ARCTOC '96 - April/May 1996 Ny Aalesund, Spitsbergen

In the fall of 1995, Prof. Ulrich Platt invited us to participate in the ambitious "Arctoc '96" campaign to study the cause of rapid disappearance of ozone in the arctic boundary layer. This phenomenon had been observed nearly a decade earlier, and long-path measurements had shown that BrO (and possibly ClO and IO) were present during the depletion events. Without new funding for
equipment, it was difficult to develop and build a new instrument, so we decided to modify our existing lightweight balloon instrument to determine whether or not chemical conversion, resonance fluorescence could work at the ground as well as in the stratosphere. The photo above is of Ny Aalesund, Spitsbergen looking slighly east of north from the air monitoring station on nearby Zeppelin Mountain.

Provided with seed money from the California Space Institute and National Science Foundation, Linnea Avallone, Tara Fortin, Ralph Kolbush and I constructed a pumping system and special inlet that would allow us to measure bromine and chlorine atoms by a technique that, in the presence of water vapor and oxygen, only works at low pressures. To achieve high flow rates, we used a rotary vane pump to pull ambient air through a small (~ 2 mm) orifice in a conical teflon nozzle. To ensure that we were sampling clear air, with little shear, the flow was first straightened by a cylindrical tube backed with an axial fan. The fan, straightening tube, and detection axes are shown in this photo.

Unfortunately, the Greenland Sea was frozen over by the time we finished modifying the instrument, so we had to ship everything by small plane. This restricted the size of the vacuum pump to one smaller than was optimal for the measurement. The airplane is shown on the runway in this view to the south from the "parking lot", with Zeppelin Mountain at the left.

We set the instrument up about 10 meters east of the "Blacksmith's Shop" to the southwest of town. This view is to the southwest. It took about 5 hours to shovel enough snow to fill the 1 meter deep "gap" between the snowpack and the building. It then took another day or two to assemble and test the instrument. Somewhere on the ridge in the background in this photo is the retroreflector for one of the two DOAS instruments. Karena McKinney and Tara Fortin then spent the second half of April and the first week of May operating the instrument during good and bad weather. The data were stored on a hard-drive that had to be backed-up periodically, resulting in gaps in the data record. In addition, in order to preserve the lamps (which are run "bright" and tend to burn out relatively fast on our balloon and aircraft instruments) we set the system up for lower sensitivity and Karena and Tara ran the instrument daily, but not continously until they observed a real "ozone loss" event, which occurred the first week of May as the campaign was winding down.

The Blacksmith's Shop is the building in the lower left corner of this photo looking down and to the north from Zeppelin Mountain. We were close enough to town that we didn't need to take a rifle with us (for protection from polar bears) as we commuted back and forth to work. Our measurements were near the ground. Two DOAS spectrometers were measuring BrO and ClO, one with a path from town (in the upper right in this photo) to a retroreflector to the southwest, and nearly directly overhead of our location. The other DOAS was measuring from the airport (at the middle left in this photo) to a location across the fiord (upper middle of the photo). Our main goal was to determine how well our measurements agreed with the others, although we did not expect to necessarily be measuring in the same air.

The instrument, as it was deployed, is shown in this photo, a view to the south. The detectors are at the top of the cart. The computer and data acquisition system were packaged in an insulated cardboard box, and placed next to the 24 V power supply on the second shelf. The vacuum pump and a bottle of nitric oxide are on the bottom shelf. The data were relayed by a serial line back to a heated room in the Blacksmith's Shop. The exhaust was filtered to remove oil and particulates, and directed away from the instrument by a long piece of flexible tubing, with the end placed in the snow. This was necessary to minimize contamination from the nitric oxide used to convert ClO and BrO to halogen atoms.

This is the front view of the instrument, also looking to the northeast. At this sun angle (about 9 pm, local time) our measurement was shaded by the Blacksmith's Shop, whereas the paths of the DOAS instruments were in full or partial sunlight. This arrangement resulted in some complicated behavior in the ratios of our measurements to those of the DOAS instruments, and confused us until we pulled out a topographic map to determine when each of the measurements were in sun or shade. Sometimes our measurements were higher than the DOAS measurements, and sometimes their's were higher than ours. Next time we do this experiment, we'll bring a solar flux monitor (and measure both diffuse and direct radiation).

The local topography complicated the intercomparison especially in the middle of the "night". This photo was taken about an hour before local solar "midnight." Between about 10 pm and 4 am, the sun travels along a ridge of mountains on the north side of the fiord, alternately appearing in valleys and disappearing behind peaks. The long shadows cast by the mountains did not necessarily aling with the DOAS and in situ measurements. Therefore, our best intercomparisons were in the middle of day when the sun was higher in the sky and all instruments were in bright sunlight.