Atmospheric oxidation, ozone production, and their dependence on nitrogen oxides and radical production

The hydroxyl radical, OH, drives atmospheric oxidation by reacting with chemicals emitted from Earth's surface, thus creating new chemicals that are more easily scavenged and removed by aerosols, clouds, and rain. In the oxidation process, the hydroperoxyl radical, HO₂, is created. Its reaction with nitric oxide, NO, leads to ozone production. Both atmospheric oxidation (OH abundance) and ozone production initially increase as NO is added to the atmosphere, but then decrease as more NO is added. The peak value of both atmospheric oxidation and ozone production depends not only on NO, but also on the production rate of the sum of OH and HO₂, called HO_x.

Recent atmospheric chemistry field studies included measurements of a large suite of meteorological variables and chemical species, including the hydroxyl radical, the hydroperoxyl radical, and nitric oxide. The NO levels and HO_x production rates varied widely for the sampled environments, which include air in remote Pacific Ocean troposphere, the upper troposphere and lower stratosphere at high latitudes, a moderately rural forest, and a polluted city. With observations in these diverse environments, we can examine the fundamental relationships among atmospheric oxidation, ozone production, NO, and HO_x production. This examination involves both the comparison of observations to photochemical models and the determination of the functional dependence of the observed OH, HO₂, and ozone production on NO_x.