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OZONE UPTAKE TO POLAR AND MID-LATITUDE SNOWPACKS

BOCQUET, FLORENCE  Instaar.
Rick, Ursula K  Instaar.
Helmig, Detlev  Instaar.

Previous research in Polar Regions has demonstrated that chemical and physical interactions between the snowpack and the overlying troposphere have a substantial impact on the composition of the lower atmosphere. The deposition of atmospheric trace gases and aerosols during the cold and dark winter results in an accumulation in the snowpack, which subsequently acts as a chemical reservoir. During polar sunrise, under conditions of increasing temperature and solar radiation, this reservoir is activated by photochemical reactions which result in the formation, depletion and cycling of important atmospheric gases.

During the Northern hemisphere summer of 2003, atmospheric and snowpack ozone chemistry was studied at Summit, Greenland (72.34N, 38.29W, 3200 m). Diurnal trends in the boundary layer, ozone deposition to the snowpack and photochemical depletion of ozone in the firn air (30 cm depth) were investigated. Ambient ozone levels were between 40 and 50 ppbv. Ozone in the firn air exhibited distinct diurnal cycles which correlated with incoming solar radiation. During nighttime, ozone in the snowpack equilibrated with ambient levels, whereas under conditions of high incoming shortwave radiation, ozone in the snowpack was substantially depleted. These data strongly support the hypothesis that ozone deposition to the polar snowpack is driven by solar radiation and consequently has strong diurnal and seasonal dependencies.

During the winter 2003-04, a similar ozone study was conducted at the Soddie site, Niwot Research Station, Colorado (40.04N, 105.54W, 3340 m). Besides in ambient air, ozone was measured in the seasonal snowpack at ground level and at 30, 60 and 90 cm above ground. In contrast to the Summit observations, very low ozone levels were found in the Niwot ridge snowpack. It appears that the snow physical and chemical properties (seasonal versus perennial snow) influence the degree of ozone uptake to the snowpack.

Previous literature reports conflicting findings on ozone depletion or ozone accumulation in the snowpack. These observations may be due to the varying snowpack characteristics. Our continuing research will investigate ozone snowpack chemistry in other Arctic, Antarctic, as well as mid-latitude environments to further elucidate ozone fluxes and their dependency on the snowpack chemical composition and physical micro and macro structure.


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