Acid rain, or acid deposition as it should be correctly termed, is one of the major environmental issues of our time. Acid rain however is not a new problem. In the mid 19th century, a Scottish scientist, Robert Angus Smith, began to study the effects of air pollution in Manchester where he coined the term acid rain' to describe his findings. In Smith's time, acid rain fell in both towns and cities and downwind from them but now, following Clean Air Acts, levels of smoke and sulphur dioxide have been greatly reduced. Gaseous and particulate airborne pollutants are now dispersed higher into the atmosphere via tall chimney stacks. Other sources of pollutants such as vehicle exhausts may also be transported high into the atmosphere, depending on weather conditions.
Complex chemical reactions occur over time in the atmosphere including the formation of sulphuric and nitric acids, leading to the deposition of acidic precipitation. Because pollutants can be carried many hundreds of kilometres by winds, acid pollutants emitted in one country may be deposited as acid precipitation in other countries. Acid deposition has become an international problem.
Acid rain can occur naturally as a result of, for example, carbon dioxide dissolving in water or from volcanic emissions of sulphur and nitrogen, which with water can form acids. However, increased acidity of precipitation occurs due to human activities. Waste gases, particularly sulphur dioxide (SO2) and oxides of nitrogen (NOx) produced from the burning of fossil fuels have caused a large increase in the emissions of acidifying gases over recent decades. Table 1 shows the global emission estimates of sulphur and nitrogen for reference year 1985. In 1980, Europe accounted for approximately 28 million tonnes of sulphur and 7 million tonnes of nitrogen (Acid News, Dec. 1995).
Table 1: Estimates of global emissions of sulphur and nitrogen for reference year 1985.
| Source | Sulphur (million tonnes/yr) | Nitrogen (million tonnes / yr) |
|---|---|---|
| Anthropogenic | 65 | 21 |
| Natural | 25 | 15 - 20 |
Emissions of sulphur from anthropogenic sources are far greater than those from natural sources, particularly in the industrialised northern hemisphere. Most of the sulphur emitted from anthropogenic sources arises from the burning of fossil fuels and the smelting of sulphide ores whilst the major natural sources of sulphur are the oxidation of dimethyl sulphide from the sea and emissions from volcanoes.
Emissions of nitrogen on the global scale are roughly equal from both anthropogenic and natural sources; almost all anthropogenic emissions result from the burning of fossil fuels particularly from transport whilst natural sources include lightning, biomass burning and biogenic emissions from soils.
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 vehicles and political attitudes on environmental issues.
Table 2 shows the estimated emissions and depositions of sulphur and nitrogen (as nitrogen dioxide) for 1993/94 for European countries. The figures for emissions and depositions highlight the fact that emission 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, eg Norway, Sweden, Austria and Switzerland. Other countries such as Bulgaria, Italy and the UK emit more pollution than is deposited in their country because of prevailing wind directions.
Table 2: Estimated emissions and depositions of sulphur and nitrogen for European countries ('000 tonnes per year), 1993/94
| Country | Sulphur emissions | Sulphur deposition | Nitrogen dioxide emissions | Nitrogen deposition |
|---|---|---|---|---|
| Albania | (60) | 30 | (30) | 9 |
| Austria | 36 | 111 | 182 | 63 |
| Belarus | 216 | 214 | 207 | 70 |
| Belgium | 152* | 62 | 350* | 27 |
| Bosnia & Herzegovina | 240* | 77 | (54) | 22 |
| Bulgaria | 711 | 167 | 238 | 31 |
| Croatia | 90* | 73 | 83* | 28 |
| Czech Republic | 710 | 260 | 574 | 70 |
| Denmark | 78 | 45 | 264 | 21 |
| Estonia | (120) | 36 | (66) | 13 |
| Finland | 60 | 106 | 253 | 55 |
| France | 568 | 362 | 1519 | 210 |
| Georgia | (81) | (188) | ||
| Germany | 1948 | 803 | 2904 | 332 |
| Greece | 255* | 111 | 306* | 26 |
| Hungary | 414* | 170 | 183* | 48 |
| Iceland | 3* | 5 | 12* | 4 |
| Ireland | 78 | 32 | 122 | 15 |
| Italy | 1126 | 299 | 2053 | 140 |
| Kazakstan | (70) | (76) | ||
| Latvia | (41) | 49 | (54) | 19 |
| Lithuania | (68) | 65 | (56) | 23 |
| Luxembourg | 8* | 5 | 19* | 3 |
| Macedonia | (5) | 22 | (2) | 6 |
| Moldovia | (46) | 36 | (35) | 9 |
| Netherlands | 84 | 71 | 561 | 35 |
| Norway | 18 | 94 | 225 | 61 |
| Poland | 1362 | 822 | 1140 | 216 |
| Portugal | 145 | 37 | 245 | 16 |
| Romania | 280* | 268 | 443* | 76 |
| Russian Federation | 1728 | 1959 | 2269 | 690 |
| Slovakia | 162 | 107 | 184 | 31 |
| Slovenia | 91 | 32 | 57 | 13 |
| Spain | 1158* | 274 | 1257* | 103 |
| Sweden | 50 | 161 | 399 | 101 |
| Switzerland | 29 | 42 | 150 | 27 |
| Turkey | 177* | 217 | (175) | 68 |
| Ukraine | 1925* | 896 | 1097* | 205 |
| United Kingdom | 1597 | 430 | 2355 | 117 |
| Yugoslavia | 200 | 139 | 54 | 34 |
In the late 1970s, the United Nations Economic Commission for Europe (UNECE) set up an international convention concerning Long Range Transboundary Pollution. In 1984 and 1985, most UNECE members agreed to reduce sulphur dioxide emissions by 30% (on 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. Austria greatly exceeded their target reduction by achieving an 82% reduction, whilst the UK achieved a 35% reduction. Only two countries increased their emissions, Croatia (20%) and Greece (27%).
