Oxidation Flow Reactor Results in a Chinese Megacity Emphasize the Important Contribution of S/IVOCs to Ambient SOA Formation
Weiwei Hu, Huaishan Zhou, Wei Chen, Yuqing Ye, Tianle Pan, Yingkun Wang, Wei Song, Huina Zhang, Wei Deng, Ming Zhu, Chaomin Wang, Caihong Wu, Chenshuo Ye, Zelong Wang, Bin Yuan, Shan Huang, Min Shao, Zhe Peng, Douglas A. Day, Pedro Campuzano‐Jost, Andrew T. Lambe, Douglas R. Worsnop, J. L. Jiménez, Xinming Wang
Abstract
Oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) formation potential of ambient air in Guangzhou, China was investigated using a field-deployed oxidation flow reactor (OFR). The OFR was used to mimic hours to weeks of atmospheric exposure to hydroxyl (OH) radicals within the 2–3 min residence time. A comprehensive investigation on the variation of VOCs and OVOCs as a function of OH exposure is shown. Substantial formation of organic acids and nitrogen-containing OVOC species were observed. Maximum SOA formation in the OFR was observed following 1–4 equiv days’ OH exposure. SOA produced from known/measured VOC/IVOC precursors such as single-ring aromatics and long-chain alkanes can account for 52–75% of measured SOA under low NOx and 26–60% under high NOx conditions based on laboratory SOA yield parametrizations. To our knowledge, this is the first time that the contribution (8–20%) of long-chain (C8–C20) alkane oxidation to OFR SOA formation was quantified from direct measurement. By additionally estimating contribution from unmeasured semivolatile and intermediate volatility compounds (S/IVOCs) that are committed with C8–C20 alkanes, 64–100% of the SOA formation observed in the OFR can be explained, signifying the important contribution of S/IVOCs such as large cyclic alkanes to ambient SOA.