Primary pollutants are any type of pollutant directly into the environment. They differ from secondary pollutants because secondary pollutants must form in the atmosphere, whereas primary pollutants do not. Primary pollutants can be emitted from many sources including cars, coal-fired power plants, natural gas power plants, biomass burning, natural forest fires, volcanoes, and many more. The effects of primary pollutants are of concern as they can be harmful to humans, animals and plants. Their contribution to the formation of secondary pollutants is also concerning, as this is what causes harmful ground level ozone to form, along with different smog‘s, especially in densely populated cities such as Los Angeles. The emission of primary pollutants has decreased considerably in the past years, due to improved regulations, technology and economic changes.

Types of primary pollutants include:

• Nitrogen oxides (NOx)
• Carbon monoxide(CO)
• Volatile organic compounds(VOCs)
• Sulfur oxides (SOx)
• Particulate matter(PM)
• Mercury

Source: Factly