Tropospheric air pollution has impacts on scales ranging from local to
global, Reactive intermediates in the oxidation of mixtures of volati
le organic compounds (VOCs) and oxides of nitrogen (NOx) play central
roles: the hydroxyl radical (OH), during the day; the nitrate radical
(NO3), at night; and ozone (O-3), which contributes during the day and
night, Halogen atoms can also play a role during the day, Here the im
plications of the complex VOC-NOx chemistry for O-3 control are discus
sed, In addition, OH, NO3, and O-3 are shown to play a central role in
the formation and fate of airborne toxic chemicals, mutagenic polycyc
lic aromatic hydrocarbons, and fine particles.