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Acid Deposition: Definition, Causes & Effects

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  • 0:06 What Is Acid Deposition?
  • 2:35 Acid Deposition Harms Nature
  • 4:43 Effects on Human Structures
  • 5:42 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this video lesson, you will learn what causes acid deposition and how it forms in the atmosphere. You will also see some examples of the damage that acid deposition can cause to natural ecosystems and man-made structures.

What Is Acid Deposition?

The word 'acid' has a pretty nasty sound to it, and when you hear it, you probably picture an image like this one:

Acid warning sign
acid warning sign

An acid is something with a pH lower than 7. To put this number in perspective, water is a 7 on the pH scale, and this is considered neutral.

Acids come in all forms, and while some are harmful, others are not. You certainly don't want to mess with hydrochloric acid because this is a 1.1 on the pH scale and will do some serious damage! However, orange juice is also an acid (around 3.3), as well as vinegar (around 2.3), but you can safely ingest small amounts of this (and should if you want a really tasty salad dressing!).

When you think of acids, you may also think of acid rain, which is a serious environmental problem. But, acid rain is just one of the ways that acidic pollutants in the air do harm on Earth's surface. Acid deposition is when acidic or acid-forming pollutants in the atmosphere deposit on the surface of Earth, and this can occur from any precipitation (such as rain, snow or sleet), but also from fog, gases and dry particles.

In another lesson, we learned about different types of pollutants and how they get into the air, and one of the major sources of pollutants is the burning of fossil fuels from car emissions and energy producing plants. The types of pollutants that cause acid deposition are primary pollutants because once in the atmosphere, they react to form harmful substances. The substances that are formed from primary pollutants are called secondary pollutants.

So, this is how it works: Two major culprits of acid deposition, sulfur dioxide and nitrogen oxides (which, as mentioned before, come from cars, electric utility plants and industrial facilities) get emitted into the air. Once there, they react with water and oxygen (which, luckily for those of us who breathe air, are both quite abundant!) and produce sulfuric acid and nitric acid. These compounds have a very low pH and are, therefore, very acidic.

Once these compounds are formed, they can hang out in the atmosphere for really long periods of time (sometimes days or weeks). Sometimes they linger in the air but take a trip, traveling more than a thousand miles! When they do come back to Earth, they can come down in many forms - rain, snow, fog and even as dry dust particles.

Acid Deposition Harms Nature

When acid deposition does decide to come back to the surface of Earth, it can have some serious effects on the environment. Acid deposition may alter the chemistry of soil by leaching minerals, which, in turn, affects the plants and animals adapted to specific soil conditions. Changing the pH of soil can also create problems for plants because it may prevent them from taking up water and nutrients altogether.

Acid deposition can be so detrimental and widespread that it may affect entire forests, such as the Adirondacks in New York. This area has suffered greatly due to leaching of soil cations, which are ions that help counteract the acid deposition, leached nutrients from tree leaves and needles, increased sulfur and nitrogen in soils and loss of animal biodiversity.

Acid deposition can have negative effects on freshwater ecosystems because acidic runoff enters the water and alters the pH. Fish and other animals die when water becomes too acidic, and there are places all over the world where water bodies are now too acidic to support the natural plants and animals. One such place is the New Jersey Pine Barrens.

It's estimated that more than 90% of the streams in this forest are acidic due to acid deposition. Also in the Northeastern U.S. is Little Echo Pond, which has a pH of 4.2 due to acid deposition. When water becomes this acidic, fish and other animals take up the acid, causing contamination into their tissues. This is not only harmful to the animals, but also leads to human health issues because the people who eat them then take those contaminants up in their tissues as well.

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