Impact of new fuel specifications on vehicle emissions in Mexico

Abstract

Volatile Organic Compounds (VOCs) from vehicles are a significant contributor to Mexico's pollution, as a precursor to both ambient ozone and secondary particulate matter (PM). Recent updates to Mexico's gasoline specification NOM-016 allow ethanol blends up to 10 percent (E10) outside of the metropolitan areas of Mexico City, Guadalajara and Monterrey, and leave open the possibility of allowing E10 within these areas as well. The NOM-016 updates also permit E10 to have higher volatility (RVP) than previously allowed. The impact of these changes on vehicle emissions in Mexico was assessed, with a focus on evaporative VOC emissions driven by increased RVP and permeation. Roadside remote sensing (RSD) measurements from Mexico City were analyzed, finding that vehicle fleet hydrocarbon (HC) emissions are much higher than U.S. levels, with indication that high evaporative emissions contribute to this. The impact on vehicle emissions of the NOM-016 revisions and potential introduction of E10 in metropolitan zones was assessed for an ozone episode day using the MOVES-Mexico model, which reflects higher evaporative emissions from Mexico's vehicle fleet. Results show an increase in total motor vehicle VOC emissions of 13–18 percent in metropolitan areas and a 23 percent increase in other areas of the country for NOM-016 compliant E10 fuel, relative to fuel sold in Mexico prior to the NOM-016 update. Results for other pollutants showed an increase in PM2.5 and air toxics from E10 blends, a reduction in CO, and NOx impacts mixed depending on area. Total motor vehicle emissions for toluene, identified in prior work as the compound with the highest ozone forming potential in Mexico City, increased by 29–34 percent with E10 fuel in Mexico City and more in other metropolitan areas. Past studies linking emissions change with health outcomes in Mexico City suggest that the increase in vehicle emissions from NOM-016 updates would have a measurable negative effect on premature mortality, chronic bronchitis, hospital visits, and restricted activity days, with societal costs associated with health care and lost productivity.