PHOTOOXIDANTS IN THE MARINE ARCTIC TROPOSPHERE IN SUMMER

The air chemistry investigations, performed on RN Polarstern during th e expedition ARK X/1 in July/August 1994, comprised a mapping of the v ertical ozone distribution by ozone soundings and the surface mixing r atios of H2O2 and NO above the East Greenland Sea between 70 degrees N and 80 degrees N. The observed H2O2 mixing ratios varied from about 1 00 parts per trillion by volume (pptv) up to around 1000 pptv, Surface ozone concentrations can be correlated with the source region of the advected air masses. Ozone mixing ratios from around 33 parts per bill ion by volume (ppbv) up to 60 ppbv have been observed in air parcels e manating from industrialized regions. In contrast, pristine Arctic air masses showed low ozone mixing ratios of about 23 ppbv. The troposphe ric part of the vertical ozone profiles occasionally exhibited signifi cant maxima above the planetary boundary layer. Apart from cases where intrusions of stratospheric ozone were obvious, photochemical ozone f ormation along trajectories originating from polluted regions was most probably the reason for layers with enhanced ozone concentrations. Th e measured surface NO mixing ratios were extremely low, typically betw een 3 and 8 pptv. Thus local photochemical surface ozone production co uld be largely ruled out. In conclusion it can be stated that in summe r, intrusion of ozone rich stratospheric air and advection of polluted air masses from lower latitudes appeared to be the dominant ozone sou rces of the marine Arctic troposphere.