D E C banner
D E C banner


The New York State Department of Environmental Conservation has added a link to a translation service developed by Microsoft Inc., entitled Bing Translator, as a convenience to visitors to the DEC website who speak languages other than English.

Additional information can be found at DEC's Language Assistance Page.

Acid Rain Questions & Answers

Some Questions and Answers on Acid Rain

What is Acid Rain?

Small image of the forming of acid deposition
Click to see large image

Acid rain, or precipitation, comes in many forms: rain, snow, sleet, hail and fog, and as deposits of acid particles, aerosols and gases. It is formed when sulfur dioxide and nitrogen oxides combine with moisture in the atmosphere to produce sulfuric acid and nitric acid.

Acid Rain, a Recent Phenomenon

Paleoecological studies involving analysis of sediment cores collected during the 1980s showed that many of the study lakes became acidic only during the last 10 to 50 years, a period when air pollution and acidic deposition levels were highest. Other studies have documented that the decline and loss of entire fish populations also occurred in many lakes within the same timeframe. Big Moose Lake in the southwestern Adirondacks is an example of an important lake which has been impacted in recent decades by acidic deposition and lost important fish populations. Historical records from this 1,286-acre lake document healthy fish in the lake and in nearby streams during the 1930s. However, surveys conducted in the 1980s in the North Branch Moose River Watershed (which includes Big Moose Lake) showed a serious loss of many fish populations.

How Acidic is Rain in New York State?

Data collected by the National Atmospheric Deposition Program showed that the average pH for rainfall in New York State was about 4.9 to 5.1 for 2013. Acidity levels have decreased by nearly a factor of 10 since the late 1980's, when the average pH of rainfall across the state ranged from 4.1 to 4.4.

A pH scale is used to measure acidity, with 0 being the most acidic and 14 the most alkaline. A value of 7 is neutral. Solutions with a pH of less than 7 are acids, while those with a pH greater than 7 are bases. The scale also is logarithmic, meaning that a one-unit change actually represents a tenfold change.

Rainfall is somewhat acidic by nature, primarily due to carbon dioxide and water vapor combining in the atmosphere. The pH of natural (non-polluted) precipitation ranges from about 5.0 to 5.5.

Where Does Acid Rain Originate?

Satisfaction of our energy needs through the combustion of fossil fuels (coal, oil, natural gas, wood, etc.) is the basic cause of acid rain. Emissions from motor vehicles, power plants and industries all contribute to acid rain. Emissions of SO2 and NOx from the heavily industrialized Midwest have been identified as significant contributors to New York State's deteriorating air quality as well. Tall smokestacks spew emissions high into the atmosphere, and prevailing westerly winds then carry them eastward. Efforts to reduce emissions of SO2 and NOx from the Midwest are progressing, but emissions remain disproportionately high compared to those originating in the Northeast.

The EPA's acid rain data for 2000 show that Ohio's emissions of sulfur dioxide and nitrogen oxides are four times greater than New York State's level. Thus, it is evident that restricting emissions of sulfur dioxide and nitrogen oxides is the only viable solution to the problem of one region polluting and causing environmental damage to another.

How Does Acid Rain Affect the Environment?

Aquatic - Fish populations are damaged in a number of ways. Acidic water disrupts their reproductive cycle. It also leaches aluminum from the soil into the water, clogging the fish's gills and altering their blood chemistry. As a lake becomes acidified, one species after another disappears. In addition to sensitive lakes, the Adirondack region includes thousands of miles of streams and rivers also sensitive to acidic deposition. Over half of these may become acidic during spring snowmelt.

Forests - Sulfur and nitrogen deposition have caused adverse impacts on certain highly sensitive forest ecosystems, most notably the high-elevation, spruce-fir forests in the eastern United States. Forests are damaged because acid precipitation drains nutrients from the soil. Excess nitrogen in the air also may adversely affect tree growth. Evidence of decreased growth and dieback has been found in the Adirondacks already.

Visibility - Dry acidic particles in the air lessen visibility. When winds blow from the southwest at Whiteface Mountain in the Adirondacks, visibility can be reduced from 50 miles to fewer than 5 miles.

Materials - For materials and cultural resources, dry deposition (the deposition of particles and gases between rain events) is now considered to be more damaging to stone than wet deposition (the deposition of particles and gases during rain events).

Human Health - High concentrations of fine-particulate sulfate and nitrate can enter the cardiovascular and respiratory systems, resulting in disease or even death.

Metals such as mercury and cadmium from soil deposits in lakes, streams, and reservoirs can accumulate in the tissues of fish, making them toxic to humans.

Metals also can be leached from the soil into reservoirs, or from old lead and copper pipes directly into home water supplies, causing serious illness.

New York State-a Leader in Reducing Acid Rain

New York State has worked hard to reduce air emissions which contribute to acidic deposition, including passage of the first Acid Deposition Control Act in the nation in 1984. The New York State Legislature realized then that the state could not solve the acidic deposition problem by itself, due to the significant impact of air emissions originating primarily in the Midwest. DEC reported in its final Environmental Impact Statement on the Sulfur Deposition Control Program that 83 percent of the sulfur deposition that occurred in the southwestern Adirondacks originated outside of New York State.

The state's early action precipitated reductions at the national level of sulfur dioxide and nitrogen oxides, the precursors of acid rain. Title IV of the Clean Air Act of 1990 set a permanent cap on the total amount of SO2 electric utility emissions at about one half of the amount emitted in 1980. NOx emission-rate limitations for coal-fired electric utility units have resulted in about a 27 percent reduction from 1990 levels.

New York State has established the toughest acid rain control requirements in the nation. In 1999, the DEC took measures to further control emissions from New York State sources that cause acid rain. The state's acid rain initiative is helping New York lead the nation in the fight against acid rain.

What More Should be Done?

Based on the best available computer model projections, and assuming full implementation of the 1990 Clean Air Act amendment on reductions in sulfur emissions, the number of acidic waters in the Adirondacks is predicted to increase rather than decrease. In other words, even with the reductions achieved under the Clean Air Act, the problem of acidic deposition in the Adirondacks will continue to worsen.

Significant additional reductions in both nitrate and sulfate deposition are needed to stabilize the acidic deposition problem in the Adirondacks. Just to return the quality of water in the Adirondacks to 1984 levels-during which time approximately 19 percent of the water was acidic already-reductions of nitrogen oxides and sulfur dioxide must be reduced by an additional 40 to 50 percent over current requirements. The EPA admits that without such additional reductions, the percentage of acidic lakes, streams and rivers in the Adirondacks will roughly double by the year 2040, a strong indication that aggressive action is necessary now.

New York State has significantly reduced sulfur dioxide emissions, and as part of the Ozone Transport Region, will reduce nitrous oxide emissions as well. However, the upper Midwest has not made similar reductions and continues to be the major source of our acid deposition problem.

Things You Can Do to Help

  • Conserve energy in your home, office and automobile.
  • Purchase clean electric power.
  • Notify your representatives in Washington about your deep concern regarding the state's acid precipitation problem, and encourage them to support legislation limiting sulfur dioxide and nitrogen oxide emissions.

For more information, please write or call:

New York State Department of Environmental Conservation
Division of Air Resources
625 Broadway
Albany, New York 12233
(518) 402-8452

More about Acid Rain Questions & Answers: