Acid rains and its causes

The term acid rains are commonly used to mean a deposition of acid components in rain, snow fog, dew or dry particles. That is the rains that are acidified. This is more accurately called as acid precipitation.  Acidic nature is characterized by pH value (acid base equilibrium) of substance. If the substance is have pH value at 7 then that is said to be neutral. If its pH is less that 7 then that is called a acid and if pH is greater than 7 then that is called as base or alkali. If the pH value is close to 0 its strong acid and if pH value is close to 14 it’s a strong base. Anything around 7 is said to be week.

This pH is commonly used as an indicator for the level of acids in the rain. Most commonly it measures around 5.6. This indicates that the rain water that is available is not neutral. It is slightly acidic. This is because carbon dioxide and water in air react with each other to form carbonic acid a weak acid. This acidic nature of the rain will increase with the pollutants.  Due to alkaline soil dust in the atmosphere the pH value of the rains some times indicate slightly alkaline nature.

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Major pollutants that cause acid deposits are sulfur dioxide and nitrogen oxides which are produced from combustion of fossil fuels. Once these gases are released into atmosphere the get transported into sulfur dioxide and nitric acid and travel long distances before  mixing with rain and reaching earth. This is wet deposition. Some amount will settle on the plants and other surfaces are called as dry deposit.

The major sources for the release of these pollutants are from burning fossil fuels. Electricity generation contributes to 70% of the SO2 that is released into the atmosphere which is generated from combustion of coal which contains 2-3% of sulfur in it. Electricity also contributes to 30% of the NOx in the atmosphere.  Motor vehicles like buses and trucks contribute around 40% of the NOx from the combustion engines.  Natural calamities such as forests fires, volcanoes contribute around 1-5% of the  SO2. forests fires, microbial processes in the soil fuels  contribute around 11% of the atmospheric NOx. Industries processing ore containing sulfur to obtain copper, zinc and nickel also release SO2 into atmosphere.

Effects on the society:

The whole world will be affected by the effect of pollution. The destruction caused by these acid rains is not limited to a particular place. Before coming to the earth surface the atmospheric emissions travel for long distances depending the wind and climatic conditions. Thus the pollution caused at one area will show its effect around that area based on its geographical conditions. It is believed that 50% of the acidic rains in Canada are due to the industrial pollution caused in USA. The side effects of industrialization in England is seen in Norway as acid rains.

The problem of acid rains is might have originated from early 1700s where industrial revolution was at its early days and were first discovered in 1872. It gained attention  in 1950 and from then the problem have become much worse. Rural areas around the source are mostly effected as the tall chimneys from the source release the pollutants much higher into the atmosphere and the get carried to rural areas around more easily. Statistics show that half of the black forest is Germany was damaged due to acid   rains because of industrial revolution in Germany.

The most severely effected areas due to this acid rains are  northeastern parts of US, Southern parts of Canada, Central Europe and Scandinavian parts of Asia specifically India and china, where acid rains are caused by large number of factories and rapid industrialization.

 US and Canada contribution to acid deposition:

The acid rain problem in North America is most sever that is to be addressed properly. Surveys say  half of the acid rains that are caused in Canada are due to pollution from the US. The figures Fig1, Fig2, Fig3 and Fig4  below shows the amount of SO2 and NOx releases by both countries.  Regarding cross border contribution ,  observation reveal that when winds traveling from south to north in eastern North America, emissions from USA may be responsible for acid deposition in Canada, and with the winter winds flowing from north to south, emissions from Canada may contribute to acid deposition in  US. Preliminary studies reveal that 3 to 4 times of sulfur components flow from US to Canada.

Surveys revealed that around 14,000 lakes in Canadian lakes are affected by acid rains. And it is also predicted that another 20,000 to 40,000 lakes may also get affected in the eastern regions of Canada if no proper steps are taken to control the pollution. Most effected parts in Canada are Ontario, Quebec and Labrador because of westerly winds in most of the eastern North America.

