Primary pollutants
* Examples: sulfur dioxide, nitrogen oxides, carbon monoxide, particulate matter, volatile organic compounds (VOCs), and lead.
* Sources: power plants, industrial facilities, vehicles, and other sources that release pollutants directly into the air.
Secondary pollutants
* Examples: ozone, nitrogen dioxide, and fine particulate matter (PM2.5).
* Formed when primary pollutants react with other chemicals in the atmosphere, sunlight, or water droplets.
* Can be transported long distances from their sources.
Key differences
* Primary pollutants are emitted directly into the environment, while secondary pollutants are formed in the atmosphere or deposited on the Earth’s surface from precursors emitted into the air.
* Secondary pollutants can be more harmful to human health and the environment than primary pollutants.
* Secondary pollutants are more difficult to control because they are formed from a variety of sources and can be transported long distances.
