Comparison of daily ozonesondes launched from 08/21-09/14 2000 from La Marque, TX during TexAQS to midlatitude tropospheric ozone climatologies reveals strong day-to-day variability in both boundary layer and free tropospheric ozone regimes.

Comparison of average profiles for sondes launched within August and September to average profiles from ozonesonde stations operating within the United States (Trinidad Head, CA 41 N, Boulder, CO, 40 N, Huntsville, AL, 35 N, and Wallops Island, VA, 38 N) reveals characteristics that are consistent with derived climatologies, as well as those that are unique to the Houston area. Analyses of integrated tropospheric ozone and tropopause heights for the study period show agreement with derived climatologies.

The profiles show three major ozone episodes within the boundary layer. The strongest of which occurred during the record-setting heat days of 09/4-5. Forward trajectory analysis of the parcels containing the elevated ozone shows a SSW to SW path and boundary layer venting to altitudes as high as 4 km at 6:00 GMT 09/07 near the Texas – Mexico border at Laredo.

Back trajectory analysis of the free troposphere ozone profiles reveals a number of high-and low-ozone regimes. Elevated upper-tropospheric ozone mixing ratios during days 08/21-24 are associated with convective activity over the central United States two days prior in which ozone precursors lifted by the convection, coupled with NOx from lightning were used to “cook” the observed ozone en route.

Elevated middle-tropospheric ozone (0828-09/01) and low upper-tropospheric ozone result from strong vertical shear in which the ozone between 5-8 km descends from the upper troposphere across the continental United States and the low ozone between 9-14 km originates from the tropical upper troposphere. The very low ozone between 5-15 km during days 09/02-09/08 is associated with trajectories transporting clean air from the Pacific Ocean.