Pollution

Air is complex and its composition is highly variable depending on location, temperature, humidity, wind speed and direction, altitude and many other factors. Many of these variations are perfectly natural and would occur regardless of the actions of humans, though it is certainly the case that human activity has affected the composition of air globally.

In terms of air quality management, air is considered “polluted” when specific substances are present in concentrations that have negative impacts on the health of people and the environment, or even on property and infrastructure. Most, but not all, air pollution comes from industrial, domestic or automotive combustion, with other sources being construction, agricultural activity, chemicals and aerosols, and a great many others including natural causes like wildfires.