【摘 要】
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Nitrate concentrations in Greenland snow have increased substantially since the beginning of the Industrial Revolution.This trend has been attributed to the increasing emissions of nitrate precursors,
【机 构】
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Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
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Nitrate concentrations in Greenland snow have increased substantially since the beginning of the Industrial Revolution.This trend has been attributed to the increasing emissions of nitrate precursors, particularly nitrogen oxides (NOx), as a result of intensifying fossil fuel combustion.The increasing emissions have also been used to explain an apparently similar, decreasing trend in nitrogen stable isotope ratio (15N) in snow nitrate.However, a careful examination of 200-year, subannualy resolved records of 15N, concentrations of nitrate and sulfate, and snow acidity from a central Greenland ice core shows that the 15N decrease is not always associated with increasing nitrate concentration;rather, the 15N trend is closely correlated with that of acidity, which is driven by anthropogenic emissions of precursors of acidic sulfate and nitrate.Model calculations indicate that the acidity impacts the nitrogen isotope composition through the equilibrium of particulate nitrate and gaseous nitric acid in the atmosphere.Beginning around 1970, with the onset of air pollution mitigation in North America, the acidity has leveled off,along with 15N and snow nitrate concentration.These results highlight the anthropogenic impact on snow chemical composition and the importance of including atmospheric processes in the interpretation of ice core records.
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