Atmospheric Changes and Air Pollution


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Photo source: (left) and (right)

We all need clean air. Humans and all other animals need oxygen to breathe. Oxygen is produced by plants as they photosynthesize (photosynthesis illustration source: NASA's Jet Propulsion Lab). Many people know these basic principals but few people are aware that more than half of the oxygen we breathe comes from the ocean (Weber, M., 1995, p.85).  However, pollution is now reducing the oceans' ability to produce oxygen. In many large cities, the air quality reaches toxic levels high enough that the authorities advise the population to stay indoors.

Oxygen producers include all autotrophic organisms (photosynthetic plants and bacteria). One of these organisms is phytoplankton. The word plankton comes from the Greek word "planktos" which means "drifting," descriptive of the billions of single-celled plants that float on the surface of the oceans. Most phytoplankton is unicellular algae. The chlorophyll in the phytoplankton is part of the reason the ocean water looks green. Phytoplankton is very important not only as an oxygen producer, carbon dioxide and temperature regulator, but is also essential to the marine food chain. These single-celled organisms are the cornerstone of life in the ocean.  They are eaten by zooplankton which become food for krill, fish and other crustaceans which then become food for larger fish and other marine life. But these unicellular organisms are very sensitive to their surroundings. Their health and ability to produce oxygen can be reduced by temperature changes, salinity changes and pollutants. 


Eutrophication poses a threat to phytoplankton. An overabundance of carbon dioxide and a lack of oxygen resulting from eutrophication cause areas known as dead zones. (Click here for more details about dead zones). 

Chlorofluorocarbons (CFCs) are used for a variety of products including cleaning computer chips, aerosol propellants and air conditioning units. Use of CFC's damage the ozone layer. Reduction or removal of ozone allows damaging ultraviolet rays to reach earth's surface which can kill phytoplankton. During the spring, ozone is completely gone above Antarctica and during this same time, scientists have noted a 6-12% drop in plankton population. Phytoplankton reproductive cells are even more severely affected; their photosynthesis dropped by almost 65% after only one hour of exposure to UV light. 

The computer-generated image to the right (source: NASA, Goddard Space Flight Center, Image 94-hc-563) shows measurements of ozone during the Antarctic spring, September 21 to October 15, 1992, taken by the Halogen Occultation Experiment (HALOE) on board the NASA Upper Atmosphere Research Satellite (UARS). The image shows low levels of ozone at 25 kilometers (15.5 miles) over large areas of the Southern Hemisphere as well as the Antarctic region, forming a so-called "ozone hole." The white area at the South Pole, centered around 90 degrees latitude, is an area where no measurements were made. The lowest levels of ozone (shown as dark blue) are centered over the eastern part of Antarctica and represent about 1.4 parts per million by volume (ppmv). However, relatively low ozone levels also extend over the southern tip of South America; the deep green representing about 3.0 ppmv. Low levels also extend even further over South America and into the mid-latitudes and the tropics, as indicated by the light green. (image text source: NASA, Goddard Space Flight Center, Image 94-hc-563). The illustration below (NASA, Jet Propulsion Laboratory) shows how CFC's react with our atmosphere to cause long-term damage.



Some studies indicate that airborne pollutants, primarily from factories and automobiles, are responsible for almost a third of all contaminants and nutrients entering marine waters (United Nations Environment Programme, 1990). An air pollutant is any substance in the air which causes damage to life, ecosystems or property. There are natural sources of air pollution which result from volcanoes and forest fires.  However, most of the air pollution is now a direct result of human activities.  The issue of air pollution and how it relates to our ocean is very complex. The process of pollutants being deposited into the ocean is known as atmospheric deposition.  The categories of air pollution with the greatest potential to harm water quality are nitrogen, mercury, other metals, combustion emissions, and pesticides. Mercury is in its own category since it behaves so much differently in the environment than other metals. These pollutants all have the ability to settle into bodies of water and damage ecosystems as well as pose a risk to public health. Air pollution causes most short term measurable damage to the water quality when toxic chemicals fall from the air as dust, as a result of gravity or when rain rinses these chemicals to the ocean and water ways which lead to the ocean, commonly referred to as acid rain.


