A pollutant that is directly emitted from a source such as a smokestack is called a

A pollutant that is directly emitted from a source such as a smokestack is called a

• A. Primary air pollutant
• B. Secondary air pollutant
• C. Tertiary pollutant
• D. Ambient pollutant

Answer: (A)

Directly emitted pollutants are classified as primary pollutants. A smokestack spews pollutants straight into the air, so those substances are considered primary because they enter the atmosphere in their original form. Secondary pollutants, by contrast, are not released in that form; they form in the atmosphere through chemical reactions driven by sunlight and other atmospheric constituents—like ground-level ozone forming from nitrogen oxides and volatile organic compounds. Ambient simply describes what’s present in the surrounding air, not how it was formed, and tertiary isn’t a standard category used for air pollutants in this context.

Directly emitted pollutants are classified as primary pollutants. A smokestack spews pollutants straight into the air, so those substances are considered primary because they enter the atmosphere in their original form.

Secondary pollutants, by contrast, are not released in that form; they form in the atmosphere through chemical reactions driven by sunlight and other atmospheric constituents—like ground-level ozone forming from nitrogen oxides and volatile organic compounds. Ambient simply describes what’s present in the surrounding air, not how it was formed, and tertiary isn’t a standard category used for air pollutants in this context.