Organic nitrate aerosol formation via NO₃ + biogenic volatile organic compounds in the southeastern United States

• Main Authors: B. R. Ayres, H. M. Allen, D. C. Draper, S. S. Brown, R. J. Wild, J. L. Jimenez, D. A. Day, P. Campuzano-Jost, W. Hu, J. de Gouw, A. Koss, R. C. Cohen, K. C. Duffey, P. Romer, K. Baumann, E. Edgerton, S. Takahama, J. A. Thornton, B. H. Lee, F. D. Lopez-Hilfiker, C. Mohr, P. O. Wennberg, T. B. Nguyen, A. Teng, A. H. Goldstein, K. Olson, J. L. Fry
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-12-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/15/13377/2015/acp-15-13377-2015.pdf
• ISSN: 1680-7316; 1680-7324

Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that a nitrate radical (NO₃) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NO₃ to terpenes are correlated with increase in gas- and aerosol-organic nitrate concentrations made during the campaign. Correlation of NO₃ radical consumption to organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield of aerosol-phase monoterpene nitrates of 23–44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to BVOCs and show C₁₀H₁₇NO₅, likely a hydroperoxy nitrate, is a major nitrate-oxidized terpene product being incorporated into aerosols. The comparable isoprene product C₅H₉NO₅ was observed to contribute less than 1 % of the total organic nitrate in the aerosol phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45 % of the NO_<I>y</I> budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNO₃ uptake produced nitrate aerosol mass loading at a rate comparable to that of organic nitrate produced via NO₃ + BVOCs.