Role of aldehyde chemistry and NOx concentrations in secondary organic aerosol formation
Role of aldehyde chemistry and NOx concentrations in secondary organic aerosol formation
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DOI：
10.5194/acp-10-7169-2010
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发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Seinfeld, J. H.
中科院分区：
文献类型：
--
作者：
Chan, A. W. H.;Chan, M. N.;Seinfeld, J. H.
醛类化合物是碳氢化合物在大气中氧化的重要产物。异戊二烯（2-甲基-1，3-丁二烯）是大气中排放量最大的非甲烷碳氢化合物，在城市高NOx条件下通过甲基丙烯醛（一种C4-不饱和醛）产生大量的二次有机气溶胶（SOA）。以前，我们已经确定过氧甲基丙烯酰硝酸酯（MPAN）作为重要的中间体异戊二烯和甲基丙烯醛SOA在此NOx制度。在这里，我们表明，作为这种化学的结果，NO2增强SOA形成从甲基丙烯醛和其他两个α，β-不饱和醛，特别是丙烯醛和巴豆醛，SOA形成的NOx效应以前未被认识。低聚酯的二羟基羧酸和羟基nitrooxycarboxylic酸被观察到增加NO2/NO的比例，并通过在线和离线高分辨率质谱技术证实了以前的表征。分子结构也决定SOA形成的量，因为对于α，β-不饱和并且在α-碳上含有额外甲基的醛，SOA质量产率最高。2-甲基-3-丁烯-2-醇（MBO 232）的气溶胶形成是微不足道的，即使在高NO2条件下，PAN（过氧酰基硝酸酯，RC（O）OONO 2）的形成是结构上不利的。在大气相关的NO2/NO比（3-8）下，异戊二烯高NOx光氧化的SOA产率比先前在较低NO2/NO比下测量的大3倍。在足够高的NO2浓度下，在α，β-不饱和醛的体系中，由酰基过氧自由基+NO2的产物的后续氧化形成SOA可以超过在相同的无机种子条件下由RO 2 + HO 2反应形成的SOA，使得RO 2 +NO2成为SOA形成的重要通道。
Aldehydes are an important class of products from atmospheric oxidation of hydrocarbons. Isoprene (2-methyl-1,3-butadiene), the most abundantly emitted atmospheric non-methane hydrocarbon, produces a significant amount of secondary organic aerosol (SOA) via methacrolein (a C-4-unsaturated aldehyde) under urban high-NOx conditions. Previously, we have identified peroxy methacryloyl nitrate (MPAN) as the important intermediate to isoprene and methacrolein SOA in this NOx regime. Here we show that as a result of this chemistry, NO2 enhances SOA formation from methacrolein and two other alpha, beta-unsaturated aldehydes, specifically acrolein and crotonaldehyde, a NOx effect on SOA formation previously unrecognized. Oligoesters of dihydroxycarboxylic acids and hydroxynitrooxycarboxylic acids are observed to increase with increasing NO2/NO ratio, and previous characterizations are confirmed by both online and offline high-resolution mass spectrometry techniques. Molecular structure also determines the amount of SOA formation, as the SOA mass yields are the highest for aldehydes that are alpha, beta-unsaturated and contain an additional methyl group on the alpha-carbon. Aerosol formation from 2-methyl-3-buten-2-ol (MBO232) is insignificant, even under high-NO2 conditions, as PAN (peroxy acyl nitrate, RC(O)OONO2) formation is structurally unfavorable. At atmospherically relevant NO2/NO ratios (3-8), the SOA yields from isoprene high-NOx photooxidation are 3 times greater than previously measured at lower NO2/NO ratios. At sufficiently high NO2 concentrations, in systems of alpha, beta-unsaturated aldehydes, SOA formation from subsequent oxidation of products from acyl peroxyl radicals+NO2 can exceed that from RO2+HO2 reactions under the same inorganic seed conditions, making RO2+NO2 an important channel for SOA formation.