THE OZONE PATTERNS IN THE AEROLOGICAL BASIN OF MILAN (ITALY)

In the last years, photochemical pollution has been recognised as a cr itical environmental problem. Summer smog episodes occur over large pa rts of Europe and also in the North of Italy high ozone concentrations are measured. A working group is investigating the ozone distribution and estimating the contribution of breeze circulations transport to t he actual ozone levels measured in the territories of the provinces of Milan, Bergamo, Varese and Come in Northern Italy. In this paper the principal results of this outstanding study are presented. Times serie s of ozone concentrations measured in the last years by the four provi ncial air pollution networks, including 18 monitoring sites, have been analysed by comparing trends and frequency of exceedances of air qual ity standard limits. Moreover, a statistical analysis has been made to evaluate similarity among measured ozone concentrations in terms of l evels and temporal variability (frequency and peaks distribuiton, dail y shape etc.). This study covers the summer period from June to Septem ber 1992 and uses the measured 1-h ozone concentrations in two differe nt test cases. The first case considers daytime ozone data (9:00-20:00 ); the second one also includes night-time ozone data (0:00-24:00). Th e method developed is based on hierarchical Cluster Analyses technique s. Every group has been well characterized by an averaged hourly conce ntration and relative variance. The statistical analyses has shown a s ummer time gradient of surface ozone concentrations going from south t o north of the area under study and interesting similarities among mon itoring sites in the day-time maximum peak occurrence. Copyright (C) 1 996 Elsevier Science Ltd