Urbanites’ mental health undermined by air pollution

The rising mental health difficulties of the urban population in developing countries may be attributed to the high levels of air pollution. However, nationwide large-scale empirical works that examine this claim are rare. In this study, we construct a daily mental health metric using the volume of mental-health-related queries on the largest search engine in China, Baidu, to test this hypothesis. We find that air pollution causally undermines people’s mental health and that this impact becomes stronger as the duration of exposure to air pollution increases. Heterogeneity analyses reveal that men, middle-aged people and married people are more vulnerable to the impact of air pollution on mental health. More importantly, the results also demonstrate that the cumulative effects of air pollution on mental health are smaller for people living in cities with a higher gross domestic product per capita, more health resources, larger areas of green land and more sports facilities. Finally, we estimate that with a one-standard-deviation increase of fine particulate matter (26.3 μg m⁻³), the number of people who suffer from mental health problems in China increases by approximately 1.15 million. Our findings provide quantitative evidence for the benefits of reducing air pollution to promote mental health and well-being.