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

Bryant, D.J. and Dixon, W.J. and Hopkins, J.R. and Dunmore, R.E. and Pereira, K.L. and Shaw, M. and Squires, F.A. and Bannan, T.J. and Mehra, A. and Worrall, S.D. and Bacak, A. and Coe, H. and Percival, C.J. and Whalley, L.K. and Heard, D.E. and Slater, E. and Ouyang, B. and Cui, T. and Surratt, J.D. and Liu, D. and Shi, Z. and Harrison, R. and Sun, Y. and Xu, W. and Lewis, A.C. and Lee, J.D. and Rickard, A.R. and Hamilton, J.F. (2020) Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing. Atmospheric Chemistry and Physics, 20 (12). pp. 7531-7552. ISSN 1680-7316

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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 NOx and particulate SO2-4 , led to the formation of iSOA under both high- A nd low-NO oxidation conditions, with significant heterogeneous transformations of isoprene-derived oxidation products to particulate organosulfates (OSs) and nitrooxyorganosulfates (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 PM2.5 filter extracts. The co-elution of the inorganic ions in the extracts caused matrix effects that impacted two authentic standards differently. The average concentration of iSOA OSs and NOSs was 82.5 ngm-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 (O3) and particulate sulfate (SO2-4). 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 ∼ 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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Journal Article
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Atmospheric Chemistry and Physics
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21 Aug 2020 16:00
Last Modified:
15 Sep 2023 01:09