In the Air Chemistry Building at the Sable Station: O3 analyzer (A); and O3 generator (B) used in testing and calibrating the analyzer. O3 is one of the gases measured as part of the Airshed Monitoring Program that has been running on Sable since 2000. O3, hydrogen peroxide and other photochemical oxidants are components of smog. In cities, emissions from industry and vehicles combine in the presence of sunlight to form a mixture that irritates respiratory systems and can pose risks to elderly and asthmatic people. Transport by wind also allows smog to affect rural areas and to generate transboundary pollution issues.