Key Role of NO<sub>3</sub> Radicals in the Production of Isoprene Nitrates and Nitrooxyorganosulfates in Beijing
Jacqueline F. Hamilton, Daniel J. Bryant, P. M. Edwards, Bin Ouyang, Thomas J. Bannan, Archit Mehra, Alfred W. Mayhew, James R. Hopkins, Rachel E. Dunmore, Freya Squires, James Lee, Mike J. Newland, Stephen D. Worrall, Asan Bacak, Hugh Coe, Carl J. Percival, Lisa K. Whalley, Dwayne E. Heard, Eloise J. Slater, R. L. Jones, Tianqu Cui, Jason D. Surratt, Claire E. Reeves, G. Mills, Sue Grimmond, Yele Sun, Weiqi Xu, Zongbo Shi, Andrew R. Rickard
Abstract
The formation of isoprene nitrates (IsN) can lead to significant secondary organic aerosol (SOA) production and they can act as reservoirs of atmospheric nitrogen oxides. In this work, we estimate the rate of production of IsN from the reactions of isoprene with OH and NO 3 radicals during the summertime in Beijing. While OH dominates the loss of isoprene during the day, NO 3 plays an increasingly important role in the production of IsN from the early afternoon onwards. Unusually low NO concentrations during the afternoon resulted in NO 3 mixing ratios of ca. 2 pptv at approximately 15:00, which we estimate to account for around a third of the total IsN production in the gas phase. Heterogeneous uptake of IsN produces nitrooxyorganosulfates (NOS). Two mono-nitrated NOS were correlated with particulate sulfate concentrations and appear to be formed from sequential NO 3 and OH oxidation. Di- and tri-nitrated isoprene-related NOS, formed from multiple NO 3 oxidation steps, peaked during the night. This work highlights that NO 3 chemistry can play a key role in driving biogenic–anthropogenic interactive chemistry in Beijing with respect to the formation of IsN during both the day and night.