Urban air pollution has three main components: industrial and vehicle exhausts and domestic heating. The concentrations of air pollutants depend not only on the quantities emitted by also on the ability of the atmosphere either to absorb or disperse them. That is why in each individual case, so much hinges on meteorological and topographic factors. The actual siting of settlements is also of great importance. Clearly, there is a difference between a housing complex situated in a "green belt" away from industrial locations or busy motorways, and one surrounded by heavy industry enterprises and waste disposal sites. Energy generation adds considerably to the overall levels of urban air pollution, its emission greatly contributing to the intricate photochemical conversions leading both to smog and acid rain.
[Developing countries] Spectacular economic growth in Southeast Asia has led to sharp increases in consumption of energy and consequently in emissions of sulphur dioxide and other pollutants. Energy consumption has been doubling every 12 years. Local air pollution problems are already severe: 12 of the 15 most polluted cities of the world (i.e. highest levels of particulate matter) are in Asia. Less than one percent of 500 Chinese cities have clean air. Respiratory disease is the leading cause of death in China. Airborne particulate matter increased five-fold in some districts of Mexico City during the decade of the 1980s. Because of the air pollution, it is compulsory for employees at the Japanese Chamber of Commerce in Mexico City to spend 45 days a year on vacations outside the city. WHO estimates that in Latin America alone, more than 24,000 lives are lost every year through permanent exposure to high air pollution in cities.