Winter ClNO<sub>2</sub> formation in the region of fresh anthropogenic emissions: seasonal variability and insights into daytime peaks in northern China

Abstract. Nitryl chloride (ClNO2) is an important chlorine reservoir in the atmosphere that affects oxidation of volatile organic compounds (VOCs) and production ROx radicals ozone (O3). This study presents measurements ClNO2 related at urban, polluted rural, lower tropospheric (mountaintop) sites winter 2017–2018 over North China Plain (NCP). The nocturnal concentrations were urban rural but higher site. generally than summer previously observed these sites, which was due to nitrate radical (NO3) rate (P(NO3)) smaller N2O5 uptake coefficients (?(N2O5)) winter, despite ratios dinitrogen pentoxide (N2O5) NO3 winter. Significant daytime peaks all during campaigns, with mixing up 1.3 ppbv. Vertical transport from residual layers prolonged photochemical lifetime may explain elevated concentrations. daytime-averaged (Cl) rates (P(Cl)) 0.17, 0.11, 0.12 ppbv h?1 respectively, approximately 3–4 times campaign-averaged conditions. Box model calculations showed Cl atoms liberated increased levels by 27 %–37 % daily O3 productions 13 %–18 %. Our results provide new insights into processes troposphere impacted fresh intense anthropogenic emissions reveal can be source under certain conditions