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

doi:10.5194/acp-2020-518

GSTDTAP > 地球科学

DOI	10.5194/acp-2020-518
	The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene
	Ana Cristina Morales, Thilina Jayarathne, Jonathan H. Slade, Alexander Laskin, and Paul B. Shepson
	2020-06-16
发表期刊	Atmospheric Chemistry and Physics
出版年	2020
英文摘要	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 NO_x, represent important aerosol precursors, and affect the oxidative capacity of the atmosphere, in part by sequestering NO_x. 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 (< 1 %) than reported yields from cyclic terpenes, such as α-pinene, likely due to alkoxy radical decomposition and formation of smaller higher-volatility products. This is also consistent with the observed lower particle-phase organic nitrate yields of β-ocimene, 1.5(±0.5) %, under dry conditions. We observed the expected hydroxy nitrates by chemical ionization mass spectrometry (CIMS), and some secondary production of the di-hydroxy di-nitrates, likely produced by oxidation of the first-generation hydroxy nitrates. Lower RONO₂ yields were observed under high relative humidity (RH) conditions, indicating the importance of aerosol-phase RONO₂ hydrolysis under ambient RH. This study provides insight into the formation and fate of organic nitrates, ocimene SOA yields, and NO_x cycling in forested environments from daytime monoterpenes, which are not currently included in atmospheric models.
领域	地球科学
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/276549
专题	地球科学
推荐引用方式 GB/T 7714	Ana Cristina Morales, Thilina Jayarathne, Jonathan H. Slade, Alexander Laskin, and Paul B. Shepson. The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene[J]. Atmospheric Chemistry and Physics,2020.
APA	Ana Cristina Morales, Thilina Jayarathne, Jonathan H. Slade, Alexander Laskin, and Paul B. Shepson.(2020).The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene.Atmospheric Chemistry and Physics.
MLA	Ana Cristina Morales, Thilina Jayarathne, Jonathan H. Slade, Alexander Laskin, and Paul B. Shepson."The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene".Atmospheric Chemistry and Physics (2020).