In June 1994, the second protocol for sulphur was signed by many European countries. Most of the western European countries have agreed to reduce sulphur emissions by between 70 and 80% by the year 2000 (on 1980 levels) whilst eastern European countries generally have a lower target of between 40 and 50% (on 1980 levels). Table 3 shows the sulphur reduction commitments of the 1994 UNECE Convention on Long Range Transboundary Air Pollution.
Overall emissions of sulphur dioxide in Europe are estimated to have fallen by 25-30% between 1980 and 1990 and if the signatories of the 1994 protocol achieve their target reductions, European sulphur dioxide emissions are estimated to fall to 42% by 2000, 47% by 2005 and 51% by 2010 (on 1980 levels).
The Sofia protocol for reducing nitrogen oxide emissions was set up in 1988. This required all countries that signed the protocol to stabilize emissions of NOx (on 1987 levels) but some countries committed themselves to 30% reductions by 1998 (on levels of any year between 1980 and 1986). However, many of these countries are unlikely to meet these targets; several countries such as Spain and Italy have increased their NOx emissions between 1987 and 1993 by 41% and 8% respectively. With this protocol becoming outdated, a new one is expected later this decade which may also set targets for other pollutants such as volatile organic compounds.
Table 3: Commitments of the 1994 UNECE Protocol on Further Reduction of Sulphur Emission
| Country | % reduction by 2000 | % reduction by 2005 | % reduction by 2010 |
|---|---|---|---|
| Austria | 80 | - | - |
| Belgium | 70 | 72 | 74 |
| Bulgaria | 33 | 40 | 45 |
| Croatia | 11 | 17 | 22 |
| Czech Republic | 50 | 60 | 72 |
| Denmark | 80 | - | - |
| Finland | 80 | - | - |
| France | 74 | 77 | 78 |
| Germany | 83 | 87 | - |
| Greece | -49 | -45 | -43 |
| Italy | 65 | 73 | - |
| Liechenstein | 75 | - | - |
| Luxembourg | 58 | - | - |
| Netherlands | 77 | - | - |
| Norway | 76 | - | - |
| Poland | 37 | 47 | 66 |
| Russian Federation | 38 | 40 | 40 |
| Slovakia | 60 | 65 | 72 |
| Slovenia | 45 | 60 | 70 |
| Spain | 35 | - | - |
| Sweden | 80 | - | - |
| Switzerland | 52 | - | - |
| Ukraine | 40 | - | - |
| UK | 50 | 70 | 80 |
| European Union | 62 | - | - |
In 1988 a Directive was introduced for EC countries which requires Large Combustion Plants over 50MW in size to reduce emissions of SO2 and NOx by varying percentages by 1998 and 2003 (on 1980 levels). For the UK, reductions of 60% SO2 by 2003 and 30% NOx by 1998 have been set. The UK is well on course to exceed both targets through new gas-fired power stations (which produce small quantities of SO2 and NOx) replacing coal fired power stations and flue gas desulphurisation equipment fitted to Drax and Ratcliffe on Soar power stations.
In addition, all cars sold within the European union from 1993 onwards have to be fitted with a catalytic converter to help reduce emissions of vehicular pollutants. Many non EU countries also require catalytic converters to be fitted to vehicles sold within their countries.
Although SO2 emissions in Europe have been falling steadily over recent years, NOx emissions rose during the 1980s and have only recently begun to fall at a slower rate than was anticipated. Acid rain will therefore continue to be a problem in Europe until these emissions can be dramatically reduced.
Acid News 4, October (1994) New agreement on Sulphur, Swedish NGO Secretariat on Acid Rain
Acid News 5, December (1995) Latest Monitoring (European Monitoring & Evaluation Programme), Swedish NGO Secretariat on Acid Rain
Graedel, T.E., Benkovitz, C.M., Keene, W.C., Lee, D.S. & Marland, G. (1995) Global Emissions Inventories of Acid-Related Compounds Water, Air and Soil Pollution, 85: 25-36.
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