Poster #137 - Clearing the Air: The Complex Relationship Between Trucks, NOₓ Reductions, and Ozone Formation in Bogotá

• In Event: Friday Poster Reception

Abstract

Heavy-duty trucks are the backbone for logistics and supply chains. This is especially true for Colombia where trucks handle approximately 80% of total domestic cargo tonnage. Thereof, it is important to clearly identify the economic benefits and social costs related to truck operations. This study investigates how disruptions in heavy-duty truck traffic impact NOₓ and O3 levels in the capital of Colombia, Bogotá. I leverage multiple truck riots that occurred between 2015 and 2019 as exogenous disruption in heavy-duty truck traffic. Using high-frequency data on urban air quality monitors throughout the city, I estimate the impact of truck riots on NOₓ emissions and O3 concentrations in Bogotá. Specifically, I address 1) the effect of truck riots on NOₓ, PM10, PM2.5, and O3 levels and 2) the effect of NOₓ emission on O3concentrations. This study aims to establish the causal pathway through which heavy-duty truck traffic disruptions affect environmental outcomes within the city.

I employ Difference-in-Differences (DD), Two-Stage Least Squares (2SLS), and Regression Discontinuity in Time (RDiT) models to analyze . The DD analysis reveals that the truck riots led to statistically significant reductions in ambient NOₓ​ concentrations, confirming the substantial contribution of heavy-duty trucks to NOₓ​ pollution in Bogotá. For example, the 2015 riot reduced 24-hour average NOₓ​ by 11.9%, while the longer 2016 riot achieved reductions of 32-35%. However, the impact on PMs was inconsistent across events, with the 2015 riot reducing PM10​ and PM2.5 by 5.3% and 10.6% over 24 hours, respectively, while the 2016 riot showed some increases in PM10 levels​. Crucially, the DD estimates show that these same riots resulted in significant increases in O3 concentrations, with 24-hour averages rising by 8.8% during the 2015 riot and by 24-48% during the 2016 riot. Complementing this, the 2SLS estimations confirm a negative causal relationship, where a 1% increase in lagged NOₓ decreases current O3​ levels ranging from 0.28% to 1.29% depending on the hour of the day. Finally, the RDiT analysis of shorter riots corroborates the immediate impact, showing sharp NOₓ​ decreases and significant O3​ increases (e.g., up to 43.5% during the afternoon peak on the first day) right after the riots began. 

These findings hold critical implications for social well-being and environmental policy and transportation regulations. They demonstrate that disruptions in essential logistics, like trucking, yield complex environmental outcomes. Furthermore, interventions aimed solely at reducing NOₓ emissions from sources like trucks can inadvertently degrade air quality concerning ozone. This negatively impacts public health, especially in VOC-limited settings. Crafting policies that genuinely enhance social well-being through improved air quality requires integrated strategies. Such strategies must account for Bogotá's specific atmospheric chemistry, targeting both NOₓ and VOCs.

Author

• Phillip Sangwoo Lee, University of Southern California
  Presenting Author