Collaborative Research: Heterogeneous Chlorine Activation from Saline Playas

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Droughts mobilize natural dust from salt playas that can react with nitrogen oxides, criteria pollutants that are emitted by combustion sources. This reaction releases chlorine atoms that are potent atmospheric oxidants but are neglected in models used to assess regional air quality because of lack of measurements. The proposal will measure the fundamental rate constants of real-world playa dust particles with nitrogen oxides to enable robust assessments of regional air quality impacts in salt playas regions such as Texas.Reactive chlorine (Cl) atoms when activated can serve as potent atmospheric oxidants that would effect lifetimes of greenhouse gases like methane and also tropospheric ozone abundance. The proposal hypothesizes that wind blown chloride-containing dust from dried saline lake beds (playas) can be converted to nitryl-chloride (ClNO2) by heterogeneous reactions with gaseous dinitrogen pentoxide (N2O5). The ClNO2 photolysis produces Cl atoms that could alter the ozone production photochemistry and the methane lifetime significantly. The research will measure the kinetics of ClNO2 production from reactions of salt with N2O5 in a trace gas-aerosol flow reactor. Chemical ionization mass spectrometry will be used to monitor ClNO2 in the reactor and the playa dusts will be analyzed using single-particle mass spectrometry, ion chromatography and X ray diffraction. The in depth analysis of the chemical and atmospheric conditions under which chlorine can be released from the saline playas will provide a mechanistic framework that could be implemented in chemistry-climate and air-quality models to make more robust predictions and assessments.