Leave or stay? Heterogeneous impacts of air quality on intercity migration in China

Air pollution is a serious problem worldwide, and migration for environmental reasons has been emphasized. However, data deficiencies have limited research on the links between air quality and intercity migration. Based on Baidu migration big data of cross-city mobility information, an extended gravity model was built to examine the effects of air quality (PM2.5) on intercity migration. Results showed that air pollution significantly reduces immigration into cities but does not significantly encourage emigration. A 10% increase in air pollution leads to 3.78% and 11.08% decreases in the net and total inflows of the urban population, respectively. Specifically, air quality had a greater influence on the migration of central and northeastern cities and small- and medium-sized or middle-income cities. Influences of the Yangtze River and Chengdu-Chongqing urban agglomeration, two very large and important urban clusters in China, were significantly higher than those of other areas. Air pollution did not significantly drive people to flee from Beijing, Shanghai, Guangzhou, and Shenzhen, which involves, in contrast to the expected situation, people choosing to stay in first-tier cities in China. Those findings are informative for environmental as well as migration policymakers to focus on the heterogeneous nexus between the impacts of policies that is depending on the characteristics of cities.