What are the concentrations that may not be exceeded?

The European Union introduced threshold values for particulate matter (PM10) in 1999. According to the European Directive 1993/30/EC, from 2005 onwards, annual mean PM10 concentrations may not exceed 40 µg/m³ and the daily mean PM10 concentration may only exceed 50 µg/m³ on maximally 35 days per year. In this so-called 'first daughter directive'  further indicative (phase 2) threshold values (to be respected from 2010 onwards) were established: an annual mean of 20 µg/m³ and a daily limit value of 50 µg/m³ not to be exceeded on more than 7 days per year.

In 2008, this directive (along with other directives) was replaced by the new 'cleaner air for Europe' directive (2008/50/EC). The threshold values for PM10 from the 1999 directive were used, but the stricter phase 2 tresholds were replaced by limitations for the smaller (and thus more dangerous concerning health) PM2.5. In addition to target and limit values, an exposure concentration obligation was established for PM2.5. This last obligation is based on an average exposure index (AEI) that is calculated based on measurements in urban background stations (spread across Belgium). In these stations, measurements need to be representative for the exposure of the urban population. The AEI is the progressive mean of the (annual mean) concentrations in these rural background locations, calculated over three calendar years.

PM₁₀

PM2.5