Studies on the dry deposition of NO2 to coniferous species at low NO2 concentrations

Measurements of the deposition of NO₂ to seedlings of Scots pine and Norway spruce at ppbv and sub ppbv levels were made in the laboratory using a flow through chamber technique. The results show that NO₂ deposition at air concentrations above 1 ppbv was governed by stomatal uptake. The possible influence of other factors controlling the NO₂ deposition was also explored. Mean NO₂ compensation points for both Scots pine and Norway spruce were lower than 0.2 ppbv, which can be considered negligible. Throughout the experiments, there was no evidence of internal resistance to NO₂ uptake by the seedlings. At low NO₂ concentrations (0.2–1 ppbv), the NO₂ flux was generally below the detection limit of the technique.