Publications

This paper estimates the impact of ambient air pollution on the two most economically costly airborne respiratory diseases, COVID-19 and influenza. Our methods incorporate the epidemiological Susceptible-Infectious-Recovered-Deceased (SIRD) model to construct the outcome of interest, the Instrumental Variable (IV) model to establish causality, and the Flexible Distributed Lag (FDL) model to capture dynamic effects. Analyzing data from the first wave of the COVID-19 pandemic in China, we find that air pollution can significantly raise the daily growth rate of COVID-19. In contrast, air pollution shows small and statistically insignificant effects on influenza healthcare visits in Japan.

Using transboundary pollution from mainland China as an instrument, we show that air pollution leads to higher cardio-respiratory mortality in Hong Kong. However, the air pollution effect has dramatically decreased over the past two decades: before 2003, a 10-unit increase in the Air Pollution Index could lead to a 3.1% increase in monthly cardio-respiratory mortality, but this effect has declined to 0.5% using recent data and is no longer statistically significant. Exploratory analyses suggest that a well-functioning medical system and immediate access to emergency services can help mitigate the contemporaneous effects of pollution on mortality.

Rising consumer demand for online food delivery has increased the consumption of disposable cutlery, leading to plastic pollution worldwide. In this work, we investigate the impact of green nudges on single-use cutlery consumption in China. In collaboration with Alibaba's food-delivery platform, Eleme (which is similar to Uber Eats and DoorDash), we analyzed detailed customer-level data and found that the green nudges—changing the default to “no cutlery” and rewarding consumers with “green points”—increased the share of no-cutlery orders by 648%. The environmental benefits are sizable: If green nudges were applied to all of China, more than 21.75 billion sets of single-use cutlery could be saved annually, equivalent to preventing the generation of 3.26 million metric tons of plastic waste and saving 5.44 million trees.

The effects of coronavirus disease-19 (COVID-19) public health policies on non-COVID-19-related mortality are unclear. Here, using death registries based on 300 million Chinese people and a difference-in-differences design, we find that China's strict anti-contagion policies during the COVID-19 pandemic significantly reduced non-COVID-19 mortality outside Wuhan (by 4.6%). The health benefits persisted and became even greater after the measures were loosened: mortality was reduced by 12.5% in the medium term. Significant changes in people's behaviours (for example, wearing masks and practising social distancing) and reductions in air pollution and traffic accidents could have driven these results. We estimate that 54,000 lives could have been saved from non-COVID-19 causes during the 50 days of strict policies and 293,000 in the subsequent 115 days. The results suggest that virus countermeasures not only effectively controlled COVID-19 in China but also brought about unintended and substantial public health benefits.

To prevent the escalation of COVID-19 transmission, China locked down one-third of its cities, which strictly curtailed personal mobility and economic activities. Using comprehensive daily air quality data in China, we evaluated the impacts of these measures in terms of the Air Quality Index (AQI) and the concentrations of particulate matter with a diameter of less than 2.5 μm (PM_2.5). To infer their causal relationships, we employed difference-in-differences models that compare cities with and without lockdown policies. We found that city lockdowns led to a sizeable improvement in air quality. Within weeks, the AQI in the locked-down cities was brought down by 19.84 points (PM_2.5 down by 14.07 µg m⁻³) relative to the control group. In addition, air quality in cities without formal lockdowns also improved because of the enforcement of other types of counter-virus measures. The AQI in those cities was brought down by 6.34 points (PM_2.5 down by 7.05 µg m⁻³) relative to the previous year. The lockdown effects are larger in colder, richer and more industrialized cities. Despite these improvements, PM_2.5 concentrations during the lockdown periods remained four times higher than the World Health Organization recommendations, suggesting much further effort is needed. Existing environmental policies could obtain similar air quality improvements at a much lower economic cost, making city lockdowns an unsustainable option to address environmental issues.

Objectives: To estimate the short term effect of particulate air pollution (particle diameter <10 μm, or PM₁₀) on mortality and explore the heterogeneity of particulate air pollution effects in major cities in China.

Design: Generalised linear models with different lag structures using time series data.

Setting: 38 of the largest cities in 27 provinces of China (combined population >200 million).

Participants: 350,638 deaths (200,912 in males, 149,726 in females) recorded in 38 city districts by the Disease Surveillance Point System of the Chinese Center for Disease Control and Prevention from 1 January 2010 to 29 June 2013.

Main outcome measure: Daily numbers of deaths from all causes, cardiorespiratory diseases, and non-cardiorespiratory diseases and among different demographic groups were used to estimate the associations between particulate air pollution and mortality.

Results: A 10 µg/m³ change in concurrent day PM₁₀ concentrations was associated with a 0.44% (95% confidence interval 0.30% to 0.58%) increase in daily number of deaths. Previous day and two day lagged PM₁₀ levels decreased in magnitude by one third and two thirds but remained statistically significantly associated with increased mortality. The estimate for the effect of PM₁₀ on deaths from cardiorespiratory diseases was 0.62% (0.43% to 0.81%) per 10 µg/m³ compared with 0.26% (0.09% to 0.42%) for other cause mortality. Exposure to PM₁₀ had a greater impact on females than on males. Adults aged 60 and over were more vulnerable to particulate air pollution at high levels than those aged less than 60. The PM₁₀ effect varied across different cities and marginally decreased in cities with higher PM₁₀ concentrations.

Conclusion: Particulate air pollution has a greater impact on deaths from cardiorespiratory diseases than it does on other cause mortality. People aged 60 or more have a higher risk of death from particulate air pollution than people aged less than 60. The estimates of the effect varied across cities and covered a wide range of domain.