Background

Although the association between long-term exposure to PM_2.5 and mortality has been evaluated intensively, little is known about the socioeconomic disparity in the association.

Methods

We collected data on annual all-cause mortality, PM_2.5 concentration, socioeconomic and demographic characteristics of 2640 counties from the two most recent Chinese censuses in 2000 and 2010. We applied the difference-in-differences (DID) method to estimate PM_2.5-mortality association for counties at different quartiles of literacy rate, college rate, urbanization rate and GDP per capita, respectively.

Results

Overall, every 10 µg/m³ increase in annual average PM_2.5 was associated with 3.8% (95% confidence interval [CI]: 3.0–5.0) increase of all-cause mortality. The stratified analysis suggested higher health impact of exposure in counties with lower socioeconomic status. For counties of the lowest quartile (Q₁) of literacy rate, college rate, urbanization rate and GDP per capita, the effect estimates were 6.0% (95% CI: 4.2–7.7), 4.4% (95% CI: 2.8–6.0), 3.5% (95% CI: 2.0–5.1) and 4.9% (95% CI: 2.7–7.1), respectively. There was strong evidence for elevated risk in mortality associated with PM_2.5 of all socioeconomic factors in the lowest quartile (Q₁) compared with the highest quartile counties (Q₄) (p-value for difference < 0.05).

Conclusions

There was socioeconomic disparity in the PM_2.5-mortality association in China. Dwellers living in less developed counties are more vulnerable to long-term exposure to ambient PM_2.5 than those living in developed counties.