In most urban areas traffic is a dominant contributor to ambient air concentrations of

NO2. Control measures on traffic are therefore of great importance for reduction of

exceedances of health related limit values. For roadside concentrations, traffic

planning may be sufficient to reduce exceedances of short-term limit values. To

reduce long-term average concentrations in urban background and rural areas, it is

necessary to reduce the specific emissions and/or the traffic. However, there are areas,

where the contribution from point sources may be as important. Control measures for

point source emissions also need to be considered, especially for protection of the

ecosystems.

To achieve efficient reduction strategies for ambient air, the atmospheric chemical

processes must be considered. O3 and other oxidants may lead to relatively ineffective

reductions of NO2 concentration, even if the emissions of nitrogen oxides are

substantially reduced. Model calculations used for studying different emission

scenarios, must involve sufficiently detailed atmospheric chemistry.

 

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