Abstract
Abstract. The chemistry of reactive gases inside the snowpack and in the lower atmosphere was investigated at Concordia Station (Dome C), Antarctica, from December 2012 to January 2014. Measured species included ozone, nitrogen oxides, gaseous elemental mercury (GEM), and formaldehyde, for study of photochemical reactions, surface exchange, and the seasonal cycles and atmospheric chemistry of these gases. The experiment was installed ≈1 km from the station main infrastructure inside the station clean air sector and within the station electrical power grid boundary. Ambient air was sampled continuously from inlets mounted above the surface on a 10 m meteorological tower. In addition, snowpack air was collected at 30 cm intervals to 1.2 m depth from two manifolds that had both above- and below-surface sampling inlets. Despite being in the clean air sector, over the course of the 1.2-year study, we observed on the order of 50 occasions when exhaust plumes from the camp, most notably from the power generation system, were transported to the study site. Continuous monitoring of nitrogen oxides (NOx) provided a measurement of a chemical tracer for exhaust plumes. Highly elevated levels of NOx (up to 1000 × background) and lowered ozone (down to ≈50 %), most likely from reaction of ozone with nitric oxide, were measured in air from above and within the snowpack. Within 5–15 min from observing elevated pollutant levels above the snow, rapidly increasing and long-lasting concentration enhancements were measured in snowpack air. While pollution events typically lasted only a few minutes to an hour above the snow surface, elevated NOx levels were observed in the snowpack lasting from a few days to ≈ 1 week. GEM and formaldehyde measurements were less sensitive and covered a shorter measurement period; neither of these species' data showed noticeable concentration changes during these events that were above the normal variability seen in the data. Nonetheless, the clarity of the NOx and ozone observations adds important new insight into the discussion of if and how snow photochemical experiments within reach of the power grid of polar research sites are possibly compromised by the snowpack being chemically influenced (contaminated) by gaseous and particulate emissions from the research camp activities. This question is critical for evaluating if snowpack trace chemical measurements from within the camp boundaries are representative for the vast polar ice sheets.
Highlights
Research conducted during the past ≈ 15 years has revealed an active and remarkable spatial diversity of atmospheric oxidation chemistry in the polar lower atmosphere (Grannas et al, 2007)
nitric oxides (NOx) has been shown to be formed from photochemical reactions in the snowpack (Honrath et al, 1999; Jones et al, 2000), with deposited nitrate constituting the reservoir of this chemistry
300 m3 of Special Antarctic Blend (SAB) diesel fuel are burned in the plant for electricity and heat generation per year
Summary
Research conducted during the past ≈ 15 years has revealed an active and remarkable spatial diversity of atmospheric oxidation chemistry in the polar lower atmosphere (Grannas et al, 2007). Ozone plays a fundamental role in controlling the lifetime of many atmospheric trace gases directly and indirectly by modulating atmospheric OH. The discovery of ozone production chemistry in the remote and pristine Antarctic environment was rather surprising because hitherto photochemical production in the lower atmosphere had exclusively been associated with polluted urban environments (Molina and Molina, 2004). Photochemical production and snowpack emissions of nitric oxides (NOx) have been identi-. NOx has been shown to be formed from photochemical reactions in the snowpack (Honrath et al, 1999; Jones et al, 2000), with deposited nitrate constituting the reservoir of this chemistry. NOx plays a crucial role in snow photochemical reactivity (Murray et al, 2015). NOx mixing ratios in interstitial air resulting from photochemical reactions can exceed those in the air above the snowpack by a factor of ≈ 50 (Van Dam et al, 2015)
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