Our atmosphere contains many pollutants from human activities. Some of these come from fossil fuels, which release large amounts of sulfur dioxide (SO2) and nitrogen oxides (NOX) into the air. Combined with water and powerful oxidants like ozone, sulfur and nitrogen oxides become sulfuric and nitric acid. These acids may travel long distances before falling to the earth as rain, snow, sleet, hail, fog, dew or dust.

Basic facts

Acid rain is measured using the pH scale. The pH scale ranges from 0 (very acidic) to 14 (most alkaline). Seven is neutral. Rain is by nature slightly acidic, with a pH of 5.6. Any precipitation below that is considered "acid rain". Because the scale is logarithmic, a pH of 4.6 is ten times more acidic than normal rainwater and a pH of 3.6 is a hundred times more acidic. The average pH of rain in Vermont is between 4.2 and 4.4 with extremes ranging from 2.4 to 7.4. Highly acidic rain has been linked to the destruction of stone statues and gravestones.

pH Scale with Reference to Vermont Aquatic Ecosystems

What Can You Do?

Consider your lifestyle. Do you drive a car? Do you carpool? Is your electricity produced by burning fossil fuels? Are there changes you can make to conserve energy or to use different energy sources?

• Make your home energy efficient. Check out the Energy Rated Homes of Vermont website.
• Carpool. Contact Vermont Ride Share: 800-685-7433.
• Check out EcoLogical Solutions: Global Warming for suggestions on how to make your daily lifestyle earth friendly. Global Warming and Acid Rain have similar origins. Some of the primary greenhouse gases: carbon dioxide and nitrous oxide are also contributors to acid rain. For more information on Global Warming go to EPA's Global Warming website.

Frequently Asked Questions (FAQs)

Is acid rain getting better?
A recent article in the journal Nature ("Regional trends in aquatic recovery from acidification in North America and Europe", October 7, 1999) has demonstrated limited recovery in aquatic systems (lakes and ponds) from acid rain. The researchers looked at acidic deposition in North America and Europe. They found that all regions in Europe were experiencing some recovery. However, the only region in North America to experience chemical recovery was the Vermont-Quebec region. According to this study, Vermont experienced a strong decline in sulfates and a small yet statistically significant increase in alkalinity (the buffering capacity of water). Sulphur deposition in monitored lakes has declined by 29% from 1980-1995 in the northeast United States. This means that Vermont is beginning to see positive effects from the 1990 Clean Air Act. Progress has yet to be made on lowering nitrogen oxides, a more powerful acid than sulfates. Additional reductions in sulfur and nitrogen oxide emissions are needed before Vermont sees an improvement in the pH of its waters. To date, there has been no measurable improvement in the biological communities of Vermont's acidic lakes.

Why does acid rain affect some lakes more than others?
Lakes that are most sensitive to acid rain are small, at high elevation, and located in areas with low buffering bedrock. The majority of Vermont's sensitive lakes are found in remote and undeveloped regions of the Green Mountains and pockets in the Northeast Kingdom. Most of our highly acidic lakes are found in the southern Green Mountains.

How does acid rain affect aquatic life?
Acidified lakes show the following changes:

• Disappearance of the highly sensitive clams, snails, crayfish, and other animals dependent upon calcium carbonate for shells or exoskeletons.
• Disappearance of young or entire populations of the more sensitive species of fish, including rainbow trout and smallmouth bass.
• Disappearance of frogs, tadpoles, turtles, and certain species of salamanders.
• Disappearance of the most sensitive aquatic insects, primarily the mayflies.
• Increases in mosses, attached green algae, and fungal mats.
• Increases in plant species commonly associated with acidic environments.
• Increases in the more tolerant aquatic insects, including whirligigs and predaceous diving beetles, water boatmen, alderflies, dragonflies, damselflies, and other true flies.
• Lake transparency may increase because of the decline in zooplankton and phytoplankton (small animals and plants) suspended in the water column.

More on Acid Rain

• Vermont Monitoring Programs
• The Vermont Perspective
• TMDL for 30 Acid Impaired Lakes (pdf, 1.1 MB)

Links of Interest

• Canadian Primer on Acid Rain
• National Atmospheric Deposition Program
• US EPA Acid Rain Home Page
• State of Vermont Air Pollution Home Page
• Vermont Monitoring Cooperative Home Page

Updated: March 2004