We report vertical ozone profiles from ozonesondes launched during the Texas Air Quality Study 2000. The launch site at the Coastal Research Center in La Marque, TX is about 40 km SE of downtown Houston, and about 5 km WSW of Texas City. Soundings were launched on a daily basis at 15:00 LT, 20:00 GMT from 08/21-09/14 2000.

The profiles show three major episodes within the boundary layer. The strongest of which occurred during the record-setting heat days of 09/4-5, on which winds veering from WNW to NE between 12:00 � 13:00 LT result in peak ozone concentrations of 148 ppb at 900 m over La Marque and surface spikes at Texas City and Galveston near 130 and 150 ppb, respectively. 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.