Vertical variations in O3 concentrations before and after a gust front passage

[1] Two consecutive increases in surface ozone, occurring after the cessation of photochemical ozone production, are investigated. A unique suite of instruments, including an ozone profiling lidar, a Doppler lidar, surface chemistry sensors, surface meteorological sensors, and a radar wind profiler, was deployed during the Southern Oxidants Study of 1999 in Nashville, Tennesee. Time series of ozone at 10, 405, and 1035 m above ground level (AGL) on 22 June 1999 showed variations in the vertical gradient of ozone over the course of the afternoon and evening. Analysis of time series of vertical velocity at 8 m AGL and its standard deviation, the variance in Doppler lidar calculated horizontal wind speed from near the surface to 500 m AGL, wind profiles, and meteorological surface station data, revealed mechanisms responsible for these changes in ozone. An early evening rise in surface ozone occurred with the passage of a thunderstorm gust front. Analysis showed that downward mixing of ozone-rich air from a residual layer (RL) of ozone above 400 m caused a sharp rise in ozone at the surface and a decrease of ozone in the RL. Doppler lidar measurements showed details of the postgust front wind flow, such as the depth of the air mass behind the front, the turbulent wake region, and inferred vertical velocities throughout a layer several hundred meters deep. The second rise in surface ozone was caused by turbulent mixing due to elevated directional wind shear, which mixed ozone-rich air down to the surface.