During the design of monitoring networks account needs to be taken of both the

number of sites and their location. It must reflect the need to measure exposure of

humans and the environment. All site groups in Table 3.1 should be considered for

inclusion in the network.

Since automatic monitoring is very expensive, it will sometimes be preferable to use

automatic monitoring in combination with indicative monitoring (passive sampling)

and/or air quality modelling to more cost effective assess the extent of high

concentration areas and the spatial variability of pollutants.

Since the limit values for exposure of humans will be for 1 hour and annual

concentrations, the measurements and other assessment tools should be applied for

these averaging times. The highest peak values of NO2 occur in street canyons, where

traffic is the main source and it is most likely that the short term value will be

exceeded here. The residence time is generally short in street canyons, but many

people may be present, when the concentration is high. The long term exposure may

be more critical at residential or suburban areas.


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