Air pollution is rarely a major concern for most people in Western Europe. You seldom notice it except when sitting in heavy traffic or when it obscures the far horizon at a scenic spot.
However until the middle of last century it was a different story, with heavy industry and domestic heating filling city air with smoke, noxious gases and ozone. These air pollutants contribute to smog: the unpleasant combination of gases and particles that irritates the lungs and can do lasting damage to health. Many parts of the developing world still suffer from the high levels of air pollution that accompany unbridled industrial expansion and rapid economic development.