EFFECTS OF REDUCTION OF NOX ON THE NO2 LEVELS IN URBAN STREETS

Nitrogen dioxide is a major problem in urban areas. Persons suffering from respiratory diseases, especially asthma patients, are sensitive t o NO( )at high concentrations. Nitrogen oxide emissions from private c ars have decreased due to the introduction of catalysts. However, the catalyst technique is today limited to petrol vehicles. Since heavy di esel vehicles, e.g. buses, contribute significantly to the NOx emissio ns, this will limit the reduction in emissions in many urban streets. Another factor is the continued increase in the car fleet in all count ries. Most of the NOx from traffic is emitted as NO, which is thought to be harmless. NO is rapidly transformed to NO2 by a reaction with oz one in the air. Tropospheric ozone levels have been increasing in Euro pe for many years as a consequence of increasing pollution. Ozone in D anish streets is seen to be the limiting factor for the production of NO2. Thereby O-3, is also the limiting factor for the NO2 levels in th e streets. In this paper the above will be supported both by observati ons from the Danish air quality measurement programmes and by model si mulations with the Danish Operational Street Pollution Model.