Air pollution - State and impacts (Belgium)

Population exposure to ozone

The European target value for ozone for the protection of human health is 120 μg/m³ (as the daily highest eight-hourly mean) not to be exceeded on more than 25 days per calendar year averaged over three years.

The percentage of the Belgian population potentially (*) exposed to ozone concentrations above the EU target (light blue bars) was around 20 % in 2003 (based on the exceedances above the daily highest eight-hourly mean of 120 µg/m³ in the years 2001, 2002 and 2003) and 2005 (based on annual exceedances in 2003, 2004 and 2005). These were the highest exposures during the last decade and were due to the extremely hot and dry summer of 2003.

During warm and sunny summers (2003, 2006) around 70 % of the Belgian population is potentially exposed to ozone concentrations higher than 120 μg/m³ (as the daily highest eight-hourly mean) on more than 25 days per year (dark blue dots). There is no clear trend but under comparative meteorological conditions, the duration and intensity of ozone peaks (and consequently the population exposure) have been decreasing in later years. This is due to decreasing emissions of ozone precursors (NOx and VOC).

The long-term objective for ozone for the protection of human health is no more exceedances of 120 μg/m³ (as the daily highest eight-hourly mean). This objective is even in very favorable meteorological years far from reachable. Since 1990 (with exception of 1991 and 2007) the entire Belgian population was potentially exposed to ozone concentrations above 120 µg/m³ on at least one day.

Ozone pollution will only experience a long-lasting decrease when the ozone precursor emissions are drastically reduced, not only in Europe but also in the whole northern hemisphere. 

 (*) NOTE: population exposure was calculated using the combination of population density maps and concentrations calculated by an ’intelligent‘ interpolation model (RIO-corine, Janssen et al., 2008). This interpolation technique has a resolution of 5x5 km and calculates the ozone concentrations for every 5x5 km gridcell. It is assumed that the total population living in a 5x5 gridcell will be exposed to concentrations that are higher than the limit values, when the interpolated concentrations exceed these limit values. When the interpolated concentrations are below the limit values, it is assumed that not everybody in the corresponding gridcell is exposed.