Yale geology and geophysics professor Ron Smith explains why the atmosphere has two distinct ozone problems: too much ozone near the ground and too little high above. In the troposphere, sunlight reacts with nitrogen oxides from automobile exhaust to form photochemical smog, an ozone concentration dangerous to human airways, with pollutant levels typically peaking twice a day during morning and evening rush hours. Smith reviews EPA concentration limits and notes that several US counties still exceed them. He then contrasts this with the separate problem of stratospheric ozone depletion, walking through ozone's chemical properties and how it forms and breaks down differently at different altitudes. Chapters cover air pollutants generally, the two ozone problems, ozone properties, photochemical smog, concentration limits, and the primary pollutants behind ozone creation. Part of his Yale course The Atmosphere, the Ocean and Environmental Change, recorded in 2011.