Because pollutants can be carried many hundreds of kilometres by winds, acid pollutants emitted in one country may be deposited as acid rain in other countries. Acid deposition has become an international problem. This problem is highlighted by the fact that emissions of a particular pollutant from one country does not equal the deposition of that pollutant in the same country. Some countries emit small quantities of pollutants yet deposition can be several times greater. Other countries emit more pollution than is deposited in their country because of prevailing wind directions.
In 1979, the United Nations Economic Commission for Europe (UNECE) implemented the Convention on Long-Range Transboundary Pollution. In 1985 most UNECE members adopted the Protocol on the Reduction of Sulphur Emissions, agreeing to reduce sulphur dioxide emissions by 30% (from 1980 levels) by 1993. This was called the 30% club. All of the countries that signed the Protocol achieved this reduction, and many of those that did not sign, have met these reductions.
In June 1994, a number of European countries signed the Second Protocol for sulphur. Most of the western European countries agreed to reduce sulphur emissions by between 70 and 80% by the year 2000 (against 1980 levels) whilst eastern European countries generally have a lower target of between 40 and 50% (against 1980 levels).
Overall, emissions of sulphur dioxide in Europe are estimated to have fallen by 25-30% between 1980 and 1990, and by 40% by the year 2000. Further falls in sulphur dioxide emissions are expected over the next decade.
The Sofia Protocol for reducing nitrogen oxide emissions was adopted in 1988. This required all countries that signed the Protocol to stabilise emissions of nitrogen oxide (against 1987 levels), although some countries committed themselves to 30% reductions by 1998 (against levels of any year between 1980 and 1986). However, many of these countries are unlikely to meet these targets, due to increases in road traffic, despite European Union legislation requiring cars built after 1993 to be fitted with a catalytic converter.
In 1988 a Directive was introduced for European Community (EC) countries which required power stations to reduce emissions of sulphur dioxide and nitrogen oxides. For the UK, reductions of sulphur dioxide by 60% by 2003 and nitrogen oxides by 30% by 1998 (against 1980 levels) have been set. The UK is well on course to exceed both targets through new gas-fired power stations (which have lower emissions) replacing coal fired power stations, and flue gas desulphurisation equipment fitted to some of the existing coal-fired power stations.
The most recent UNECE Convention on Long Range Transboundary Air Pollution protocol was signed by 27 countries in December 1999. The Gothenburg Protocol, designed to Abate Acidification, Eutrophication and Ground-level Ozone aims to cut emissions of four pollutants: sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs), and ammonia (NH3), by setting country-by-country emission ceilings to be achieved by the year 2010.