These fossil fuels are also the source of most emissions of carbon dioxide, which contributes to climate change. Most comes from burning coal and oil, during which the sulphur in the fuel is converted into sulphur dioxide. Nitrogen oxides are always produced during combustion. More than half of the emissions in Europe come from traffic, and most of the rest from combustion plants. Oxides of sulphur and nitrogen can be converted into sulphuric acid and nitric acid in the atmosphere.
Ammonia is another nitrogen compound that contributes to the acidification of soil and water.
Most emissions of ammonia result from the handling of manure in livestock farming. This means that the problem of acidification recognizes no borders. In Sweden and Norway around 90 per cent of the acid deposition comes from other countries, primarily the United Kingdom, Germany and Poland, and international shipping. S ensitivity to acid deposition varies. Where the level of acidifying deposition exceeds the soil's buffering capacity, problems of acidification arise sooner or later.