Using observed urban NOx sinks to constrain VOC reactivity and the ozone and radical budget in the Seoul Metropolitan Area

Eastern Asia has high regional O-3 background due to the numerous sources and increasing and rapid industrial growth, which impacts the Seoul Metropolitan Area (SMA). However, SMA has also been experiencing increasing O-3 driven by decreasing NOx emissions, highlighting the role of local, in-situ O-3 production on SMA.

Here, comprehensive gas-phase measurements collected on the NASA DC-8 during the NIER/NASA Korea United States-Air Quality (KORUS-AQ) study are used to constrain the instantaneous O-3 production rate over the SMA. The observed NOx oxidized products support the importance of non-measured peroxy nitrates (PNs) in the O-3 chemistry in SMA, as they accounted for similar to 49 % of the total PNs. Using the total measured PNs (Sigma PNs) and alkyl and multifunctional nitrates (Sigma ANs), unmeasured volatile organic compound (VOC) reactivity (R(VOC)) is constrained and found to range from 1.4 - 2.1 s(-1).