Variations of CH2O and C2H2 determined from ground-based FTIR measurements and comparison with model results Original Research Article

High resolution FTIR observations were performed to measure the concentration of tropospheric trace gases in the Arctic at Spitsbergen (79°N, 12°E) and at mid latitudes in Potsdam (53°N, 13°E) using the sun or moon as the infrared light source. We focus the interest in this paper on two short-lived gases in the atmosphere, CH2O and C2H2. For CH2O the measurements have been compared with model simulations. Both trace gases show a strong seasonal cycle. The total columns of CH2O observed at Potsdam are higher than at Ny-Ålesund, especially during the summer, most probably caused by higher concentrations of precursors at mid latitudes. The data for C2H2 reveal similar values at Spitsbergen and Potsdam. While CH2O shows a strong diurnal cycle C2H2 does not, in agreement with the different lifetimes of both compounds. The model results for the seasonal variations of formaldehyde in Spitsbergen considering only methane oxidation as source of CH2O during the summer give 20% lower columns than the observations. We assume two reactions to be responsible for this discrepancy; DMS-transport from the North Atlantic Ocean into the high Arctic followed by oxidation to CH2O, or the photo oxidation of NMHCʹs such as propene in the Arctic. During the polar night the differences between the measurements and the model runs increase to about 50%. Also C2H2 shows high total columns during the polar night at Spitsbergen. These high columns observed during the polar night are most probably caused by precursors from mid latitudes plus photochemical reactions under sunlight conditions followed by the efficient long range transport into the high Arctic.