Deposition of atmospheric nitrous acid on alkaline snow surfaces

Abstract

The photolysis of atmospheric nitrous acid (HONO) is a significant source of OH radicals in remote and Polar Regions. HONO is produced in/ on snow surfaces in a photochemical reaction from nitrate ions. In an attempt to quantify the production of HONO at a snow covered mid-latitude location we made measurements of HONO fluxes for a 10-day period at the Mt. Cimone (MTC) research station in the Italian northern Apennines (2165 m asl) during March 2004. Production fluxes under normal background conditions were small, and reached maximum values of 20 nmol m-2 h-1 on only two occasions. However, during a transport event of Saharan dust to MTC we observed deposition fluxes of up to -120 nmol m-2 h-1 of HONO on to the snow surface. The deposited Sahara dust had rendered the surface snow alkaline, so that large amounts of acids could be absorbed from the atmosphere. Copyright 2005 by the American Geophysical Union.