Acid Rain on Earth
Tyler J Golightly
College of Southern Nevada
Citizens of the United States will not truly be aware of the destruction caused by acid rain until they experience the effects first hand. Acid rain is slowly destroying the environment, and should be reduced to preserve the earth’s ability to sustain life. By compounding research from federal environmental websites, academic journals, and a chemistry textbook section catering to the subject of acid rain, I have compiled the causes and effects of the misunderstood phenomenon. Hyposulfite and nitrogen oxides reacting with water vapor in the atmosphere are the cause of acid rain. These ions are the byproducts of industrial processes, combustion engines, natural events, and bacteria. Acid rain lowers the pH of soil, damages leaves, and weakens the immune systems of plants and trees. The acidic runoff waters leach aluminum ions and nutrients from the soil depositing them in high concentrations in lakes and streams. Runoff water from melted snow or heavy rainfall can drastically lower the pH of lakes that have small buffering capacities. The low pH reduces and can even eliminate fish’s ability to reproduce. Acidic waters promote the growth of algae, plankton, and other invasive species. These species produce toxic phosphorus and cause eutrophication. Particles that cause acid rain also create toxic smog in sunlight and reduce visibility. Acid rain is not directly detrimental to human health but the hyposulfite and nitrite particle are shown to increase the risk of asthma and bronchitis. Increasing regulation on industrial processes and increasing the efficiency of combustion engines can reduce acid rain.
Acid rain consists mainly of sulfuric and nitric acid. Uncontaminated rainwater is naturally acidic and has a pH of 5.6 (Brown, LeMay Jr., Bursten, Murphey & Woodward, 2012). The acidity of uncontaminated rainwater mainly comes from carbon dioxide reacting with water to form carbonic acid. Acid rain usually has a pH of around 4. A substance with a pH of 7 is a neutral substance, while a pH less than 7 is acidic, and a pH above 7 is basic. As the pH falls below 7, the substance becomes more acidic. What makes an acid an acid, is the amount of free-floating positive hydrogen ions, or put more plainly, protons, in the substance. Sulfur dioxide and nitrogen oxides react with water to form sulfuric acid and nitric acid. Both sulfuric and nitric acids are considered strong acids, meaning that they dissociate completely when dissolved in water. For example, sulfuric acid consists of two hydrogen ions in an ionic bond with one sulfate ion, when dissolved in water the ionic bonds break and the hydrogen and sulfate ions become free-floating ions that are very reactive. Sulfur dioxide is produced from volcanic gasses, forest fires, bacterial action, fossil fuel combustion, and industrial processes (Brown, LeMay Jr., Bursten, Murphey & Woodward, 2012). However, nitrogen oxides are mainly the byproducts of atmospheric electrical discharges, internal combustion engines, and the combustion of organic matter. According to Brown et al. (2012) the combustion of coal accounts for roughly 60% of the sulfur dioxide released into the atmosphere, while the combustion of oil accounts for another 20%. That means that over 80% of acid rain is produced by the burning of fossil fuels alone.
Acid rain is detrimental to the health of forests and other plant life. Leaves and pine needles are damaged by acidic rainwater. The waxy surface layer of a plants leaves or needles are stripped, which allows the acidic rainwater to leach nutrients from the leaves and also can be a precursor to disease. This rainwater also leaches essential plant nutrients such as calcium, magnesium, and potassium from the soil, making it unavailable to plant life (Likens, Driscoll, & Buso, 1996). Nitrogen oxides, which are contributors to acid rain, react with light to form nitrogen and ozone. Nitrogen is an inert gas, and surprisingly makes up over seventy percent of our atmosphere, while ozone is highly reactive and toxic to all forms of life. Plants and trees affected by acid rain experience slowed growth and according to Our changing planet (2011) can cause trees to suffer the loss of 25% or more of their leaves or needles. These detrimental effects of acid rain where discovered after foresters and scientists observed the browning of leaves, slowed growth rates and the death of trees that otherwise should have been prospering. In special cases even whole sections of forest were decimated.
