= Solution
Lower <carbon monoxide> and <VOC> emissions generally reduce the supply of <peroxy radicals> from their <oxidation> and therefore reduce <photochemical ozone production> where <nitrogen monoxide> is available. Lower <nitrogen oxides> abundance suppresses the <nitrogen monoxide>-to-<nitrogen dioxide> pathway in <NOx-limited ozone production> regions. These are reasons for a regional/background <ozone> decrease when fossil-fuel precursor emissions decline.
The response can have the opposite local sign in a <nitrogen monoxide>-rich urban core: reducing <nitrogen monoxide> weakens <ozone titration>, and reducing <nitrogen oxides> in a <VOC-limited ozone production> regime can initially lessen <radical termination> and raise <ozone>. Less <carbon monoxide> can also leave more <hydroxyl radical> available to remove <methane>, partly opposing the <hydroxyl radical> demand from leaked hydrogen. Changes in precursor transport, chemistry and sunlight matter. \b[Reduced emissions usually reduce net regional <ozone> production, but do not guarantee a lower <ozone> <concentration> at every monitoring site.]
Back to article page
