Factors influencing real-world emissions of light-duty vehicles in Mexico

Air pollution is the fourth greatest risk factor for human health worldwide and the transport sector is considered the biggest responsible for air pollution in urban areas. Public policies are constantly generated to guarantee air quality based on limiting vehicular emissions through type-approval procedures. However, previous studies have remarked an increasing discrepancy between the vehicles’ real-world emissions and those reported through type-approval emissions procedures. Like most countries around the world, Mexico based its emissions regulations on those that were specifically designed for the United States (US) and/or Europe (EU) based on their historical data and experiences. Consequently, the discrepancy between real-world emissions and type approval emissions is even higher for these cases. As the first step toward implementing strategies to reduce the environmental impact of vehicles in Mexico, highly influencing factors in this emissions discrepancy must be identified and assessed to determine the most effective actions that should be included in short and long-term plans. Based on four emissions’ measurement campaigns using remote sensing devices and one fuel consumption measurement campaign using On-board Diagnostic (OBD) data, it was determined that fuel formulation, altitude, and vehicle age were not the most significant factors for the high emissions concentrations observed in Mexico over the years. It is mainly due to the notable presence of gross-polluters which are strongly connected to outdated vehicle technologies being sold as a consequence of permissive regulations and to the absence of inspection and maintenance programs in most metropolitan areas. A single outdated technology raises the overall CO, HC, and NO emissions by 16%, 12%, and 29%, respectively, in Mexico City. And the lack of a mandatory I/M program in Monterrey resulted in 19.3%, 23.9%, and 36.7% of the vehicles not complying 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. And finally, it was identified that the use of Air Conditioning (A/C) systems increased fuel consumption rate (and consequently CO2 emissions) between 20% to 40% under real-world driving conditions, which has great importance since the use of A/C is not considered in current Mexican type-approval regulations.

https://orcid.org/0000-0003-4508-6453