Specifics and temporal changes in air pollution in areas affected by emissions from oil shale industry, Estonia

Atmospheric air pollution levels and long-term effects on the environment c aused by simultaneous presence of SO2 and oil shale alkaline fly ash during the last five decades (since 1950) were investigated. The annual critical value of SO2 for forest (20 mug m(-3)) was surpassed in 1% (similar to 35 k m(2)) of the study area where the load was 30-40 mug m(-3). No effect of lo ng-term SO2 concentrations of up to 10-11 mug m(-3) (0.5-h max up to 270 mu g m(-3)) and simultaneous fly ash loads of up to 95 mug m(-3) (1000 mug m(- 3)) on the growth and needle longevity of Pinus sylvestris was established. The yearly deposition (average load up to 20-100 kg S ha(-1)) was alkaline rather than acidic due to an elevated base cation deposition in 1960-1989. Since 1990, the proportion of SO2 in the balance of components increased: about 70-85% of the total area was affected while the ratio of annual avera ge concentrations of SO2 to fly ash was over 1. The limit values of fly ash for Sphagnum mosses and conifers in the presence of SO2 are recommended.