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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 7497-7522, 2015
https://doi.org/10.5194/acp-15-7497-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
10 Jul 2015
Secondary organic aerosol formation from the β-pinene+NO3 system: effect of humidity and peroxy radical fate
C. M. Boyd1, J. Sanchez1, L. Xu1, A. J. Eugene2, T. Nah1, W. Y. Tuet1, M. I. Guzman2, and N. L. Ng1,3 1School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
2Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA
3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract. The formation of secondary organic aerosol (SOA) from the oxidation of β-pinene via nitrate radicals is investigated in the Georgia Tech Environmental Chamber (GTEC) facility. Aerosol yields are determined for experiments performed under both dry (relative humidity (RH) < 2 %) and humid (RH = 50 % and RH = 70 %) conditions. To probe the effects of peroxy radical (RO2) fate on aerosol formation, "RO2 + NO3 dominant" and "RO2 + HO2 dominant" experiments are performed. Gas-phase organic nitrate species (with molecular weights of 215, 229, 231, and 245 amu, which likely correspond to molecular formulas of C10H17NO4, C10H15NO5, C10H17NO5, and C10H15NO6, respectively) are detected by chemical ionization mass spectrometry (CIMS) and their formation mechanisms are proposed. The NO+ (at m/z 30) and NO2+ (at m/z 46) ions contribute about 11 % to the combined organics and nitrate signals in the typical aerosol mass spectrum, with the NO+ : NO2+ ratio ranging from 4.8 to 10.2 in all experiments conducted. The SOA yields in the "RO2 + NO3 dominant" and "RO2 + HO2 dominant" experiments are comparable. For a wide range of organic mass loadings (5.1–216.1 μg m−3), the aerosol mass yield is calculated to be 27.0–104.1 %. Although humidity does not appear to affect SOA yields, there is evidence of particle-phase hydrolysis of organic nitrates, which are estimated to compose 45–74 % of the organic aerosol. The extent of organic nitrate hydrolysis is significantly lower than that observed in previous studies on photooxidation of volatile organic compounds in the presence of NOx. It is estimated that about 90 and 10 % of the organic nitrates formed from the β-pinene+NO3 reaction are primary organic nitrates and tertiary organic nitrates, respectively. While the primary organic nitrates do not appear to hydrolyze, the tertiary organic nitrates undergo hydrolysis with a lifetime of 3–4.5 h. Results from this laboratory chamber study provide the fundamental data to evaluate the contributions of monoterpene + NO3 reaction to ambient organic aerosol measured in the southeastern United States, including the Southern Oxidant and Aerosol Study (SOAS) and the Southeastern Center for Air Pollution and Epidemiology (SCAPE) study.

Citation: Boyd, C. M., Sanchez, J., Xu, L., Eugene, A. J., Nah, T., Tuet, W. Y., Guzman, M. I., and Ng, N. L.: Secondary organic aerosol formation from the β-pinene+NO3 system: effect of humidity and peroxy radical fate, Atmos. Chem. Phys., 15, 7497-7522, https://doi.org/10.5194/acp-15-7497-2015, 2015.
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Short summary
Laboratory chamber studies were conducted to investigate the formation of secondary organic aerosol from β-pinene oxidation by nitrate radicals. These experiments probed the effects of peroxy radical fate and relative humidity on the mass and chemical composition of secondary organic aerosol formed from nighttime chemistry. Results from this study were used to evaluate the contributions of NO3+monoterpene reaction to ambient organic aerosol recently measured in the southeastern United States.
Laboratory chamber studies were conducted to investigate the formation of secondary organic...
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