Elevated ozone in the boundary layer at South Pole - Doug Davis

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ARTICLE IN PRESS D. Helmig et al. / Atmospheric Environment 42 (2008) 2788–2803 2793 surface are in excellent agreement with the continuous surface measurements at this time (19–20 ppbv, Fig. 2). The temporal behavior of the observed surface layer ozone gradient was investigated in another balloon experiment on December 21 where the long sampling line was raised and ‘‘parked’’ for 3 h at 110 m. During this experiment ambient air was sampled from two inlet lines that were alternated every 5 min and analyzed with the TEI monitor (Fig. 4). First, the short and long sampling line inlets were both near the surface (balloon line inlet at 2 m, short sampling line inlet at 4 m). Ozone in air from both inlets showed no discernable difference; both samples agreed within better than 0.5 ppbv. Next, the long line inlet was raised with the balloon in 7 min to 110 m. Ozone in air collected from the balloon during the ascent dropped instantaneously from 45 ppbv to 40 ppbv. Over the next three hours ozone at 110 m remained lower, approximately 5 ppbv below the surface readings. During this time surface ozone increased by 1 ppbv. Similarly, an increase in ozone at 110 m was observed; towards the end of this experiment, the vertical ozone gradient decreased slightly. After 3 h the balloon was brought back down, and another, more rapid up and down profile (25 min) was measured with continuous sampling through the long balloon sampling line. These data confirm the results from the previous intermittent sampling and that the ozone gradient between the surface and 110 m had declined to 3 ppbv. 3.3. Vertical and temporal ozone distribution The vertical and temporal (December 13–31) distribution of ozone shown in the 3D contour plot in Fig. 5 combines the data from all ECC sonde profiles, the continuous monitoring at the ARO at 17 m, the continuous monitoring at the tethered balloon launch site (at 2 and 4 m height) and from the long sampling line profile measurements. The results of this analysis reemphasize the conditions with enhanced and variable boundary layer ozone at SP. During most times ozone near the surface (e.g. in the 0–300 m layer) was elevated compared to air aloft. The observed gradients varied widely. During two isolated conditions with overall low concentrations (DOY 354, 361) ozone showed a homogenous vertical distribution (also see Fig. 2). During all other times, ozone near the surface was enhanced, with gradients of typically 5–25 ppbv higher ozone near the surface. During a four-day period from DOY 355–359, sustained conditions with 20–25 ppbv enhanced ozone in the surface layer were observed. The depth of this enhanced ozone layer varied from 60 to 200 m. In the following section we will analyze 49 47 45 110 90 Ozone (ppbv) 43 41 70 50 Height (m) 39 30 Roof Inlet 37 Long Line at 2 m 10 Balloon Inlet Balloon Inlet Height 35 -10 355.15 355.20 355.25 355.30 355.35 355.40 Time Fig. 4. Approximately 4 h of ozone measurements from two surface inlets (roof inlet at 4 m height, and long line inlet at 2 m height) and from 110 m. First, two inlet lines were sampled side by side near the surface. Next the long sampling line inlet was lifted to 110 m and air was alternated between the raised balloon inlet and the tower inlet every 5 min. After 3 h, the balloon was brought back to the surface, equipped with a new pressure sensor and another vertical profile was measured with continuous sampling from the balloon inlet.
2794 ARTICLE IN PRESS D. Helmig et al. / Atmospheric Environment 42 (2008) 2788–2803 A 500 Height [m] B 400 300 200 100 0 500 15 Ozone (ppbv) 350 355 360 365 45 40 35 30 25 20 Height [m] C 400 300 200 100 0 500 350 355 360 365 Temp (K) 290 288 280 284 282 280 278 276 274 Height [m] 400 300 200 100 0 350 355 360 365 WS (m/s) 14 12 10 8 6 4 2 Fig. 5. Ozone (A), potential temperature (B), wind speed (C), wind direction (D, next page), and water vapor partial pressure (E, next page) at South Pole (in ppbv) between the surface and 500 m height during day of year 2003 (December 13–30) with data from all available balloon (up to 179 vertical profile data series) and surface measurements. The black dots indicate the distribution of data points that went into the contour plot analyses.
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