Air pollutants arise from a wide variety of sources, although they are mainly a result of the combustion process. It is easy to assume that most of these air pollutants arise as a result of human activity, but large amounts are also produced by natural processes such as forest fires, volcanoes and bacteria. The largest sources of pollutants produced by human activities include motor vehicles and industry. Motor vehicles emit a wide variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NO_x), volatile organic compounds (VOCs) and particulates (PM₁₀). In addition, photochemical reactions resulting from the action of sunlight on nitrogen dioxide (NO₂) and VOCs from vehicles lead to the formation of ozone, a secondary long-range pollutant, which impacts in rural areas often far from the original emission site.

The activities look at air pollution and how it is monitored. Pupils can collect data for their own area and analyse it in terms of the levels of air pollution and the effect on human health.