New Insights on the Chemical Composition of the Siberian Air Shed from the YAK-AEROSIB Aircraft Campaigns

International audienceThere are very few large-scale observations of the chemical composition of the Siberian airshed. The Airborne Extensive Regional Observations in Siberia (YAK-AEROSIB) French-Russian research program aims to fill this gap by collecting repeated aircraft high-precision measurements of the vertical distribution of CO2, CO, O3, and aerosol size distribution in the Siberian troposphere on a transect of 4,000 km during campaigns lasting approximately one week. This manuscript gives an overview of the results from five campaigns executed in April 2006, September 2006, August 2007, and early and late July 2008. The dense set of CO2 vertical profiles, consisting of some 50 profiles in each campaign, is shown to constrain large-scale models of CO2 synoptic transport, in particular frontal transport processes. The observed seasonal cycle of CO2 in altitude reduces uncertainty on the seasonal covariance between vegetation fluxes and vertical mixing, known as the "seasonal rectifier effect." Regarding carbon dioxide, we illustrate the potential of the YAK-AEROSIB data to cross-validate a global CO2 transport model. When compared to the CO2 data, the model is likely to be biased toward too-weak mixing in winter, as it overestimates the CO2 vertical gradient compared to the observation. Regarding pollutants, we illustrate through case studies the occurence of CO enhancements of 30-50 ppb above background values, coincident with high O3. These high CO values correspond to large-scale transport of anthropogenic emissions from Europe, and to wildfires in the Caspian Sea area, over much cleaner Arctic air (September 2006). An occurence of extremely high CO values above 5,000 km in eastern Siberia is found to be related to the very fast transport and uplift of Chinese anthropogenic emissions caused by a cold front (April 2006)