N₂O₅ uptake by chloride-containing surfaces produces ClNO₂, which photolyzes, producing NO₂ and highly reactive Cl radicals that impact air quality. In the inland urban atmosphere, ClNO₂ was elevated during lower air turbulence and over snow-covered ground, from snowpack ClNO₂ production. N₂O₅ and ClNO₂ levels were lowest, on average, during rainfall and fog because of scavenging, with N₂O₅ scavenging by fog droplets likely contributing to observed increased particulate nitrate concentrations.