The indoor air quality is outside the scope of the FWD, but the indoor air quality is

significantly influenced by the outdoor air quality, which means that outdoor air

quality monitoring is relevant for estimates of the contribution to the indoor exposure.

The suggested design of the network is i.e. based on experiences with design of

networks in Italy (Allegrini, 1996), Denmark (Palmgren, 1995) and discussions in the

working group. The NO2 levels in an urban area is a result of,


· the rural background air pollution, which is the NO2 pollution transported over

long distances, e.g. from other urban areas or by recirculation in the region. The air

pollutants have had time to react with other components of the atmosphere. The

rural background concentration is measured away from local emission sources.


· the urban background air pollution, which is the rural background plus the air

pollution from the urban area. This air pollution is a result of the emissions in the

city as a whole, the dispersion conditions and many chemical reactions. ,


· the local air pollution, which is the air pollution close to the emission sources, e.g.

traffic or point sources . Only the fastest chemical reactions are important for the

local emitted pollutants. The concentrations of these pollutants are mainly

determined by the dispersion.


Air pollution at all three levels must be taken into account in order to obtain a total

description of the NO2 pollution in an urban area.

page 35


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