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  • Pure water has a pH of 7.0 (neutral); however, acid rain has a pH of about 5.6 (acidic).
  • The acidity of rainwater is due to the presence of three substances (CO2, NO and SO2) found in the troposphere (the lowest layer of the atmosphere).
  • As carbon dioxide (CO2) is present in great concentration, it contributes the most to the natural acidity of rainwater.
  • Carbon dioxide, produced due to the decomposition of organic material, is the primary source of acidity of unpolluted rainwater.

Acidity of Polluted Rainwater

  • Unfortunately, human industrial activity produces additional acid-forming compounds in far greater quantities than the natural sources of acidity described above.
  • In some areas of the United States, the pH of rainwater can be 3.0 or lower, approximately 1000 times more acidic than normal rainwater.
  • In 1982, the pH of a fog in the west coast of the United States was measured to be at 1.8.

Impact of Acid Rain

Impact on Soil

  • Hydrogen ions (produced due to acid rain) react with nutrients like potassium and magnesium in the soil and cause leaching of nutrients rendering the soil infertile.
  • Acid rain leads to increase in relative concentration of ammonia (NH3) in the soil because of decrease in the concentration of other nutrients.
  • Increase in the concentration of NH3 decreases the rate of decomposition resulting in less humus in the soil.
  • Impact of acid rain on soils is less in India, because Indian soils are mostly alkaline (basic) in nature.
  • Indian soils are alkaline, because the density of forests is low due to the monsoon type of climate.
  • On the other hand, soils of equatorial region are comparatively acidic, because of high availability of organic matter.

Impact on Microorganisms

  • Optimum pH levels for most bacteria and protozoa are nearly neutral. The fungi prefer acidic environment and the blue-green algae prefer alkaline environment.
  • Due to acid rain, the growth of fungi increases and the growth of other microorganisms in the soil and water decreases.

Impact on Objects

  • Metals undergo corrosion when they come into contact with acid rain.
  • Corrosion of metals such as mercury, cadmium, lead, etc., causes their concentration to rise in water bodies, with further repercussions for human beings.
  • Marble experiences discolouration and plaque formation on contact with acid rain.

Impact on Humans, Wildlife and Plants

  • Contact with acid rain can cause various diseases and even death of human beings.


Environment & Biodiversity