Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing

Bryant, Daniel J.; Dixon, William J.; Hopkins, James R.; Dunmore, Rachel E.; Pereira, Kelly L.; Shaw, Marvin; Squires, Freya A.; Bannan, Thomas J.; Mehra, Archit; Worrall, Stephen D.; Bacak, Asan; Coe, Hugh; Percival, Carl J.; Whalley, Lisa K.; Heard, Dwayne E.; Slater, Eloise J.; Ouyang, Bin; Cui, Tianqu; Surratt, Jason D.; Liu, Di; Shi, Zongbo; Harrison, Roy; Sun, Yele; Xu, Weiqi; Lewis, Alastair C.; Lee, James D.; Rickard, Andrew R.; Hamilton, Jacqueline F.

Isoprene-derived secondary organic aerosol (iSOA) is a significant contributor to organic carbon (OC) in some forested regions, such as tropical rainforests and the Southeastern US. However, its contribution to organic aerosol in urban areas that have high levels of anthropogenic pollutants is poorly understood. In this study, we examined the formation of anthropogenically influenced iSOA during summer in Beijing, China. Local isoprene emissions and high levels of anthropogenic pollutants, in particular inline-formulaNOx and particulate inline-formula M2inlinescrollmathml chem normal SO normal 4 normal 2 - 29pt17ptsvg-formulamathimg74b4be02f6bf1e477b176a208786a61b acp-20-7531-2020-ie00001.svg29pt17ptacp-20-7531-2020-ie00001.png , led to the formation of iSOA under both high- and low-NO oxidation conditions, with significant heterogeneous transformations of isoprene-derived oxidation products to particulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs). Ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry was combined with a rapid automated data processing technique to quantify 31 proposed iSOA tracers in offline PMinline-formula2.5 filter extracts. The co-elution of the inorganic ions in thepage7532 extracts caused matrix effects that impacted two authentic standards differently. The average concentration of iSOA OSs and NOSs was 82.5 ng minline-formula−3, which was around 3 times higher than the observed concentrations of their oxygenated precursors (2-methyltetrols and 2-methylglyceric acid). OS formation was dependant on both photochemistry and the sulfate available for reactive uptake, as shown by a strong correlation with the product of ozone (inline-formulaO3) and particulate sulfate (inline-formula M6inlinescrollmathml chem normal SO normal 4 normal 2 - 29pt17ptsvg-formulamathimga8455a3a3390243c17ea2f3ca419ac4e acp-20-7531-2020-ie00002.svg29pt17ptacp-20-7531-2020-ie00002.png ). A greater proportion of high-NO OS products were observed in Beijing compared with previous studies in less polluted environments. The iSOA-derived OSs and NOSs represented 0.62 % of the oxidized organic aerosol measured by aerosol mass spectrometry on average, but this increased to inline-formula∼3 % on certain days. These results indicate for the first time that iSOA formation in urban Beijing is strongly controlled by anthropogenic emissions and results in extensive conversion to OS products from heterogenous reactions.

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Bryant, Daniel J. / Dixon, William J. / Hopkins, James R. / et al: Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing. 2020. Copernicus Publications.

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