Pollutants occur as gases (e.g. carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, and VOCs such as benzene and formaldehyde) and PM. In air pollution, PM refers to solid and liquid particles suspended in air, and the PM and air mixture is referred to as aerosol.
Pollution sources are often characterised as anthropogenic (i.e. human-made), biogenic (i.e. natural and living) or geogenic (i.e. natural and nonliving).
Motor vehicles emit a wide range of pollutants from their tailpipes, and are a major source of nitrogen oxides (NOx) and carbon monoxide (e.g. Figure ATM30).
Emissions from domestic wood heaters—particularly smoke, but also VOCs—remain a significant pressure on ambient air quality during cooler months of the year in several parts of Australia.
Emissions from commercial and domestic sources (domestic wood heaters are considered separately) exert pressure on local air quality and on airshed quality. Domestic sources, for example, can affect photochemical smog by releasing VOCs.
Both prescribed burns and bushfires emit smoke plumes, which are visible because of the PM they contain. The smoke is the product of incomplete combustion. Fire emissions rates are affected by fire behaviour and the amount of fuel being burned.
Nonroad diesel engines and equipment are used in a wide variety of applications, including rail transport, mining, construction, industrial, shipping and airport services, and can be high pollution emitters.
Keywood MD, Emmerson KM, Hibberd MF (2016). Ambient air quality: Topics. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/ambient-air-quality/topics?framework=106, DOI 10.4226/94/58b65c70bc372