INCREASING CONCENTRATIONS OF NITROGEN-DIOXIDE POLLUTION IN RURAL WALES

Monitoring of nitrogen dioxide pollution was carried out in rural envi ronments throughout Wales during a 1-year survey to quantify any chang es in background concentrations and distribution of the pollutant sinc e an earlier survey in 1986. There were 23 sites in the present survey of which 16 had been monitored during the 1986 survey. The remaining 7 sites were based on moorland in mid-Wales within map squares for whi ch critical loads for soil acidification are expected to be exceeded b y the year 2005. All sites were chosen so as to be remote from major l ocal sources of NO2 and the values obtained were deemed to be minimum concentrations for the different regions. Measurements were made using diffusion tubes which aimed to provide mean concentrations of NO2 for 2-week exposure periods. Concentrations of NO2 were found to be highe r in the winter months for most sites and this is probably related to a greater use of fossil fuels for heating buildings at this time of ye ar. The exception was the high concentrations of NO2 in May and June f or several sites in North Wales, and in July and August for a site on Mount Snowdon. These high summer concentrations in North Wales are tho ught to be related to increased traffic associated with tourism. It is apparent that there has been a substantial increase in rural concentr ations of NO2 throughout Wales since the earlier survey of 1986. As an average of all 16 sites used in both surveys, there was a 53% increas e in the annual mean concentration of NO2. Also, it is evident that, s ince 1986, there has been a substantial increase in the area of south- eastern Wales which has a background level in excess of 10 ppb NO2 and a notable reduction in land area with concentrations below 6 ppb NO2 as an annual mean concentration. The possible future impact of increas ing rural concentrations of NO2 on Welsh vegetation is discussed with references to estimates of critical levels of NO2 for adverse effects on plants.