Acid Rain

Acid Rain

What is acid rain

Acid Rain is any type of precipitation with acidic components that falls to the ground from the atmosphere. It can be wet or dry. When nitrogen oxides (NOx) and sulfur dioxide (SO2) are released into the atmosphere, they react with water and create sulfuric and nitric acids. These compounds can be carried away by air currents for hundreds of miles. They fall back to earth in the form of rain, sleet, hail, snow and dust.


Most acid rain is caused by humans in the form of burning of fossil fuels. A very small percentage of acid rain is caused by natural causes such as volcanoes or wildfires. The biggest source of acid rain producing pollutants comes from power plants that burn coal to produce electricity, as well as cars, trucks, busses and construction vehicles that emit nitrogen oxides and sulfur dioxide in the form of exhaust.  

Effects of acid rain

The pollutants that cause acid rain also cause smog and fine particle pollution, both of which harm human health.  Because sulfur- and nitrogen-based air pollution travel long distances, they are a problem for everyone -- and everything -- downwind of the smokestack or tailpipe, not just those in close proximity to power plants.  

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Acid rain harms:  

  • Humans- The same pollution that causes acid rain also cause respiratory disease and worsen existing conditions. Acid rain also causes mercury contamination of the food chain, including fish, fish-eating birds and fish-eating mammals (such as people).  
  • Forests and Plants- When acid rain seeps into the soil, it dissolves and eliminates nutrients needed for healthy tree growth, such as calcium.  At the same time, it releases aluminum from the soil, which trees absorb. The aluminum kills tree roots, making it harder for trees to get water. These combined stresses cause otherwise healthy trees to die from extremes of cold, drought or disease that they would easily survive in non-acidic conditions. This is especially true at high elevations, where all three stress factors are increased and soils are thinnest and nutrient-poorest.
  • Wildlife- By robbing the soil of calcium, acid rain weakens and kills insects, snails and other calcium-shelled invertebrates that summit-nesting birds eat to survive.  By releasing aluminum from the soil, acid rain destroys adult fish gills, suffocating them.  It also halts reproduction by making fish egg membranes too tough for hatchlings to break.
  • Buildings, monuments and sculpture- Acidic precipitation erodes stone, brick and concrete buildings; cemetery headstones and mausoleums, bronze statues and monuments; copper roofing and drains; and, leaded stained-glass windows.
  • Water supplies- Both on-site wells and municipal water supplies become corrosive if they are allowed to become acidic.  Long before the tragedy in Flint, MI, Adirondack homeowners and local governments struggled to identify and correct the source of high levels of copper and lead in local tap water, but not before people were sickened by drinking their pipes.
  • Caustic fog- Day after day, even when it doesn't even rain or snow, the pollution hangs in acid clouds that shroud the mountains in a caustic fog.
  • Smog at high elevations- Ground-level ozone (smog) is worst in the Adirondacks at high elevations, as pollution wafting from other states passes over our mountains.  Some falls to the ground as acid rain, while the rest hangs in the air, harming everyone/everything with lungs.
  • Black Flies- Adding insult to a long list of injuries, Canadian studies show that the larvae of black flies, the bane of spring outdoor activities in the Northeast and southern Canada, seem to thrive in acidic waters.  Acid rain kills the fish that eat black fly larvae as well as the other insects that would compete for stream-bottom space with black fly eggs.
  • Scenic vistas- Sulfur dioxide pollution causes haze that restricts visibility and obscures scenic views in mountain ranges.

Where does acid rain occur?  

The Adirondack Park has suffered the worst acid rain damage in the nation. But we are not suffering alone. Nearby, the Catskill Mountains, the Taconic Ridge and east end of Long Island are all areas where acid rain has caused significant harm. To our south, the Appalachian Mountain Range is showing damage similar to the Adirondacks, even though the region’s soils are thicker than ours and provide more suffering against acidification. Florida’s lakes region and Everglades wetlands are showing signs of acid damage as well.  Out West in the Rocky Mountains, power plant emissions are saturating high-elevation watersheds in Colorado with acid-causing nitrogen.  There, evergreen forests are losing their needles and tree health is declining throughout the Front Range.

Acid rain damage is not limited to forests and aquatic ecosystems. In Pennsylvania, the monuments at the Civil War battlefield in Gettysburg are deteriorating far more quickly than similar structures in places not affected by acid rain. Throughout the Northeast, stone, brick and block buildings, as well as automobile finishes, show signs of more extensive and rapid weathering than counterparts in other regions of the country.  

In the Chesapeake Bay and Long Island Sound, nitrogen-based pollution is overloading the water with nutrients. This contributes to the overabundance of algae, which when they die and decay, deplete the water of precious oxygen needed by all aquatic animals. The condition is known as hypoxia.

Why is acid rain damage worse in the Adirondacks?

The air pollution that causes acid rain has been falling on some areas of the United States for nearly a century. But the damage acid rain causes can take a long time to develop. In many of the most heavily damaged regions -- such as the forests of New England -- scientists have been documenting ecological damage since the 1960's.

In the Adirondacks, our soils were scraped away by the glaciers of the last Ice Age, some 10,000 to 12,000 years ago.  Because the underlying rock is anorthosite -- a very hard granite -- it takes longer here to make new soil from weathering and decomposition of forest litter.  Our steep slopes, heavy precipitation and proximity to the coal-fired smokestacks of the Midwest all combine to wreak havoc on our ecosystems and human-built environment.

