See BT pollutant. secondhand smoke: See SN sidestream smoke. secretion: 1. Process by which a substance such as a hormone or enzyme produced in a cell is passed through a plasma membrane to the outside, for example the intestinal lumen or the blood (internal secretion). 2. Solid, liquid or gaseous material passed from the inside of a cell through a plasma membrane to the outside as a result of cell activity.
contaminant formed from other pollutants in the atmosphere.
Harmful chemical formed in the atmosphere when a primary air pollutant reacts with normal air components or other air pollutants. Compare primary pollutant.
a pollutant formed by chemical reaction in the atmosphere, water, sediments, or soil
a pollutant created when two or more pollutants are mixed together and a chemical reaction happens to turn them into a new pollutant. Ground-level ozone is a secondary pollutant because it is formed when two other types of pollutants, NOx and VOCs, get baked by the sun. (Back to Ozone Action! Days)
An air pollutant formed in the atmosphere from other pollutants instead of being emitted directly by a source.