The question of whether trees “make air” seeks to understand the biological mechanisms supporting life on Earth, specifically the continuous renewal of breathable components in the atmosphere. To answer this, one must explore the microscopic chemical reactions taking place within the tree’s structure. The answer involves understanding how trees process energy and how their function compares to other, less visible contributors to the planetary gas balance.
The Chemistry of Oxygen Production
The process by which trees and other green plants generate oxygen is called photosynthesis, a complex reaction that converts light energy into stored chemical energy. This biological mechanism relies on three inputs: carbon dioxide, water, and sunlight. The tree absorbs water through its roots and carbon dioxide from the atmosphere through tiny pores on its leaves called stomata.
Inside specialized cell structures called chloroplasts, the energy from sunlight is captured by the pigment chlorophyll to power the conversion. The overall reaction uses six molecules of carbon dioxide and six molecules of water to produce one molecule of glucose, which is the plant’s food source, and six molecules of oxygen. Oxygen is not the intended product of the plant’s energy-making process but is instead a byproduct released when water molecules are split in the initial, light-dependent stage of the reaction. The tree releases this excess oxygen back into the atmosphere through the stomata, making it available for virtually all aerobic life forms.
The Global Oxygen Supply
While trees are highly visible producers of oxygen, they contribute only a fraction of the total atmospheric supply. Terrestrial plants, including all the world’s forests and grasslands, are responsible for generating an estimated 28% to 50% of the planet’s oxygen. This means that the majority of the oxygen we breathe originates not from the land, but from the ocean.
Photosynthetic organisms in marine environments, predominantly microscopic algae and cyanobacteria known as phytoplankton, generate the remaining 50% to 72% of the Earth’s oxygen. These tiny, floating organisms are so numerous and efficient that a single species of oceanic plankton, Prochlorococcus, is estimated to produce more oxygen than all the tropical rainforests combined. The oxygen produced by both terrestrial and marine sources is continuously consumed by organisms for respiration, maintaining a dynamic balance in the atmosphere.
Beyond Oxygen: Trees as Air Regulators
Trees perform several functions that regulate the atmosphere’s composition beyond oxygen production. They act as significant carbon sinks, actively removing carbon dioxide ($\text{CO}_2$) from the atmosphere and storing it in their biomass. This process, known as carbon sequestration, locks the carbon into the tree’s wood, roots, and leaves. A mature tree can store hundreds of kilograms of carbon over its lifespan, mitigating the concentration of this major greenhouse gas.
Trees also serve as natural air filters, physically removing harmful pollutants and particulate matter from the air we breathe. Their leaves and bark surfaces are highly effective at trapping tiny airborne particles, such as soot, dust, and fine particulate matter ($\text{PM}$). Additionally, trees absorb gaseous pollutants like nitrogen oxides, sulfur dioxide, and ground-level ozone through their stomata as they take in $\text{CO}_2$ for photosynthesis. These pollutants are then either broken down within the plant tissue or rendered harmless, significantly improving the air quality in local environments, particularly in urban and industrial areas.