How Does Acid Rain Form

• Enormous quantities of manmade and natural material are added to the air every day.

• Most of the materials added to the atmosphere return to the ground through a process known as deposition. Deposition occurs when it rains and snows, but it can also occur when dust settles out of the atmosphere during dry periods.

• The earth's gravity works to continually pull dry particles back to earth.

• Uneven heating of the earth results in global winds in the atmosphere. Global winds provide the energy for long-range travel of the gases, liquids, and dust in the atmosphere, which can travel great distances before falling back to the ground.

• The burning of fossil fuels like coal and oil products by automobiles and power plants releases large amounts of sulfur dioxide and nitrogen oxides into the air.

• While being transported by winds, some of these particles get caught up in clouds.

• When sulfur dioxide and nitrogen oxides gases and particles come in contact with water droplets in clouds, chemical reactions can occur, resulting in acid rain.

• Additional processes called rainout and washout mix these acidic gases, liquids, and particles into rain drops and snowflakes and carry them to the ground.

• Acid rain is less a problem in regions where the bedrock is composed of limestone and dolostone (carbonate rocks containing the minerals calcite and dolomite).

• CaCO3 + H2CO3 -> Ca (2+ ion) + 2(HCO3) (-ion)

• Rain and snow that falls in the Eastern U.S. typically has a much lower pH than precipitation in other parts of the country. The pH of rain and snow in the Eastern U.S. is much lower than in less populated areas.

• Graph comparing pH readings for the Eastern U.S. with parts of the world with fewer coal burning powerplants and automobiles.

• U.S. Nitrogen Oxide Emissions

• U.S. Sulphur Dioxide Emissions

What are the Effects of Acid Rain?

• More than thirty years ago, scientists noticed that in certain lakes in remote wilderness areas, fish populations were mysteriously declining. Some lakes that once teemed with fish were found to contain none at all.

• In their search for what caused the fish to die, scientists concluded that acid rain was the problem. Researchers continue to document that acid rain is harmful or fatal to fish.

• Acid rain also has been found to speed up the natural decay of stone monuments and historical buildings.

• Other materials such as iron, steel, zinc and paint also can be damaged by acid rain.

• The human health effects of acid rain are also of concern. Although people aren't directly in danger from exposure to acid rain, the particles in air that lead to acid rain may be a risk to human health.

What is Being Done to Control Acid Rain?

• The Clean Air Act Amendments that became law in December 1990 mandate stricter controls of sulfur dioxide pollution from coal-burning power plants.

Acid Rain Links to Methane Emission from Wetlands: Controls and Reversibility

• Two of the largest global environmental problems of our times - climate change and acidic deposition - have largely been studied as unconnected phenomena, but appear now to be highly interrelated.

• New research suggests that the enhanced sulphur in acid rain can, when deposited on nutrient-poor wetlands, greatly suppress the release of methane from these wetlands because sulphate-reducing bacteria out-compete methane-producing bacteria for nutrients.

• In the laboratory, addition of sulphate to peat cores at doses similar to that received by polluted areas of central Europe has consistently suppressed methane emission by 20-50%.

• This suppression and its potential reversibility are important since sulphate deposition is rapidly decreasing across wide areas of Europe and North America (due to pollution control legislation) while rapidly increasing in Asia (due to industrialisation and population growth).

• This project will:
  1. test the reversibility of the effect of sulphate on methane emission in the laboratory.

  2. artificially increase sulphate deposition to a natural peat bog in the field.

• Researchers hypothesise that methane emission will be increased by up to 50% in the reduced-sulphate experiments, and reduced by a comparable percentage in the elevated-sulphate experiments.