STUDIES ON THE DRY DEPOSITION OF NO2 TO CONIFEROUS SPECIES AT LOW NO2CONCENTRATIONS

Measurements of the deposition of NO2 to seedlings of Scots pine and N orway spruce at ppbv and sub ppbv levels were made in the laboratory u sing a flow through chamber technique. The results show that NO2 depos ition at air concentrations above 1 ppbv was governed by stomatal upta ke. The possible influence of other factors controlling the NO2 deposi tion was also explored. Mean NO2 compensation points for both Scots pi ne and Norway spruce were lower than 0.2 ppbv, which can be considered negligible. Throughout the experiments, there was no evidence of inte rnal resistance to NO2 uptake by the seedlings. At low NO2 concentrati ons (0.2-1 ppbv), the NO2 flux was generally below the detection limit of the technique.