Acid rain is most severe in the northeastern United States, particularly in New York, Pennsylvania, and the New England states. New York City, for example, recorded a mean precipitation pH of 4.95 over a study period from 2003 to 2019, well below the 5.6 threshold that defines acidic rainfall. The western U.S. generally sees much less acidic precipitation, with cities like Denver recording pH levels above 6.0 in some years.
Why the Northeast Gets Hit Hardest
The Northeast’s acid rain problem is largely imported. Six states clustered around the Ohio River Valley (Illinois, Indiana, Kentucky, Ohio, Pennsylvania, and West Virginia) accounted for 41% of national sulfur dioxide emissions in 1998, making the Midwest the single biggest source of acid rain precursors in the country. Prevailing winds blow west to east, carrying those pollutants hundreds of miles before they convert into sulfuric and nitric acids and fall as rain or snow over New England and eastern Canada.
This means the places generating the pollution and the places suffering the worst effects are often different states entirely. New York’s Adirondack Mountains, Vermont’s Green Mountains, and New Hampshire’s White Mountains all sit directly in the path of these wind-carried acids, and their high elevations squeeze out more precipitation, concentrating the effect.
The East-West Divide
U.S. Geological Survey mapping shows a clear geographic split. Eastern states consistently record lower pH values in rainfall (meaning more acidic), while western states tend to have near-neutral or even slightly alkaline precipitation. Los Angeles is a notable exception on the West Coast, with a mean pH of 5.29, likely driven by its dense vehicle traffic and industrial activity. But even L.A.’s rainfall is substantially less acidic than New York City’s.
Part of the reason the West fares better is geology. Alkaline dust from desert soils can neutralize acids in the atmosphere before they reach the ground. The East lacks this natural buffer, and its soils tend to be thinner and more naturally acidic, which makes the landscape less able to absorb what falls on it.
Damage to Lakes and Forests
The Adirondack Mountains of upstate New York are the most studied example of ecological damage from acid rain in the U.S. Fish populations have been harmed by acidification in roughly 75% of the region’s high-elevation lakes. Effects range from complete extinction of fish in some lakes to stunted growth and altered population structures in others. During surveys in the 1930s, comparable levels of acidity were found only in isolated bogs and seepage ponds, not in the open drainage lakes where it now appears.
Forests across the Appalachian range have also suffered. Acid rain strips calcium and other essential nutrients from the soil, weakening trees that depend on those minerals. Southern Appalachian forest soils have lost substantial nutrient reserves since the pre-industrial era, and modeling suggests that by 2100, soil calcium levels will be at least 20% lower than they were before industrialization. Red spruce and sugar maple, two species sensitive to nutrient-poor soil, have shown visible decline in areas with the heaviest acid deposition.
Buildings and Monuments at Risk
Acid rain also eats away at stone. When sulfuric and nitric acids react with calcite, the mineral that makes up marble and limestone, the stone dissolves. On exposed surfaces, this shows up as roughened textures, eroded details, and eventual loss of material. Washington, D.C., which sits in the affected eastern corridor and is filled with marble structures like the U.S. Capitol and the Library of Congress buildings, faces ongoing maintenance challenges from this corrosion.
How Much Conditions Have Improved
The picture today is dramatically better than it was a few decades ago. The EPA’s Acid Rain Program, launched under the 1990 Clean Air Act amendments, set a permanent cap on total sulfur dioxide emissions from power plants. The results have been striking: from 1995 to 2023, annual sulfur dioxide emissions from power plants dropped by 95%, and nitrogen oxide emissions fell by 89%. In raw numbers, power plants cut sulfur dioxide output by more than 16 million tons compared to 1980 levels.
These reductions have meaningfully lowered the acidity of rainfall across the eastern U.S. Some Adirondack lakes have shown early signs of chemical recovery, though biological recovery (fish and invertebrate populations bouncing back) lags behind by years or decades. The USGS has noted that maps from 2002 already look different from those of the 1980s, and current conditions are better still.
Still, the Northeast remains the most affected region. Soils depleted of nutrients over decades don’t recover quickly, even after the rain becomes less acidic. Forest Service projections suggest that nearly as much nutrient loss is expected over the next century as has already occurred, partly because the damage compounds over time and partly because even reduced acid levels continue to leach minerals from already-weakened soils. The pollution has improved enormously, but the ecological debt it created in the mountains and lakes of the Northeast will take generations to repay.