Figure 4 shows the air pollution status of Chinese
cities of different sizes. Air pollution in mega- and large
cities is more severe than in medium and small cities,especially in large cities with the population between one
and two million. These cities are provincial capitals or
more economically developed cities and often have a
large energy, chemical, or iron and steel industry. They
mostly suffer from coal-combustion pollution and have
less experience, technical support, and economic power
to prevent air pollution compared with the megacities,