This paper examines the relationship between air pollution and acid rain, tracing the phenomenon from its early observation by Robert Angus Smith in the nineteenth century to modern legislative efforts such as the Clean Air Act Amendments of 1990. The paper explains how elevated concentrations of sulfur and nitrogen oxides lower the pH of precipitation, and details the wide-ranging damage acid rain inflicts on aquatic ecosystems, plant life, human health, and built structures such as buildings and monuments. It also considers the geographic patterns of acid rain intensity and concludes that controlling industrial emissions is essential to mitigating this environmental hazard.
Acid rain is now commonly perceived as a major environmental threat, but the term is still relatively new and many people remain confused about its causes. While some naturally occurring sources are occasionally cited, the main cause of acidity in rain is air pollution, which increases the concentration of sulfur oxides and nitrogen oxides, thereby lowering the pH level of precipitation to below 7. Air pollution is defined as "the introduction by humankind, directly or indirectly, of substances or energy into the environment resulting in deleterious effects of such a nature as to endanger human health, harm living resources and ecosystems, impair amenities, or interfere with other legitimate uses of the environment." [1]
The reason pollution is seen as the biggest cause of acid rain is that human activities tend to contaminate the air, and it has been observed that the more densely populated an area is, the more acidic its rainfall tends to be. In other words, when more people are concentrated within a limited geographical area, their collective activities have a more profoundly negative impact on the environment than similar activities in less densely populated regions. "The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain." [4]
Acid rain can be considered a relatively modern phenomenon, as it essentially emerged alongside industrialization. The hazardous fumes released by factories were among the principal causes of air pollution and thus responsible for raising the acidity levels of rainwater. In 1858, Robert Angus Smith, a London chemist, observed that elevated acid levels in rain were causing environmental problems and wrote: "It has often been observed that the stones and bricks of buildings … crumble more readily in large towns, where much coal is burnt, than elsewhere. I was led to attribute this effect to the slow but constant action of the acid rain." These observations were later published in his book Air and Rain: The Beginnings of a Chemical Climatology in 1872. [2]
The term acid rain now refers broadly to rainwater, snow, and fog containing acidic deposits. The presence of elevated levels of sulfur and nitrogen oxides causes a reduction in pH, producing an acidic character in precipitation. The higher the acidity, the greater the damage to the environment and ecosystem. Acid rain is "caused mainly by the discharge into the air of sulphur and nitrogen compounds from stationary combustion sources, industrial noncombustion processes, nonindustrial and domestic activities (including residential heating), and mobile sources. The harm caused by acid rain usually results from the emission of sulphur and nitrogen compounds taking place at such a distance that it is not generally possible to distinguish the contribution of individual emission sources or groups of sources." [3]
Because acid rain can cause immense damage to aquatic life and entire ecosystems, laws were formulated around the world to control hazardous atmospheric emissions. One such effort resulted in the Acid Precipitation Act (Title VII of the Energy Security Act of 1980, Public Law 96-294). "In 1990, the Clean Air Act was amended to include provisions that would substantially reduce sulfur dioxide and nitrogen oxides emitted from fossil fuel-burning electrical utilities. Research provisions as well as control measures were included in the amendment, which is intended to implement a suitable regulatory program." (The Journal of Coatings Technology, 1995)
"Details harm to plants, marine life, and forests"
"Covers respiratory illness and monument deterioration"
"Reviews Clean Air Act and emission control goals"
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