Dissertation (Ph.D.) - Indiana University, School of Public and Environmental Affairs, 2020The flagship air pollution control program in Mexico City Metro Area (MCMA) named Hoy No Circula -HNC- (loosely translated as No Driving Day) regulates the frequency in which motor vehicles can be used in the city from Monday to Saturday based on a biannual vehicle-emissions checkup. Such mandate was first implemented in November 1989, then changed in July 2014 from the emissions-based standard to vehicles’ age regulation, and changed again to its original form in July 2015. It can be argued that neither of the two policy changes responded to shifts in the trends of air pollution concentrations in the city, but rather to increased levels of corruption in the emissions checkup centers in 2014, and to judicial contentions about the new rules in 2015, making them exogenous policy changes. The goal of this paper is to conduct an impact evaluation of HNC on MCMA’s air quality at its three most relevant moments in time: its first implementation (1989), and the two policy changes (2014 and 2015). Past studies used interrupted time-series to show that the program, when first implemented, was relatively ineffective for reducing pollution; however, it substantially increased the number of vehicles in the city, offsetting environmental quality improvements. While the effects are consistent in the short run, in the longer run they remain elusive. This research builds upon those studies by using two difference-in-differences specifications with alternative controls, and addressing potential spatial confounders between monitoring stations that are inherent to ambient data, thus providing a more robust quasi-experimental design. In addition, this research looks at the program’s first implementation, but also at the latest two policy changes that have not been subject to evaluation. For HNC’s first implementation, the results show statistically significant decreases in CO and O3 concentrations in the short run, and increments in the middle/long run. A similar pattern is observed for NOX and NO2 in the long run. This evidence supports the findings of past studies, where HNC had a positive impact on air quality right after its implementation, but a reversion of this effect after about six months due to increments in the size of the vehicle fleet and the amount of driving. For the policy change of 2014, the results show extremely modest improvements in air quality, close to nonexistent. CO experienced mild increases in concentrations, however the opposite is true for NOX, NO2 and O3. Finally, the evidence of the 2015 return to the original rules suggests significant loses in air quality. CO, NO2 and O3 experienced short and long run increments in concentrations, however this was not the case for NOX.