Contribution of Subway Expansions to Air Quality Improvement and the Corresponding Health Implications in Nanjing, China

Meina Zheng, Xiucheng Guo, Feng Liu and Jiayan Shen
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Meina Zheng: Jiangsu Key Laboratory of Urban ITS, Southeast University, Nanjing 210096, China
Xiucheng Guo: Jiangsu Key Laboratory of Urban ITS, Southeast University, Nanjing 210096, China
Feng Liu: School of Economics and Management, Southeast University, Nanjing 210096, China
Jiayan Shen: Jiangsu Key Laboratory of Urban ITS, Southeast University, Nanjing 210096, China

IJERPH, 2021, vol. 18, issue 3, 1-19

Abstract: With China’s rapid economic development, particularly its accelerated urbanization, air pollution has been one of the serious environmental issues across China. Most major cities in China expand their subway systems to handle this problem. This study takes both long- and short-term effects of subway expansions on air quality and its corresponding health implications into account based on a network density-based time series analysis and a distance-based difference-in-differences analysis. The daily and hourly monitor-level air quality data on Nanjing from 13 May 2014 to 31 December 2018, combining with corresponding weather variables, are used to quantify the effect of subway expansions on local air pollution caused by eight new subway lines in Nanjing. The results reveal that subway expansions result in a statistically significant decrease in the air pollution level; specifically, the air pollution level experiences a 3.93% larger reduction in the areas close to subway lines. Heterogeneous analysis of different air pollutants indicates that the air pollution reduction effect of subway expansions is more significant in terms of Particulate Matter (PM 2.5 ) and CO. A back-of-the-envelope analysis of the health benefits from this air improvement shows that the total number of yearly averted premature deaths is around 300,214 to 443,498. A set of alternative specifications confirm the robustness of our results. These results provide strong support for putting more emphasis on the environmental effect of subway expansions in the cost-benefit analysis of subway planning.

Keywords: subway; air pollution; difference-in-differences analysis; network density (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2021
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