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 caused 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 μg m-3) was surpassed in 1% (~35 km2) of the study area where the load was 30–40 μg m-3. No effect of long-term SO₂ concentrations of up to 10–11 μg m-3 (0.5-h max up to 270 μg m-3) and simultaneous fly ash loads of up to 95 μg m-3 (1000 μg 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 average 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.