Is carbon dioxide (CO₂) a secondary pollutant?

Air pollution occurs when harmful gases and particles accumulate in the atmosphere to levels that affect human health and the environment. These harmful substances, called pollutants, are often released by human activities such as the burning of fossil fuels, though natural events like volcanic eruptions and forest fires can also contribute.

One of the most significant pollutants is carbon dioxide (CO₂), a major greenhouse gas. It is mainly produced as a byproduct of fossil fuel combustion. During the burning of organic matter, chemical energy is released as heat and light, while CO₂ is formed. For example, the combustion of glucose produces carbon dioxide and water.

Sources of Carbon Dioxide

• A large portion of atmospheric CO₂ is naturally maintained through the carbon cycle.
• However, a significant fraction comes from human activities, particularly from burning coal, oil, and natural gas.

Thus, carbon dioxide is a primary pollutant, not a secondary one, because its natural presence in the atmosphere is essential for photosynthesis in plants.

Note on Pollutants

• Primary pollutants are emitted directly from sources and can be controlled at their origin (e.g., CO₂, SO₂).
• Secondary pollutants are formed by chemical reactions in the atmosphere (e.g., ozone, smog) and require complex control methods.