The study addresses several shortcomings in our understanding
about the health effects of air pollution. First, the research design
provides estimates of the impact of long-run exposure to TSPs on
life expectancy. The policy caused long-run differences in TSP
concentrations between cities north and south of the Huai River
(6). Moreover, during the period in question, the hukou (household
registrations) system restricted mobility, so in general individuals
will be observed where they lived most of their lives. In
contrast, studies that use data for the United States or other
developed countries must assume no migration, which is undermined
by the high rates of migration in the United States and the
potential selection of location based on air pollution concentrations,
or alternatively assume that short-run variation in air
pollution is informative about life expectancy (7, 8). Second, the
availability of a regression discontinuity design based on the Huai
River policy provides an appealing quasi-experimental approach
that can help to move the existing literature from documenting a
robust association between particulates and health toward documenting
a causal relationship (9). Third, China’s air is extremely
polluted and we are unaware of any previous direct evidence on the
impact of air pollution on life expectancy at these concentrations,
although important research has applied results from the United
States to the Chinese setting (10). Fourth, the analysis is conducted
with the most comprehensive data file ever compiled on mortality
and air pollution in China or any other developing country.