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Community Multiscale Air Quality Modeling System (CMAQ)

CMAQ Application to the Southern Oxidant and Aerosol Study (SOAS)

SOAS Field Site in AlabamaThe SOAS ground site in Alabama for measuring atmospheric species.

The Southeast Atmosphere Study (SAS) , which included the Southern Oxidant and Aerosol Study (SOAS) , took place during the summer of 2013 in Alabama as well as other locations around the southeast U.S. to understand how physical and chemical processes result in air pollution and climate effects. The SAS collaborative effort involved more than 100 investigators, the National Science Foundation (NSF), the National Oceanographic and Atmospheric Administration (NOAA), the Electric Power Research Institute (EPRI), and EPA. The EPA funded 13 investigators under the STAR Grants Program to study Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications. In addition, EPA staff scientists participated in data collection and analysis of SOAS observations.

side by side maps showing hygrocopicity and aerosol liquid waterThe hygroscopicity parameter (κ) of organic aerosol (left) and aerosol liquid water (in micrograms/m3)  due to organic compounds (right) estimated with CMAQ (Pye et al., 2017). The SOAS ground site is at the center of the circle over Alabama.

Data collected as part of this study included a suite of particle and gas-phase properties that have been used to perform diagnostic model evaluation and inform model improvements. In particular, observations of particle-phase organic nitrates (Pye et al., 2015), organic aerosol, and aerosol liquid water (Pye et al., 2017) were used to constrain the formation and partitioning of particle species in the CMAQ model.

Reactions of nitrate compounds in the particle were found to be an important factor governing the amount of particulate matter mass formed and represent a removal of oxides of nitrogen (NOx) from the gas phase. In addition, the solubility of many model species were examined for the first time in the context of ambient water concentrations. The SAS data set is publically available and remains a valuable source of data for understanding the atmosphere of the southeastern U.S. where some areas still exceed the ozone National Ambient Air Quality Standards (NAAQS).

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Pye, H.O.T., Luecken, D.J., Xu, L., Boyd, C.M., Ng, N.L., Baker, K., Ayres, B.A., Bash, J.O., Baumann, K., Carter, W.P.L., Edgerton, E., Fry, J.L., Hutzell, W.T., Schwede, D., Shepson, P.B. (2015). Modeling the current and future roles of particulate organic nitrates in the southeastern United States. Environ. Sci. Technol., 49(25), 14195–14203. doi: 10.1021/acs.est.5b03738.

Pye, H. O. T., Murphy, B. N., Xu, L., Ng, N. L., Carlton, A. G., Guo, H., Weber, R., Vasilakos, P., Appel, K. W., Budisulistiorini, S. H., Surratt, J. D., Nenes, A., Hu, W., Jimenez, J. L., Isaacman-VanWertz, G., Misztal, P. K., and Goldstein, A. H. (2017). On the implications of aerosol liquid water and phase separation for organic aerosol mass, Atmos. Chem. Phys., 17, 343-369, doi: 10.5194/acp-17-343-2017.