Acid Rain Control:

The acid rains issue gained its prominence and scientists keeps on saying about the  its potential devastating effects.  In the year 1990, US has amended Clean Air Act and in the year 1991 US and Canada have signed Quality Air agreement.  Since then the total of SO2 and NOx have decreased significantly. By the year 1996 US emissions have declined by 27% lower than 1980 and it is expected to reach around 40% by the year 2010.

US Acid Rain Control Program:

In the year 1990 US amended clean air act and authorized  the Environmental protection Agency to establish a acid rain control program. The targets of this amendments is to reduce the levels of sulfur and nitrogen components into the atmospheres. This program will effect the electric uses which is the main source of SO2 emission.  The program is implemented in two phases. I the first phase the 110 coal- electric power generation stations  of eastern and Midwestern stated  will be monitored  from 1995 -1999. In the second phase 20 smaller power generation stations will be regulated.  Emission limits on all the coal burning plants will be tightened.  The emissions trading system  regulations are known as the core rules., These consists of fixing rules on Allowance systems Excess emission  and administrative policies , permits and excess emission monitoring systems etc.

The results obtained from the allowance are positive and it was found that the cost of SO2 allowances which are $500-600/ton in 1996 have reduced to $70/ton by 1998 and the costs we maintained around $100/ton. The reasons being betters removal efficiencies, low cost of low sulfur coal.  The Geographical survey of US has reported a significant reduction in the acid content in the rain water. 20-25% drop of acid levels I rainfall in Mideast , Northeast and mid-Atlantic locations is seen.

Canada Acid Rain Control Program:

Canada announced its first acid rain control program in the year 1985. The committee target the  reduction in SO2 levels by 50% by 1994 from a base of 4.56millio tons. The first agreement lapsed I 1994 and new agreement came into begin. It targeted a cap on SO2 emission at 2,300kilotonns until 2000.  In the year 1996 the eastern provinces registered 1,741 tons which is 24% below the cap amount.  All the eastern provinces met their targets except Newfoundland. In 1997 SO2 emissions went well below the cap.

Monitoring the lakes have also should that sulphate levels in  Ontario and Quebec have not shown much significant. Climatic conditions, like raise in temperatures droughts caused the delay of recovery of the lakes. The mentoring team have made the following conclusions that  SO2 reduction should be further achieved and pollution to be prevented, endorsements by ministers that “Keep clean area clean” and continuing the support to  scientific and research programs.

US Canada Air Quality Agreement:

In the year 1991 on March 13 US signed Air Quality Agreement with Canada. The agreement is concerned with  air pollution traveling from both the borders. The first issue that is addressed is acid rains. Both the countries agreed to reduce approximately 13.3 million tons by the year 2010 in US and 3.2 million tons by Canada. The graph mentioned above will resemble the quantity and the years wise data. Besides this limitations are also imposed on NOx emission and motor vehicle pollution.  A joint committee was formed to monitor the and assist the implementation of the agreement.

Third report released in year 1996 showed that both countries achieved their obligations as set by the Air Quality Agreement. Few key identifications are  reduction in wet sulphate deposition reduction, decrease in surface water sulphate and healthy hardwood forests were  identified.  Many points are still left undressed or less concerted of which trans border pollution is the key issue. Pollutants like ground-level ozone, air toxics and inhalable particles need to get focus.


The main source of acid rains is pollutants that are released from power plants, industries and automobiles. They pose big threat to the ecosystems and continue to do in the future.  The advent effects on the natural life are very badly affected due to acid rains.  Individual has very little role in the controlling acid rains. All individuals when act together can make significant changes. Government needs to monitor all the causes of the air pollution and should impose strict actions. As this is a global problem all the nations in the world should act combined by monitoring the sources.  Strict regulations must be kept on emission trading.

The problem of the acid rains is most sever in North America. US and Canada should act jointly to reduce the problem. The provinces that are largely damaged are also the large contributors, so they should be monitored and emission levels should be reduced.  US should take regionalized approach to reduced its part in the pollution. The governments of both the countries should make strict policies to make our earth pollution free. Both the countries should have bilateral cooperation in solving the issue.





4)        Jurgen Schmandt “Acid rians and friendly neighbours: The policy dispute between Canada and US.”






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