Although most regions outpaced their targets, the most populated cities had some of the greatest declines. Beijing’s readings on concentrations of fine particulates declined by 35 percent; Hebei Province’s capital city, Shijiazhuang, cut its concentration by 39 percent; and Baoding, called China’s most polluted city in 2015, reduced its concentration by 38 percent.

To investigate the effects on people’s lives in China, I used two of my studies (more here and here) to convert the fine particulate concentrations into their effect on life spans. This is the same method that underlies the Air Quality-Life Index that can be explored here. These studies are based on data from China, so they don’t require extrapolation from the United States or some other country with relatively low concentrations of pollution.

The results suggest that China’s fight against pollution has already laid the foundation for extraordinary gains in life expectancy. Applying this method to the available data from 204 prefectures, residents nationally could expect to live 2.4 years longer on average if the declines in air pollution persisted.

The roughly 20 million residents in Beijing would live an estimated 3.3 years longer, while those in Shijiazhuang would add 5.3 years, and those in Baoding 4.5 years. Notably, my research suggests that these improvements in life expectancy would be experienced by people of all ages, not just the young and old.

To put the astounding scale and speed of China’s recent progress in context, it’s useful to think back to the severe pollution levels in many American cities in the 1950s and 1960s, especially in the Rust Belt.

The U.S. Clean Air Act is widely regarded as having produced large reductions in air pollution. In the four years after its 1970 enactment, American air pollution declined by 20 percent on average. But it took about a dozen years and the 1981-1982 recession for the United States to achieve the 32 percent reduction China has achieved in just four years.

Of course, air pollution levels still exceed China’s own standards and far surpass World Health Organization recommendations for what is considered safe. Bringing all of China into compliance with its own standards would increase average life expectancies by an additional 1.7 years (as measured in the areas where data is available). Complying with the stricter World Health Organization standards instead would yield 4.1 years.