Impacts of snowpack emissions on deduced levels of OH and peroxy radicals at Summit, Greenland

Levels of OH and peroxy radicals in the atmospheric boundary layer at Summit, Greenland, a location surrounded by snow from which HO _x radical precursors are known to be emitted, were deduced using steady-state analyses applied to (OH+HO ₂+CH ₃O ₂), (OH+HO ₂), and OH-HO ₂ cycling. The results indicate that HO _x levels at Summit are significantly increased over those that would result from O ₃ photolysis alone, as a result of elevated concentrations of HONO, HCHO, H ₂O ₂, and other compounds. Estimated midday levels of (HO ₂+CH ₃O ₂) reached 30-40 pptv during two summer seasons. Calculated OH concentrations averaged between 05:00 and 20:00 (or 21:00) exceeded 4×10 ⁶ molecules cm ^-3, comparable to (or higher than) levels expected in the tropical marine boundary layer. These findings imply rapid photochemical cycling within the boundary layer at Summit, as well as in the upper pore spaces of the surface snowpack. The photolysis rate constants and OH levels calculated here imply that gas-phase photochemistry plays a significant role in the budgets of NO _x, HCHO, H ₂O ₂, HONO, and O ₃, compounds that are also directly affected by processes within the snowpack.