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Title: Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol

Abstract

Abstract. Secondary organic aerosol (SOA) is a complex mixture of hundreds of semi-volatile to extremely low-volatility organic compounds that are chemically processed in the atmosphere, including via heterogeneous oxidation by gas-phase radicals. Relative humidity (RH) has a substantial impact on particle phase, which can affect how SOA evolves in the atmosphere. In this study, SOA from dark α-pinene ozonolysis is heterogeneously aged by OH radicals in a flow tube at low and high RH. At high RH (RH = 89%) there is substantial loss of particle volume (~60%) at an equivalent atmospheric OH exposure of 3 weeks. In contrast, at low RH (RH = 25%) there is little mass loss (< 20%) at the same OH exposure. Mass spectra of the SOA particles were measured as a function of OH exposure using a vacuum ultraviolet aerosol mass spectrometer (VUV-AMS). The mass spectra observed at low RH overall exhibit minor changes with oxidation and negligible further changes above an OH exposure = 2×10 12moleculecm -3s suggesting limited impact of oxidation on the particle composition. In contrast, the mass spectra observed at high RH exhibit substantial and continuous changes as a function of OH exposure. Further, at high RH clusters of peaks inmore » the mass spectra exhibit unique decay patterns, suggesting different responses of various species to oxidation. A model of heterogeneous oxidation has been developed to understand the origin of the difference in aging between the low- and high-RH experiments. Differences in diffusivity of the SOA between the low- and high-RH experiments alone can explain the difference in compositional change but cannot explain the difference in mass loss. Instead, the difference in mass loss is attributable to RH-dependent differences in the OH uptake coefficient and/or the net probability of fragmentation, with either or both larger at high RH compared to low RH. These results illustrate the important impact of relative humidity on the fate of SOA in the atmosphere.« less

Authors:
ORCiD logo; ; ORCiD logo
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1477131
Grant/Contract Number:  
AC02- 05CH1123
Resource Type:
Journal Article: Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online) Journal Volume: 18 Journal Issue: 19; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Country of Publication:
Germany
Language:
English

Citation Formats

Li, Ziyue, Smith, Katherine A., and Cappa, Christopher D. Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol. Germany: N. p., 2018. Web. doi:10.5194/acp-18-14585-2018.
Li, Ziyue, Smith, Katherine A., & Cappa, Christopher D. Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol. Germany. doi:10.5194/acp-18-14585-2018.
Li, Ziyue, Smith, Katherine A., and Cappa, Christopher D. Thu . "Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol". Germany. doi:10.5194/acp-18-14585-2018.
@article{osti_1477131,
title = {Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol},
author = {Li, Ziyue and Smith, Katherine A. and Cappa, Christopher D.},
abstractNote = {Abstract. Secondary organic aerosol (SOA) is a complex mixture of hundreds of semi-volatile to extremely low-volatility organic compounds that are chemically processed in the atmosphere, including via heterogeneous oxidation by gas-phase radicals. Relative humidity (RH) has a substantial impact on particle phase, which can affect how SOA evolves in the atmosphere. In this study, SOA from dark α-pinene ozonolysis is heterogeneously aged by OH radicals in a flow tube at low and high RH. At high RH (RH = 89%) there is substantial loss of particle volume (~60%) at an equivalent atmospheric OH exposure of 3 weeks. In contrast, at low RH (RH = 25%) there is little mass loss (< 20%) at the same OH exposure. Mass spectra of the SOA particles were measured as a function of OH exposure using a vacuum ultraviolet aerosol mass spectrometer (VUV-AMS). The mass spectra observed at low RH overall exhibit minor changes with oxidation and negligible further changes above an OH exposure = 2×1012moleculecm-3s suggesting limited impact of oxidation on the particle composition. In contrast, the mass spectra observed at high RH exhibit substantial and continuous changes as a function of OH exposure. Further, at high RH clusters of peaks in the mass spectra exhibit unique decay patterns, suggesting different responses of various species to oxidation. A model of heterogeneous oxidation has been developed to understand the origin of the difference in aging between the low- and high-RH experiments. Differences in diffusivity of the SOA between the low- and high-RH experiments alone can explain the difference in compositional change but cannot explain the difference in mass loss. Instead, the difference in mass loss is attributable to RH-dependent differences in the OH uptake coefficient and/or the net probability of fragmentation, with either or both larger at high RH compared to low RH. These results illustrate the important impact of relative humidity on the fate of SOA in the atmosphere.},
doi = {10.5194/acp-18-14585-2018},
journal = {Atmospheric Chemistry and Physics (Online)},
issn = {1680-7324},
number = 19,
volume = 18,
place = {Germany},
year = {2018},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.5194/acp-18-14585-2018

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