Acid rain: Quick Facts

Written and fact-checked by

The Information Architects of Encyclopaedia Britannica

Facts

Also Known As	acid precipitation • acid deposition

Photos and Videos

Effects of acid rain

Diagram illustrating the nitrogen cycle, showing how nitrogen moves between the atmosphere, biosphere, and soil through natural processes like nitrogen fixation, assimilation, ammonification, nitrification, and denitrification, as well as through human activities such as fertilizer use and industrial emissions. Blue arrows indicate natural activities, and red arrows indicate human activities.

Diagram illustrating the sulfur cycle, showing how sulfur moves through the biosphere and atmosphere. Arrows trace sulfur emissions from fossil fuel burning and decomposition, deposition from the air, plant uptake, runoff into water, and sediment formation.

Two pie charts compare sources of sulfur dioxide and nitrogen oxides emissions contributing to acid rain. The first chart shows electric utilities produce 66% of SO2, other sources 29%, and vehicles 5%. The second chart shows vehicles produce 58% of NOx, other sources 24%, and electric utilities 18%.

Severely defoliated spruce trees stand amid snow in Karkonosze National Park, Poland.

World map highlighting regions with high acid sensitivity in orange and areas of acid deposition with purple hatching. Notable high sensitivity regions appear in eastern North America, northern and central Europe, parts of South America, Africa, and Asia, with some overlap between acid sensitivity and deposition zones. Continents and major oceans are labeled for reference.

Weathered statue with a damaged face and surface, showing significant erosion from acid rain and pollution.

Line graph showing U.S. emissions of ammonia (NH3), sulfur dioxide (SO2), and nitrogen oxides (NOx) from 1970 to 2008. SO2 and NOx emissions decline steadily, while NH3 remains nearly constant. The graph relates to acid rain.

Color-coded map of the contiguous United States showing the annual pH of precipitation weighted by volume in 1994. The western and central regions are shaded in green, indicating higher pH values (less acidic, generally above 5.0), while the eastern United States is shaded in orange and red, representing lower pH values (more acidic, below 4.6). Specific pH values are labeled at various locations, with the lowest pH levels concentrated in the Northeast and parts of the Midwest.

Color-coded map of the contiguous United States showing the annual pH of precipitation in 2008, with values ranging from 5.3 and above in the West (green shades) to below 4.5 in parts of the Northeast and Midwest (orange and yellow shades), indicating more acidic precipitation in the eastern regions. State boundaries and major pH measurement points are marked throughout the map.

Learn about the causes and effects of acid rain

Learn how pollution from industrialization in Europe damaged the limestone of Cologne Cathedral

Discover how researchers sample clouds for acidity and pollution caused by industrial and automobile emissions

Visit Germany's Black Forest to study the effects of industrial emissions, urban smog, and acid rain

See All Videos and Images →

Topics

nitrogen oxide What Happened to Acid Rain?What causes acid rain?nitrogen dioxide Rain sulfur dioxide air pollution particulate matter Atmospheric brown cloud smog What Are the Different Types of Pollution?Do cows pollute as much as cars?The six criteria air pollutants

Dig Deeper: More Articles That Discuss This Topic