Atmospheric Chemistry and Physics α-pinene photooxidation under controlled chemical conditions – Part 2 : SOA yield and composition in low-and high-NO x environments
Atmospheric Chemistry and Physics α-pinene photooxidation under controlled chemical conditions – Part 2 : SOA yield and composition in low-and high-NO x environments
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发表时间：
2012
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通讯作者：
N. Eddingsaas;C. L. Loza;L. Yee;M. Chan;K. Schilling;P. Chhabra;J. Seinfeld;P. Wennberg
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作者：
N. Eddingsaas;C. L. Loza;L. Yee;M. Chan;K. Schilling;P. Chhabra;J. Seinfeld;P. Wennberg
α-蒎烯的气相氧化会在大气中产生大量的二次有机气溶胶。在野外样品中发现了许多与α-Pinene有关的羧酸、有机硫酸盐和硝氧基有机硫酸盐，其中一些被用作α-Pinene氧化的示踪剂。在大气中，α-Pinene很容易与OH和O_3反应，然后与HO_2和NO反应。由于存在大量潜在的反应途径，因此很难确定是什么条件导致了SOA。为了更好地了解低NOx和高NOx OH氧化α-Pinene的SO产率和化学组成，我们在加州理工学院的常压室中进行了可控化学条件下的研究。实验使用低浓度的臭氧以确保OH是主要的氧化剂，并使用低浓度的α-Pinene，以使过氧化自由基(RO2)在低NOx条件下主要与Ho2反应，或在高NOx条件下主要与NO反应。SOA产率在高NOx条件下受到抑制。在高NOx条件下，在生长开始之前存在硫酸铵/硫酸粒子(高度酸性)时的SOA产率高于存在硫酸铵(中等酸性)时的SOA产率；而在低NOx条件下没有观察到这种依赖关系。当在OH氧化后引入气溶胶种子颗粒，允许下一代物种暴露在新鲜的无机种子颗粒中时，许多低NOx产物分配到高度酸性的气溶胶中。这表明，在传统的实验中，在氧化之前引入气溶胶种子颗粒，可能低估了种子酸度和SOA产量的影响。我们还确定了一些羧酸的存在，这些羧酸在野外被用作α-Pinene氧化的示踪化合物，以及有机硫酸盐和氮氧基有机硫酸盐的形成。在所有条件下都观察到了大量的羧酸，但只有在低NOx条件下才能观察到Pinic和Pinonic酸。为多官能团醇的颗粒相硫酸盐酯化反应提供了依据。
The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of αpinene oxidation.α-pinene reacts readily with OH and O 3 in the atmosphere followed by reactions with both HO 2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from lowand high-NOx OH oxidation ofα-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and lowα-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO 2 under low-NOx conditions or NO under high-NO x conditions. SOA yield was suppressed under conditions of high-NO x. SOA yield under high-NOx conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NO x conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NO x products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under lowNOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.