The term “acid rain” is used in reference to the precipitation of acidic products when water vapor from the evaporation and transpiration process reaches the lifting condensation level and falls back in form of rain. A mixture of ordinary rainwater and suspended acidic gases in the atmosphere are the main components of acid rain (1). When gaseous products such as nitrogen oxides and sulfur (IV) oxide are suspended in the atmosphere, they readily combine with rainwater to form acidic acid rain. When addressing the concept of acid rain, it is imperative to mention acid deposition which is subdivided into two categories namely wet and dry deposition.
Firstly, wet deposition is the combination of acid rain itself (a mixture of rainwater and other gaseous products), snow and most importantly fog (3). Different types of plants and animals are impacted by wet deposition as it moves through the land surface. There are quite a number of factors that determine the effect of acids on living organisms. For instance, the level of acidity contained in the wet deposition as well the capacity of the soils to buffer will determine the degree of impact of the acids on living organisms.
On the other hand, dry deposition is composed of the actual acidic gaseous compounds and other acidic particles which usually dissolve in rain water to form acidic rain that has a pH slightly lower than 7(3). Practically, dry deposition eliminates about 50 % of all the acidic components in the atmosphere. The acidic particles and gaseous products are literarily blown by the wind into different directions and destinations like on building tops and settlements.
Moreover, rain storms can also sweep away these acidic particles and gaseous products from different surfaces such as tress. The runoff which is obtained from such events adds up to the already built-up acid rain thereby increasing the acidity of precipitation. Active ingredients which are responsible for acid rain are usually blown by the wind across the national borders. The acidic substances may even be transported several miles away. Hence, the main cause of acid rain is the chemical reaction between acidic particles or gaseous compounds with normal rain water, the active part of the air which is oxygen alongside other atmospheric chemicals.
The rate of these reactions and the degree of acidity formed are largely precipitated by the presence of sunlight. Both sulfuric acid and nitric acid which are fairly mild in concentration due to a higher pH are formed from the reaction. Therefore, the composition of acid rain is largely dependent on the mature of gaseous compounds suspended in the atmosphere although carbon (IV) oxide and gaseous compounds derived from nitrogen are the main contributors of acid rain (1).
Effects of acid rain
Surface waters and aquatic animals
The aquatic environment such as lakes, oceans and rivers is the worst affected by the effect of acid rain. The ecology of the aquatic environment is usually interfered with or disrupted when exposed to unusually high acidic concentrations. Once the forests are in contact with acid rain, the acidic water gradually finds its way into watercourses like river beds, streams and lakes (1). Besides, this acidic rain also falls on roads, constructions and open fields. The aquatic habitat also receives an equal share of acid rain. Lakes and streams have a pH that is slightly basic at round 8, neutral at 7 or slightly acidic at a pH of 6.
However, there are those lakes which possess natural acidity even without being affected by acid rain. The most sensitive components of water are usually affected by acid rain. The effect is especially pronounced in soils which have a lower buffering ability. These are soil samples that do not have the ability to neutralize the effect of acid rain. Upon receiving acid rain, these water bodies become more acidic than they used to be before (1). This implies these lakes and rivers will experience a gradual drop in their pH. Aluminium is released from soils especially in locations where the ability to buffer is rather low. The released aluminium is transported into other watersheds in spite of the fact that it is a toxic metal to most species of animals which are aquatic.
Europe has experienced some of the worst effects of acid rain on forests. About one-third of forests in Germany have been spoilt by pollution related to acid rain. Trees that have been attacked by acid rain develop weak tissue cells and therefore are more prone to attack by diseases and insects (2). One of the most affected tree species is the conifers bearing in mind that its sharp needles openly protrude and therefore more vulnerable to acid attack throughout the year. There are those trees which after being affected by acid, their leaves fall off. Besides, biomass measurement of a typical forest has been found to diminish by a significant margin of 20 % in forests that have been prominently affected by acid rain.
