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Secondary Organic Aerosol Formation From Isoprene Epoxides in the Pearl River Delta, South China: IEPOX‐ and HMML‐Derived Tracers
Author(s) -
He QuanFu,
Ding Xiang,
Fu XiaoXin,
Zhang YuQing,
Wang JunQi,
Liu YeXin,
Tang MingJin,
Wang XinMing,
Rudich Yi
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2017jd028242
Subject(s) - isoprene , environmental chemistry , chemistry , sulfate , aerosol , organic chemistry , copolymer , polymer
Atmospheric photooxidation of isoprene forms isoprene epoxydiols (IEPOX) and hydroxymethel‐methyl‐α‐lactone (HMML) via hydroperoxyl radical (HO 2 ) channel and NO/NO 2 channel, respectively. Reactive uptake of these epoxides onto particles produces isoprene secondary organic aerosols (iSOA). Currently, there is little information regarding these two epoxides during iSOA formation in polluted regions. In this study, iSOA tracers from IEPOX and HMML were measured from summer to fall in the heavily polluted Pearl River Delta (PRD) region. The total concentration of the iSOA tracers ranged from 5.77 to 466 ng m −3 . Isoprene SOA tracers correlated well with sulfate ( p < 0.01), indicating that the abundant sulfate in the PRD plays an important role in iSOA formation. A kinetic model of IEPOX loss showed that 58% of IEPOX could undergo ring‐opening reactions under the polluted PRD conditions in summer. This leads to high levels of IEPOX‐derived SOA tracers in the PRD. High temperature in the PRD (>22 °C) suppresses the production of HMML, likely as a result of fast decomposition of HMML's precursor under high temperatures. Thus, the HMML‐derived tracers had lower levels than the IEPOX‐derived SOA tracers during the whole campaign. The ratios of the IEPOX‐derived tracers to the HMML‐derived SOA tracers in summer were ~3 times higher than those in fall. This seasonal trend may be explained by the relative high isoprene/NO x ratio, temperature, and fast heterogeneous reaction of IEPOX in summer. Our study shows that in highly polluted regions like PRD, reduction in SO 2 emission can significantly reduce iSOA formation.