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Coupling of organic and inorganic aerosol systems and the effect on gas-particle partitioning in the southeastern US

Pye, Havala O. T. and Zuend, Andreas and Fry, Juliane L. and Isaacman-VanWertz, Gabriel and Capps, Shannon L. and Appel, K. Wyat and Foroutan, Hosein and Xu, Lu and Ng, Nga L. and Goldstein, Allen H. (2018) Coupling of organic and inorganic aerosol systems and the effect on gas-particle partitioning in the southeastern US. Atmospheric Chemistry and Physics, 18 (1). pp. 357-370. ISSN 1680-7324. doi:10.5194/acp-18-357-2018.

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Several models were used to describe the partitioning of ammonia, water, and organic compounds between the gas and particle phases for conditions in the southeastern US during summer 2013. Existing equilibrium models and frameworks were found to be sufficient, although additional improvements in terms of estimating pure-species vapor pressures are needed. Thermodynamic model predictions were consistent, to first order, with a molar ratio of ammonium to sulfate of approximately 1.6 to 1.8 (ratio of ammonium to 2  ×  sulfate, R_(N∕2S)  ≈  0.8 to 0.9) with approximately 70 % of total ammonia and ammonium (NH_x) in the particle. Southeastern Aerosol Research and Characterization Network (SEARCH) gas and aerosol and Southern Oxidant and Aerosol Study (SOAS) Monitor for AeRosols and Gases in Ambient air (MARGA) aerosol measurements were consistent with these conditions. CMAQv5.2 regional chemical transport model predictions did not reflect these conditions due to a factor of 3 overestimate of the nonvolatile cations. In addition, gas-phase ammonia was overestimated in the CMAQ model leading to an even lower fraction of total ammonia in the particle. Chemical Speciation Network (CSN) and aerosol mass spectrometer (AMS) measurements indicated less ammonium per sulfate than SEARCH and MARGA measurements and were inconsistent with thermodynamic model predictions. Organic compounds were predicted to be present to some extent in the same phase as inorganic constituents, modifying their activity and resulting in a decrease in [H^+]_(air) (H^+ in µg m^(−3) air), increase in ammonia partitioning to the gas phase, and increase in pH compared to complete organic vs. inorganic liquid–liquid phase separation. In addition, accounting for nonideal mixing modified the pH such that a fully interactive inorganic–organic system had a pH roughly 0.7 units higher than predicted using traditional methods (pH  =  1.5 vs. 0.7). Particle-phase interactions of organic and inorganic compounds were found to increase partitioning towards the particle phase (vs. gas phase) for highly oxygenated (O : C  ≥  0.6) compounds including several isoprene-derived tracers as well as levoglucosan but decrease particle-phase partitioning for low O : C, monoterpene-derived species.

Item Type:Article
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URLURL TypeDescription
Pye, Havala O. T.0000-0002-2014-2140
Zuend, Andreas0000-0003-3101-8521
Xu, Lu0000-0002-0021-9876
Ng, Nga L.0000-0001-8460-4765
Goldstein, Allen H.0000-0003-4014-4896
Additional Information:© Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Received: 04 Jul 2017. Discussion started: 18 Jul 2017. Revised: 11 Oct 2017. Accepted: 28 Nov 2017. Published: 12 Jan 2018. The authors declare that they have no conflict of interest. Disclaimer: The US EPA through its Office of Research and Development supported the research described here. It has been subjected to agency administrative review and approved for publication but may not necessarily reflect official agency policy. We thank J. Jimenez, G. Ruggeri, S. Takahama, and S. Lee for providing additional data sets that are summarized in the supporting information. We thank the CSN and SEARCH networks for providing long-term measurements. We thank the two reviewers at the EPA. We thank Paul Solomon for useful discussion. We thank CSRA for preparing emissions and meteorology input for CMAQ simulations. Andreas Zuend was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), grant RGPIN/04315-2014. Juliane L. Fry acknowledges support from EPA-STAR RD-83539901. Gabriel Isaacman-VanWertz was supported by the NSF Graduate Research Fellowship (DGE 1106400). Fp of organic compounds collected by SV-TAG at SOAS was supported by grants to UC Berkeley, including NSF Atmospheric Chemistry Program 1250569 and Department of Energy SBIR grant DE-SC0004698. Lu Xu and Nga L. Ng acknowledge support from National Science Foundation (NSF) grant 1242258 and US Environmental Protection Agency (EPA) STAR grant RD-83540301. Edited by: Yafang Cheng Reviewed by: two anonymous referees
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)RGPIN/04315-2014
Environmental Protection Agency (EPA)RD-83539901
NSF Graduate Research FellowshipDGE-1106400
Department of Energy (DOE)DE-SC0004698
Environmental Protection Agency (EPA)RD-83540301
Issue or Number:1
Record Number:CaltechAUTHORS:20180202-135249540
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Official Citation:Pye, H. O. T., Zuend, A., Fry, J. L., Isaacman-VanWertz, G., Capps, S. L., Appel, K. W., Foroutan, H., Xu, L., Ng, N. L., and Goldstein, A. H.: Coupling of organic and inorganic aerosol systems and the effect on gas–particle partitioning in the southeastern US, Atmos. Chem. Phys., 18, 357-370,, 2018
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84657
Deposited By: Ruth Sustaita
Deposited On:02 Feb 2018 23:04
Last Modified:15 Nov 2021 20:21

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