Ozone Exposure Indexes AOT 40

Cumulative effects of agricultural crops, forest stand and other ecosystems exposure above the definite threshold level are characterised by the so called exposure index (AOT40), expressed in units of ppb.h. According the UN/ECE experts the value of 40 ppb is the proposed threshold level of O₃ concentration. The critical AOT 40 level of 3 000 ppb.h responds to decrease in agricultural crops yield by 5 %. AOT 40 level is calculated for daily hours, from May to July. Preliminary proposed short-time critical value of AOT 40 for noticeable harm to agricultural crops is 500 ppb.h at high saturation deficit and 200 ppb.h at low saturation deficit. This value is calculated for daily hours during 5 consecutive days. Preliminary proposed critical level for forests protection in Europe is 10 000 ppb.h. In this case cumulating is also calculated for daily values but during the 6 months period (April - September). It is recommended to use the same critical AOT 40 value for native vegetation as the one for agricultural crops.

Within the whole Slovak territory, ozone exposure indexes AOT40 regarding agricultural crop and forest ecosystems were exceeded. At the upper tree line, the value doubled.