Air pollution may be caused by various processes, either natural or anthropogenic (man-made). Some of them leave evident traces in the air; others can go unnoticed unless specific tests are conducted - or until you become ill from their effects.
- Volcanic activities – volcanic eruptions emit a series of toxic gases (including sulfur and chlorine) as well as particulate matter (ash particles) but are usually restricted to localized areas;
- Winds and air currents – can mobilize pollutants from the ground and transport them over large areas;
- Wildfires – add carbon monoxide, as well as particulate matter, to the atmosphere (containing organic contaminants such as PAHs); could affect significant areas, although in general they are restricted and may be contained;
- Microbial decaying processes – microorganisms which are present in any environment have a major role in natural decaying processes of living organisms as well as environmental contaminants; this activity results in the natural release of gases especially methane gas;
- Radioactive decay processes – for example, radon gas is emitted due to natural decay processes of Earth’s crust which has potential to accumulate in enclosed spaces such as basements;
- Increasing temperatures – contribute to an increase in the amounts of contaminants volatilizing from polluted soil and water into the air.
- Mining and smelting – emit into the air a variety of metals adsorbed on particulate matter that is suspended in the air due to crushing & processing of mineralogical deposits;
- Mine tailing disposal – due to their fine particulate nature (resulting after crushing and processing mineral ores) constitute a source of metals to ambient air which could be spread by the wind over large areas;
- Foundry activities – emit into the air a variety of metals absorbed on particulate matter that is suspended in the air due to processing of metallic raw materials (including the use of furnaces);
- Various industrial processes may emit both organic and inorganic contaminants through accidental spills and leaks of stored chemicals or the handling and storage of chemicals – especially of volatile inorganic chemicals
- Transportation – emits a series of air pollutants (gases – including carbon monoxide, sulfur oxides, and nitrogen oxides - and particulate matter) through the tailpipe gases due to internal combustion of various fuels (usually gasses such as oxides of carbons, of sulfur, of nitrogen, as well as organic chemicals as PAHs)
- Construction and Demolition activities – pollute the air with various construction materials. Of special threat is the demolition of old buildings which may contain a series of banned chemicals such as PCBs, PBDEs, asbestos.
- Coal Power Plants – when burning coal this may emit a series of gases as well as particulate matter with metals (such as As, Pb, Hg) and organic compounds (especially PAHs);
- Heating of buildings – emits a series of gases and particulate matters due to burning fossil fuels;
- Waste Incineration – depending on waste composition, various toxic gases, and particulate matter is emitted into the atmosphere;
- Landfill disposal practices – usually generate methane due to the intensification of natural microbial decaying activity in the disposal area;
- Agriculture – pollute the air usually through emissions of ammonia gas and the application of pesticides/herbicides/insecticides which contain toxic volatile organic compounds;
- Control burning in forest and agriculture management – includes controlled burning that will emit gases and particulate matter (similar to wildfires described above)
- Military activities – may introduce toxic gases through practices and training;
- Smoking – emits a series of toxic chemicals including a series of organic and inorganic chemicals, some of which are carcinogenic;
- Storage and use of household products such as paint, sprays, varnish, etc that contains organic solvents which volatilize in the air (hence the smell we all feel while using them);
- Dry cleaned clothes - may retain and emit in the atmosphere small amounts of chlorinated solvents (such as PCE) or petroleum solvents that have been used by the dry cleaners; this could eventually create a health risk if the clothes returned from the dry cleaners are stored in enclosed indoor spaces.