![]() ![]() Various studies have reported the formation mechanisms of multifunctional isoprene oxidation products and their contribution to SOA formation under low-NO conditions (Berndt et al., 2016 Krechmer et al., 2015 Riva et al., 2016 Wang et al., 2018), with SOA yield ranging from 5.8% to 11%. ![]() Aside from the IEPOX pathway, the multifunctional compounds formed through isoprene oxidation would be of low enough volatility to partition efficiently to the particle phase (Kroll & Seinfeld, 2008). The reactive uptake of IEPOX onto aerosol seeds has been confirmed to form SOA (D'Ambro et al., 2017 Lin et al., 2011 Liu et al., 2015 Nguyen et al., 2014 Xu et al., 2015 Zhang, Chen, et al., 2018). ![]() The formation of dihydroxy epoxides (IEPOX) dominates the isoprene oxidation process (Paulot et al., 2009) at yields greater than 75% (Bates et al., 2014). Isoprene oxidation and SOA contribution under NO x free or low-NO x condition (<1 ppb) have been well studied during past years (Kroll et al., 2006). Although significant progress has been made on the isoprene oxidation scheme, uncertainties about isoprene oxidation under various polluted conditions still exist, which would affect the estimation of the isoprene SOA yield among polluted environments. The state-of-the-art isoprene oxidation mechanisms have been incorporated into the model to estimate global budget of isoprene SOA (Bates & Jacob, 2019 Müller et al., 2019 Pai et al., 2019 Stadtler et al., 2018) during recent years. Isoprene is highly reactive and can be readily oxidized by various oxidants (mainly OH, NO 3, and O 3) in the atmosphere, affecting the abundance of global SOA (Carlton et al., 2009 Claeys et al., 2004 Wennberg et al., 2018). Isoprene (2-methyl-1, 3-butadiene), mainly originating from biogenic sources, has the largest emission of all nonmethane VOCs with a global emission of ∼600 Tg C yr −1 (Guenther et al., 2006). Secondary organic aerosol (SOA) forms through the oxidation of various volatile organic compounds (VOCs) and consists of a large proportion of the total aerosol mass (Huang et al., 2014 Ng et al., 2010 Sun et al., 2013 Zhang et al., 2007 Zhang, Yee, et al., 2018). These multifunctional products are mostly semi-volatile species and can contribute considerably to the observed SOA, highlighting an important role of biogenic volatile organic compounds oxidation on SOA formation under high-NOx conditions, for example, anthropogenic emission dominant regions. Here, we used state-of-the-art instruments to measure isoprene, highly functionalized intermediate compounds and organic aerosol simultaneously at two suburban sites in eastern China region and identify several tens of isoprene oxidation products with most of which identified as nitrogen-containing species, confirming the significant interaction between the isoprene derived peroxy radicals and NO x. In polluted urban areas, where isoprene would interact significantly with anthropogenic emissions, for example, NO x, the understanding of SOA formation potential of isoprene is rather controversial. Isoprene, as one of the most important precursors to form secondary organic aerosol (SOA) globally, has been extensively studied, most of which however focused in the pristine regions. ![]() The results showed that the multifunctional products derived from isoprene oxidation can contribute to 2.6% of the total organic aerosol mass (0.28 ± 0.27 μg/m 3), highlighting the potential importance of isoprene oxidation in polluted regions. We calculated the volatility using the group-contribution method and estimated the particle-phase concentration by equilibrium gas/particle partitioning. We identified multiple functionalized isoprene oxidation products, of which 72% and 88% of the total mole concentration were nitrogen-containing species with the dominant compound being C5 dihydroxyl dinitrate (C 5H 10N 2O 8). Here, we conducted comprehensive observations in polluted megacities of Nanjing and Shanghai during summer of 2018. The oxidation of isoprene is crucial to atmospheric photochemistry and contributes significantly to the global formation of secondary organic aerosol. Isoprene (2-methyl-1, 3-butadiene) is a nonmethane volatile organic compound (VOC) with the largest global emission and high reactivity. ![]()
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