Impact Type: Direct exposure to pollutant
Foot et al. (1996, 1997) have shown that heather (Calluna vulgaris) exposed to O3 has an increased susceptibility to damage from frost. This, coupled with the reduced frost hardiness due to exposure to NO2 and SO2 (Caporn et al. 2000), could have a significant effect. However, no significant effect of O3 exposure on the growth or health of Calluna has been found in summer so it is difficult to judge the potential effect of this interaction (Foot et al. 1996, 1997). The timing is relevant since peak O3 concentrations generally occur in summer.
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
AOT40 3000ppb hours over 3 months or AOT40 5000ppb over 6 months
|UNECE, 2010||expert judgement i.e. only limited or no data are avaliable for this type of receptor||
AOT40 is the Accumulated concentration Over a Threshold of 40 ppb. If an hourly average ozone concentration exceeds 40 ppb the difference between the concentration and 40 ppb is added to a running total. The units are therefore ppb multiplied by hours. For natural vegetation, the AOT40 is summed for the daylight hours for a period of three months. Daylight hours are defined as when solar radiation exceeds 50 W m-2. The daylight hours are when plant stomata are normally open.
Flux-based critical levels, based on biomass reduction, are also available for local and regional assessment but are not yet incorporated into APIS. See critical levels chapter of the UNECE Mapping Manual.