Acid Rain

WHAT CAUSES ACID RAIN?

One of the main causes of acid rain is sulphur dioxide. Natural sources which emit this gas are volcanoes, sea spray , rotting vegetation and plankton. However, the burning of fossil fuels, such as coal and oil, are largely to be blamed for approximately half of the emissions of this gas in the world. When sulphur dioxide reaches the atmosphere, it oxidizes to first form a sulphate ion. It then becomes sulphuric acid as it joins with hydrogen atoms in the air and falls back down to earth. Oxidation occurs the most in clouds and especially in heavily polluted air where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulphur dioxide to sulphuric acid. However, not all of the sulphur dioxide is converted to sulphuric acid. In fact, a substantial amount can float up into the atmosphere, move over to another area and return to earth unconverted. The following are the stoichiometric equations for the formation of sulphuric acid: S (in coal) + O2® SO2 2 SO2 + O2® 2 SO3 SO3® + H2O H2SO4 Nitric oxide and nitric dioxide are also components of acid rain. Its sources are mainly from power stations and ehaust fumes. Like sulphur dioxide, these nitrogen oxides rise into the atmosphere and are oxidized in clouds to form nitric acid. These reactions are also catalysed in heavily polluted clouds where iron, manganese, ammonia and hydrogen peroxide are present.

The causes of Air Pollution(from Japan) We are investigating causes of air pollution. We suppose there are many causes of air pollution, http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (1 of 6) [6/8/2002 11:18:13 AM]

Acid Rain

for instance, mold, ticks and VOC. In our life, we can check how much the air is polluted with those elements. 1. when you feel you have an irritaion in your eyes. 2. when you feel the smell of chemical materials. 3. when you are irritating 4. when you have headache 5. when a child who has an allergy crying 6. when you feel you don't want to stay longer in that area.

What causes acid rain? Acid rain-is caused by emissions of sulphur dioxide and nitrogen oxides .Althought natural sources of surphur o- xides and nitrogen oxides do exist, more than 90%of the sulphur and 95% of the nitrogen emissions occurring in eastern North America are of human orgin .These primary air pollutants arise from the use of coal in the production of electricity ,from base-metal smelting ,and from fuel condustion in vehicles .Once released into the atmosphere, they can be converted chemically into nitric acid and sul- furic acid ,both of wich dissolve easily in water . The resulting acidic water droplets can be carried long distan- ces by prevailing winds ,returning to Earth as acid rain ,snow,or fog.

What causes acid rain /continue Q 3.50 Is acid rain always wet? No. The acids can be transformed chemically into sulphur dioxide gas or into sulphur and nitrogen salts. In this form they are deposited 'dry', causing the same damage as when they land dissolved in rain or snow. In this form they can also do internal damage to plants as they are taken up from the soil. Q 3.51 Is natural precipitation acidic? Yes. Water solutions vary in their degree of http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (2 of 6) [6/8/2002 11:18:13 AM]

Acid Rain

acidity. If pure water is defined as neutral, baking soda solutions are basic (alkaline) and household ammonia is very basic (very alkaline). On the other side of this scale there are ascending degrees of acidity; milk is slightly acidic, tomato juice is slightly more acidic, vinegar is mediumly acidic, lemon juice is still more acidic, and battery acid is extremely acidic. If there were no pollution at all, normal rainwater would fall on the acid side of this scale, not the alkaline side. Normal rainwater is less acidic than tomato juice, but more acidic than milk. What pollution does is cause the acidity of rain to increase. In some areas of Canada, rain can be as acidic as vinegar or lemon juice. Q 3.52 If rain is naturally acidic, why does it matter if pollution makes it more acidic? The problem is one of balance; nature depends upon balance. Normal precipitation reacts with alkaline chemicals derived from the region's bedrock and found in the air, soils, lakes, and streams and is thereby neutralized. However, if precipitation is more highly acidic, then acid-buffering chemicals can eventually become depleted. In this case, the buffering effect will no longer occur, and nature's ability to maintain balance will have been destroyed. Q 3.53 Do all regions have the same acid-neutralizing capacity? No. Different types of bedrock contain variable amounts of contain variable amounts of alkaline chemicals. Regions with bedrock containing less alkali have a lower capacity for reducing acidity, and thus are more sensitive to acid rain. Q 3.54 What happens when this buffering effect is disrupted? When the environment cannot neutralize acid rain, damage occurs to forests, crops, lakes, and fish. Toxic metals such as copper and lead can also be leached from water pipes into drinking water. Q 3.55 How does acid rain affect aquatic ecosystems? The interactions between living organisms and the chemistry of their aquatic habitats are extremely complex. If the number of one species or group of http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (3 of 6) [6/8/2002 11:18:13 AM]