In addition to the above, there are those categories of forests that lie on high altitudes and as a result, are covered by fog or cloud quite often. Cloud droplets have a lower pH of about 3.6 which is equally lower than the pH of the actual acid rain which often stands at a mean of 4.2. moreover, acid rain affects young growing plants in the forest owing to the fact that these tender plants have very soft tissues which are easily affected the acidic downpour (1).
The cells are damaged thereby hampering the growth and development of the young plants. In addition, acid rain has the capacity to leach nutrients from leaves and other plant surfaces (2). Acid rain can quickly leach and reduce the amount of important macronutrients from leaves at a faster rate than the root system can supply. The waxy coat found on leaves can also be spoilt by both acid rain and tri-atomic oxygen. When the coating is removed, it will definitely make the plant to be more susceptible to pest and disease attacks.
Paints as well as a coating for automotive bodies have been damaged by acid rain. The horizontal surface of the automotive bodies seems to be more vulnerable to acid attack as has been reported in many cases. The acidic attack on these surfaces appears in the form of irregularly patched spots which have been etched. In order to detect the damage in the best way possible, fluorescent lamps are used (2). Vehicles which are fairly dark in color can be easily observed since the effect of the acid is quite visible on them. Immediately a drop of moisture evaporates from these automotive surfaces, the etches caused by acid attack can be observed. Besides, there is also sufficient evidence that etching takes place on automotive surfaces that have been painted afresh.
The damage caused by acid rain is usually permanent and cannot be reversed. Painting the surface again is the only solution to reverse the damage. Hence, acid rain has the ability to cause a visible scar on automotive surfaces.
When laboratory tests are carried out on attacked surfaces, it indicates the presence of sulfates which are also at elevated levels implying that acid rain is indeed responsible for the damage.
The mess in this case is caused by evaporation of acidified water droplets from the surface of automotive bodies. Hence, there are certain steps which are usually taken on body parts which have been freshly painted to avoid the attack by acid rain. One of the steps taken is to carry out regular washing of the automotive surface and then drying using the hand. Additionally, during precipitation, the vehicle can be covered to avoid any contact with rain. Finally, there are protective coatings which can be used to protect the finished surface so that the effect of acid attack is reduced significantly.
Metals are usually corroded in the presence of both wet and dry deposition on their surfaces. In addition, other materials such as stone and paint are also deteriorated by acid rain due the chemical reaction which is initiated by the wet deposition (3). After the acidic attack, these materials lose the value significantly. For instance, bridges become weak, buildings are worn out and monument surfaces are etched thereby appearing dull.
Moreover, buildings can be made dirty by the presence of wet deposition which often calls for the need to repaint them and consequently increasing the costs of maintenance. However, the problem can be reversed using paints that are resistant to acid attack.
Visibility through the atmosphere is usually impaired when sulfates and nitrates that form sulfur (IV) oxide gas and nitrogen oxides respectively are suspended in air. These gaseous compounds reduce the ability to see clearly because they potentially cause atmospheric blockage (4). For instance, sulfates have been found to reduce visibility by a margin of between 50-70 % in some parts in Eastern United States.
Poor visibility is a serious environmental concern. Accidents have occurred when motorists fail to see clearly on road surfaces. Poor visibility is also a matter of concern in aviation climatology. Pilots need to have a clear visibility of the run ways during take-offs and landing.
Human beings are gradually harmed by acid rain in an indirect way. Oxides of nitrogen and sulfur which cause acid rain are harmful to human health. These gaseous compounds are toxic and once human beings inhale them and find their way in lungs and internal respiratory system, incidences of increased illnesses especially those associated with breathing are realized. For example, certain chronic lung disorders such as cancer, bronchitis and asthma are aggravated when these acidic gaseous compounds are inhaled (1). In fact, oxides of sulfur and nitrogen act as environmental triggers of asthma. Scientific research has drawn a close relationship between the presence of dry deposition on air and the prevalence of certain illnesses which attacks lung and heart.
