Measurement of loss rates of organic compounds in snow using in situ experiments and isotopically labelled compounds

Abstract

Organic molecular marker compounds are widely used to identify emissions from anthropogenic and biogenic air pollution sources in atmospheric samples and in deposition. Specific organic compounds have been detected in polar regions, but their fate after deposition to snow is poorly characterized. Within this context, a series of exposure experiments were carried out to observe the post-depositional processing of organic compounds under real-world conditions in snow on the surface of the Greenland Ice Sheet, at the Summit research station. Snow was prepared from water spiked with isotopically labelled organic compounds, representative of typical molecular marker compounds emitted from anthropogenic activities. Reaction rate constants and reaction order were determined based on a decrease in concentration to a stable, non-zero, threshold concentration. Fluoranthene-d ₁₀, docosane-d ₄₆, hexadecanoic acid-d ₃₁, docosanoic acid-d ₄₃ and azelaic acid-d ₁₄ were estimated to have first order loss rates within surface snow with reaction rate constants of 0.068, 0.040, 0.070, 0.067 and 0.047 h⁻¹, respectively. No loss of heptadecane-d ₃₆ was observed. Overall, these results suggest that organic contaminants are archived in polar snow, although significant post-depositional losses of specific organic compounds occur. This has implications for the environmental fate of organic contaminants, as well as for ice-core studies that seek to use organic molecular markers to infer past atmospheric loadings, and source emissions.

• Snow
• photochemistry
• air pollution
• Greenland
• Arctic

Acknowledgements

This project was funded by the US National Science Foundation (grant no. 0425399). We thank Brandon Shelton at the Wisconsin State Laboratory of Hygiene for sample analysis; Jack Dibb and Casey Anderson of the University of New Hampshire and Gayle Hagler at the Georgia Institute of Technology for planning and field support; Veco Polar Resources staff for servicing Summit Camp and technical support; and New York Air National Guard 109th Airlift Wing for air transit.