THE DISTRIBUTION OF NMHC IN EUROPE - RESULTS FROM THE EUROTRAC TOR PROJECT

Within the EUROTRAC sub project TOR, an European network of advanced m onitoring stations situated at representative sites is operated, start ing in 1988. Within the EMEP Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe measurements of VOC started in August 1992. In this study the combine d TOR-EMEP data base has been used. Sector analyses have been performe d in order to distinguish between unpolluted and the polluted air mass es at each site. The seasonal averages have been calculated for each s ector and site, and the results are discussed. Data allocated to the u npolluted sectors represents the common European background, and in th e winter similar NMHC concentrations are found at all sites north of 5 0 degrees N. These sites cover the area from North Europe into the Arc tic (79 degrees N), and the small north-south gradient indicates that NMHC builds up in the northern troposphere in winter, probably due to an efficient meridional mixing and slow photochemical reactions.