A secondary aerosol is formed by the interaction of 2 or more gas molecules and/or primary aerosols. Secondary aerosols are not directly released into the atmosphere but instead are created by physical and chemical processes in the atmosphere.
Sources: Hardy, Colin C., Ottmar, Roger D., Peterson, Janice L., Core, John E., and Seamon, Paula. 2001. Smoke Management Guide for Prescribed and Wildland Fire 2001 Edition. Produced by the National Wildfire coordinating Group Fire Use Working Team.