Theses Doctoral

Essays in Applied Environmental Economics

Zhu, Yining

This dissertation consists of three essays in the field of applied environmental economics. The first two essays study the effect of daily ambient temperature on police officer behavior. Police officers often exercise substantial discretion when making highly consequential decisions, which can lead to unfair and arbitrary law enforcement. In the first chapter, I exploit daily ambient temperature as a source of transitory, high-frequency shocks and examine how it affects an officer’s decision whether to discount a driver’s speeding penalty in Florida. I find that a 1-standard-deviation increase in temperature lowers the driver’s probability of receiving a lenient ticket by 2%. In addition, using traffic monitoring data and crash reports, I do not find evidence of decreased police effort or increased reckless driving on hot days. I show that the reduction in leniency is disproportionally borne by white drivers, who on average benefit more from officer leniency.

In addition, I find that newly hired officers become less affected by temperature as they accumulate more experience on the job. The first chapter shows that daily ambient temperature has a significant effect on police officers’ professional performance. Inspired by this result, in the second chapter I study the effect of temperature on officers’ online expressed sentiment. Mood changes caused by temperature could be a potential mechanism for officers’ behavioral changes observed in the first chapter. To study this question, I obtained messages posted on an online police forum that is popular among Florida police departments. I find that a 1-standard-deviation increase in temperature leads to a 3.5% increase in the use of profanity. In addition, higher temperature has a negative but nonlinear relationship with expressed sentiment. I also find limited evidence of a change in forum activity or discussion topics on relatively hot days, which suggests that these results are likely to be driven by temperature’s effect on officers’ mood. Taken together, the first two chapters highlight the sensitivity of law enforcement behavior to transitory shocks such as environmental conditions.

The third chapter, which is joint work with Xinming Du, explores the impact of the 2018 China- U.S. trade war on air pollution in China. Since the Chinese economic data is heavily censored, we take air pollution as a proxy for measuring economic activity. Using city-industry level trade data, we construct a Bartik-style trade war exposure measure for cities in China and compare the pollution trajectory of cities in the top quartile of our measure to those in the bottom quartile under a difference-in-difference design. In addition, to test whether local governments relaxed their enforcement of environmental policies in response to the trade war, we look at whether firms changed their tendency of polluting in the dark during the trade war. Our analysis finds a negative but small and not robust effect of the U.S. tariffs on China’s air quality and no effect of the Chinese retaliatory tariffs. In addition, we find no impact on disguised pollution behaviors of local firms. We conclude that the trade war had minimal effect on China’s economic activity.

Geographic Areas


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More About This Work

Academic Units
Thesis Advisors
Almond, Douglas V.
Ph.D., Columbia University
Published Here
May 25, 2022