Biomass burning pollution in the summer time Arctic atmosphere : Development and deployment of a novel airborne CI-ITMS instrument for PAN detection

The present work aims for a better understanding of the reactive nitrogen and ozone budgets of the Arctic summer atmosphere. Special focus is paid to the organic nitrogen compound PAN (Peroxyacetyl nitrate), which as temporary reservoir species plays a key role especially during longrange transport of pollutants. For the first time, a chemical ionization - ion trap mass spectrometer (CI-ITMS) was equipped with an I- ion source for the detection of PAN. The new FASTPEX (Fast Measurement of Peroxyacyl nitrates) instrument successfully was deployed aboard the research aircraft Falcon during POLARCAT - GRACE campaign (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport - Greenland Aerosol and Chemistry Experiment) in summer 2008, which was conducted within the framework of the International Polar Year (IPY) 2007 - 2009. Continuous in-flight calibrations were performed using a newly set-up isotopic PAN calibration source. An in-flight intercomparison during GRACE showed very good agreement between the PAN measurements of the new FASTPEX instrument and the PAN measurements aboard the research aircraft NASA DC8. The GRACE measurements revealed that the Arctic free troposphere in summer is heavily perturbed by aged inflow from the boreal fire regions of Canada and Siberia. PAN was found to be the dominant reactive nitrogen species at altitudes between ca. 4 and 9km. While nitrogen oxide (NO) in the free troposphere was close to the detection limit of several pmol/mol, PAN was abundant at median mixing ratios of ca. 300pmol/mol. Low photochemical ozone formation was observed in imported pollution plumes. This is the result of fast conversion of NOx (NOx =NO+NO2) to PAN in young fire emissions, in combination with the high thermal stability of PAN during subsequent transport towards Greenland. A detailed case study provided first observational evidence of an efficient transport pathway for surface emissions into the lowermost stratosphere, which was previously suggested by model simulations. The anthropogenic pollution was detected by enhanced mixing ratios of PAN and CO above the tropopause. Air mass trajectory calculations showed that the Asian emissions were lifted within a warm conveyor belt (WCB) and reached the lowermost stratosphere within a few days after emission