Nocturnal ozone enhancement in the lower troposphere observed by lidar

An ozone enhancement in the nocturnal residual layer was observed by the Huntsville ozone lidar from the late evening to midnight on 4 October 2008. The well-correlated ozone, aerosol, water vapor, and wind structures suggest a low-level jet is responsible for this ozone enhancement. HYSPLIT backward trajectories support this conclusion with southerly transport suggesting Birmingham, AL as the source. Correspondingly, the higher increasing rate of surface ozone observed in the morning of 5 October can be explained by the entrainment into the mixed layer of higher ozone aloft on this day as compared with 4 October. This case study demonstrates the importance of continuous high-resolution lidar profiling for capturing short-duration ozone variations in the lower troposphere.

► A nocturnal ozone enhancement was observed associated with a low-level jet.
► This enhancement resulted in a higher increasing rate of the 2nd-day surface ozone.
► However, higher daily-surface maximum ozone was not observed as expected.