Root causes of the differences in the real-world vehicle emissions between Mexico and the US

Abstract

• Vehicle emissions in Mexico have been historically higher than in the United States. • The proposed methodology uses Remote Sensing studies to identify the root causes. • Discrepancies are linked to outdated vehicle technologies (gross polluters) in Mexico. • Differences in fuel characteristics, altitude, or fleet age have no relevant impact. • An I/M program in Monterrey could reduce CO, HC, and NO by 47%, 67%, and 55%. Previous studies have remarked that real-world tailpipe emissions are much higher in Mexico than in the US. This work investigates the reason for those differences by comparing results from remote sensing measurements obtained in four different locations within Mexico and the US. Statistical analyses showed that fuel formulation, altitude, and vehicle age were not significant factors for those differences. It was due to the notable presence of one outdated vehicle technology, which raises the overall CO, HC, and NO emissions by 16%, 12%, and 29%, respectively, in Mexico City. It was also due to the lack of a mandatory I/M program in Monterrey, where 19.3%, 23.9%, and 36.7% of the vehicles do not comply with the regulation for CO, NO, and HC emissions, respectively. If these vehicles were detected and repaired, the city's mean CO, HC, and NO vehicle emissions could be reduced by ∼47%, ∼67%, and ∼55%, respectively.