Articles | Volume 17, issue 8
Atmos. Chem. Phys., 17, 5107–5118, 2017
https://doi.org/10.5194/acp-17-5107-2017
Atmos. Chem. Phys., 17, 5107–5118, 2017
https://doi.org/10.5194/acp-17-5107-2017

Research article 19 Apr 2017

Research article | 19 Apr 2017

Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol

Rachel F. Silvern et al.

Data sets

SEARCH PM2.5 Atmospheric Research and Analysis http://www.atmospheric-research.com/studies/SEARCH/index.html

Daily PM2.5 Speciation Summary EPA AQS http://aqsdr1.epa.gov/aqsweb/aqstmp/airdata/download_files.html

National Atmospheric Deposition Program (NRSP-3) NADP http://nadp.sws.uiuc.edu/data/ntn/

Southern Oxidant and Aerosol Study Earth System Research Laboratory https://esrl.noaa.gov/csd/groups/csd7/measurements/2013senex/Ground/DataDownload/index.php?page=/csd/groups/csd7/measurements/2013senex/Ground/DataDownload/

NASA LaRC Airborne Science Data for Atmospheric Composition NASA https://eosweb.larc.nasa.gov/project/seac4rs/seac4rs_table

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Short summary
We identify a fundamental discrepancy between thermodynamic equilibrium theory and observations of inorganic aerosol composition in the eastern US in summer that shows low ammonium sulfate aerosol ratios. In addition, from 2003 to 2013, while SO2 emissions have declined due to US emission controls, aerosols have become more acidic in the southeastern US. To explain these observations, we suggest that the large and increasing source of organic aerosol may be affecting thermodynamic equilibrium.
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