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AOT40 Vegetation

O3 Jahresmittelwerte | NET60 | AOT60 | AOT40 Veg | AOT40 Wald

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. The AOT40 (= Accumulated Ozone exposure over a Threshold of 40 ppb (=80 µg/m³))for vegetation 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) in the months of May, June, July (=growth season). This indicator is designed for the protection of crops and (semi)natural vegetation. The AOT40 quantifies only ozone exposure, i.e. not the effective ozone uptake by (and therefore damage caused to) vegetation. The European target value is 18000 (μg/m³).h averaged over 5 years. The long-term objective is 6000 (μg/m³).h.

Evolution of percentiles

The figure below uses box plots to show the evolution of the minimum, the 25th percentile (P25), the 50th percentile (P50), the 75th percentile (P75) and the maximum of the ozone excess for vegetation (AOT40 for vegetation) in Belgium since 1990. The years 1994 and 2006 are clearly shown to be unfavourable ozone years for vegetation. The last 8 years are relatively favourable; the maximum excess in Belgium never exceeds the European target value of 18000 (μg/m³).h. The long-term objective of 6000 (μg/m³).h is, however, each year exceeded somewhere in Belgium.


Box plots of the ozone excess for vegetation (AOT40 for vegetation) in Belgium (1990-2015). The vegetation-weighted averages for Belgium are indicated by the blue circles. The green dotted line indicates the vegetation-weighted average of the 5-year averaged AOT40. All data were calculated using the RIO interpolation technique.

Click here for more information on how to interpret a boxplot.

Spatial trend

Just as for the other ozone indicators, the largest AOT40 for vegetation iss to be found in the southern and eastern 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, and the High Fens. In Flanders, the maxium AOT is found in Limburg. West Flanders shows the lowest AOT40 for vegetation. The European target value of 18000 (μg/m³).h avaraged over 5 years was met everywhere in Belgium. The maximum value was 13372 (μg/m³).h.


Spatial distribution of the ozone excess for vegetation (AOT40 for vegetation), 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.