Atmospheric nitryl chloride impacts air quality by modifying oxidant budgets, pollutant fate, and particulate matter formation. Contrary to original assumptions of chlorine chemistry confined to areas with oceanic influence, recent observations and modeling suggest widespread inland chlorine chemistry, particularly in the winter. However, the inland source(s) of particulate chloride remain highly uncertain and unquantified, hindering air quality assessments. Here, we identify road salt, applied in deicing practices, as the primary source (80-100%) of nitryl chloride in the wintertime inland urban environment. Given increasing and nearly ubiquitous use of road salt across much of North America during winter inland wintertime particulate chloride concentrations can be nearly as high as in coastal environments influenced by sea spray particles. Nonetheless, this substantial chloride source is currently not included in emissions inventories for atmospheric modeling of nitryl chloride limiting the quantitation of the broad implications of this chlorine chemistry. The traditional method of simulating nitryl chloride considers chloride to be homogeneously distributed across the atmospheric particle population yet we show that only a fraction of the particulate surface area contains chloride. Our new single-particle modeling parametrization, which considers this heterogeneity, significantly reduces previous model overestimates in nitryl chloride, enabling improved air quality predictions.
Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry
McNamara S.M., K.R. Kolesar, S. Wang, R.M. Kirpes, N.W. May, M.J. Gunsch, and R.D. Cook, et al. 2020. "Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry." <i>ACS Central Science</i> 6, no. 5:684-694. PNNL-SA-144344. doi:10.1021/acscentsci.9b00994