Particulate matter is a ______ pollutant.

Particulate matter is a ______ pollutant.

• A. Secondary
• B. Tertiary
• C. Quaternary
• D. Primary

Answer: (D)

Particulate matter is defined by the form in which it enters the air—tiny particles of solid or liquid that are released directly from a source. Since these particles are emitted directly as matter, rather than formed in the atmosphere from gases, particulate matter is classified as a primary pollutant. There is also secondary particulate matter, which can form in the air from gaseous precursors, but the term particulate matter is typically treated as a primary pollutant because its defining feature is direct emission of particles. This helps explain why the correct choice highlights the direct particle emission aspect.

Particulate matter is defined by the form in which it enters the air—tiny particles of solid or liquid that are released directly from a source. Since these particles are emitted directly as matter, rather than formed in the atmosphere from gases, particulate matter is classified as a primary pollutant. There is also secondary particulate matter, which can form in the air from gaseous precursors, but the term particulate matter is typically treated as a primary pollutant because its defining feature is direct emission of particles. This helps explain why the correct choice highlights the direct particle emission aspect.