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Average Exposure Index (AEI)

The "average exposure index" (AEI) is included as an additional provision in European Directive 2008/50/EC in order to reduce the exposure of the population to PM2.5. The AEI is a national target value and is calculated as the three-year average of the PM2.5 concentrations measured in urban background stations. For this AEI, a limit value of 20 μg/m³ and a reduction percentage to be attained by 2015 and 2020 respectively, have been established. For Belgium, this reduction percentage1 is determined by the AEI which has been calculated based on the years 2009, 2010 and 2011, and is to be attained by 2020 based on the AEI for the years 2018, 2019 and 2020.

For the calculation of the AEI, only those stations that have met the data quality objectives, i.e. for which at least 90% validated data are available, are taken into account. Table 1 gives an overview of the urban background monitoring stations selected by the three Regions for the calculation of the AEI, together with the eventually calculated (national) AEI. The rounding of the calculation complies with the Commission Implementing Decision of 12 December 2011 (2011/850/EU) (Implementing Provisions for Reporting - IPR), i.e. the rounding should be the final step of the calculation and should be performed only once. For Belgium this results in an AEI of 19.0 μg/m³. In accordance with Annex XIV of Directive 2008/50/EC, this AEI falls into category “=18 -> 22 μg/m³”, meaning that Belgium is required to reduce the AEI by 20% by 2020. This would yield an AEI of 15.2 μg/m³. The final assessment will be made on the basis of the measurements (in the same urban background monitoring stations) in the period 2018, 2019 and 2020.


1 In accordance with Annex XIV of European Directive 2008/50/EC on ambient air quality and cleaner air for Europe.

Table 1: Overview of the PM2.5 concentrations for 2009, 2010 & 2011 per urban background station to be included in the calculation of the average exposure index
Average Exposure Index