Research

Publications

1. Lunyu Xie, Tianhua Zou, Joshua Linn, and Haosheng Yan (2024). “Can Building Subway Systems Improve Air Quality? New Evidence from Multiple Cities and Machine Learning.” Environmental and Resource Economics, 87(4), 1009–1044. [DOI] Recognized as a 2024 Outstanding Publication in Environmental and Resource Economics.
   Abstract

   Public investments in subway systems are often motivated by improving local air quality. Recent studies, however, have reached different conclusions on the air quality benefits of subway investment. To reconcile these findings, this paper examines the air quality effects of all 359 subway line openings in China between 2013 and 2018. The machine learning method adopted in this paper substantially improves the consistency and precision of the estimates by purging seasonality, volatility, and the nonlinear effects of meteorological conditions in air quality data. The empirical results suggest an insignificant short-term effect and a significant long-term effect, which is expected as the adjustment of commuting mode takes time. Using the causal forest approach, the heterogeneity analysis find that a city that is experiencing rapid economic growth from a lower income level and currently has fewer subway lines is more likely to experience statistically significant improvements in air quality from a subway opening. These findings help reconcile the different findings in the literature and shed light on air pollution reduction as one of the objectives of public transit investment.

Working Papers

1. Cooling Inequality on a Hotter Planet (with Lunyu Xie and Guilan Li).
   Abstract

   Drawing on a novel, long-term, nationwide micro-level dataset of Chinese residential energy consumption, this paper investigates households' heterogeneous adaptation behavior to global warming. We find that lower-income households exhibit weaker responses to heat in both the number of air conditioners (ACs) they own and their use, leaving them more vulnerable to rising temperatures. We further show that housing insulation acts as a complement to AC, while fans serve as an imperfect substitute for it. The poorer insulation of lower-income homes widens the cooling gap, whereas fans partly offset it. Using simulations under both climate and income-growth scenarios, we show that the cooling gap between richer and poorer households widens as the planet warms and as incomes rise, widening most when both are rapid. Furthermore, we discuss the potential equity-pollution dilemma, revealing a trade-off between reducing cooling inequality and lowering carbon emissions. These findings highlight a new source of climate-related inequality and provide insights for policies aimed at addressing both carbon emissions and cooling inequality.

2. How Local Discretion Shapes the Effects of a Central Mandate: Evidence from China's Clean Heating Policy (with Lunyu Xie and Yuheng Zhao).
   Abstract

   This paper studies how local implementation shapes the realized effects of a centrally mandated policy. We examine China's Clean Heating Policy, a uniform environmental mandate rolled out across northern China between 2017 and 2022. Using satellite-derived pollution data residualized by machine learning, a staggered difference-in-differences design, and a text-based measure of local discretion from government work reports, we document four findings. First, the policy reduced heating-related ambient PM2.5 by 11.6 percent on average. Second, this average masks substantial dispersion across treated counties. Third, heterogeneity is more clearly visible along local constraints: counties with greater heating demand and tighter financial constraints realized smaller gains on average, while differences associated with officials' career incentives are weaker. Fourth, local discretion amplifies these differences. In cities with higher discretion, heterogeneity along constraint-related dimensions becomes more pronounced, and incentive-related differences also become more visible. These results suggest that the realized effects of a uniform mandate depend not only on policy design at the center, but also on how local constraints interact with local discretion during implementation.

Work in Progress

1. A Second Pair of Hands: Intergenerational Co-parenting and the Effects of Parental Training on Early Childhood Development in Rural China (with Scott Rozelle and Lei Wang).
2. Housing Structure, Network Externalities, and Optimal Subsidy Dynamics (with Mengjia Hu, Joshua Linn, and Lunyu Xie).
3. Information Provision and Electric-Vehicle Adoption: A Randomized Field Experiment.
4. The Long-Term Impact of China's Aid and Investment in Africa (with Huning Wan, Lunyu Xie, and Yuheng Zhao).

Pre-Doctoral Publications

1. Bin Liu, Tianhua Zou (corresponding author), and Han Zhang (2023). “The Impact of the Belt and Road Initiative on Cultural-Product Exports: Evidence from a Staggered DID Model” (in Chinese). 南方经济 (South China Journal of Economics), 42(7), 135–152.