1. Formation of air-polluting compounds while burning oil shale;Ots;Oil Shale,1992
2. Oil shale consumption quantities in Estonia 1994;Öpik;Oil Shale,1995
3. L. Öispuu and R. Rootamm, Environmental pollution by burning pulverized oil-shale. Transactions of Tallin Technical University, Thermal Power Engineering, XLII, No. 739, 79–85 (in Estonian, English summary).
4. Components of oil-shale ash deposited on ash fields, consumed or ejcted with exhaust gases;Öispuu;Transactions of Tallin Technical University, Thermal Power Engineering,1994
5. The environmental problems in Estonia;Kallaste,1992