Quantifying the contributions of aerosol - and snow-produced ClNO 2 through observations and 1D modeling

Upon sunrise, ClNO2 rapidly photolyzes to generate highly reactive chlorine radicals (Cl-center dot) that affect the air quality by generating secondary air pollutants. Recent studies have shown road salt aerosols and saline snowpack to be sources of ClNO2 in the wintertime urban environment; however, the quantitative contributions of each chloride source are not known.

In this study, we examine the vertically resolved contributions of aerosol particles and saline snowpack as sources of ClNO2 by using an observationally constrained snow-atmosphere coupled one-dimensional model applied to wintertime Kalamazoo, Michigan, U.S. Model simulations show that ClNO2 emitted from urban snowpack can be vertically transported throughout the entire atmospheric boundary layer and can be a significant source of ClNO2, contributing up to similar to 60% of the ClNO2 budget near the surface.