Impact Type: Direct exposure to pollutant
The magnitude of O3 impacts on bryophytes in the UK is currently very uncertain. The largest O3 concentrations occur at high altitude sites, and the most severe bryophyte impacts are therefore expected for species at Scottish mountain sites. However, with the exception of the experimental studies of Potter et al. (1996a,b) and others, there has been little demonstration of actual species responses in the field.
Lee et al. (1998) suggest that Racomitrium lanuginosum is sensitive to acute ozone if exposure is continued for more than two days.
|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.