What is Being Done about Acid Rain?


In 1990, Congress amended the Clean Air Act and instructed the U.S. Environmental Protection Agency to create the nation's first acid rain control program. In 1992, the Bush Administration boasted that the new program would "end acidity in Adirondack lakes and streams." But many recognize right away that the program would be inadequate to stop the destruction in the Adirondack Park and the nation's other sensitive ecosystems.

In 1993, the NYS Dept. Of Environmental Conservation, the Natural Resources Defense Council and the Adirondack Council sued the EPA over the new program. In a partial settlement of the suit, the EPA agreed to complete a 1996 report to Congress on whether the new program would have the desired effect. The report confirmed our fears.

The EPA noted that the current federal acid rain program could only slow the rate of damage done to the Adirondack Park. More lakes would die without additional cuts in pollution.

This spurred both regulatory action and lawsuits.  Most of the litigation came from New York and New England.  The lawsuits brought by New York Attorneys General Eliot Spitzer, Andrew Cuomo and Eric Schneiderman have resulted in significant settlements with polluters, forcing the closing or modernization of some of the nation’s largest and dirtiest power plants.  Faced with massive fines for violating the Clean Air Act, the plants’ owners made deep cuts in emissions.

In the mid-1990s, the EPA proposed a new Clean Air Interstate Rule (CAIR) in an effort to comply with the Clean Air Act’s National Ambient Air Quality Standards for human health.  Those standards required cuts in sulfur dioxide and nitrogen oxides, which cause smog and fine particle pollution.  Those same pollutants also cause acid rain.


While the Bush-era CAIR was held up in federal court, the Obama Administration proposed a replacement called the Cross-State Air Pollution Rule. This rule was also challenged in court by polluters, but the EPA prevailed in those cases.  The rule has brought additional emissions cuts and significant relief from acid rain to the Adirondack Park.  But additional cuts are still needed to ensure that the entire Adirondack Park can recover from decades of damage.  

2018 & Today-

In 2018, the Clean Power Plan (CPP) was repealed by the Trump administration, which announced it would replace the plan with the Affordable Clean Energy Rule. While the CPP was designed to curb greenhouse gas emissions, it would have provided the additional benefit forcing some of the nation’s dirtiest power plants to close, or eliminate coal as a fuel. This, in turn, would have helped to further curb acid rain. The proposed replacement rule, however, is not expected to provide significant reductions in acid rain or greenhouse gases.

Each of the Adirondack Park’s watershed is different and each reacts to pollution changes at its own pace. Scientists say some Adirondack lakes have already recovered their vitality, as illustrated by the return of trophy-sized trout. But trout are among the hardiest of Adirondack fish when it comes to surviving acid rain. And fish are only one measure of a watershed’s health. Mercury contamination, for example, may linger in the food chain even after acid rain subsides.

At current pollution rates, some of the most profoundly damaged Adirondack waters will take hundreds of years just to regain their chemical balance. It will take much longer for native life to return to them. In the years ahead, the Adirondack Council will continue to press for additional cuts in the air pollution that causes acid rain. We will also work with scientists and government officials to identify and implement plans to speed the recovery of the Park’s soils and waters.

Looking Ahead

The EPA still has not really fulfilled its obligation to protect nature by setting a National Ambient Air Quality Standard (NAAQS) for public welfare. Unlike the NAAQS human health standard that led to the Cross-State rule, this one requires the federal government to protect water quality, plants (forests) and wildlife from air pollution. The EPA said it could not set the standard because it didn’t know how to determine what pollution levels might be safe for all fish and all forests and all wildlife.

However, New York scientists are already working on this problem. New York has the nation’s longest and most detailed record of pollution-monitoring and research related to acid rain’s impacts. In 2014, the Adirondack Council and partners convened a conference at which the Park’s most prominent research scientists and regulators discussed a new approach: critical loads.  

For decades, Adirondack scientists have been carefully monitoring the responses of our ecosystems to increases and decreases in air pollution. Scientists say they can now predict how much pollution can fall in a certain area before it harms the viability of plant and animal life. By controlling upwind pollution sources (smokestacks, automobile emissions, etc.) government regulators can set safe emissions standards for every area of the United States.  

Ideally, those standards would be strictest upwind of sensitive places such as the Adirondacks and Catskills and less strict upwind of locations with thicker soils, fewer lakes and rivers, and fewer steep slopes.

In 2018, the Council reconvened the Acid Rain conference group to develop an action plan for securing the gains we have achieved, while we work to preventing backsliding as the Trump administration encourages new coal use.

In 2019, the Council worked with the Congressional delegation across the Northeast to stop proposed cuts to EPA’s budget that would have crippled its data collection efforts.  While the Trump administration proposed a 31 percent reduction, Congress increased EPA’s budget by $5 million.

The Council also opposed EPA’s proposed changes to the New Source Review portion of the Clean Air Act, which requires the nation’s oldest power plants to meet new-plant emissions standards if their owners renovate or expand them.    

If you’d like to help in the fight against Acid Rain, consider purchasing an emissions reduction certificate to keep pollution out of the air.

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