APPLICATION OF A PHOTOCHEMICAL GRID MODEL TO MILAN METROPOLITAN-AREA

High ozone levels are regularly reached during summer period in South- European urban areas, calling for careful design of primary pollutants emission reduction strategies. In this perspective the CALGRID modell ing system has been applied to Milan metropolitan area, located in the Po Valley, the most industrialised and populated area in Italy. For t he first modelling exercise, a simulation domain of 100 x 100 km(2) ha s been considered and a summer period, characterised by high photochem ical activity, has been selected. Hourly emissions have been derived b y spatially and temporally disaggregating national inventories data, w hile standard upper-air and ground-based meteorological data have been used as input to the CALMET pre-processor. A careful analysis of simu lation results versus local network monitoring data has revealed some critical points, related to both modelling assumptions and practical d ata availability. A satisfactory reproduction of daytime ozone behavio ur has been, in fact, accomplished, both in urban and suburban sites, while nighttime primary pollutants accumulations and consequent ozone consumption simulated by the model have not found correspondence in th e measurements. Nitrogen dioxide has been also successfully modelled, mostly in city surroundings, whereas higher discrepancies have been fo und in some urban stations. Possible explanations of these facts are d iscussed in the paper, giving an insight for further work. (C) 1998 El sevier Science Ltd. All rights reserved.