Hydroxyl radical and NOx production rates, black carbon concentrations and light-absorbing impurities in snow from field measurements of light penetration and nadir reflectivity of onshore and offshore coastal Alaskan snow

Photolytic production rates of NO, NO₂ and OH radicals in snow and the total absorption spectrum due to impurities in snowpack have been calculated for the Ocean-Atmosphere-Sea-Ice-Snowpack (OASIS) campaign during Spring 2009 at Barrow, Alaska. The photolytic production rate and snowpack absorption cross-sections were calculated from measurements of snowpack stratigraphy, light penetration depths (e-folding depths), nadir reflectivity (350-700 nm) and UV broadband atmospheric radiation. Maximum NO_x fluxes calculated during the campaign owing to combined nitrate and nitrite photolysis were calculated as 72 nmol m^-2 h^-1 for the inland snowpack and 44 nmol m^-2 h^-1 for the snow on sea-ice and snowpack around the Barrow Arctic Research Center (BARC). Depth-integrated photochemical production rates of OH radicals were calculated giving maximum OH depth-integrated production rates of ∼160 nmol m ^-2 h^-1 for the inland snowpack and ∼110-120 nmol m^-2 h^-1 for the snow around BARC and snow on sea-ice. Light penetration (e-folding) depths at a wavelength of 400 nm measured for snowpack in the vicinity of Barrow and snow on sea-ice are ∼9 cm and 14 cm for snow 15 km inland. Fitting scaled HULIS (HUmic-LIke Substances) and black carbon absorption cross-sections to the determined snow impurity absorption cross-sections show a humic-like component to snowpack absorption, with typical concentrations of 1.2-1.5 μgC g^-1. Estimates of black carbon concentrations for the four snowpacks are ∼40 to 70 ng g^-1 for the terrestrial Arctic snowpacks and ∼90 ng g^-1 for snow on sea-ice.