Discerning Trends in Wintertime Reactive Chlorine Chemistry And Air Quality

Abstract:

The chlorine atom (Cl) can impact atmospheric oxidation chemistry but the extent of its impact is not well understood. HCl is the dominant product of chlorine atom reactions and acts as the major atmospheric reservoir of chlorine. Most previous measurements of HCl have had a low-time resolution due to the analytical challenges present when measuring this compound. It is not until recently that measurements of a high-time resolution have become more prevalent for HCl. A potential precursor of atmospheric chlorine species that has received relatively little attention is road salt, which can act as a source of chlorine directly, but also through road spray aerosol suspension and subsequent deposition on other urban surfaces. Road salt is chiefly applied in wintertime environments and thus that is the period of interest for these field measurements. Presented here are high-time resolution HCl measurements using cavity ring-down spectroscopy (CRDS) in an urban wintertime environment (Toronto, Canada). Along with HCl are a plethora of auxiliary measurements including NO_x, ozone, irradiance, meteorology, and size-resolved particulate matter composition. Using this data we better constrain the roles of HCl and road salt in both reactive chlorine chemistry and wintertime air quality.