Presentation description

The nitrate radical (NO3) is a key oxidizing agent in the atmosphere and participates in numerous oxidative reactions. Importantly, NO3 reacts with volatile organic compounds (VOCs) to form secondary pollutants, which can have many harmful effects on human health and the climate. Although NO3 is generally considered to be more important at night due to rapid photolysis and reaction with NO during the day, some instances allow for daytime NO3 to be observed. For example, high levels of ozone (O3) can react with NO, resulting in decreased NO concentrations, which can reduce daytime NO3 losses and allow for observable daytime NO3 concentrations. Salt Lake City, Utah, typically exhibits high O3 concentrations in the summer, regularly exceeding EPA standards. So, in this study, a steady state approximation is applied to estimate daytime NO3 in Salt Lake City during summer months. This analysis revealed daytime NO3 levels to be around 1 pptv in the hours leading up to sunset. Further analysis of data from the global chemical transport model, GEOS-Chem, was conducted to pinpoint areas with heightened daytime NO3 levels and evaluate the global significance of this phenomenon. Results from this analysis showed daytime NO3 to be most considerable in the hours before sunset, particularly in highly urban areas, and can be responsible for up to 85% of the losses of major VOCs. The results of this study will contribute to research on the significance of daytime NO3 chemistry in the formation of secondary pollutants across various environmental settings.