Monday, January 28, 2013

Acid Rain

Water supply acidification can have drastic consequences for survival of some plant and animal species.

  • Humans burning of fossil fuels contribute to ocean acidification.
  • When fuels are burned, CO2 is produced. The ocean absorbs approximately 25% of the CO2 produced through the burning of fossil fuels.
  • The decreasing pH of the ocean through carbonic acid formation is known as ocean acidification.
  • New research suggests that the ocean's pH will decrease by an additional .03 to 0.5 pH units before the end of the century.
  • Fossil fuel burning also creates a large amount of sulfur dioxides and nitrogen oxides. These compounds form strong acids when they react with water.
  • If sulfur dioxides and nitrogen oxides react with water in the air, a strong acid is formed and can fall to the ground as rain or snow. This is referred to as acid precipitation, which is when rain, snow, or fog has a pH of 5.2 or lower. A pH of 5.6 is normal for uncontaminated rain.
  • acid precipitation
    Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infrastructure.
  • ocean acidification
    Ocean acidification is the name given to the ongoing decrease in the pH of the earth's oceans, caused by the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere.


  • Ocean acidification leads to decreased levels of carbonate ions in oceans. Since carbonate ions and calcium are main building blocks of calcium carbonate skeletons and shells (Figure 2), ocean acidification can potentially lead to their dissociation.


    1. fig. 1
      What impact does human-generated carbon dioxide have on oceans?

      Carbon dioxide cycles from the atmosphere into the ocean where it is stored in various forms, including dissolved molecules that increase the acidity of ocean water.
    2. fig. 2
      Ocean acidification poses a major threat to coral reefs

      Coral reefs, like the healthy one pictured in the first image, can be severely damaged by ocean acidification. If CO2 levels continue to increase, the future of coral reefs will likely resemble the damaged coral reef shown in the second image.
    3. fig. 3
      Processes Involved in Acid Deposition

      Processes involved in acid deposition (note that only SO2 and NOxplay a significant role in acid rain).

      Water is one of the world's most precious renewable resources. Unfortunately, human activities, inclusive of rapid industrial growth, are contributing to the deterioration of global water quality.

      Since the beginning of the industrial revolution, atmospheric gases have been absorbed into precipitation and bodies of water around the globe rendering them incrementally more acidic. When atmospheric CO2, NO, and/or SO2 are dissolved in water, that water becomes acidic.

      When the aforementioned gases dissolve in rain water, we experience a phenomenon known as acid precipitation (Figure 3). While acid rain is most commonly referenced, acid precipitation also includes acidic, sleet, snow, and fog, all of which can have a very damaging effect on global ecosystems. In rivers, dams, and lakes, increased acidity can mean that some species of animals and plants will not survive. Acid precipitation has additional impacts on agriculture and thus the global food supply as it can degrade soil quality, producing metal ions that are washed into water systems.

      It is estimated that the surface pH of the globe's most reliable water supply, the ocean, has decreased by slightly more than 0.1 units on the logarithmic scale of pH, representing an approximately 29% increase in H+ since the industrial revolution. It is estimated that it will further decrease 0.3 to 0.5 pH units (an additional doubling to tripling of today's post-industrial acid concentrations) by the year 2100 as the oceans absorb more anthropogenic CO2 from the atmosphere.

      Ocean acidification is expected to impact ocean species to varying degrees. Photosynthetic algae and sea grasses may benefit from higher CO2 conditions in the ocean, as they require CO2 to live just like plants on land. On the other hand, studies have shown that a more acidic environment has a dramatic effect on some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton. When shelled organisms are at risk, the entire food web may also be at risk. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Many jobs and economies in the United States and around the world depend on the fish and shellfish in our oceans.

      Without quality water supply, life on this planet will become increasingly unsustainable. It is incumbent upon environmental policy makers to consider that the acidification of the global water supply has broad implications for global growth and global economies and to act to implement policies accordingly.

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