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 NO3 radicals during the summertime in Beijing. While OH dominates the loss of isoprene during the day, NO3 plays an increasingly important role in the production of IsN from the early afternoon onwards. Unusually low NO concentrations during the afternoon resulted in NO3 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 NO3 and OH oxidation. Di- and tri-nitrated isoprene-related NOS, formed from multiple NO3 oxidation steps, peaked during the night. This work highlights that NO3 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.
This project was funded by the Natural Environment Research Council, the Newton Fund and Medical Research Council in the U.K., and the National Natural Science Foundation of China (NE/N00700X/1, NE/N00695X/1, NE/N006895/1, NE/N007190/1, NE/N006917/1, NE/N006909/1). D.J.B., F.A.S., and E.J.S. acknowledge NERC SPHERES Ph.D. studentships. A.W.M. acknowledges a NERC PANORAMA Ph.D. studentship. P.M.E acknowledges funding the European Research Council Grant ERC-StG-802685. The Orbitrap-MS was funded by a Natural Environment Research Council strategic capital grant, CC090. J.D.S. and T.C. acknowledge support from the United States National Science Foundation (NSF) under Atmospheric and Geospace (AGS) Grant 1703535.