Las Vegas Ozone Study (LVOS) 2013 TOPAZ Data

May 24, 2013

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Daily Summary:

May 24. Friday. Clear and breezy with spreading cirrus and persistent contrails in the afternoon. The valley was fairly clear Friday afternoon and evening, but became hazy by early Saturday morning. Lidar data was collected from 1334 to 0639 PDT (17 hours). The models showed a significant stratospheric intrusion passing across central NV to the north of Angel Peak. The first profiles in the preliminary TOPAZ curtain plot show O3 concentrations of 80-90 ppbv at 2.0 km AGL with 60-70 ppbv at lower altitudes. The latter are in good agreement with the in situ O3/CO measurements of 66/135 ppbv at 2000 UT (1300 PDT). The higher O3 descended to the surface over the next several hours with the in situ O3/CO concentrations trending to 89/120 ppbv at 2035 PDT. The slight decrease in low level O3 seen in the curtain plot at about 2100 PDT is reflected in the in situ measurements which were 74/128 ppbv at 2130 PDT and 88/119 at 2148 PDT. A second, larger filament with O3 concentrations in excess of 120 ppbv appeared in the lidar measurements between 2330 and 0230 PDT, but only descended to within about 0.5 km of the surface at Angel Peak and the surface concentrations remained near 75/125 ppbv. A third, smaller filament descended all the way to the surface leading to in situ concentrations of 83/109 at 0534 PDT. Ozone remained high (>70 ppbv) throughout the following day at all of the Clark County surface sites with marginal exceedances (MDA8 O3 = 76 ppbv) at four of these sites as well as the Mojave and Great Basin National Parks. Joshua Tree and Death Valley NPs reported MDA8 values of 79 and 73 ppbv, respectively.
Note: the low (purple) ozone values seen near the top of the curtain plot near midday are biased by the solar background in these preliminary analyses.