Air pollution: causes, effects, and mitigation strategies

Air Pollution and Acid Rain

Acid rain is now commonly perceived as a major environmental threat but the term is still relatively new and many are confused about its causes. While there are some other commonly cited reasons including natural sources, the main cause of acidity in rain is air pollution, which increases the composition of sulphur oxides and nitrogen oxides and thus lowering the pH level to less than 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 eco-systems, impair amenities or interfere with other legitimate uses of the environment." [1]

Acid rain can be called a new phenomenon since it basically emerged with industrialization. The hazardous fumes from factories were one of the main causes of air pollution and thus are responsible for causing higher levels of acidity in rainwater. In 1858, Robert Angus Smith, a London chemist, observed that acid level in rain was 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 on the slow but constant action of the acid rain." These thoughts were later expressed in his book Air and Rain, The Beginnings of a Chemical Climatology in 1872. [2]

The term acid rain now refers to rainwater, snow and fog containing acidic deposits. The composition or presence of higher levels of sulphur and nitrogen oxides causes reduction in pH level, resulting in an acidic taste. The higher the acidic level, the greater the havoc it wreaks on the environment and eco-system. 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]

Acid rain can cause immense damage to sea-life and the entire eco-system and thus laws were formulated around the world to control hazardous emissions into the atmosphere causing air pollution. 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)

The reason why pollution is seen as the biggest cause of acid rain is because human activities tend to pollute air and it has been noticed that areas more densely populated an area is, more acidic rain is. In other words, when more people are concentrated in one limited geographical area, naturally their activities have more profound negative impact on the environment than similar activities in less densely populated area. "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 is a serious problem since it rapidly destroys the environment including plant and marine life. When acid rain falls on the surface of leaves, it causes erosion in the upper layer that affects the leaves' ability to reproduce. Similarly plan life is hurt when solid loses important minerals including calcium, potassium, and magnesium due to consistent exposure to acidic rain. While it is true that nitrogen is important for plants, acidic rain carries nitrogen that is accompanied by some undesired substances such as mercury and lead that tend to cause nitrogen saturation. This may in turn damage roots. Similarly Marine life is hurt because to leakage of aluminum. Lower pH level also tends to stunts growth of plants.

The effects of acid rain are more far reaching than we are commonly told. What we mostly hear is that acid rain causes havoc to sea life, lakes, forests etc. But it is believed that acid rain causes more sweeping damage that includes buildings, monuments and mountains too. For example in Europe, we notice that most old buildings wear a worn out look and the deterioration process is marked and rapid. This is mainly due to consistent exposure of these buildings to acid rain. In the United States, the effects on monuments and buildings are less obvious since most of them are relatively new. Mountains are affected too since stones naturally deteriorate with passage of time as they are exposed to environment. The presence of various substances in the atmosphere that cause acid rain, affect chemical and physical composition of stones thus causing huge mountains like the Appalachian Mountains to turn into small mounds. [4]