COMPARISON OF AIR-QUALITY IN STREETS OF COPENHAGEN AND MILAN, IN VIEWOF THE CLIMATOLOGICAL CONDITIONS

In most cities the traffic is the prime source of air pollution. The w ind flow determines the levels of air pollution in urban areas. For gr ound level sources, like traffic, the highest concentrations occur at low wind speed conditions. The frequency of low wind speed conditions is considerably higher in Milan than in Copenhagen. As a result of tha t, the pollution levels in Milan are much higher than in Copenhagen. A n additional factor is that the contribution of domestic heating to NO x concentration in Milan is substantial especially in winter months. I n the case of higher wind speeds, pollution levels in Milan and Copenh agen are comparable. The atmospheric stability is less important for d ispersion of pollutants from vehicle exhaust gases within the street. Urban background concentrations exhibit strong dependence on wind spee d too. The highest levels occur during conditions with a strong ground level inversion, conditions which are also characterized by low wind speed.