Natural sources release pollutants through processes occurring without direct human activity, whereas anthropogenic sources result from human activities such as transport, industry, agriculture, and energy production. The distinction concerns the pollutant's origin, not necessarily its chemical identity or environmental impact.
This is core SL and HL content in 8.3 Urban air pollution. A pollutant such as sulfur dioxide may come from either category: volcanoes release it naturally, while coal-fired power stations release it anthropogenically.
| Source type | Mechanism | Examples of pollutants and sources |
|---|---|---|
| Natural | Physical, chemical, or biological processes not directly caused by humans | Sulfur dioxide from volcanoes; particulate matter from dust storms; carbon monoxide and particulates from naturally ignited wildfires; pollen from plants |
| Anthropogenic | Human production, consumption, transport, or land-use activities | Nitrogen oxides and carbon monoxide from vehicles; sulfur dioxide from burning sulfur-containing fuels; particulate matter from construction and industry; ammonia from agriculture |
Pollutants can also be classified as primary pollutants, emitted directly from a source, or secondary pollutants, formed in the atmosphere when primary pollutants react. For example, vehicles emit nitrogen oxides directly, but sunlight drives reactions that produce tropospheric ozone, a secondary pollutant in photochemical smog.
A common misconception is that natural pollutants are harmless. Their natural origin does not prevent them from damaging health or ecosystems: Saharan dust can raise particulate concentrations in European cities, while volcanic sulfur dioxide can contribute to respiratory problems and acid deposition. Conversely, anthropogenic emissions are often more concentrated in urban areas because transport, industry, and energy use occur close to large populations. This can create environmental justice concerns when lower-income communities experience greater exposure.
Exam technique: If asked to distinguish the sources, state the difference clearly and give one accurate example of each. Do not confuse source origin with primary versus secondary pollutants; these are separate classifications. For an explain question, connect the source to the pollutant and then to an environmental or human-health impact.