Title: Sea Spray Chemistry Over Denver: Implications for the Tropospheric Chlorine Atom Source




Abstract: The nighttime chemistry of nitrogen oxide reservoirs affects air quality and climate by directly and indirectly regulating the oxidant budgets which drive ozone and aerosol formation as well as the removal of hydrocarbons such as the greenhouse gas methane. It is typically assumed that this nighttime chemistry represents a sink of ozone and nitrogen oxide radicals and thus decreases the regional and global tropospheric oxidizing capacity. In this talk, I'll provide evidence that chemistry leading to the formation of a chlorine atom precursor, nitryl chloride, is likely far more important than previously recognized, occurring efficiently in both polluted continental and coastal regions. Chlorine atoms are highly reactive oxidants known to exist in the troposphere but with highly uncertain sources. The chlorine atom source we infer from nighttime nitrogen oxide chemistry is of the same order as previous global estimates that neglected this process. Our findings thus suggest that anthropogenic emissions of nitrogen oxides have strongly influenced tropospheric halogen budgets, and that nighttime chemistry may in fact be a source of oxidants, especially in the oxidant-poor wintertime. As such, anthropogenic nitrogen oxide emissions may have had a larger effect on the tropospheric oxidizing capacity than currently predicted.