Sulfur dioxide (SO2) was formerly viewed as the most important phytotoxic pollutant in Europe,
and until the early 1980s was the subject of the greatest research in this field.
It has since attracted less attention because of its declining concentrations in much of western and northern Europe,
as emissions have been reduced,
and also because nitrogen gases and ozone have been found to be of increasing significance. Nevertheless,
it presents a potential threat to vegetation in many parts of Europe,
in particular in the heavily industrialized regions of the Czech
Republic, Poland and the eastern part of Germany.