All data below are the result of the RIO interpolation technique, in which the measurement observations are interpolated to a 4x4 km² grid resolution. Locally, concentrations can be higher or lower.
The European Union has defined an excess indicator for the protection of vegetation and forests. The AOT40 for forests (= Accumulated Ozone exposure over a Threshold of 40 ppb (=80 µg/m³)) is the accumulated excess of hourly ozone concentrations above 80 µg/m³ between 8:00 and 20:00 CET (Central European Time = Universal Time (UT) +1) over the period April-September. This indicator quantifies only ozone exposure, i.e. not the effective ozone uptake by (and therefor damage caused to) vegetation.
Just as for the other ozone indicators, the largest AOT40 for forests was to be found in the southern part of the country, where also most forest resources are situated. The largest AOT40 was recorded in particular in the area below the Samber and Meuse valley. The maximum in 2015 totalled 21493 (µg/m³).h. Less than 1% of Belgian forests were exposed to an AOT40 above the reference value of 20000 (µg/m³).h. Yet in virtually all forest resources (95%) the AOT40 exceeded the critical UNECE level of 10000 (µg/m³).h.
Spatial distribution of the ozone excess for forests (AOT40 for forests), 5-year average 2011-2015. 'No data' means that the data do not meet the criteria set out in 2008/50/EC Annex VII for aggregating the measurement data. All data were calculated using the RIO interpolation technique.