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What is Acid Rain?


Acid rain is a general term used to describe any precipitation containing sulfuric or nitric acid. Caused primarily by human activity, acid rain can have a devastating effect on ecosystems by altering the pH of lakes, ponds, rivers, and streams.

rain and nature

Causes of Acid Rain

A small amount of acid rain occurs naturally, originating in sources such as volcanic eruptions. The majority, however, comes from the burning of fossil fuels.

Roughly two-thirds of acid rain can be traced to burning fuel for electricity generation. Vehicle emissions are another major contributing factor, as are heavy equipment, industrial activity, and oil refineries.

When released into the environment, sulfur dioxide and nitrogen oxide is transported by the wind and air currents. The compounds react with water, oxygen, and other airborne substances to form sulfuric and nitric acid, which eventually falls back to the ground, often dissolved in raindrops.

Acid rain is a global, not local, problem. Once airborne, sulfuric and nitric acid can travel great distances, so the industrial emissions of one country can have a negative effect on another nation’s environment.

Types of Acid Deposition

While commonly called acid rain, some scientists prefer the term acid deposition, as rain is not always involved in the spread of acidic compounds. Fog, snow, and hail can also be acidic. Airborne acids can also settle back to the ground without moisture as acidic dust.

Acid Rain and the Environment

A substance’s acidity is measured using the pH level, which ranges from 0 (highly acidic) to 14 (highly alkaline). A pH of 7.0 is considered neutral.

You might expect rain to have a neutral pH, but the presence of dissolved carbon dioxide typically gives rain a pH of 5.6, making it slightly acidic. Add in sulfuric and nitric acids, however, and rain’s acidity drops as low as 4.2 to 4.4.

Once it hits the ground, acid rain drains through the soil. Its acidic properties allow it to strip minerals, nutrients, and aluminum out of the ground, ultimately depositing them in water systems.

An increase in acidity may devastate an ecosystem. At pH levels of 5.0, the eggs of most fish species fail to hatch. At levels more acidic than 5.0, adult fish start to die. Plants and trees, starved of nutrients because of acid rain, can also wither and die.

Even in environments with acidic-resistant plants and animals, acid rain may still cripple an ecosystem by removing vital parts of the food chain. For instance, a species of fish may be acid-tolerant, but if the insects that species eats are killed off by low acidity, the fish population will collapse.

Acid Rain and Humans

Acid rain also has an effect on human health and man-made structures. Dry acid deposition has a corrosive effect on metal, paint, and stone, and is slowly eroding some of antiquity’s greatest monuments, including the Athenian Acropolis.

On a more personal level, acid rain affects human health. Sulfuric acid and nitric acid have been connected to heart and lung disorders. Nitric acid is known to increase levels of ground level ozone, which is linked to asthma and emphysema.

Acid rain’s ability to leach minerals into water supplies also increases the risk of hard water, which can damage a home’s plumbing and water-based appliances. Installing a combo whole house carbon water filter and salt-free water softener removes damaging minerals from your water without producing the wastewater associated with traditional salt-based softening systems.

Pelican Combo System Salt-Free Water Softener Whole-House Water Filter