Rain is one of the most essential ingredients for human and animal life. The water provided by rain allows all life on Earth to survive. Although rain is naturally acidic, it is being increasingly acidified by pollution from homes, factories, power stations and cars. The term used to describe this problem is “acid rain”. Acid rain hasn’t just occurred in the last twenty to thirty years. In fact a chemist named Robert Smith found rainfall in Manchester, U.K., to be very acidic. He suggested a link between acid rain and SO2 given off when coal was burnt by local factories. This was over 100 years ago.
Acid rain is caused when pollutants from cars, homes, factories and power stations mix with atmospheric moisture. These pollutants may be carried in clouds for long distances before falling, which means that forests and lakes far away from factories may be damaged by acid rain.
Two of the major ingredients of acid rain are the chemicals sulphur dioxide [SO2] and nitrogen oxides [NOx]. When large quantities of these two particular chemicals come in contact with the atmosphere, they team up with moisture [H2O] to produce strong acids called sulphuric and nitric acid. These two acids which are formed in the atmosphere, are very strong pollutants.
Some air pollution as a matter of fact comes from natural sources, but most is human made. The burning of oil and coal by plants and factories, homes and cars, is the main source of chemicals that cause acid rain. Power stations and factories emit large amounts of sulphur dioxide and also nitrogen oxides, whilst car exhausts contain large amounts of nitrogen oxides. When volcanoes erupt, they emit various gases which have been trapped under the ground, including sulphur dioxide. This can cause air pollution, which can then be made much worse by the addition of human-made emissions. The air in many towns and cities is overfull of harmful pollutants. In the northern hemisphere sulphur emissions are decreasing steadily, due to pollution controls in industry. NOx emissions, however, are not yet in such steady decline.
The acid from rain takes important minerals from the leaves of trees and from the soil. Acid rain also releases toxic metals from the soil which damage the roots of the trees. The trees are weakened, cannot grow properly and are attacked by viruses, fungi and pests. Eventually the trees may die. Direct damage to trees occurs when SO2 blocks the pores on the leaves, through which the trees takes in the air they need to live. Forest floods that are affected by acid rain have high concentrations of metals like aluminium and lead. When animals drink from acidic lakes and dew that have been affected, the metals they take in may gradually poison them.
There is an obvious link between acid rain and damage to human health. People can be harmed by breathing in the chemicals from dry deposition, causing chest illness. Also when acid rain causes the release of metals and chemicals into drinking water, it can damage people’s health. When air pollution is breathed in as people walk along the street, it gets into their lungs. Once in the lungs, it acts like a poison, causing the airways in the respiratory system to become narrower. This lets in less oxygen and breathing becomes difficult. If SO2 is breathed in, it can pass deep into the alveoli, which is where oxygen is passed into the blood. The moisture in the lungs can turn the sulphur dioxide into sulphuric acid, and cause damage to the body. In some polluted cities, such as those in California, smog stations have been set up to monitor the output of polluting exhaust gases.
To reduce acid rain industry’s have to cut down the amount of SO2 being produced when fossil fuels are burnt. Therefore, they can: use coal which contains little sulphur, remove the sulphur which is in the coal, use another type of fuel, or burn the coal in such a way that the sulphur is destroyed. There are many other ways of combating this problem, however, the best way to solve this issue is to prevent emissions of pollutants in the first place. Reducing the amount of NOx emissions caused by car exhaust is an effective solution. Public transport systems need to be improved so that people can travel without having to use their cars. If more people used public transport, it would cut the number of private vehicles on the roads, and would reduce pollution dramatically. Everybody needs to work together to reduce pollutants to make the world a safer and healthier place to live.