Besides, these sulfur and nitrogen oxides also react with other organic compounds to form tri-atomic oxygen which is commonly known as ozone. Mortality and morbidity rates are high in areas where ozone level is notably at higher level. The lung is inflamed in the presence of ozone. Besides, emphysema is a common lung condition associated with exposure to elevated ozone levels.
Reducing acid rain
There are quite a number of ways and methods which can be adopted in reducing the effect of acid rain. However, it is very important for people to understand and acknowledge how acid rain impacts both the environment and human health (4). Such an understanding will make the human population to appreciate the need of reducing the emission of sulfur and nitrogen pollutants into the atmosphere.
To begin with, it is imperative to perform a cleaning exercise of exhaust pipes and smokestacks. The main source of energy in the contemporary world is obtained from combustion of fossil fuels. Oxides of nitrogen and sulfur (IV) oxide are the main pollutants released into the atmosphere as a result of this combustion. Hence, is only through reducing the emission of SO2 that the effect of acid rain can be reduced. For instance, coal which contains minimal sulfur can be used for combustion. In addition, the coal to be burnt can be washed using the scrubbing process. This process facilitates the chemical reaction of SO2 with calcium hydroxide and neutralizes SO2 in smoke chimneys before being released into the atmosphere (4).
Using alternative sources of energy is yet another step that can be taken to reduce acid rain. For example, geothermal energy, wind energy and hydro power can be used to provide energy instead of relying on the combustion of fossil fuels. In fact, these other sources of energy are relatively clean and also renewable. Fuel cells, batteries and natural gas are other alternative sources of energy. Moreover, the environment which has already been damaged should be restored. This will reverse the effects of acid deposition. One way of restoring the degraded environment is by adding lime water to lakes and other watercourses as well as soils which are already acidic so that the effect of the acid can be neutralized (4).
Finally, acid rain can be reduced if some decisive actions are taken at the individual level. For example, turning off lights when not in use, using vehicles which emit low acidic gases and home insulation are all important steps in reducing the effects of acid rain
In summing up this essay, it is imperative to note that acid rain refers to the type of precipitation that is characterized by deposition of acidic substances derived from sulfur (IV) oxide and oxides of nitrogen. Usually, these acidic gaseous products chemically react with rain water in the atmosphere and falls as acid rain with a pH slightly lower than 7. However, when addressing the concept of acid rain, two main aspects come into play namely wet and dry deposition.
In wet deposition, a combination of fog, snow and gaseous acidic products are deposited on the different surfaces in form a weak acidic solution. On the other hand, dry deposition refers to a mixture of sulfur (IV) oxide, oxides of nitrogen and other acidic particles deposited into the environment. Therefore, the main cause of acid rain is the emission of acidic gaseous compounds as a result of different human activities like combustion of fossil fuels.
Acid rain has a myriad of negative effects both to human health and the environment at large. It has been associated with worsening conditions of the lungs and heart especially in patients with pre-existing conditions such as asthma. For example, it is a major environmental trigger of asthma.
The suspension of SO2 and oxides of nitrogen in the atmosphere also impairs visibility. In the case of forests, acid rain is known to leach nutrients from leaves and other protruding plant parts. Cells and tissues in young plants are adversely affected by acid rain since the tender tissues or cells are scotched by the acid rain leading to substantial reduction in forest growth.
Finally, there are several mitigation measures which can be taken to reduce the effect of acid rain. Burning coal with low content of sulfur is necessary. Better still, cleaning of SO2 in smoking fumes using “scrubbing” method is recommended.
- Petheram, Louise, “Acid Rain”. Capstone Press, Minnesota, 2003.
- Godbold, L. Douglas and Hüttermann Aloys, “Effects of acid rain on forest processes”, Willey-Liss Inc., New York, 1994.
- Brimblecombe, Peter, Hara Hiroshi and Houle, Daniel, “Acid Rain – Deposition to Recovery”, Springer, Dordrecht, 2007.
- Raufer, K. Roger and Feldman, L. Stephen, “Acid rain and emissions trading: implementing a market approach to pollution control”, Rowman & Litterfield Publishers, New Jersey, 1987.