ESTIMATE OF OZONE PRODUCTION AND DESTRUCTION OVER NORTHWESTERN EUROPE

Ozone data from more than 70 monitoring sites in the European TOR and EMEP networks from 1989 were evaluated. In summer the general spatial pattern showed a gradient in the average diurnal maximum ozone concent ration with lower values (30-40 ppb) in the northwestern part and high er concentrations (60-70 ppb) towards the southeastern part of the net works. In winter a decreasing gradient was exhibited from the northwes t to the southeast. The current UN-ECE 1-h guide value (75 ppb) for th e prevention of vegetation damage was exceeded regularly at nearly all sites; the provisional O-3 exposure limit of 300 ppb.h (product of th e residual ozone concentration above a threshold (40 ppb) value and ex posure duration) was exceeded at all monitoring sites. An estimate of the European internal production and destruction of ozone was made by analyzing the diurnal variation in ozone at European boundary layer ba ckground ''reference'' sites and ''polluted' sites. The assessment led to a summer mean internal production of 10-15 ppb in some areas in ce ntral Europe, while during winter an ozone sink was found. A complicat ing factor in this work proved to be the degree of influence of local factors, e.g. emission of oxides of nitrogen and dry deposition. This study therefore emphasizes the importance of spatial characterization of the monitoring sites.