n. A chemical entity produced during combustion.
Combustion of woody fuel or other hydrocarbons produces a variety of gases (such as carbon monoxide, carbon dioxide, methane, and water) and particulates. Each of these substances is considered a distinct emission species (also called chemical species). Depending on context and convention, some distinct chemical species may be considered as a single emission species. For example, “nonmethane hydrocarbons” is a grouping that may be considered a single emission species in some contexts, yet it actually includes alkenes, alkanes, isoprenes, and terpenes, among other substances.