Measurements of lower carbonyls and hydrocarbons at Ny-Alesund, Svalbard.

Measurements of gaseous organic compounds were carried out near Ny-Alesund, in the Norwegian Arctic, during September 2004. Twenty alkanes, alkenes and aromatic hydrocarbons from ethane to toluene and six aldehydes and ketones from formaldehyde to butanal, were identified and quantified in air samples. Hydrocarbons showed a quite uniform distribution, with ethane being by far the most abundant component (> 1 ppb), followed by propane (> 0.4 ppb) and butanes (> 0.3 ppb), while for unsaturated homologues, except ethene, concentrations never exceeding 0.05 ppb were observed. This distribution confirmed that hydrocarbon depletion during the transport time from Europe into the Arctic was depending upon their atmospheric lifetimes, calculated relatively to the OH reactivity scale. The presence of short lived hydrocarbons could be associated to local sources of anthropogenic and/or biogenic origin. Although the local air photochemistry played a primary role in the production of lower aldehydes in late summer, the observed mixing ratios of formaldehyde (in the 0.25 - 0.50 ppb range) could not be fully explained by known gas-phase chemistry. In this case additional sources, such as fluxes of formaldehyde from snow pack to the atmosphere and/or local anthropogenic activities, were to be taken into consideration. The possible influences of these sources on HCHO mixing ratios were analysed by means of a backward-trajectory circulation model.