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Title: Modeling Organic Aerosols in a Megacity: Comparison of Simple and Complex Representations of the Volatility Basis Set Approach

Abstract

The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to include a volatility basis set (VBS) treatment of secondary organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase chemistry mechanism, is used to model gas-particle partitioning and multiple generations of gas-phase oxidation of organic vapors. In addition to the detailed 9-species VBS, a simplified mechanism using 2 volatility species (2-species VBS) is developed and tested for similarity to the 9-species VBS in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the atmosphere. WRF-Chem results are evaluated against field measurements of organic aerosols collected during the MILAGRO 2006 campaign in the vicinity of Mexico City. The simplified 2-species mechanism reduces the computational cost by a factor of 2 as compared to 9-species VBS. Both ground site and aircraft measurements suggest that the 9-species and 2-species VBS predictions of total organic aerosol mass as well as individual organic aerosol components including primary, secondary, and biomass burning are comparable in magnitude. In addition, oxygen-to-carbon ratio predictions from both approaches agree within 25%, providing evidence that the 2-species VBS is well suited to represent the complex evolution of organic aerosols. Model sensitivity to amount of anthropogenic semi-volatilemore » and intermediate volatility (S/IVOC) precursor emissions is also examined by doubling the default emissions. Both the emission cases significantly under-predict primary organic aerosols in the city center and along aircraft flight transects. Secondary organic aerosols are predicted reasonably well along flight tracks surrounding the city, but are consistently over-predicted downwind of the city. Also, oxygen-to-carbon ratio predictions are significantly improved compared to prior studies by adding 15% oxygen mass per generation of oxidation; however, all modeling cases still under-predict these ratios downwind as compared to measurements, suggesting a need to further improve chemistry parameterizations of secondary organic aerosol formation.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1027177
Report Number(s):
PNNL-SA-75763
Journal ID: ISSN 1680-7316; KP1701000; TRN: US201121%%344
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Atmospheric Chemistry and Physics
Additional Journal Information:
Journal Volume: 11; Journal Issue: 13; Journal ID: ISSN 1680-7316
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; AEROSOLS; AIRCRAFT; BIOMASS; CHEMISTRY; FORECASTING; MEXICO; OXIDATION; OXYGEN; PRECURSOR; SENSITIVITY; SIMULATION; VOLATILITY; WEATHER

Citation Formats

Shrivastava, ManishKumar B, Fast, Jerome D, Easter, Richard C, Gustafson, William I, Zaveri, Rahul A, Jimenez, Jose L, Saide, Pablo, and Hodzic, Alma. Modeling Organic Aerosols in a Megacity: Comparison of Simple and Complex Representations of the Volatility Basis Set Approach. United States: N. p., 2011. Web. doi:10.5194/acp-11-6639-2011.
Shrivastava, ManishKumar B, Fast, Jerome D, Easter, Richard C, Gustafson, William I, Zaveri, Rahul A, Jimenez, Jose L, Saide, Pablo, & Hodzic, Alma. Modeling Organic Aerosols in a Megacity: Comparison of Simple and Complex Representations of the Volatility Basis Set Approach. United States. https://doi.org/10.5194/acp-11-6639-2011
Shrivastava, ManishKumar B, Fast, Jerome D, Easter, Richard C, Gustafson, William I, Zaveri, Rahul A, Jimenez, Jose L, Saide, Pablo, and Hodzic, Alma. 2011. "Modeling Organic Aerosols in a Megacity: Comparison of Simple and Complex Representations of the Volatility Basis Set Approach". United States. https://doi.org/10.5194/acp-11-6639-2011.
@article{osti_1027177,
title = {Modeling Organic Aerosols in a Megacity: Comparison of Simple and Complex Representations of the Volatility Basis Set Approach},
author = {Shrivastava, ManishKumar B and Fast, Jerome D and Easter, Richard C and Gustafson, William I and Zaveri, Rahul A and Jimenez, Jose L and Saide, Pablo and Hodzic, Alma},
abstractNote = {The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to include a volatility basis set (VBS) treatment of secondary organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase chemistry mechanism, is used to model gas-particle partitioning and multiple generations of gas-phase oxidation of organic vapors. In addition to the detailed 9-species VBS, a simplified mechanism using 2 volatility species (2-species VBS) is developed and tested for similarity to the 9-species VBS in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the atmosphere. WRF-Chem results are evaluated against field measurements of organic aerosols collected during the MILAGRO 2006 campaign in the vicinity of Mexico City. The simplified 2-species mechanism reduces the computational cost by a factor of 2 as compared to 9-species VBS. Both ground site and aircraft measurements suggest that the 9-species and 2-species VBS predictions of total organic aerosol mass as well as individual organic aerosol components including primary, secondary, and biomass burning are comparable in magnitude. In addition, oxygen-to-carbon ratio predictions from both approaches agree within 25%, providing evidence that the 2-species VBS is well suited to represent the complex evolution of organic aerosols. Model sensitivity to amount of anthropogenic semi-volatile and intermediate volatility (S/IVOC) precursor emissions is also examined by doubling the default emissions. Both the emission cases significantly under-predict primary organic aerosols in the city center and along aircraft flight transects. Secondary organic aerosols are predicted reasonably well along flight tracks surrounding the city, but are consistently over-predicted downwind of the city. Also, oxygen-to-carbon ratio predictions are significantly improved compared to prior studies by adding 15% oxygen mass per generation of oxidation; however, all modeling cases still under-predict these ratios downwind as compared to measurements, suggesting a need to further improve chemistry parameterizations of secondary organic aerosol formation.},
doi = {10.5194/acp-11-6639-2011},
url = {https://www.osti.gov/biblio/1027177}, journal = {Atmospheric Chemistry and Physics},
issn = {1680-7316},
number = 13,
volume = 11,
place = {United States},
year = {Wed Jul 13 00:00:00 EDT 2011},
month = {Wed Jul 13 00:00:00 EDT 2011}
}