Air-Snow Interactions and Atmospheric Chemistry

Abstract

The presence of snow greatly perturbs the composition of near-surface polar air, and the higher concentrations of hydroxyl radicals (OH) observed result in a greater oxidative capacity of the lower atmosphere. Emissions of nitrogen oxides, nitrous acid, light aldehydes, acetone, and molecular halogens have also been detected. Photolysis of nitrate ions contained in the snow appears to play an important role in creating these perturbations. OH formed in the snowpack can oxidize organic matter and halide ions in the snow, producing carbonyl compounds and halogens that are released to the atmosphere or incorporated into snow crystals. These reactions modify the composition of the snow, of the interstitial air, and of the overlying atmosphere. Reconstructing the composition of past atmospheres from ice-core analyses may therefore require complex corrections and modeling for reactive species.

Evolution of the Snow Area Index of the Subarctic Snowpack in Central Alaska over a Whole Season. Consequences for the Air to Snow Transfer of Pollutants

“…Snow is a material with a high surface area (1) that interacts with atmospheric chemistry through processes such as adsorption of trace gases, trapping of particles, and catalysis of heterogeneous photochemical reactions, resulting in a major impact on polar atmospheric chemistry (2). For example, measurements and models showed that falling snow adsorbs semivolatile organic chemicals (SVOCs) and removes them from the troposphere more efficiently than rain (3,4).…”

Application of thermal-dissociation laser induced fluorescence (TD-LIF) to measurement of HNO<sub>3</sub>, Σalkyl nitrates, Σperoxy nitrates, and NO<sub>2</sub> fluxes using eddy covariance

“…As the NO 2 mixing ratios are low, a compensation point may cause plants within the ecosystem to release NO 2 , as observed on the leaf scale for tropical plants (Sparks et al, 2001). As the ground was covered by snow during the winter, a direct release of NO 2 as a result of snow photochemistry could also cause emission (Domine and Shepson, 2002). A third mechanism potentially responsible for the upward NO 2 fluxes is emission of NO, either from plants (Wildt et al, 1997) or snow (Domine and Shepson, 2002), followed by reaction with O 3 in the canopy, resulting in a net observed upward flux.…”

“…As the ground was covered by snow during the winter, a direct release of NO 2 as a result of snow photochemistry could also cause emission (Domine and Shepson, 2002). A third mechanism potentially responsible for the upward NO 2 fluxes is emission of NO, either from plants (Wildt et al, 1997) or snow (Domine and Shepson, 2002), followed by reaction with O 3 in the canopy, resulting in a net observed upward flux. Fluxes of all species are significantly smaller at nighttime than daytime, likely due to the low turbulence (u * <0.17 m s −1 ) and significant attenuation.…”

Adsorption of Methylene Fluoride and Methylene Chloride at the Surface of Ice under Tropospheric Conditions: A Grand Canonical Monte Carlo Simulation Study

“…3 Moreover, recent evidence has also shown that sequestration of persistent organic pollutants in all snow-covered regions of the globe can have a significant influence on the overlying atmosphere. 4,5 As mentioned above, ice-halogen chemistry was first explored for its implication into the formation of the Antarctic ozone hole, a phenomenon in which the majority of ozone within the polar stratospheric vortex is depleted annually for months at a time. 1 It has thus been shown that halogens released from ice particles interacting with long-lived anthropogenic substances, such as chlorofluorocarbons (CFCs) in Polar Stratospheric Clouds (PSCs) are the principal cause for subsequent chemical reactions leading to ozone consumption.…”