•Physical properties of air toxics span the entire range of pollutants present in the atmosphere
–As particles and gases
and in semi-volatile form.
–As both primary
(directly emitted) and secondary (formed
in the atmosphere).
–From mostly
anthropogenic sources, but include some biogenic sources.
–Have a wide range of
atmospheric lifetimes.
•Some air toxics such as VOCs (e.g., benzene and toluene) are precursors to ozone and particulate matter (PM); and other toxics such as heavy metals are components of PM.