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Changes in Mass Yield, Volatility Distribution, and Chemical Composition of Secondary Organic Aerosol Formed From Simultaneous and Sequential Oxidation of α-Pinene and Limonene by Nitrate Radicals
MASAYUKI TAKEUCHI, Thomas Berkemeier, Gamze Eris, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 247
Working Group: Aerosol Chemistry
Abstract
Traditional approaches to study secondary organic aerosol (SOA) in laboratory studies often focus on the oxidation of one single volatile organic compound (VOC) at a time, whereas chemical transport models also treat SOA formation explicitly from each precursor VOC assuming linear additivity. However, it has been shown recently that SOA formation in multi-VOC systems cannot be explained by linear combination of each species involved. Specifically, McFiggans et al. (2019) observed a reduced SOA mass yield of α-pinene+OH in the presence of isoprene. In this study, we focused on the following research questions:
(1) What multi-VOC effects can be observed for nitrate radical oxidation?
(2) Do multi-VOC effects differ between simultaneous and sequential VOC oxidation of two precursors?
Here, we performed four chamber experiments: nitrate radical oxidation of α-pinene, limonene, α-pinene and limonene simultaneously, and limonene followed by α-pinene oxidation. Oxidation products were measured by a filter inlet for gases and aerosols coupled to a chemical ionization mass spectrometer (FIGAERO-CIMS), an aerosol mass spectrometer, and a scanning mobility particle sizer. We found that SOA mass yield from limonene oxidation reduced almost by half when oxidized simultaneously, but not during sequential oxidation. On the other hand, SOA mass yield of α-pinene showed little difference regardless of the presence of limonene. The reduced SOA mass yield in the simultaneous oxidation experiment is attributed to the inhibited formation of low-volatility limonene oxidation products, evident by the lack of signal at a high desorption temperature in the FIGAERO-CIMS thermogram. This likely arises from altered gas-phase chemistry between α-pinene and limonene oxidation products. Without considering this multi-VOC effect, the modelled SOA mass concentration via nitrate radical oxidation of biogenic VOCs in the southeastern U.S. could be overestimated by ~40%.