Ozone is formed when nitrogen oxides and certain hydrocarbons, produced mainly from automobiles, combine in the presence of sunlight.
Ozone is one component of photochemical smog.
It can affect the tissues in plants and is irritating to the eye, nose, throat and respiratory system. Ozone is measured continuously by analyzers that operate using the monochromatic ultraviolet absorption spectrophotometry principle. As ultraviolet light at 253.7 nanometers is passed through the optic bench, a fixed quantity of zero air and ambient air are drawn into the bench. The intensity of the ultraviolet radiation traversing the optic bench is attenuated by the ozone present in the ambient sample. This attenuated signal is detected and compared with the unattenuated signal from the zero air cycle.