Measurements of hydrogen peroxide and formaldehyde exchange between the atmosphere and surface snow at Summit, Greenland

Tower-based measurements of hydrogen peroxide (H2O2) and formaldehyde (HCHO) exchange were performed above the snowpack of the Greenland ice sheet. H2O2 and HCHO fluxes were measured continuously between 16 June and 7 July 2000, at the Summit Environmental Observatory. The fluxes were determined using coil scrubber-aqueous phase fluorometry systems together with micrometeorological techniques. Both compounds exhibit strong diet cycles in the observed concentrations as well as in the fluxes with emission from the snow during the day and the evening and deposition during the night. The averaged diet variations of the observed fluxes were in the range of + 1.3 x 10(13) molecules m(-2) s(-1) (deposition) and -1.6 x 10(13) molecules m(-2) s(-1) (emission) for H2O2 and + 1.1 x 10(12) and -4.2 x 10(12) molecules m(-2) s(-1) for HCHO, while the net exchange per day for both compounds were much smaller. During the study period of 22 days on average (0.8(-4.3)(+4.6)) x 10(17) molecules of H2O2 were deposited and (7.0(-12.2)(+12.6)) x 10(16) molecules m(-2) of HCHO were emitted from the snow per day. A comparison with the inventory in the gas phase demonstrates that the exchange influences the diet variations in the boundary layer above snow covered areas. Flux measurements during and after the precipitation of new snow shows that < 16% of the H2O2 and more than 25% of the HCHO originally present in the new snow were available for fast release to the atmospheric boundary layer within hours after precipitation. This release can effectively disturb the normally observed diet variations of the exchange between the surface snow and the atmosphere, thus perturbing also the diet variations of corresponding gas-phase concentrations. (C) 2002 Elsevier Science Ltd. All rights reserved.