Abstract
Abstract. Nitryl chloride (ClNO2) is a radical reservoir species that releases chlorine radicals upon photolysis. An integrated analysis of the impact of ClNO2 on regional photochemistry in the Seoul metropolitan area (SMA) during the Korea–United States Air Quality Study (KORUS-AQ) 2016 field campaign is presented. Comprehensive multiplatform observations were conducted aboard the NASA DC-8 and at two ground sites (Olympic Park, OP; Taehwa Research Forest, TRF), representing an urbanized area and a forested suburban region, respectively. Positive correlations between daytime Cl2 and ClNO2 were observed at both sites, the slope of which was dependent on O3 levels. The possible mechanisms are explored through box model simulations constrained with observations. The overall diurnal variations in ClNO2 at both sites appeared similar but the nighttime variations were systematically different. For about half of the observation days at the OP site the level of ClNO2 increased at sunset but rapidly decreased at around midnight. On the other hand, high levels were observed throughout the night at the TRF site. Significant levels of ClNO2 were observed at both sites for 4–5 h after sunrise. Airborne observations, box model calculations, and back-trajectory analysis consistently show that these high levels of ClNO2 in the morning are likely from vertical or horizontal transport of air masses from the west. Box model results show that chlorine-radical-initiated chemistry can impact the regional photochemistry by elevating net chemical production rates of ozone by ∼25 % in the morning.
Highlights
Nitryl chloride (ClNO2) is generates chlorine radicals hutptoimnesurnadriiscealRreeascetrivoonir(Rth1a)t, with a lifetime of around 30 min at midday in the Northern Hemisphere midlatitude summer, under clearsky conditions (JClNO2 ≈ 5.47 × 10−4 s−1; Madronich and Flocke, 1998)
We present ClNO2 observation results from the Korea–United States Air Quality (KORUS-AQ) study conducted in the Seoul metropolitan area (SMA), South Korea, during late spring (2 May to 12 June 2016)
At the Taehwa Research Forest (TRF) site, which is a forested region downwind of the urban area, O3 remained at ∼ 30 ppbv throughout the night
Summary
Nitryl chloride (ClNO2) is generates chlorine radicals (aCnl iqg) hutptoimnesurnadriiscealRreeascetrivoonir(Rth1a)t, with a lifetime (τClNO2 ) of around 30 min at midday in the Northern Hemisphere midlatitude summer, under clearsky conditions (JClNO2 ≈ 5.47 × 10−4 s−1; Madronich and Flocke, 1998). It is produced through heterogeneous reaction of chloride-containing aerosols and dinitrogen pentoxide (N2O5(g)), which is generated tion with gas-phase nitrate radical f(rNoOm3qa)nanedquniiltirborgiuemn reacdioxide (NO2) (Reactions R2–R4; Finlayson-Pitts et al, 1989).
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