Acid Rain

species changes in response to acidification, then the ecosystem of the entire water body is likely to be affected through the predator-prey relationships of the food web. At first, the effects of acid deposition may be almost imperceptible, but as acidity increases, more and more species of plants and animals decline or disappear. As the water pH approaches 6.0, crustaceans, insects, and some plankton species begin to disappear. As pH approaches 5.0, major changes in the makeup of the plankton community occur, less desirable species of mosses and plankton may begin to invade, and the progressive loss of some fish populations is likely, with the more highly valued species being generally the least tolerant of acidity. Below pH of 5.0, the water is largely devoid of fish, the bottom is covered with undecayed material, and the nearshore areas may be dominated by mosses. Terrestrial animals dependent on aquatic ecosystems are also affected. Waterfowl, for example, depend on aquatic organisms for nourishment and nutrients. As these food sources are reduced or eliminated, the quality of habitat declines and the reproductive success of the birds is affected. Q 3.56 How does acid deposition affect terrestrial plant life? Both natural vegetation and crops can be affected. It can alter the protective waxy surface of leaves, lowering disease resistance. It may inhibit plant germination and reproduction. It accelerates soil weathering and removal of nutrients. It makes some toxic elements, such as aluminum, more soluble. High aluminum http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (4 of 6) [6/8/2002 11:18:13 AM]

Acid Rain

concentrations in soil can prevent the uptake and use of nutrients by plants. Q 3.57 How does acid deposition affect animal life? The effects on terrestrial wildlife are hard to assess. As a result of pollution-induced alteration of habitat or food resources, acid deposition may cause population decline through stress (because of decreases in available resources) and lower reproductive success. Q 3.58 What are the socioeconomic consequences of acidification? Lower productivity in fisheries, forestry, and agriculture translates to lower profits and fewer jobs for some of Canada's important industries. Acid deposition causes accelerated corrosion, fracturing, and discoloration of buildings, structures, and monuments. Q 3.59 How does acid deposition affect human health? We eat food, drink water, and breathe air that has come in contact with rain acid. Canadian and U.S. studies indicate that there is a link between this pollution and respirator problems in sensitive populations such as children and asthmatics. Acid deposition can increase the levels of toxic metals such as aluminum, copper, and mercury in untreated drinking water supplies. It has been estimated that acid rain causes $1 billion worth of damage in Canada every year. Thousands of lakes have been damaged; a large part of the salmon habitat in the Maritimes has been lost; a significant proportion of eastern Canada's forests has been affected; and considerable damage to buildings and monuments has been documented. The Canadian Council of Resource and Environment Ministers in established 20 kg/hectare per year as the target for Canadian sulphur dioxide loading. In eastern Canada, 96% of the land http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (5 of 6) [6/8/2002 11:18:13 AM]

Acid Rain

with high capability for forestry is subject to acidic deposition in excess of 20 kg/ha per year. In recent years, important instances of dieback and declines in growth rate have been noted in sugar maple groves in parts of Canada that receive high levels of these and other air pollutants, such as ozone. Significant growth declines in northern Ontario forests, most notable over the past 30 years, coincide with a period of rapidly increasing industrialization and urbanization across much of the province. Q 3.60 Is acid deposition occurring to the same extent across Canada? No. Sulphur emissions tend to be concentrated in relatively few locations, while the sources of nitrogen emissions are widely distributed; however, where they are deposited depends on more than just where they are produced. Airborne acidic pollutants are often transported by large scale weather systems thousands of kilometres from their point of origin before being deposited. In eastern North America, weather systems generally travel from southwest to northeast. Thus, pollutants emitted from sources in the industrial heartland of the midwestern states and central Canada regularly fall on the more rural and comparatively pristine areas of the northeastern U.S. and southeastern Canada. TAKE ACTION! The challenge is to reduce sulphur and nitrogen emissions. The two principal ways individuals can help are by reducing the amount of energy used in the home (energy efficiency) by reducing the stress your driving habits put on the environment.

Back to Home

http://www.att.virtualclassroom.org/vc98/vc_63/iwai/rain.html (6 of 6) [6/8/2002 11:18:13 AM]