| Summary: | We present aircraft-borne observations of Asian pollution in the upper troposphere and lowermost stratosphere above Greenland. The measurements were performed within the GRACE campaign (Greenland Aerosol and Chemistry Experiment), a sub-project of the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) initiative. The GRACE campaign was conducted in summer 2008 and aimed to study the influence of both boreal forest fire and anthropogenic emissions on the composition of the UT/LS in the summer-time Arctic. We used the DLR Falcon operated from Kangerlussuaq (Greenland) and performed a total of 16 flights up to altitudes of 12 km. Here we focus on measurements of a flight on 10th July 2008, where we probed an air mass with unusually high CO, PAN and H2O mixing ratios of up to 136 nmol mol-1, 350 pmol mol-1 and 80 µmol mol-1, respectively. The air mass was encountered at 11.3 km altitude, well above the dynamical tropopause. In-situ measurements of ozone, NO, and NOy indicate that this layer was a mixed air mass containing both air from the troposphere and stratosphere. Backward tracer and trajectory analysis with FLEXPART and LAGRANTO suggest that we probed the top of a polluted air mass originating from the coastal regions of South East Asia. This anthropogenic pollution experienced strong up-lift to more than 10 km altitude in a warm conveyor belt (WCB) located over the Russian east-coast. Due to a low pressure system moving from Siberia towards Spitsbergen, the polluted air mass was transported across the North Pole into the sampling area, hereby up-lifting the local tropopause by ~2.5 km. Mixing with Arctic stratospheric air most likely took place along the sides of the plume when the tropospheric air mass was stretched into long and narrow filaments. The transport pathway presented in this study could be an important mechanism to bring pollution into the polar lowermost stratosphere.
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