| Summary: | International audience Despite their potential relevance to atmospheric environment issues, measurements in Siberia, in the outflow of Europe and upstream of Eastern Asia and the Arctic, are sparse. Impacts of remote and regional sources on this air shed’s composition remain virtually unexplored. We document the tropospheric composition and address these issues using CO2, CO, O3 and novel CH4 measurement data from the 2010 YAK-AEROSIB intensive airborne campaign over Siberia. The campaign took place in April, spring being highly relevant here because of longer lifetime of pollutants, transported especially to the Arctic. We analysed the data by comparing trace gases concentrations enhancements, FLEXPART simulations of backward transport and by comparison with other campaigns. We illustrate our findings by three case studies. Typical observed mixing ratios of trace gases were 394 ppm CO2, 140 ppb CO, 59 ppb O3 and 1843 ppb CH4 across the campaign. CO2 increased by ~4 ppm relative to a similar 2006 spring campaign (Paris et al., 2010), a slightly slower pace than the hemispheric increase of 1.75 ppm/yr (as estimated over the period 2006-2008). This difference could be due to different transport pattern, with more air from the Arctic, and hence less affected by pollution, than in 2006; vegetation respiration is low in largely snow-covered Siberia. CO mixing ratio is also ~5 ppb lower than our 2006 spring values, possibly also explained by a pervasive airmass of Arctic origin in 2010. But large enhancements of CO and other trace gases have been observed. CO enhancements were connected to biomass burning through tracer correlation and FLEXPART simulations convolved with fire emissions. We find that contributions from fires in agricultural areas in Western Russia and Northern Kazakhstan influence significantly CO concentrations over Siberia (+50 ppb) strongly correlated (r=0.86) to an O3 enhancement of ~+5 ppb (regression slope 2.5 ppb/ppb). O3 concentrations as high as 210 ppb were observed during flight from ...
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