SPATIAL AND TEMPORAL VARIATION IN NITROGEN-DIOXIDE POLLUTION ADJACENTTO RURAL ROADS

Concentrations of nitrogen dioxide were measured near to a major, mino r and unclassified (serving only a few farmhouses) road in Snowdonia N ational Park, North Wales. Diffusion tubes were place along transects, at right angles to the roads, and changed weekly. Background concentr ations of NO2, recorded for comparison at a remote site, 2 km from the nearest road, were up to 40% higher in winter than in summer. Close t o the major road this pattern was reversed, with concentrations 50-60% higher in summer than winter. Near the major road, monthly mean conce ntrations were consistently higher than those found 250 m away, by up to 20 nl L-1 NO2. Near the minor road, concentrations of NO2 were 6-10 nl L-1 higher than at 250 m away but only during summer months (touri st season). There were no differences between mean NO2 concentrations at 1 and 250 m from the unclassified road. The concentrations of NO2 n ear to the major and minor roads exceeded UN-ECE critical levels. It i s concluded that many roadside plant communities are threatened by NO2 pollution toxicity.