Relative humidity effect on the formation of highly oxidized molecules and new particles during monoterpene oxidation
Relative humidity effect on the formation of highly oxidized molecules and new particles during monoterpene oxidation
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DOI：
10.5194/acp-19-1555-2019
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发表时间：
2019-02-06
影响因子：
6.3
通讯作者：
Smith, James N.
中科院分区：
文献类型：
--
作者：
Li, Xiaoxiao;Chee, Sabrina;Smith, James N.
全球范围内广泛观察到，在高相对湿度（RH）期间，新粒子形成（NPF）事件的频率和强度降低。目前的研究重点是RH如何影响高度氧化分子（HOM）的形成，这是NPF的关键组成部分和氧化有机物引起的初始生长。在低氮氧化物条件下，在相对湿度（RH）为3%~ 92%的条件下，在温控流管中，对α-蒎烯、柠檬烯和δ（3）-<$烯进行了臭氧分解，生成二次有机气溶胶（SOA）。采用扫描迁移率粒度仪（SMPS）测量生成粒子的粒径分布，采用新型横向电离化学电离入口和高分辨率飞行时间质谱仪检测HOMs。这项工作的一个主要发现是，检测到的HOMs及其丰度都没有随RH显著变化，这表明检测到的HOMs必须由水独立的途径形成。事实上，区别OH-和O-3-衍生的过氧自由基（RO 2），HOM单体，和HOM二聚体可以主要解释为RO 2的自氧化，然后与其他RO 2或氢过氧自由基（HO 2）的双分子反应，而不是从水的影响途径，如通过形成稳定的Criegee中间体（sCI）。然而，随着相对湿度从接近3%增加到接近92%，总的SOA数量浓度下降了2-3倍，而SOA质量浓度保持相对恒定。这些观察结果表明，虽然高RH似乎抑制NPF，如通过降低数量浓度所证明的，但这种减少不是由RO 2衍生的HOM形成的减少引起的。对这些现象的可能解释进行了讨论。
It has been widely observed around the world that the frequency and intensity of new particle formation (NPF) events are reduced during periods of high relative humidity (RH). The current study focuses on how RH affects the formation of highly oxidized molecules (HOMs), which are key components of NPF and initial growth caused by oxidized organics. The ozonolysis of alpha-pinene, limonene, and Delta(3)-carene, with and without OH scavengers, were carried out under low NOx conditions under a range of RH (from similar to 3% to similar to 92 %) in a temperature-controlled flow tube to generate secondary organic aerosol (SOA). A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution of generated particles, and a novel transverse ionization chemical ionization inlet with a high-resolution time-of-fight mass spectrometer detected HOMs. A major finding from this work is that neither the detected HOMs nor their abundance changed significantly with RH, which indicates that the detected HOMs must be formed from water-independent pathways. In fact, the distinguished OH- and O-3-derived peroxy radicals (RO2), HOM monomers, and HOM dimers could mostly be explained by the autoxidation of RO2 followed by bimolecular reactions with other RO2 or hydroperoxy radicals (HO2), rather than from a water-influenced pathway like through the formation of a stabilized Criegee intermediate (sCI). However, as RH increased from similar to 3% to similar to 92 %, the total SOA number concentrations decreased by a factor of 2-3 while SOA mass concentrations remained relatively constant. These observations show that, while high RH appears to inhibit NPF as evident by the decreasing number concentration, this reduction is not caused by a decrease in RO2-derived HOM formation. Possible explanations for these phenomena were discussed.