5 Causes of Acid Rain Explained

Causes of acid rain are; fuel combustion, unsustainable waste management, natural hazards, mining and exploration, and deforestation.

This article discusses the causes of acid rain, as follows;

1). Fuel Combustion (as one of the Causes of Acid Rain)

Although acid rain is not formed by combustion reaction (but rather by dissolution), combustion reactions play a major role in the formation of acid rain.

The combustion of all types of carbon-rich fuels can cause acid rain. Namely, fuels that produce acid rain include; petroleum, coal, natural gas, and biofuel.

This is because carbonaceous fuels contain at least one of the three elements; carbon, nitrogen and sulfur, whose gaseous oxides are anhydrous and react with water in the atmosphere to form what is known as acid rain.

These anhydrous gases; the most common being carbon dioxide (CO2), nitrogen dioxide (NO2), and sulfur dioxide (SO2) are emitted from fuel-based systems into the atmosphere and may reduce air quality, and facilitate global warming within their environs [2].

Acid rain can therefore be linked to all possible outlets of fuel combustion byproducts; including power plants, gasoline vehicles, portable electric generators, biorefineries, and other waste-to-energy facilities.

Although nuclear fuel combustion does not produce any significant emissions, the process of mining this fuel usually involves combustion of fossil fuels, which emit acidic gases.

It also shares links to other environmental impacts of fossil fuel combustion like climate change and pollution.

2). Unsustainable Waste Management

When waste is not managed optimally, it can result in the formation of acid rain.

This is because waste materials that are exposed to the environment can release nitrogenous, sulfuric or carbon compounds that may enter into the atmosphere and react with precipitation, leading to acidification.

For example, exposed organic waste in a landfill can undergo biodegradation and release any of the anhydrous gases (CO2, NO2, SO2) that form acid rain. Other reactions between elements and compounds in waste may also produce anhydrous gases.

Efforts to manage waste may also contribute to acid rain formation. An example is incineration or waste burning, whereby large amounts of emissions can be released into the atmosphere to react with water and oxygen [3].

Recycling may also involve machines that derive energy from fuel combustion, which is a cause of acid rain formation.

Nuclear waste also causes acid rain, although this is very rare. High-level waste (HLW) from nuclear power plants, contains nitrate which may evaporate and play the same atmospheric roles as anhydrous NOx from fossil fuels.

In agriculture, an unsustainable approach to the handling of farm waste through composting, mulching or other practices, can also emit gases that react with atmospheric moisture to form acid rain.

3). Natural Hazards (as one of the Causes of Acid Rain)

Natural rainwater is slightly acidic, with an average pH of 5.6 [1].

This is due to the introduction of sulfuric; nitric and carbon dioxides into the atmosphere from natural sources like decomposing biomass, and dust particles transported by wind.

Natural hazards can also cause acid rain. The most common and effective example of a natural hazard that causes acid rain is volcanic eruption that leads to the release of large volumes of ash, sulfur dioxide, hydrogen fluoride and carbon dioxide, all of which may react with, and acidify, atmospheric precipitation [5].

Regions around active volcanoes are therefore likely to experience acid rain, although the level of acidity and the frequency of occurrence may vary significantly, with differences in scale and activity levels.

Flooding is another natural hazard that is linked to acid rain events. Although it does not cause these events, flooding can intensify or magnify the effects of acid rain, by increasing the scale of infrastructural and ecologic damage that is caused by acidic rainwater.

4). Mining and Exploration

Mining and exploration activities can cause acid rain.

These include prospecting, drilling, excavation, use of explosives, and mineral processing, among others.

Petroleum, natural gas, and most mineral ores are rich in elements like sulfur, nitrogen and carbon, which may be oxidized to yield anhydrides that dissolve in atmospheric precipitate to form acid rain.

Minerals like pyrite are especially rich in sulfur, alongside metallic ores of copper and silver [4]. During mining, large amounts of sulfur dioxide are usually emitted into the atmosphere from such deposits.

The release of waste energy from mining equipment occurs alongside greenhouse emissions, the bulk of which includes acid anhydrides.

Mine tailings or waste can also produce dust, or other byproducts of internal reactions, that can contribute to the formation of acid rain.

Acid rain formation from mining and exploration, is similar to acid mine drainage processes; whereby surface water and air react with emissions and ores of minerals within the vicinity of mines, causing the acidification of the surface water bodies.

5). Deforestation (as one of the Causes of Acid Rain)

Although deforestation is not a major cause of acid rain, it can facilitate the formation of acid rain both directly and indirectly.

The direct influence of deforestation on acid rain formation comes through decomposition of plant biomass that includes leaves, roots and other vegetative parts which are produced as residue from deforestation activities.

In some cases, such as large-scale deforestation, these materials can release large amounts of anhydrous gases into the atmosphere, as they decay.

Alternatively, deforestation facilitates acid rain formation by diminishing the role of forests as carbon sinks.

In the absence of vegetation, atmospheric levels of CO2, NO2, HF, and SO2 among other gases, will increase, alongside the risk of acid rain.

Conclusion

The causes of acid rain are;

1. Fuel Combustion

2. Unsustainable Waste Management

3. Natural Hazards

4. Mining and Exploration

5. Deforestation

References

1). Liljestrand, H. (1985). “Average rainwater pH, concepts of atmospheric acidity, and buffering in open systems.” Atmospheric Environment (1967) 19(3):487-499. Available at: https://doi.org/10.1016/0004-6981(85)90169-6. (Accessed 12 November 2022).

2). Manisalidia, I.; Stavropoulou, E.; Stavropoulos, A.; Bezirtzoglou, E. (2020). “Environmental and Health Impacts of Air Pollution: A Review.” Frontiers in Public Health 8. Available at: https://doi.org/10.3389/fpubh.2020.00014. (Accessed 12 November 2022).

3). Rim-Rukeh, A. (2014). “An Assessment of the Contribution of Municipal Solid Waste Dump Sites Fire to Atmospheric Pollution.” Open Journal of Air Pollution 03(03):53-60. Available at: https://doi.org/10.4236/ojap.2014.33006. (Accessed 12 November 2022).

4). Salas-Martell, D.; Pareja-Guzman, G.; Tello-Hijar, J.; Rodriguez-Reyes, J. C. (2020). “Leaching of a pyrite-based ore containing copper using sulfuric acid and hydrogen peroxide.” Available at: https://doi.org/10.1007/s40090-020-00212-2. (Accessed 12 November 2022).

5). Sierra-Vargas, M. P.; Vargas, C.; Bobadilla-Lozoya, K.; Aztatzi-Aguilar, O. G. (2018). “Health Impact of Volcanic Emissions.” Volcanoes – Geological and Geophysical Setting, Theoretical Aspects and Numerical Modeling, Applications to Industry and Their Impact on the Human Health. Available at: https://doi.org/10.5772/intechopen.73283. (Accessed 12 November 2022).