Environmental Science elementary May 24, 2026

How Does a Forest Clean the Air?

Trees take in gases, store carbon, and trap dust

A forest showing leaves taking in carbon dioxide, releasing oxygen, and catching tiny dust particles from the air.

A forest cleans air in more than one way. Leaves take in carbon dioxide and use sunlight to help trees grow. Leaf surfaces also catch dust and smoke bits, and tree wood stores carbon that would otherwise be in the air.

Big Idea. NGSS 5-LS2-1 connects to how matter moves among air, plants, animals, and the environment in an ecosystem.

A forest is not a giant vacuum cleaner, but it does change the air around it. Each tree has thousands of leaves. Those leaves are tiny living factories. In sunlight, they take in carbon dioxide from the air and water from the ground. The tree uses these materials to make sugar, grow new cells, and build wood. Some oxygen goes back into the air. Forests also help with air in a second way. Leaves, bark, and needles have surfaces that catch dust, ash, pollen, and tiny pollution bits. Rain can wash some of those particles down to the soil. This does not make pollution disappear, but it can lower what is floating near the trees. When a forest is cut down, the air loses both jobs. Fewer leaves clean the air, and stored carbon can return to the atmosphere as wood decays or burns.

Leaves take in carbon dioxide

A close view of a leaf showing carbon dioxide entering, sunlight reaching the leaf, water arriving from the stem, and oxygen leaving. — Leaves use air, water, and sunlight to make food.

Leaves have tiny openings that let gases move in and out. Carbon dioxide enters through these openings. Water moves up from the roots through the trunk and branches. With sunlight, the leaf changes carbon dioxide and water into sugar. The tree uses sugar for energy and for building new parts. Oxygen leaves the leaf and mixes with the air. This process is called photosynthesis. It is one reason a forest can affect the air over many years. A single leaf is small, but a forest has millions of leaves working at the same time during the growing season. Trees do not remove all carbon dioxide from the sky. Cars, factories, fires, and living things keep adding it. Still, forests are an important part of the carbon cycle because they move carbon from the air into living matter.

Photosynthesis moves carbon from the air into plant matter.

Wood stores carbon

A tree cross section and roots showing carbon stored in the trunk, branches, and soil. — Carbon can be stored in wood and soil.

When a tree grows, some of the carbon from carbon dioxide becomes part of its trunk, branches, roots, and leaves. The trunk is a long-term storage place because wood can last for many years. This stored carbon is not floating in the air as carbon dioxide while it stays in the tree. A young tree stores carbon as it adds new wood. An older tree can also store a large amount because it has a big trunk and many branches. Forest soil stores carbon too. Dead leaves and roots break down and mix into the ground. Some of that carbon stays in soil for a long time. Scientists call this carbon storage, but students can think of it as carbon being parked in wood and soil. A forest is like a living bank for carbon, with deposits and withdrawals happening all the time.

Wood and soil keep some carbon out of the air for years.

Leaf surfaces catch particles

A magnified leaf surface catching dust and smoke particles while rain washes some particles toward the soil. — Leaves can act like sticky landing places for tiny particles.

Forests also clean air by catching tiny particles. Particles are small bits of matter. They can come from dust, smoke, fires, roads, or factories. Leaves, needles, twigs, and bark have surfaces that these bits can stick to. Some leaves are waxy. Some are rough or hairy. These surfaces give particles places to land. Wind can later blow some particles away again, so this is not a perfect filter. Rain can wash some particles from leaves to the ground. Once there, they may mix with soil or wash into streams. This kind of cleaning works best near the forest, along streets with trees, and around sources of dust. It does not replace reducing pollution at its source. It does show that the shape and surface of living plants can change what is in the air we breathe.

Leaves can lower some particle pollution near the trees.

Forests are part of a cycle

A simple forest carbon cycle showing carbon moving among air, trees, animals, decomposers, and soil. — Carbon moves through air, living things, and soil.

Carbon is always moving. It moves from the air into plants during photosynthesis. It moves into animals when they eat plants or other animals. It moves back to the air when living things breathe, decay, or burn. A forest does not lock carbon away forever. Leaves fall. Branches break. Dead trees become food for fungi, insects, and bacteria. These decomposers return nutrients to the soil and release some carbon dioxide. At the same time, new plants grow and take in more carbon dioxide. A healthy forest can keep a large amount of carbon stored because growth and decay are balanced over time. This matches the ecosystem idea in NGSS 5-LS2-1. Matter cycles through plants, animals, decomposers, soil, water, and air. The forest is not separate from the atmosphere. It is connected to it every day.

A forest stores carbon, but carbon still moves through the ecosystem.

Deforestation is a double hit

A comparison of a standing forest and a cleared area showing fewer leaves taking in carbon dioxide and stored carbon leaving from burning or decay. — Losing a forest removes leaves and can release stored carbon.

Cutting down a forest affects the carbon cycle in two ways. First, there are fewer leaves to take carbon dioxide from the air. That means less photosynthesis in that place. Second, the carbon already stored in trees may return to the atmosphere. If wood is burned, carbon dioxide rises quickly. If logs, roots, and leaves decay, carbon dioxide is released more slowly. Some wood can keep storing carbon if it is used in long-lasting buildings or furniture. Even then, the lost forest no longer grows in the same way. Deforestation can also disturb soil. Soil can release carbon when it is dug up, dried out, or washed away. Planting new trees can help over time, but a young forest does not instantly replace an old one. Protecting forests keeps both air-cleaning jobs working at once.

Deforestation removes future carbon uptake and can release past carbon storage.

Vocabulary

photosynthesis: The process plants use to make sugar from carbon dioxide, water, and sunlight.
carbon dioxide: A gas in the air that plants use for photosynthesis and that also traps heat in the atmosphere.
carbon storage: The holding of carbon in places such as tree trunks, roots, leaves, and soil.
particles: Tiny bits of matter in the air, such as dust, ash, smoke, or pollen.
decomposers: Living things such as fungi and bacteria that break down dead plants and animals.
deforestation: The clearing or removal of forests from an area.

In the Classroom

Leaf filter observation

20 minutes | Grades 3-5

Give students clear tape and leaves from different plants. Students press tape gently on leaf surfaces, place it on white paper, and compare the dust or particles they see with hand lenses.

Carbon in a paper tree

30 minutes | Grades 4-5

Students build a paper tree with leaves, branches, trunk, roots, air, and soil. They move paper carbon dots through the model to show photosynthesis, eating, decay, and storage.

Deforestation cause and effect chart

25 minutes | Grades 4-5

Students make a two-column chart showing what happens when a forest stays and what happens when it is cut down. They should include leaves, wood, soil, particles, and carbon dioxide.

Key Takeaways

• Forests clean air by taking in carbon dioxide during photosynthesis.
• Some carbon from the air becomes part of tree wood, roots, leaves, and soil.
• Leaf and bark surfaces can catch tiny particles from dust, smoke, and other pollution.
• Carbon keeps cycling through air, plants, animals, decomposers, and soil.
• Deforestation is a double hit because it removes living leaves and can release stored carbon.

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