SO2 is a suffocating gas with a sharp scent, formed by the burning of materials containing sulfur. It is a gas that, in typical ambient air concentrations, can react with humidity in the air thus forming sulfur acid. In combustion of fuel containing sulfur, the sulfur oxidizes to SO2, further reacting with other polluting substances and thus forming aerosols. In liquid form it can be found in the clouds, fog, rain, aerosol and on the surface of the particles. SO2 is also the main precursor of PM2.5. Sulfur dioxide is mainly formed by coal combustion, especially in electricity producing installations. This pollutant is released from industrial processes in smelters, oil refineries, paper and pulp processing industries, metal industry as well as in transport.
High concentrations of this pollutant, in the form of acid rains, disturb the fish population in rivers and lakes and adversely affect forest soil. It also causes high level damage of ecosystems, including chlorophyll degradation, reduced photosynthesis and changes in the protein metabolism. The deposition of pollution caused from emissions of sulfur dioxide cause acidification of soils and waters and consecutive loss of biodiversity quite often at places on great distance from the original emission.