Atmospheric chemistry

Contributions to the understanding of polar atmospheric chemistry and its reconstruction over the past centuries through ice cores include: the characterization of summer boundary layer levels of hydrogen peroxide, organic peroxides, formaldehyde, acetaldehyde and acetone in air above the snow pack and in the interstitial pore space in the firn. Data will be used to estimate the HOx radical budget with photo-stationary state models.

US ITASE has undertaken the first quantitative measurements of higher organic peroxides over West Antarctica and demonstrated that they consist exclusively of methylhydroperoxide. Trifluoroacetate (a product of atmospheric degradation of HFCs and HCFCs) is also measured in snow pits to develop a better understanding of the processes that control deposition of trifluoroacetate in polar snow because there is concern that this highly stable, man-made molecule will accumulate in the hydrosphere.

Results from US ITASE atmospheric studies will further elucidate the impact of the upper snow pack on levels of atmospheric trace gases in the boundary layer. Measurements of hydrogen peroxide and formaldehyde in air, snow pits, and ice cores are used to validate existing physical atmosphere-snow transfer models and to develop a spatial picture of preservation of these species in snow and firn, Initial results from U.S. ITASE cores demonstrate that the seasonal signal of hydrogen peroxide is preserved at sites where the accumulation rate is sufficiently high and the mean annual temperature sufficiently low.

Figure 6 – Covariance of atmospheric circulation with time series from the Antarctic ice sheet surface and from global climate indices. A) Contours show covariance of annual 500 mbar geopotential height (NCEP/NCAR reanalyses) with the Southern Osciallation Index (sign reversed to illustrate the typical pressure anomaly pattern characteristic of an El Niño year). Colors show covariance with the 2nd principal component (time variation of the spatial pattern) of ice sheet surface temperature derived from passive microwave satellite observations (Schneider and Steig, 2002). B) Contours and colors show covariance of springtime 500 mbar geopotential height with sodium concentrations in ITASE core 2000-01 (central West Antarctica) after Kreutz et al. (2000).