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

Abstract

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 NOx 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.