Comparison of air quality in streets of Copenhagen and Milan, in view of the climatological conditions

Abstract

In most cities the traffic is the prime source of air pollution. The wind flow determines the levels of air pollution in urban areas. For ground 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 that, the pollution levels in Milan are much higher than in Copenhagen. An additional factor is that the contribution of domestic heating to NOx concentration in Milan is substantial especially in winter months. In the case of higher wind speeds, pollution levels in Milan and Copenhagen are comparable. The atmospheric stability is less important for dispersion of pollutants from vehicle exhaust gases within the street. Urban background concentrations exhibit strong dependence on wind speed too. The highest levels occur during conditions with a strong ground level inversion, conditions which are also characterized by low wind speed.