Runoff waters from acidic rain and snow are deposited in bodies of water such as lakes and streams, lowering their pH and depositing toxic solutes, endangering aquatic life. Natural waters normally have a pH between 6.5 and 8.5 while a 2008 study shows that the pH of ground waters is far below these values (Brown, LeMay Jr., Bursten, Murphey & Woodward, 2012). Fish must maintain osmoregulation, the delicate balance of solutes in their tissue, to survive (Emily, 2002). Acidity changes the equilibrium of the water, which in turn reduces a fish’s ability to maintain minerals such as calcium ions from being displaced. This reduction in nutrients causes fish to grow to smaller sizes and reduces a female’s ability to produce eggs. Aluminum, which is normally insoluble in higher pH water, is dissolved from deposits in the ground by the acidic runoff water where it eventually is deposited in lakes and streams. Aluminum ions are shown to damage the gills of fish, impairing their ability to take in oxygen. Studies have shown that the majority of fish killed in waters of high aluminum concentration die of starvation (Butcher, 1988). Aluminum ions have been shown to be lethal to some species of algae and reduce the reproductive rate of plankton, this reduction of food sources is a definite reason for the large amount of fish dying of starvation in waters of high aluminum concentration (Butcher, 1988). Nitrogen ions from fertilizer are dissolved by the acidic runoff and can end up in lakes and ponds, which can begin the process of eutrophication. Nitrogen stimulates the growth of algae, which over time increases the amount of decaying matter to the point where aerobic bacteria consume oxygen faster than the living algae and plants are able to produce it (Brown, LeMay Jr., Bursten, Murphey & Woodward, 2012). Eventually all oxygen breathing animals are eliminated leaving only anaerobic bacteria to thrive on the dead matter.
Acid rain is not directly detrimental to ones health, but the precursors sulfur dioxide and nitrogen dioxide are both highly toxic. The EPA states that scientific evidence shows that short-term nitrogen dioxide and sulfur dioxide exposures and adverse respiratory effects are linked. These effects including airway inflammation and bronchoconstriction were shown to be present in healthy people with symptoms being increased in individuals with asthma ("Six common air," 2012). Combustion engine driven automobiles, a leading producer of nitrogen dioxide, are very prominent in cities and highways. Individuals who live near highways and high traffic roadways are at higher risk of experiencing these respiratory symptoms. Electromagnetic radiation with a wavelength of 393nm breaks the nitrogen-oxygen bond; this free oxygen reacts with diatomic oxygen forming ozone. Ozone is highly toxic and has similar respiratory effects as sulfur dioxide and nitrogen dioxide. Nitrogen dioxide and sulfur dioxide react with moisture in the lungs forming strong acids; this attacks the tissues of the lungs and can cause emphysema and bronchitis. The negative effects of these acid rain precursors can cause chronic health problems and even premature death in people who are at high risk of exposure.
The effects of acid rain cannot be extinguished overnight, there is much humankind can do to reduce acid rain as well as diminish the symptoms. The clean air act of 1970 was calls for the regulation of stationary and mobile pollutants such as nitrogen dioxide and sulfur dioxide. In 1990, the clean air act was revised specifically targeting acid rain, urban pollution, toxic air emissions, and stratospheric ozone depletion. The Clean Air Act of 1990 greatly reduced the amount of acid rain with the Acid Rain Program. The Acid Rain Program was the first large-scale cap and trade program in the world. A cap and trade program allows for companies to buy unused emission allowance from other companies. Newer, more high tech factories are subsidized for upgrading to cleaner, more efficient equipment by selling their unused emissions. From 1990 to 2008 the cleaner air act has reduced acid rain causing sulfur dioxide by 51%, all while GDP has grown 64% ("40th anniversary of," 2010). It is possible to reduce the acidity of lakes and ponds by neutralizing the acidity with powdered limestone (Simonin, 1988). The limestone reacts with the hydrogen ions in the waters and by doing so increases the pH of the water. Research has shown that lake liming cans reverse the downward spiral that acid rain initiates allowing for a more diverse ecosystem.
Acidic rainwater has the potential to ravage the environment and thanks to innovations in science and lawmaking the detrimental effects that acid rain has had on the environment can be stopped and possibly even reversed. Sulfur dioxide and nitrogen oxides being released in large amounts into the atmosphere is what causes acid rain, the main producers of these gasses being the combustion of coal and other fossil fuels. Forests and farms are drastically affected by acid rain especially in areas where soil has a weak buffering capacity. The runoff waters reach land water poisoning aquatic life and decreasing biodiversity. The dry precursors to this acidic rainwater are toxic to animals, including humans, and causes respiratory problems that can lead to premature death. With innovation and an increase in strict regulation the effects of acid rain can diminish and eventually be reversed. By protecting our environment future citizens of the world will be able to breath easy knowing that the Earth has remained fertile.
Brown, T. L., LeMay Jr., H. E., Bursten, B. E., Murphey, C. J., & Woodward, P. M.
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