Strong similarities between night-time deposition velocities of carbonyl sulphide and molecular hydrogen inferred from semi-continuous atmospheric observations in Gif-sur-Yvette, Paris region

We investigated the diurnal variations of atmospheric carbonyl sulphide (COS) during 2011 at Gif-sur-Yvette, a suburban atmospheric measurement site in France. These data were collected semi-continuously in parallel with hydrogen (H2), carbon monoxide (CO) and 222Radon (222Rn) measurements. Fluxes and deposition velocities were calculated for nocturnal situations of low boundary layer height using the Radon-Tracer Method. Contrary to CO and H2, the diurnal cycles of COS are not impacted by emissions from nearby automobile traffic. In the absence of local anthropogenic combustion sources, COS and H2 mole fractions generally show similar temporal variations with night-time depletion coinciding with 222Rn accumulation during stable nocturnal conditions. Nocturnal COS deposition velocities range from 0.07 to 0.40 mm s−1, with an annual mean of 0.18±0.12 mm s−1 (n=14). We found strong similarities between COS and H2 dry deposition velocities in terms of annual mean and ranges of variation, and data showed linear correlation between the two. This study provides new evidence of the loss of COS near the ground via non-photosynthetic processes. Although the dominant sink of atmospheric H2 is diffusion and subsequent destruction in soils, it is not all certain that COS is taken up at night solely by soils.