[1] Photolytic production rates of NO, NO 2 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 À2 h À1 for the inland snowpack and 44 nmol m À2 h À1 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 À2 h À1 for the inland snowpack and $110-120 nmol m À2 h À1 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 mgC g À1 . Estimates of black carbon concentrations for the four snowpacks are $40 to 70 ng g À1 for the terrestrial Arctic snowpacks and $90 ng g À1 for snow on sea-ice.Citation: France, J. L., H. J. Reay, M. D. King, D. Voisin, H. W. Jacobi, F. Domine, H. Beine, C. Anastasio, A. MacArthur, and J. Lee-Taylor (2012), Hydroxyl radical and NO x 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,

[1] Snowpacks contain many carbonaceous species that can potentially impact on snow albedo and arctic atmospheric chemistry. During the OASIS field campaign, in March and April 2009, Elemental Carbon (EC), Water insoluble Organic Carbon (WinOC) and Dissolved Organic Carbon (DOC) were investigated in various types of snow: precipitating snows, remobilized snows, wind slabs and depth hoars. EC was found to represent less than 5% of the Total Carbon Content (TCC = EC + WinOC + DOC), whereas WinOC was found to represent an unusual 28 to 42% of TCC. Snow type was used to infer physical processes influencing the evolution of different fractions of DOC. DOC is highest in soil influenced indurated depth hoar layers due to specific wind related formation mechanisms in the early season. Apart from this specific snow type, DOC is found to decrease from precipitating snow to remobilized snow to regular depth hoar. This decrease is interpreted as due to cleaving photochemistry and physical equilibration of the most volatile fraction of DOC. Depending on the relative proportions of diamond dust and fresh snow in the deposition of the seasonal snowpack, we estimate that 31 to 76% of DOC deposited to the snowpack is reemitted back to the boundary layer. Under the assumption that this reemission is purely photochemical, we estimate an average flux of VOC out of the snowpack of 20 to 170 mg C m À2 h À1 . Humic like substances (HULIS), short chain diacids and aldehydes are quantified, and showed to represent altogether a modest (<20%) proportion of DOC, and less than 10% of DOC + WinOC. HULIS optical properties are measured and could be consistent with aged biomass burning or a possible marine source.

The contribution of snow photochemistry to snow and atmospheric oxidative capacity is controlled, in part, by snow albedo and e‐folding depths in snow. Albedo ande‐folding depths (and thus snow photochemistry) are a function of black carbon concentration in snow. The paper presented here demonstrates the complicated response of albedo, e‐folding depth (wavelengths 300–600 nm) and depth‐integrated production rates of NO2and OH radicals to increasing black carbon concentration in well‐characterized snowpacks of the Barrow OASIS campaign, Alaska. All snowpacks were reworked layered windpacks and were found to have similar responses to changes in black carbon concentration. The radiative‐transfer calculations demonstrate two light absorption regimes: ice‐dominated and black carbon dominated. The ice‐dominated and black carbon dominated behavior of albedo,e‐folding depth and depth‐integrated production rates with increasing black carbon concentrations are presented. For black carbon concentrations greater than 20 ng g−1 (wavelength range of 300–600 nm), e‐folding depth and depth‐integrated production rate have an inverse power law relationship with black carbon concentration. Doubling the black carbon concentration decreases thee‐folding depth to ∼70% of the initial value and for solar zenith angles greater than 60°, doubling the black carbon concentration decreases depth‐integrated production rates of NO2 and OH to ∼70% and ∼65% of their original values respectively.