The long-term critical level of ozone for crops of an AOT40 of 3000 ppb.hours for May-July (used as a typical growing season) and for daylight hours was used to define areas at risk where the critical level is exceeded.
The long-term critical level for ozone:
Definition
An AOT40 of 3000 ppb.h accumulated over three months.
The critical level is the concentration of pollutants in the atmosphere above which adverse effects occur on sensitive receptors, such as plants, ecosystems or materials according to present knowledge. This critical level was derived experimentally using open-top chambers to expose field-grown wheat to ozone. The data from spring wheat experiments in 6 countries, 10 seasons and with 10 cultivars were used to derive an exposure response relationship with an r2 of 0.88. The AOT40 associated with a 5% reduction in yield, 3000 ppb.h, was accepted as the critical level of ozone for yield reduction in crops.
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