Acid Rain: Effects on the ecosystem

ACID RAIN

Rain contributes considerably to the water cycle and it’s also very important for the survival of the plants and animals that inhabit this planet as it brings freshwater to the surface of the earth. Human beings are equally relying extensively on rain considering it helps with the production of food as well as electricity, but should we be certain that the rain is absolutely harmless for both us and the environment?


          Even though clouds primarily contain vapor water, they also contain other kinds of vapors or rather gases that fall down mixed with the rain droplets. This occurrence is referred to as Acid Rain.


HISTORY OF ACID RAIN

In Manchester, England, 1852, a pharmacist named Robert Angus Smith was the first to demonstrate the connection between acid rain and pollution by comparing the levels of acidity in the rain falling over industrial areas to the levels in areas near the coast that were much less contaminated. He came up with the term "acid rain" in 1872. Scientists started seriously investigating and researching the phenomena in the late 1960s. 
           In North America., when working with colleagues at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, Gene E. Likens discovered acid rain in the United States. In Canada to mimic the effects of acid rain, researchers applied sulfuric acid to entire lakes in regulated environmental studies in the 1970s and 1980s. Because of the remote location, studies revealed that the impact of acid rain on fish stocks began at a much smaller rate than those found in laboratory trials, with fish populations collapsing much sooner than when acid rain has immediate toxic effects on the fish caused by the crashes in prey populations.


CAUSES AND CHEMISTRY BEHIND IT.

  • Few toxins are emitted by decaying vegetation, erupting volcanoes and even lightning strikes.
  • Burning fossil fuels to power electric generators are responsible for one-fourth of nitrogen oxide and two-thirds of sulfur dioxide in the ambiance.  
  • Manufacturing, oil refineries, and other sectors are only a few other examples. 
  • Mostly, acid rain is caused by human activities.


        
Cycle of the formation on acid rain
          
                
       High amounts of nitrogen oxide (NO) and sulfur dioxide (SO2) are released into the atmosphere, they interact with the oxygen, water, and other chemicals which result in the creation of nitric and sulfuric acids that later on mix with water and may take the form of frost, rain, fog, or small pieces of dry material that fall to the ground.

          Pure or filtered water has a neutral pH of 7 meaning that is neither acidic nor alkaline. But with a pH of 5.6, normal rain is mildly acidic, because of the carbon dioxide (CO2), which dissolves and ends up causing carbon acids, while acid rain has a pH of 4.4 and below. 

          Sulfur dioxide is oxidized in the gas phase by an intermolecular reaction with the hydroxyl radical, and as it transforms into sulfur trioxide (SO3), is then readily converted to sulfuric acid in the presence of water

SO2 + OH· → HOSO2·

HOSO2· + O2 → HO2· + SO3

SO3 (g) + H2O (l) → H2SO4 (aq)


           Nitric acid is formed when nitrogen dioxide reacts with OH.

NO2 + OH· → HNO3

Dry deposition occurs in the absence of precipitation. Particles and gases attach to the earth, and other surfaces, allowing this to happen. This could account for up to 60% of all acid deposition.


EFFECTS OF THE ACID RAIN

  • There are no organisms in some acidic waters. And if an animal happens to survive mildly acidic water, the animals or plants it consumes may not.
  •  Acidic rain kills nitrogen-fixing microorganisms and damaged leaves and branches leaving them less likely to tolerate freezing temperatures as a result of their decreased ability to absorb sunlight. 
  • Besides biodiversity, acid deposition has an effect on the infrastructure and buildings. It can be considered a threat to agricultural fields.
  • Acid rain does not directly affect humankind, but it does have an indirect impact on us. As the sulfur dioxide that aids in its creation also induces chronic lung diseases such as asthma and bronchitis. 
  • Nitrogen oxide also produces ground-level ozone, which facilitates pulmonary illnesses such as pneumonia. 
  • In places with high altitude where acidic rain is present, it becomes acid fog which leads to visibility problems as it irritates the eyes, as well as the nose.
                       
 

ADVANTAGES 

  • Despite all of the limitations previously described and as harmful as it looks, we can still find some helpful advantages. 
  •  The compounds that make up acid rain are gases, but they don't contribute to global warming. In fact, by absorbing sunlight rather than trapping it in the atmosphere sulfur dioxide may provide a local cooling effect on the planet. 
  • Methane is responsible for about 22% of the human-enhanced greenhouse gas emissions. Acid rain can decrease methane emissions by up to 30% by dispersing sulfur compounds.
  • The presence of ozone high up in the atmosphere aids in the blocking of ultraviolet radiation.




RESEARCH PAPERS

       There is a lot of research done about this topic, yet one of the most important if not the most relevant is the investigation made by Gene E. Likens published by the Scientific American Journal in which he and his partners give a very detailed insight into the appearance of Acid Rain in the United States. 
         Likens, G., Wright, R., Galloway, J., & Butler, T. (1979). Acid Rain. Scientific American, 241(4), 43-51. Retrieved April 17, 2021, from http://www.jstor.org/stable/24965312

      Another very interesting research paper is by Anita Singh and Madhoolika Agrawal for the Journal of Environmental Biology in which they investigate the levels of pollution that contribute with the phenomenon in India. 

       Agrawal, M., & Singh, A. (2008). Acid rain and its ecological consequences. Journal of Environmental Biology. 15-24. Retrieved April 17, 2021, from   http://www.jeb.co.in/journal_issues/200801_jan08/paper_02.pdf

      Also, scientists from the Norwegian Institute for Water Research and the University of Oslo conducted a study about China as it is known as one of the most polluted countries in the world explaining the risks of industrialization as it helps in the production of gases that contribute in the Acid Rain and how it damages our ecosystem.

       Larssen, T., Lydersen, E., Tang, D., He, Y., Gao, J., Liu, H., and others. (2006). ACID RAIN in China. American Chemical Society, 418-425. Retrieved April 17, 2021, from https://pubs.acs.org/doi/pdf/10.1021/es0626133

 

DIY EXPERIMENT

      There are a few ways we can mimic the effects of Acid Rain so we can see for ourselves how it actually reacts.
      For example in the following experiment done by TeachEngineering, they try to recreate how the acid precipitation interacts with different materials.


        We can notice that in the spam of a day the materials used in the experiments deteriorate at a faster rate when submerged in vinegar rather than in water because as we know pure water has a balanced pH and vinegar instead has a very low pH, around 2.5 which makes it very acidic, making it a perfect representation of the interaction of Acid rain with the environment.