These hydrocarbons, together with olefinic minor LPG components, furnish substantial amounts of hydroxyl radical reactivity, a major precursor to formation of the ozone component of urban smog. (science.sciencemag.org)
... Most stratospheric ozone is created in the tropics, because the intensity of the solar radiation that causes formation of ozone is higher nearer the equator. (harrytodd.org)
Unless emissions of specific pollutants that are associated with the formation of ozone are sharply cut, almost all of the continental United States will experience at least a few days with unhealthy air during the summers, the research shows. (sciencedaily.com)