Meteorological Effects on Nitryl Chloride in an Urban Wintertime Environment

The photolysis of atmospheric nitryl chloride (ClNO₂) produces chlorine radicals and nitrogen dioxide (NO₂), which alter pollutant fates and air quality. ClNO₂ is formed at night from the reaction of dinitrogen pentoxide (N₂O₅) on chloride-containing aerosols. Both ClNO₂ and N₂O₅ are important nocturnal reservoir species for nitrogen oxides (NO_x = NO + NO₂), an EPA-regulated pollutant ubiquitous in urban environments that drives the production tropospheric ozone (O₃). Meteorological parameters influence the abundance of ClNO₂ and N₂O₅, as well as their precursors, including NO_x, O₃, and particulate chloride. However, the effects of meteorology on ClNO₂ production are not yet well understood, as most observational and modeling studies focus on periods of clear air. During a field campaign in Kalamazoo, Michigan from Jan - Feb 2018, N₂O₅ and ClNO₂ were measured using chemical ionization mass spectrometry (CIMS), with simultaneous measurements of atmospheric particulate matter and meteorology. We examine the impacts of atmospheric turbulence, precipitation (rain, snow, and fog), and ground cover (snow covered vs. bare ground) on the abundances of ClNO₂ and N₂O₅. These observations aid our understanding of chlorine chemistry under conditions that are not ideal for atmospheric modeling.