By origin:
-Pollutants of natural origin, e.g. volcanic eruption gases, vapours.
-Pollutants of artificial origin, e.g. combustion products emitted by aviation.
By state of formation:
-gaseous, e.g. carbon dioxide, carbon monoxide
-liquid, e.g. acid, alkaline vapours -solid e.g. soot, fly ash.
By chemical composition:
-organic e.g. fungal spores, viruses, bacteria
-inorganic pollutants.
By their harmful effects:
-health and infectious effects
-greenhouse effect
-damage to the ozone shield
-Contribution to smog formation
-radioactivity
-acid rain, deforestation.