Industrial pollution can lower the pH of precipitation, creating acid rain. This type of acid precipitation can directly kill some organisms, like trees and fish, devastating ecosystems.

While impacts of acid rain on humans is not very dramatic, it can indirectly cause health problems, particularly lung issues. Acid rain has decreased since the late 1970s in North America, where tighter U.S. regulations have improved air quality.

All rainwater has a slightly acidic pH level due to ambient levels of carbon dioxide in the air. Certain industrial pollutants, however, can decrease the pH excessively, causing it to pose a danger to the environment. Sulfur dioxides and nitrogen oxides, for example, can have a dramatic effect on rainwater's pH.

Rain contaminated by these compounds changes the pH of water and soil, making them more acidic. Certain trees and fish have adapted to specific pH levels and changes in pH can kill them, leaving parts of forests, lakes and rivers devoid of life.

While acid tends to bring to mind the image of corrosive chemicals dissolving metals and other materials, acid precipitation does not have direct effects on human health. Acid rain does not have an acidic enough pH to burn human skin.

According to the U.S. Environmental Protection Agency, "Swimming in an acidic lake or walking in an acidic puddle is no more harmful to people than swimming or walking in clean water." While acid rain cannot burn your skin, it is linked to several indirect health effects.

Everything is connected in air quality. While acid rain cannot harm humans directly, the sulfur dioxide that creates it can cause health problems. Specifically, sulfur dioxide particles in the air can encourage chronic lung problems, like asthma and bronchitis.

Additionally, the nitrogen oxides that create acid rain promote the formation of ground-level ozone. While ozone high above the Earth helps block ultraviolet radiation, ground-level ozone promotes severe lung problems like chronic pneumonia and emphysema.

When acid rains fall at places located at higher altitudes, acid rains lead to thick acidic fog that hangs low, affecting visibility and causing irritation to eyes and nose. Acidic fog also affects trees and plants and causes their leaves to turn brown and wilt.

Apart from the effects of acid rain on air quality, acid rains also greatly affect environmental balance. Acid rain falling directly on trees and crops can harm them. Runoff from acid rain leaches minerals such as aluminum from soil, thereby decreasing its pH and making the soil acidic. Acidic soil is detrimental for the growth of crops and results in damaged harvests.

When the acidic runoff flows into lakes, rivers and seas, it disturbs the balance of these aquatic ecosystems and causes injury or even death of aquatic organisms. Imbalance in aquatic ecosystems has an adverse effect on fishing industry.

In some ways, the reduction of acid rain in the United States is one of the biggest successes of environmental policy. Since the 1970s, various laws have reduced the emission of sulfur dioxides and nitrogen oxides from power plants, including the Clean Air Act of 1970 and the Canada-United States Air Quality Agreement of 1991.

The longest continuous rain-chemistry monitoring station in North America, the Hubbard Brook Experimental Forrest in New Hampshire, found that hydrogen ion concentration (pH) decreased by roughly 60 percent since the 1960s.

The EPA estimates that the reduction in the acid rain-producing emissions has saved $50 billion in health care costs. Despite the overall positive picture, some areas in New England are still recovering.