Areas of China can act as a laboratory for the impact of particulate air pollution on long-term health. There are good reasons to think that the established correlations between air pollution and life expectancy are due to physical and biochemical mechanisms such as increased chronic inflammation. It has been equally possible to argue that that the relationship has more to do with relative wealth of populations, however, as wealthier regions tend to have lower levels of pollution. In this study, researchers put some numbers to the correlation, and improve on previous attempts to rule out wealth and other effects as significant contributing causes.
A study finds that a Chinese policy is unintentionally causing people in northern China to live 3.1 years less than people in the south, due to air pollution concentrations that are 46 percent higher. These findings imply that every additional 10 micrograms per cubic meter of particulate matter pollution reduces life expectancy by 0.6 years. The elevated mortality is entirely due to an increase in cardiorespiratory deaths, indicating that air pollution is the cause of reduced life expectancies to the north. "These results greatly strengthen the case that long-term exposure to particulates air pollution causes substantial reductions in life expectancy."
The study exploits China's Huai River policy, which provided free coal to power boilers for winter heating to people living north of the river and provided almost no resources toward heating south of the river. The policy's partial provision of heating was implemented because China did not have enough resources to provide free coal nationwide. Additionally, since migration was greatly restricted, people exposed to pollution were generally not able to migrate to less polluted areas. Together, the discrete change in policy at the river's edge and the migration restrictions provide the basis for a powerful natural experiment that offers an opportunity to isolate the impact of sustained exposure to particulates air pollution from other factors that affect health.
Overall, the study provides solutions to several challenges that have plagued previous research. In particular, prior studies rely on research designs that may be unlikely to isolate the causal effects of air pollution; measure the effect of pollution exposure for relatively short periods of time (e.g., weekly or annually), failing to shed light on the effect of sustained exposure; examine settings with much lower pollution concentrations than those currently faced by billions of people in countries, including China and India, leaving questions about their applicability unanswered; measure effects on mortality rates but leave the full loss of life expectancy unanswered.
The study follows on an earlier study, conducted by some of the same researchers, which also utilized the unique Huai River design. Despite using data from two separate time periods, both studies revealed the same basic relationship between pollution and life expectancy. However, the new study's more recent data covers a population eight times greater than the previous one. It also provides direct evidence on smaller pollution particles that are more often the subject of environmental regulations.