Yes, burning fossil fuels is the primary cause of acid rain. Coal-fired power plants and vehicles that burn oil and gas release sulfur dioxide and nitrogen dioxide into the atmosphere, where these gases react with water to form sulfuric and nitric acid. This acidified moisture then falls as rain, snow, or fog with a pH between 4.2 and 4.4, compared to normal rain’s pH of about 5.6.
How Fossil Fuels Create Acid Rain
The process starts at the smokestack or tailpipe. Coal combustion is the single largest source of sulfur dioxide, because coal naturally contains sulfur that gets released when burned to generate electricity. Nitrogen dioxide comes from burning all types of fossil fuels, including gasoline and diesel, at high temperatures.
Once these gases enter the atmosphere, they don’t stay in gas form for long. Water vapor, oxygen, and other airborne particles act as surfaces and catalysts for chemical reactions that convert sulfur dioxide into sulfuric acid and nitrogen dioxide into nitric acid. These acids dissolve into cloud droplets and rainwater, sometimes traveling hundreds or even thousands of kilometers from where the original pollution was released. A coal plant in one country can acidify lakes in another, which is why the United Nations describes acid rain as a fundamentally transboundary problem.
What Acid Rain Does to Lakes and Rivers
Aquatic ecosystems are especially vulnerable because even small shifts in water pH can cascade through the food chain. At a pH of 5, most fish eggs cannot hatch. Adult fish begin dying at even lower levels. The damage often starts further down the food web: mayflies, a critical food source for frogs and fish, may not survive below a pH of 5.5. Frogs themselves have a critical threshold around pH 4, but by the time conditions are that acidic, the insects they depend on are already gone. The result is lakes that look pristine but are biologically empty.
Damage to Forests and Soil
Acid rain doesn’t kill trees outright. Instead, it slowly strips the soil of calcium and other essential nutrients that trees need to grow. Research at Hubbard Brook Experimental Forest in New Hampshire has documented pronounced depletion of calcium across multiple watersheds since 1900, driven by decades of acid deposition. As calcium washes out of the soil and into streams, the trees that need it most suffer first.
Sugar maples are a clear example. These trees have high calcium requirements, and their decline in the northeastern United States has been directly attributed to calcium limitation caused by acid rain. In their place, American beech trees, which need less calcium, have become dominant. This shift isn’t just an ecological curiosity. It changes forest composition for decades, altering everything from leaf litter chemistry to the fungi that live among tree roots. Even as forests regrow after disturbance, recovering trees must invest heavily in belowground processes to access nutrients from bedrock, a sign that the soil’s natural nutrient reserves have been fundamentally depleted.
Effects on Buildings and Monuments
Marble and limestone are made of calcite, which dissolves when it comes in contact with sulfuric and nitric acid. On buildings and statues, this shows up as roughened surfaces, eroded material, and the gradual loss of carved details. The U.S. Geological Survey has flagged several prominent structures in Washington, D.C., as affected, including the marble exterior of the Library of Congress Thomas Jefferson Building and the U.S. Capitol. The damage is slow but irreversible: once stone dissolves, it cannot be restored.
Health Effects of the Same Pollutants
The gases that cause acid rain also directly harm human health before they ever reach the ground as rain. Sulfur dioxide irritates the airways, causes bronchitis, increases mucus production, and reduces lung function with long-term exposure. Nitrogen dioxide penetrates deep into the lungs, triggering coughing, wheezing, and worsening asthma symptoms.
Perhaps more dangerous is what these gases become. As sulfur dioxide and nitrogen dioxide react in the atmosphere, they form fine particulate matter small enough to reach the deepest parts of the lungs. Spikes in this type of air pollution are associated with increases in emergency room visits, hospitalizations, and death rates from respiratory and cardiovascular disease. In other words, the same fossil fuel emissions that acidify rain also create the tiny particles responsible for some of the most serious air quality health risks.
How Regulations Have Reduced Acid Rain
The link between fossil fuels and acid rain was recognized internationally as early as the 1970s, when Scandinavian scientists traced the acidification of their lakes to industrial emissions released thousands of kilometers away. In 1979, European nations signed the first international treaty on transboundary air pollution. Two decades later, the 1999 Gothenburg Protocol specifically targeted acidification, ground-level ozone, and nutrient pollution across borders.
In the United States, the results of domestic regulation have been dramatic. The Acid Rain Program, established under the 1990 Clean Air Act amendments, required power plants to cut sulfur dioxide and nitrogen oxide emissions. By 2023, sulfur dioxide emissions from regulated power plants had dropped 96 percent from 1990 levels, a reduction of 15.1 million tons. Nitrogen oxide emissions fell 90 percent over the same period, a cut of 5.8 million tons. These reductions came primarily from installing scrubbers on coal plants, switching to lower-sulfur fuels, and transitioning to natural gas and renewable energy.
The ecological recovery, however, is slower than the emissions decline. Soil that lost decades’ worth of calcium doesn’t replenish quickly, and lake ecosystems that were hollowed out take years to rebuild their food webs. The pollution problem has been largely addressed in North America and Europe, but acid rain remains a concern in parts of Asia where coal consumption is still high and emission controls are less stringent.