Since they can be carried many hundreds of kilometres by winds, acid pollutants emitted in one country may be deposited as acid rain in other countries. As industrialisation expanded across Europe during the 1970 and 1980s, with the use of tall chimneys in industry and power generation increasing, acid deposition became a particularly prevalent problem.
Within Europe, emissions of air pollutants vary greatly, depending upon many factors such as size of population, degree of industrialisation, pollution control equipment used, agricultural practices, number of road vehicles and political attitudes on environmental issues.
Across Europe the amounts of sulphur dioxide and nitrogen oxides being emitted from a country were found to be different to the amounts of acidic pollution being deposited there. Some countries were emitting only small quantities of pollutants yet deposition was observed to be several times greater, for example in Norway, Sweden, Austria and Switzerland. Other countries such as Bulgaria, Italy, the Czech Republic and the UK emit more pollution than is deposited in their country because of prevailing wind directions.
In a response to clean up Europes air, in 1979 the United Nations Economic Commission for Europe (UNECE) implemented the Convention on Long Range Transboundary Pollution, with the aim of reducing acidic emissions. Since its implementation, sulphur emissions across Europe have fallen significantly, but with the increase in vehicle traffic nitrogen oxides emissions have been reduced only slowly. Acid rain in Europe will therefore continue to be a problem in Europe until these emissions can be dramatically reduced.