Gases mix, mingle and react in our atmosphere, often turning into poisonous substances capable of returning to earth as acidic rain or snow, as the image to the left illustrates (NASA) ( Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides as well as carbon dioxide. These chemicals are released into the atmosphere by burning fossil fuels. Burning fuels include the use of coal in the production of electricity, base-metal smelting (manufacturing of metal), and from fuel combustion in vehicles. Some of these airborne chemicals fall into the ocean as a result of gravity, as the graphic on the left shows, when rain falls through carbon and sulfur dioxide molecules which are suspended in our atmosphere.  The result is carbonic acid (H2CO3) or acid rain. 

 Acid rain releases aluminum from soil into rivers which ultimately ends up in the ocean. The aluminum clogs the gills of aquatic animals, attacks calcium in their bodies, and causes life-threatening deformities in their young.  Ocean water normally has an average pH value of 7.8 - 8.1, which is slightly basic.  "Scientists believe that the oceans have already become slightly more acidic over the last century" (Black, R., 2003). The reaction to this change in the ocean is very difficult to measure as the changes are very slow due to the size of the ocean. We have learned from smaller bodies of water that as the water pH approaches 6.0 (more acidic), crustaceans, insects, and some plankton species begin to disappear. As it approaches 5.0, major changes in the makeup of the plankton community occur, less desirable species of mosses and plankton may begin to invade, and the progressive loss of some fish populations is likely. In smaller inland lakes where the pH can fall below 5.0, the water is largely devoid of fish, the bottom is covered with undecayed material, and the areas close to shore may be dominated by mosses. Most of the serious problems have been caused on land and in bodies of water smaller than the ocean. There is still some debate about the exact role of the ocean in sulfur cycles. According to a recent article published by researchers from the Lawrence Livermore National Laboratory, 80% of the carbon dioxide released into the atmosphere will end up in the ocean in a form that will make the ocean more acidic. When carbon dioxide is in the atmosphere, it contributes to the greenhouse effect causing adverse climate change. When it enters the ocean, the acidification is harmful to the natural balance of the ocean as well as marine life.


Mercury is a toxic chemical which is introduced into our environment naturally (it is found in rocks and minerals) as well as from man-made sources. Studies show that human activities have more than tripled its concentration in the environment since 1990. It is estimated that 75% of the mercury in our environment is from man-made sources (United States Environmental Protection Agency, 1997). Human sources include incinerators, coal-burning facilities, certain industrial processes, and household items such as batteries, fluorescent lights, thermometers, electrical switches and dental fillings. 

Mercury can travel great distances in the atmosphere and mercury pollution can rise through atmospheric deposition. The chemical characteristics of this metal are very different from other metal pollution. Mercury can be transformed through biological processes into methyl mercury which has the ability to accumulate in the tissues of fish and shellfish and can pose a threat to the health of humans and wildlife. The concentration of mercury within the tissue of a fish or shellfish may be tens of thousands of times greater than the concentration of mercury in the water. The primary health effects from mercury are on the development of the brain and nervous system.  Pregnant women and women of child-bearing age are advised to be aware of how much mercury they consume because of these effects. Some people can also be extra sensitive or allergic to mercury.


During the 1970's, it became widely recognized that the concentrations of environmental lead had been rising quickly.   In 1978, there were an estimated 3-4 million children in the United States with elevated blood lead levels (United States Environmental Protection Agency, 2003). Lead is a naturally occurring bluish-gray metal found in small amounts in the earth's crust.  It is known to cause a range of health effects including damage to kidneys and reproductive system, behavioral problems and learning disabilities, seizures and even death. The use of lead additives in fuel, which began in the 1920's, was proven to dramatically increase lead in our environment, as this illustration from NASA's Jet Propulsion Laboratory shows.  The graph on the left shows lead levels in Greenland glacial snow since 800 B.C.  The graph on the right shows the decrease in lead in the Canadian atmosphere due to the use of unleaded gasoline. Between 1973 and 1985, airborne lead concentrations fell by 76%, following the introduction of unleaded gasoline in 1975, a figure that matches almost exactly the increased use of unleaded gasoline (Health Canada, 2005). 


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