Discussions about greenhouse gases usually include mention of common terms such as methane and CO₂. However, air pollutants such as particulate matter and ammonia do no less damage to the climate, since they can also act as greenhouse gases or serve as precursor compounds of them.
Air pollutants are substances in the air that can compromise human health and the environment. They can come from natural or anthropogenic (i.e., man-made) sources. Natural pollutants include soot and sulfur dioxide, which are produced by volcanic eruptions. Particulate matter and carbon monoxide caused by traffic are examples of anthropogenic air pollutants.