Impact of Biomass Burning and Anthropogenic Emissions on the Chemical Composition of the summertime Arctic Troposphere - Aircraft Observations during POLARCAT-GRACE

We report on chemical aircraft measurements in pollution plumes transported into the European sector of the Arctic from forest fires and urban sources in North America and Siberia. Our observations were part of the POLARCAT subproject GRACE (Greenland Aerosol and Chemistry Experiment (GRACE) performed in July 2008 using the DLR Falcon research aircraft. Data were sampled during 16 flights covering altitudes up to 12 km in order to study the pathways, dispersion and chemical processing of pollution during long-range transport into the Arctic. We found that the entire free troposphere above 4 km was strongly polluted and detected more than 30 distinct pollution plumes with enhanced CO and NOy mixing ratios of up to 300 and 1.5 nmol/mol (ppbv), respectively. According to FLEXPART analysis, the plumes were sampled after transport times of 5-10 days from Canadian fires and 10-15 days from Siberian fires. Interestingly, an anthropogenic pollution plume originating from East Asia was sampled in the lowermost stratosphere at an altitude of 11.3 km after being transported over the North pole. We will discuss differences in the chemical composition of the probed pollution plumes (e.g. in the ozone mixing ratios) dependent on the source region and transport history. Simulations with a photochemical model, CiTTyCAT, were used to study the chemical evolution in the pollution plumes during transport from the measurement area to Europe