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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-950
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
06 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ: application to continental US
Shupeng Zhu1, Jeremy R. Horne1, Julia Montoya-Aguilera2, Mallory L. Hinks2, Sergey A. Nizkorodov2, and Donald Dabdub1 1Computational Environmental Sciences Laboratory, Department of Mechanical & Aerospace Engineering, University of California, Irvine, Irvine, CA, 92697-3975, USA
2Department of Chemistry, University of California, Irvine, Irvine, CA, 92697-3975, USA
Abstract. Ammonium salts such as ammonium nitrate and ammonium sulfate constitute an important fraction of the total fine particulate matter (PM2.5) mass. While the conversion of inorganic gases into particulate phase sulfate, nitrate, and ammonium is now well understood, there is considerable uncertainty over interactions between gas-phase ammonia and secondary organic aerosols (SOA). Observations have confirmed that ammonia can react with carbonyl compounds in SOA, forming nitrogen-containing organic compounds (NOC). This chemistry can reduce gas-phase NH3 concentration and therefore affect the amount of ammonium nitrate and ammonium sulfate in particulate matter (PM). In order to investigate the importance of such reactions, a first-order loss rate for ammonia onto SOA was implemented into the Community Multiscale Air Quality (CMAQ) model based on the ammonia uptake coefficients reported in the literature. Simulations over the continental US were performed for the winter and summer of 2011 with a range of uptake coefficients (10−3–10−5). Simulation results indicate that a significant reduction in gas-phase ammonia is possible due to its uptake onto SOA; domain-averaged ammonia concentrations decrease by 31.3 % in the winter, and 67.0 % in the summer with the highest uptake coefficient (10−3). As a result, the concentration of particulate matter is also significantly affected, with a distinct spatial pattern over different seasons. PM concentrations decreased during the winter, largely due to the reduction in ammonium nitrate concentrations. On the other hand, PM concentrations increased during the summer due to increased production of biogenic SOA production resulting from enhanced acid-catalyzed uptake of isoprene-derived epoxides. While ammonia emissions expected to increase in the future, it is important to include NH3 + SOA chemistry in air quality models.

Citation: Zhu, S., Horne, J. R., Montoya-Aguilera, J., Hinks, M. L., Nizkorodov, S. A., and Dabdub, D.: Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ: application to continental US, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-950, in review, 2017.
Shupeng Zhu et al.
Shupeng Zhu et al.
Shupeng Zhu et al.

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Short summary
For the first time, the interaction between ammonia and secondary organic aerosol (SOA) is integrated in an air quality model and investigated at a national scale. Our original analysis from simulation results indicate a significant reduction in gas-phase ammonia is possible due to its uptake onto SOA. Significant impact is also observed in the concentration of particulate matter, with a distinct spatial pattern over different seasons.
For the first time, the interaction between ammonia and secondary organic aerosol (SOA) is...
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