Air/snow interactions of volatile organic compounds in the Arctic

Ambient gas-phase and snow-phase measurements of formaldehyde (HCHO) were conducted at Summit, Greenland, during several summers, in order to understand the role of air-snow exchange on remote tropospheric HCHO and factors that determine snowpack HCHO. A gas-phase model was developed that included known chemistry relevant to Summit and was constrained by data from the 1999 and 2000 field campaigns. This gas-phase-only model could not account for the high ambient levels of HCHO observed at Summit in 1999 ($600 ppt). Simulations were conducted that included a snowpack flux of HCHO, based on HCHO flux measurements from 2000 and 1996. We conclude that, although the flux of HCHO from the surface likely has a significant impact on atmospheric HCHO above the snowpack, the time-dependent fluxes need to be better understood and quantified. It is also necessary to identify the HCHO precursors so we can better understand condensed phase HCHO chemistry at Summit. Peroxyacetyl nitrate (PAN) is a NOx reservoir compound that has the ability to transport NOx to remote environments, allowing for NOx photochemistry and/or deposition of nitrogen to these clean locations. Measurements of PAN have been made at Alert, Nunavut and Summit, Greenland aimed at understanding the impact of PAN chemistry on atmospheric nitrogen in the Arctic. These measurements show concentrations of PAN that are only slowly varying, even during ozone depletion events at polar sunrise, when free radical photochemistry is relatively active. We used a zero-dimensional photochemical model incorporating known gas phase chemistry to simulate the observed behavior of PAN at Alert, Nunavut and Summit, Greenland. The model simulations suggest a substantial net production rate for PAN over sunlit surfaces, which is inconsistent with the measured gas phase concentrations. These observations allow us to explore the possibility that we are missing an important sink for atmospheric PAN above snow-covered surfaces