Monitoring street air quality in Danish towns

A monitoring system has been set up on the basis of traffic counts and calculations specified in the “Calculation Model of Air pollution in Urban Street, a Calculation Model common to the Nordic countries”. The air quality is monitored in 34 streets distributed in eight towns. The monitoring system has been tested on traffic data from the period 1985–1992. The calculations show a decrease in the levels of CO on all streets. There is also a decrease in NO2 but it does not apply to all streets. The reason for the decrease in air pollution is twofold; there is a small decrease in background levels during the last part of the calculation period, and there is a decrease in the emission factors from the individual vehicles, mainly as a consequence of the introduction of catalytic converters on new cars at the end of the period. These factors lead to reduced pollution because traffic is unchanged for all streets taken together.