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
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.