Updating Real-World Profiles of Volatile Organic Compounds and Their Reactivity Estimation in Tunnels of Mexico City

Abstract

The main objective of this work was to bring to date the exhaust and evaporative volatile organic compound (VOC) profiles from light-duty gasoline vehicles, carrying out a sampling and analysis campaign in two tunnels of Mexico City. The abundance of exhaust-emission VOC profiles was the same in 2018 as in 1998 (alkanes > aromatics > olefins > acetylene), albeit exhibiting large differences (67%, 17%, 12%, and 4% for 2018, and 50%, 26%, 16%, and 8% for 1998, respectively). An important reduction of 69% and 77% in VOC concentrations was registered inside and outside of the tunnel, respectively, in comparison with 1998. In the ambient air, alkanes accounted for 77%, since high concentrations of liquefied petroleum (LP) gas species are still present. Ethylene, propylene, 1-butene, and toluene from tunnel emissions contributed prominently to ozone formation, while the most reactive gasoline vapors were pentenes, pentanes, and butenes, although the ozone formation potential due to VOCs in tunnel emissions and ambient air also had a significant reduction. These results demonstrate that strategies carried out in the last 20 years were successful in achieving a better air quality, although the aromatic and olefin content in gasolines needs to be further reduced to lower the concentrations of toxic and reactive species.

Keywords

• VOCs
• tunnel
• ozone
• ozone formation potential
• gasolines
• VOC profiles