Investigation of the role of the snowpack on atmospheric formaldehyde chemistry at Summit, Greenland

[1] 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. To investigate the impact of the known snowpack emission of HCHO, a gas-phase model was developed that includes known chemistry relevant to Summit and that is constrained by data from the 1999 and 2000 field campaigns. This gas-phase-only model does not account for the high ambient levels of HCHO observed at Summit for several previous measurement campaigns, predicting approximately 150 ppt from predominantly CH4 chemistry, which is similar to25-50% of the observed concentrations for several years. Simulations were conducted that included a snowpack flux of HCHO based on HCHO flux measurements from 2000 and 1996. Using the fluxes obtained for 2000, the snowpack does not appear to be a substantial source of gas-phase HCHO in summer. The 1996 flux estimates predict much higher HCHO concentrations, but with a strong diel cycle that does not match the observations. Thus, 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 the nature and importance of snowpack photochemistry.