Decreased albedo, e ‐folding depth and photolytic OH radical and NO 2 production with increasing black carbon content in Arctic snow

Abstract

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 and e‐ 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 NO 2 and 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 the e ‐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 NO 2 and OH to ∼70% and ∼65% of their original values respectively. With ~10‐20 ng g‐1 of black carbon (BC) in snow, absorption becomes BC dominated Doubling black carbon reduces the e‐folding depth to ~70% of its initial value Doubling black carbon decreases F(OH) and F(NO2) to ~70% and ~65% respectively