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Describe natural sources of CO₂ and particulates.

Atmospheric Carbon Dioxide

Carbon dioxide (CO₂) is an odorless, colorless naturally occurring gas that plays a significant role in the Earth's atmosphere. It is produced through various natural processes such as respiration, where living organisms exhale CO₂ as a byproduct of their metabolic functions.

CO₂ is also released during the decomposition of organic matter, such as dead plants and animals, as they break down and return carbon to the environment.

The natural boom and bust cycle of forest carbon. Carbon uptake and storage during growth and re-growth and carbon release during fires and decomposition. — **Forests are natural reservoirs of carbon, but they aren't always storing carbon. Forests release and store carbon in a cyclical pattern.**

Apart from biological sources, volcanic eruptions also contribute to the presence of CO₂ in the atmosphere. During volcanic eruptions, carbon dioxide is expelled into the atmosphere. These large, violent eruptions can match the rate of human emissions for the few hours they last. However, such eruptions are rare and fleeting, so they don’t rival humanity’s annual emissions. In fact, several individual U.S. states emit more carbon dioxide in a year than all the volcanoes on the planet combined.

The differences between active volcanoes, dormant volcanoes, and hydrothermal systems/calderas in terms of the gases they emit and their impact on the Earth’s crust and mantle. — **Volcanoes release carbon dioxide through eruptions and venting underground magma.**

To put things in perspective, human activities—such as burning coal, fossil fuels, cement production, and deforestation—emit 60 or more times the amount of carbon dioxide released by volcanoes each year. Since the start of the Industrial Revolution, human activities have added over 2,000 billion metric tons of carbon dioxide to the atmosphere, far surpassing volcanic emissions.

Carbon dioxide is also released from underground magma. This occurs through vents, porous rocks, soils, and water that feeds volcanic lakes and hot springs. Even when a volcano is not erupting, much of the carbon dioxide is emitted by degassing of subterranean magma.

Essential Knowledge

CO₂ appears naturally in the atmosphere from sources such as respiration, decomposition, and volcanic eruptions.

Atmospheric Particulates

The EPA refers to particulates as Suspended Particulate Matter (SPM) which is sometimes just called “PM.” Two sizes of particulates are regulated by law: PM 10 and PM 2.5. The numbers “10” and “2.5” refer to the size of the particles in microns. These particles can have adverse effects on both climate and human health. This image depicts some comparisons of the two particle sizes:

The sizes of different particulates, including human hair, fine beach sand, and particulate matter (PM 2.5 and PM 10). The purpose is to provide a perspective on their relative scales and compositions. — **Particulate pollution is very small, smaller than hair or grains of sand.**

There are several natural sources of particulate pollution. Explore the natural sources of particulates below. Have you experienced any of these? For example, I am very allergic to smoke. When I am near soot, fires, or other similar particulates (even a campfire or cigarette smoke), I cough uncontrollably. Sometimes these coughs last for weeks or months after the exposure.

Take a few minutes to read and click through the presentation below and click the arrow to progress.

Essential Knowledge

There are a variety of natural sources of particulate matter.

AP Exam Tip

CO₂ and particulates can be released naturally into the atmosphere.

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