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Saturday, June 10
TOPAZ data were recorded from 08:32 to 21:36 PDT. Cooldown prior to the arrival of the deep trough continued with a max temperature of 32 C. After a clear morning, a thick Cirrus cloud deck moved in from the SW around midday and cleared out of the area after sunset. Strong SW to SSW winds from 15 to 20 m/s with higher gusts swept away locally produced O3. The Pacific streamer, with ozone concentrations exceeding 100 ppb at times, reappeared at 10 PDT and persisted into the evening. Compared to the previous days, the streamer descended to lower altitudes (1.5 - 3 km AGL) but stayed mostly above the mixed layer with only minimal entrainment in the late afternoon and evening, which caused a slight increase in surface ozone concentrations. The high-ozone streamer was also sampled by the ozone sondes launched at Joe Neal at 9 and 12 PDT, the Mooney aircraft, and the mobile van at Angel Peak. The air above the streamer up to about 5 km AGL was very clean with ozone concentrations around 30 ppbv and very little aerosol.