Assertion: smog's pollutant | /r/HasProperty | formed
Facets:
value: naturally
type: MANNER
Source sentences:
text: Secondary pollutants, such as ozone, are formed when primary pollutants undergo chemical reactions in the atmosphere.
text: An important secondary pollutant for photochemical smog is ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NO x ) combine in the presence of sunlight; nitrogen dioxide (NO 2 ), which is formed as nitric oxide (NO) combines with oxygen (O 2 ) in the air.
text: The pollutants are formed both naturally and by humans, however, the human-induced pollutants are of most concern due to the magnitude of pollutants produced by the burning and extraction of fossil fuels, which are known to cause extreme health effects.