Impact Type: Direct exposure to pollutant
Exposure to raised levels of nitrogen oxides can interfere with the plant's metabolism which has the effect of reducing photosynthetic activity and therefore growth (Angold 1997). Morgan et al. (1992) have shown that Hylocomium splendens is susceptible to disruption of its metabolism when exposed to high rates dry nitrogen deposition (35 nl l-1 NO2). However, plants can recover normal rates of metabolism after a pollution free period (Morgan et al. 1992).
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
|all vegetation categories||
30 µg NOX (as NO2) m-3 annual mean; 75 µg NOX (as NO2 ) m-3 24-hour mean
|UNECE 2004||Uncertainty: quite reliable i.e. the results of some studies are comparable||
The concentration units are referenced as if all the NOX were in the form of NO2. (see Unit Conversion). The level for NOX should only be applied where levels of SO2 and O3 are close to their critical levels.