
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Ansari AS, Pandis SN. An analysis of four models predicting the partitioning of semi volatile inorganic aerosol components. Aerosol Science and Technology 1999;31(2-3):129-153. |
R826371 (Final) R826371C005 (Final) R824793 (Final) |
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Ansari AS, Pandis SN. The effect of metastable equilibrium states on the partitioning of nitrate between the gas and aerosol phases. Atmospheric Environment 2000;34(1):157-168. |
R826371C005 (Final) R824793 (Final) |
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Ansari AS, Pandis SN. Water Absorption by Secondary Organic Aerosol and its Effect on Inorganic Aerosol Behavior. Environmental Science & Technology 2000;34(1):71-77. |
R826371 (Final) R826371C005 (Final) |
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Capaldo KP, Pilinis C, Pandis SN. A Computationally Efficient Hybrid Approach for Dynamic Gas/Aerosol Transfer in Air Quality Models. Atmospheric Environment. 2000;34(21):3617-3627. |
R826371 (Final) R826371C005 (Final) |
not available |
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Fahey KM, Pandis SN. Optimizing model performance: variable size resolution in cloud chemistry modeling. Atmospheric Environment 2001;35(26):4471-4478. |
R826371 (Final) R826371C005 (Final) |
not available |
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Gaydos TM, Koo B, Pandis SN, Chock DP. Development and application of an efficient moving sectional approach for the solution of the atmospheric aerosol condensation/evaporation equations. Atmospheric Environment. 2003;37(23):3303-3316. |
R826371 (Final) R826371C005 (Final) |
not available |
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Koo B, Gaydos TM, Pandis SN. Evaluation of the equilibrium, dynamic, and hybrid aerosol modeling approaches. Aerosol Science And Technology. 2003;37:53-64. |
R826371 (Final) R826371C005 (Final) R831709C003 (2004) |
not available |
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Koo B, Ansari AS, Pandis SN. Integrated approaches to modeling the organic and inorganic atmospheric aerosol components. Atmospheric Environment. 2003;37(34):4757-4768. |
R826371 (Final) R826371C005 (Final) |
not available |
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Moya M, Pandis SN, Jacobson MZ. Is the size distribution of urban aerosols determined by thermodynamic equilibrium? An approach to Southern California. Atmospheric Environment 2002;36(14):2349-2365. |
R826371 (Final) R826371C005 (Final) |
not available |
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Moya M, Ansari AS, Pandis SN. Partitioning of nitrate and ammonium between the gas and aerosol phases during the1997 IMADA-AVER study in Mexico City. Atmospheric Environment. 2000;35(10):1791-1804. |
R826371 (Final) R826371C005 (Final) |
not available |
aerosols, atmospheric models, inorganic aerosol modeling, Southern California, CA, secondary organic aerosols. , Ecosystem Protection/Environmental Exposure & Risk, Air, Scientific Discipline, RFA, Analytical Chemistry, Atmospheric Sciences, particulate matter, Environmental Chemistry, Monitoring/Modeling, tropospheric ozone, secondary aerosol formation, aerosol analyzers, secondary organic aerosols, air quality, chemical composition, fine particles, ozone, air sampling, atmospheric dispersion models, ambient aerosol particles, aersol particles, microphysical treatment, fine particle formation, fine particulates, aerosol formation, atmospheric chemistry, three dimensional model, air pollution models, atmospheric particulate matter, aqueous phase modeling, California, atmospheric aerosol particles, airborne particulate matter
Progress and Final Reports:
Original Abstract
Main Center Abstract and Reports:
R826371 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R826371C001 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Cal Tech, UC-Riverside, UC-San Diego, UC-Davis Report
R826371C002 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Cal Tech, Carnegie Mellon, Georgia Institute, NJIT, Oregon Institute, UC-Irvine, UC-Riverside Report
R826371C003 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Cal Tech Report
R826371C004 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: California - Irvine Report
R826371C005 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Carnegie Mellon Report
R826371C006 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Carnegie Mellon Report
R826371C007 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: UC-Riverside
R826371C008 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: Oregon Health and Science Report
R826371C009 Research Consortium on Ozone and Fine Particle Formation in California and in the Northeastern United States: NJIT Report