ClNO₂ Production from N₂O₅ Uptake on Saline Playa Dusts: New Insights into Potential Inland Sources of ClNO₂

Nitryl chloride (ClNO₂), formed when dinitrogen pentoxide (N₂O₅) reacts with chloride-containing aerosol, photolyzes to produce chlorine radicals that facilitate the formation of tropospheric ozone. ClNO₂ has been measured in continental areas; however, the sources of particulate chloride required to form ClNO₂ in inland regions remain unclear. Dust emitted from saline playas (e.g., dried lakebeds) contains salts that can potentially form ClNO₂ in inland regions. Here, we present the first laboratory measurements demonstrating the production of ClNO₂ from playa dusts. N₂O₅ reactive uptake coefficients (γ_N2O5) ranged from ∼10^–3 to 10^–1 and ClNO₂ yields (φ_ClNO2) were >50% for all playas tested except one. In general, as the soluble ion fraction of playa dusts increases, γ_N2O5 decreases and φ_ClNO2 increases. We attribute this finding to a transition from aerosol surfaces dominated by silicates that react efficiently with N₂O₅ and produce little ClNO₂ to aerosols that behave like deliquesced chloride-containing salts that generate high yields of ClNO₂. Molecular bromine (Br₂) and nitryl bromide (BrNO₂) were also detected, highlighting that playas facilitate the heterogeneous production of brominated compounds. Our results suggest that parameterizations and models should be updated to include playas as an inland source of aerosol chloride capable of efficiently generating ClNO₂.