The annual mean limit value is 40 µg NO2/m3. Over the years 2001-2010 the total population, for which exposure estimates are made, increased from 93 to 124 million people due to an increasing number of monitoring stations reporting air quality data under the Exchange of Information Decision. Year-to-year variations in exposure classes are partly caused by the changes in spatial coverage. Only urban and sub-urban background monitoring stations have been included in the calculations. Data for Cyprus, Greece and Malta, are not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities.
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