Average ethane, CO, and O3 measured during the case study drives. Averages of one hour of measurements of ethane, CO, and O3 during the mobile laboratory drives on July 23, August 3, and August 13, 2014. The time of day of each drive that was included is shown in the legend. Average O3 at the Greeley monitoring site from 13:00–14:00 is included (gray cross hatched square) to estimate peak O3 in the drive vicinity on August 3. DOI: https://doi.org/10.1525/elementa.254.f16