The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene

Abstract

<jats:p>Abstract. Biogenic volatile organic compounds (BVOCs) emitted by plants represent the largest source of non-methane hydrocarbon emissions on Earth. Photochemical oxidation of BVOCs represents a significant pathway in the production of secondary organic aerosol (SOA), affecting Earth’s radiative balance. Organic nitrates (RONO2), formed from the oxidation of BVOCs in the presence of NOx, represent important aerosol precursors, and affect the oxidative capacity of the atmosphere, in part by sequestering NOx. In the aerosol phase, RONO2 hydrolyze to form nitric acid and numerous water-soluble products, thus contributing to an increase in aerosol mass. However, only a small number of studies have investigated the production of RONO2 from •OH oxidation of terpenes, among those, few have studied their hydrolysis. Here, we report a laboratory study of OH radical-initiated oxidation of β-ocimene, an acyclic, triolefinic monoterpene released during the daytime from vegetation, including forests, agricultural landscapes, and grasslands. We conducted studies of the OH radical oxidation of β-ocimene in the presence of NOx using a 5.5 m3 all-Teflon photochemical reaction chamber, during which we quantified the total (gas- and particle-phase) RONO2 yield and the SOA yields. We sampled the organic nitrates produced and measured their hydrolysis rate constants at different solution pH. The total organic nitrate yield was determined to be 33(±7) %, consistent with the available literature regarding the dependence of organic nitrate production (from RO2 + NO) on carbon number. We found the hydrolysis rate constants to be highly pH-dependent, with a hydrolysis lifetime of 51(±13) min at pH = 4, and 24(±3) min at pH = 2.5, a typical pH for deliquesced aerosols. We also employed high-resolution mass spectrometry for product identification, which is used to infer key mechanisms of gas–particle partitioning. The results indicate that the ocimene SOA yield under relevant aerosol mass loadings in the atmosphere is significantly lower ( </jats:p>

The First Seasonal Snowfall Impacts Plant Photosynthesis and Monoterpene Emissions

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Biogenic and anthropogenic sources of isoprene and monoterpenes and their secondary organic aerosol in Delhi, India

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