Source-receptor relationships for airborne measurements of CO2, CO and O3 above Siberia: a cluster-based approach
1Laboratoire des Sciences du Climat et de l'Environnement/IPSL, joint unit CNRS-CEA-UVSQ, L'Orme des Merisiers, 91191 Gif sur Yvette, France
2Norwegian Institute for Air Research, Kjeller, Norway
3Laboratoire d'Aérologie, Observatoire Midi Pyrénées, CNRS-UPS, Toulouse, France
4Zuev Institute of Atmospherics Optics, SB RAS, Tomsk, Russia
Abstract. We analysed three intensive campaigns above Siberia resulting in a total of ~70 h of continuous CO2, CO and O3 measurements. The flight route consists of consecutive ascents and descents between Novosibirsk (55° N, 82° E) and Yakutsk (62° N, 129° E). Our data analysis uses clustering of footprints obtained with the Lagrangian particle dispersion model FLEXPART. The model-based technique was found to be able to separate efficiently tracers' concentrations. High CO and O3 concentrations (median values 121 ppb and 54.5 pb respectively) were found in clusters associated with fires in Kazakhstan in September 2006. High correlation (as high as R2=0.68) and robust linear relationships with regression slope between −0.10 and 0.24 ppb ppb−1 were found in individual plumes. Summer (August 2007, September 2006) uptake of CO2 was found to be largely (~50% of variance) explained by exposure to boreal and sub-arctic ecosystems, most likely by photosynthesis. This results in an average 5 to 10 ppm gradient in the August 2007 campaign. European emissions seem to contribute to high O3 concentrations above Siberia in altitude were it is also near stratospheric inputs. Large-scale deposition processes reduce O3 in the boreal and sub-arctic BL, resulting in a ~20 ppb gradient. This first attempt of Lagrangian footprint clustering is very promising and could also be advantageously applied to the interpretation of ground based measurements including calculation of tracers' sources and sinks.