An evaluation of the interaction of morning residual layer and afternoon mixed layer ozone in houston using ozonesonde data

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The Tropospheric Ozone Pollution Project (TOPP) launched >220 ozonesondes in Houston (July 2004– June 2008) providing examples of pollution transported into, re-circulated within, and exported from the Houston area. Fifty-one launches occurred during the Texas Air Quality Study (TexAQS) II and the summer portion of IONS-06 (INTEX [Intercontinental Transport Experiment] Ozonesonde Network Study). On 11 days during TexAQS II and on 8 other occasions, ozonesondes were launched both at dawn and in the afternoon. Analysis of these ‘‘intensive’’ launch sequences shows that morning residual layer (RL) ozone concentrations ([O3]) explained 60–70% of the variability found in the afternoon mixed layer (ML). Furthermore, maximum RL [O3] is nearly identical to the mean ML [O3] from the previous afternoon (morning minus afternoon ¼ =-1.6 +/- 8.4 ppbv). During TexAQS II, mean [O3] below 1.3 km (the mean ML height from ozonesonde data) increased from 37 +/- 22 ppbv in the morning to 74 +/- 18 ppbv in the afternoon, suggesting an average net local daily O3 production of w500–900 tons over the metropolitan Houston area.