es9b01112_si_001.pdf (1.38 MB)
ClNO2 Production from N2O5 Uptake on Saline Playa Dusts: New Insights into Potential Inland Sources of ClNO2
journal contribution
posted on 2019-05-22, 00:00 authored by Dhruv Mitroo, Thomas E. Gill, Savannah Haas, Kerri A. Pratt, Cassandra J. GastonNitryl 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.