Trees purify the air
Forests play an essential role in purifying the air we breathe. Of course, trees don't have lungs the way human beings do. They "breathe," or respire, thanks to a process called photosynthesis.
So, what is photosynthesis? All leaves and plants contain living cells that take in sunlight. By capturing the sun's energy, the leaf's cells gain the strength to decompose the sap supplied by the roots, thus providing the tree with nutrition.
Not only does the leaf need light to decompose sap and transform it into food for the tree, it also needs air. Air is filtered by the tree and returned to the atmosphere. That is why we say that trees purify the air.
As we know, air, water, and soil are the elements essential to all life on the planet. For trees, nutrition comes from the soil and is transported by water from the roots to the leaves. The leaves capture sunlight and air to transform the sap into sugar that will then be used to feed all of the tree's living cells. As part of this process, some of the air is filtered and returned to the atmosphere.