Acidity is measured using a pH scale, with the number 7 being neutral. A substance with a pH value of less than 7 is acidic, while one of a value greater than 7 is basic. A substance with a pH of 6 is 10 times more acidic than another with a pH of 7. Usually the pH of 5.6 has been used as the baseline in identifying acid rain, although there has been much debate over the acceptance of this value. Interestingly enough, a pH of 5.6 is the pH value of carbon dioxide in equilibrium with distilled water. Hence, acid ran is defined as any rainfall that has an acidity level beyond what is expected in non-polluted rainfall. In essence, any precipitation that has a pH value of less than 5.6 is considered to be acid precipitation.
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 first . 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. Nitric oxide and nitric dioxide are also components of acid rain. The sources of these components are mainly from power stations and exhaust fumes.
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One of the most serious impacts of acid precipitation is on forests and soils. Great damage is done when sulphuric acid falls onto the earth as rain. Nutrients present in the soils are washed away. Aluminium also present in the soil is freed and this toxic element can be absorbed by the roots of trees. Thus, the trees are starved to death as they are deprived of their vital nutrients such as calcium and magnesium. Research has been made where red spruce seedlings were sprayed with different combinations of sulphuric and nitric acid of pH ranging from 2.5 to 4.5. The needles of these seedlings were observed to develop brown lesions. Eventually, the needles fall off. It was also found that new needles grew more slowly at higher concentrations of acid used. Because the rate at which the needles were falling was greater than the rate at which they were replenished, photosynthesis was greatly affected, The actual way in which these needles were killed is still not yet known. However, studies have shown that calcium and magnesium nutrients are washed away from their binding sites when sulphuric acid enters the system. They are replaced by useless hydrogen atoms and this inhibits photosynthesis.
In addition, severe frosts may also further aggravate this situation. With sulphur dioxide, ammonia and ozone present in the air, the frost-hardiness of trees are reduced. Ammonia oxidises with sulphur dioxide to form ammonium sulphate. This product forms on the surface of the trees. When ammonium sulphate reaches the soils, it reacts to form both sulphuric and nitric acid. Such conditions also stimulate the growth of fungi and pests like the ambrosia beetle. When trees are under such stress, they release chemicals such as terpenes which attract the ambrosia beetle.
... red spruce trees above 2,000 feet in elevation).In addition, acid rain accelerates the decay of building materials and paints ... leading to improvements in public health. -------------------------------------------------- ---------------------- -------------------------------------------------- ---------------------- Acid rain primarily affects sensitive bodies of water, that is, those that rest atop ...
Nitrogen oxide and nitric oxide, also components of acid rain, can force trees to grow even though they do not have the necessary nutrients. As well, the trees are sometimes forced to grow well into late autumn when it is actually time for them to prepare for severe frosts in the winter.
Forestry is an industry worth $10 billion a year in Canada. About 10 percent of all Canadian jobs depend on the harvesting and processing of trees. When forests are in danger, those jobs may disappear, too. Acid rain also affects fish and other sea creatures.
Acid particles are also deposited on to buildings and statues, causing corrosion. For example, the Capitol building in Ottawa has been disintegrating because of excess sulphur dioxide in the atmosphere. Limestone and marble turn to a crumbling substance called gypsum upon contact with the acid, which explains the corrosion of buildings and statues. In addition, bridges are corroding at a faster rate, and the railway industry as well as the airplane industry has to expend more money in repairing the corrosive damage done by acid rain. Not only is this an economically taxing problem caused by acid rain, but also a safety hazard to the general public. In 1967, the bridge over the Ohio River collapsed killing 46 people due to corrosion from acid rain.
Acid rain also damages materials such as fabrics. For example, flags that are put up are being “eaten away” by the acidic chemicals in the precipitation. Books and age-old art that are centuries old are also being affected; the ventilation systems of the libraries and museums that hold them do not prevent the acidic particles from entering the buildings and so, they get in and circulate within the building, affecting and deteriorating the materials.
Among one of the serious side effects of acid pollution on humans is respiratory problems. The chemicals in acid rain also give rise to respiratory problems such as asthma, dry coughs, headaches, eye, nose and throat irritations. An indirect effect of acid precipitation on humans is that the toxic metals dissolved in the water are absorbed in fruits, vegetables and in the tissues of animals. Although these toxic metals do not directly affect the animals, they have serious effects on humans when they are being consumed. For example, mercury that accumulates in the organs and tissues of the animals has been linked with brain damage in children as well as nerve disorders, and death. Similarly, another metal, aluminum, present in the organs of the animals, has been associated with kidney problems and recently, was suspected to be related to Alzheimer’s disease.
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The only way to stop acid rain is to stop releasing so much sulfur dioxide and nitrogen oxides into the air. The release of these gases has been cut drastically in recent decades due to new laws controlling the release of these gases.