Air pollution is a serious problem in cities across the developing world. There are, however, examples of cities that have taken advantage of existing technologies to partially mitigate the problem. With 20 million people, Mexico City is the world's second largest city after Tokyo. It is also situated in a valley where polluted air tends to become trapped. As a result, it has long suffered from pollution problems that have adversely affected public health. Mexico City's health problems became so acute in the 1990s that they prompted the government to take action. Emission standards were set and vehicles were required to undergo inspections twice a year. In addition, new vehicles had to be equipped with catalytic converters that significantly reduce noxious tail-pipe emissions. Leaded fuel damages catalytic converters; so, the introduction of catalytic converters also led to the widespread use of lead-free gasoline. Motor vehicles produce three-quarters of Mexico City's air pollution. As a result, the measures taken have created noticeable improvements in air quality. In China, where large cities also suffer from excessive air pollution, the situation is different. A larger portion of the air pollution is due to emissions from power plants and industrial facilities. Technologies also exist to curb emissions from these sources; however, power plants and industrial facilities drive economic growth in China, where, for example, one new coal-fired steam plant is being added to the electric grid every 7–10 days. The Chinese government made an enormous effort to improve air quality in Beijing for the Olympics. We can only hope that this effort will spread to other cities as well.
