Impact Type: Direct exposure to pollutant
Many studies have been carried out on the effects of ozone on growth of forest trees particularly coniferous species (Kress & Skelly 1982, Miller et al. 1982). Height of Scots pine growing in open-top chambers, was significantly less in ambient air than in filtered air in Headley, Hampshire (Lee et al. 1990), and a combination of acid mist and ozone caused needle chlorosis in 3-year old Scots pine seedlings (Skeffington & Roberts 1986). While few species studies have involved Scots pine it is likely that the growth of this commercial or amenity stands of this species would similarly be affected by long term exposure to ozone. However, natural stands are unlikely to be affected because of their geographical location in Scotland.
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
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 forests, the AOT40 is summed for the daylight hours over a six month period. Daylight hours are defined as when solar radiation exceeds 50 W m-2. The daylight hours are when plant stomata are normally open. Most research has been done on beech, and there is little on birch or the other species typical of birch woodland.
Flux-based critical levels, based on biomass reduction, are also available for local and regional assessment but are not yet incorporated into APIS. See ICP Vegetation Manual 2010.