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

Abstract

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 (γN2O5) ranged from ∼10–3 to 10–1 and ClNO2 yields (φClNO2) were >50% for all playas tested except one. In general, as the soluble ion fraction of playa dusts increases, γN2O5 decreases and φClNO2 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.

Hygroscopic Properties of Saline Mineral Dust From Different Regions in China: Geographical Variations, Compositional Dependence, and Atmospheric Implications

“…Aerosol liquid water (or surface‐adsorbed water) largely determines kinetics, mechanisms, and products of heterogeneous reactions (Rubasinghege & Grassian, ; Tang et al, ; Wu et al, ). Mitroo et al () found that at a given RH, N 2 O 5 uptake coefficients decreased whereas ClNO 2 production yield increased with soluble ion fractions in saline mineral dust samples. Furthermore, the dependence of N 2 O 5 uptake coefficients on RH was found to vary with different samples in complicated manners, indicating competing effects between uptake by clay minerals and uptake by soluble contents.…”

Dust Emission Source Characterization for Visibility Hazard Assessment on Lordsburg Playa in Southwestern New Mexico, USA

“…Soils in the Lordsburg Playa basin are classi ed primarily as aridisols of the Hondale series (Fine, mixed, superactive, Thermic Natargid) in the Animas Creek delta and along the western shoreline, Playas series (Fine, mixed, superactive, Sodic Haplocambid) in the ephemerally ooded lakebed, and small areas of vertisols of the Verhalen silty clay loam series (Fine, smectitic, thermic Typic Haplotorrerts) on the eastern shoreline. Although the playa surface is saline and alkaline with occasional salt e orescences (puffy growths of evaporite minerals on the surface) (Reynolds et al, 2007), the surface sediments are comprised of primary silicate and clay minerals with lower concentrations of evaporites (salt minerals) than many other dust-emitting playas in North America (Hibbs et al, 2000;Mitroo et al, 2019).…”

Dust Emission Source Characterization for Visibility Hazard Assessment on Lordsburg Playa in Southwestern New Mexico, USA

“…Five months of the year have average maximum temperatures in excess of 30 o C with June, the hottest month, having an average maximum of 35 o C. Soils in the Lordsburg Playa basin are classi ed primarily as aridisols of the Hondale series (Fine, mixed, superactive, Thermic Natargid) in the Animas Creek delta and along the western shoreline, Playas series (Fine, mixed, superactive, Sodic Haplocambid) in the ephemerally ooded lakebed, and small areas of vertisols of the Verhalen silty clay loam series (Fine, smectitic, thermic Typic Haplotorrerts) on the eastern shoreline. Although the playa surface is saline and alkaline with occasional salt e orescences (puffy growths of evaporite minerals on the surface) (Reynolds et al, 2007), the surface sediments are comprised of primary silicate and clay minerals with lower concentrations of evaporites (salt minerals) than many other dust-emitting playas in North America (Hibbs et al, 2000;Mitroo et al, 2019).…”