This project investigated the production of the atmospheric trace gas nitryl chloride (ClNO2) in the wintertime inland urban environment through both field measurements and numerical modeling. ClNO2 is an important trace gas that is formed at night from the reaction of dinitrogen pentoxide (N2O5) on chloride-containing surfaces. Upon sunrise, ClNO2 photolyzes (breaks apart) to produce nitrogen dioxide (NO2), which is regulated by the Clean Air Act, and chlorine atoms that are highly reactive toward hydrocarbons emitted from combustion. This chemistry is also impacts the levels of atmospheric ozone, a greenhouse gas and pollutant that is regulated by the Clean Air Act. In this project, road salt aerosol was identified and quantified as the major chloride source leading to inland atmospheric chlorine chemistry. This work transformed our understanding of wintertime atmospheric chemistry. This finding connected the deicing practice of road salt application, recently identified to be causing significant freshwater salinization, to air quality through aerosolization of road salt, deposition to snowpacks far from roadways, and production of ClNO2. This connects deicing practices, air pollution, and ecology. In addition, the deposition and reaction of N2O5 on the road salt-contaminated snowpack was observed, for the first time, to produce ClNO2. Currently road salt aerosol is missing from air quality models, and this project showed that this source needs to be added to improve air quality modeling. A new model parametrization was developed that more accurately simulates the production of ClNO2 by considering heterogeneity in the aerosol population and is expected to improve regional air quality modeling in the future. This project also showed that the saline snowpack, in addition to atmospheric particulate matter, could produce ClNO2. This has implications for the coastal, sea spray aerosol-influenced snowpack, in addition to the wintertime inland road salt-contaminated snowpack.  In addition, the trace gas HONO was also shown to be primarily produced from the snowpack, again showing the connection between the inland urban snowpack and air quality.

Project results were presented at numerous local, national, and international conferences and are reported through 4 publications, as well as 1 additional manuscript under review. These project results were also featured in the Chemical & Engineering News magazine (magazine of the American Chemical Society) and SNOW magazine (magazine of the Accredited Snow Contractors Association). This project contributed to the training and professional development of one early career professor, four postdoctoral researchers, four PhD students, one undergraduate student, and one high school student. In particular, one summer high school student spent seven weeks conducting research in the Pratt Lab through the Detroit Research Internship Summer Experience (D-RISE). Eight of these 11 individuals are members of groups underrepresented in science, and therefore, this project contributed to diversity efforts in STEM. Public outreach was conducted at the University of Michigan through the Science for Tomorrow and FEMMES (Females Excelling More in Math, Engineering, and Science) programs for middle school students from underrepresented backgrounds. Pratt Lab researchers also participated in the University of Michigan Science Communication Fellows Program and developed outreach activities about road salt that were presented at the University of Michigan Museum of Natural History Meet a Scientist virtual event.

Last Modified: 12/31/2021
Modified by: Kerri A Pratt