Application to Polar Sunrise

The most interesting results of this work involve BrO. In general, out of the three species retrieved, the least is known about the global distribution of BrO. The first few Arctic flights of POLARIS coincided with the phenomena of episodic ozone depletion in the planetary boundary layer (PBL) which is usually associated with a strong temperature inversion.

VCDs of BrO from several flights have been examined and for flights made between 26 April and 13 May, enhanced BrO is evident over much of them. Later flights revealed no such enhancements. Throughout the flights made between 2 May and 13 May, the BrO VCDs varied from 7.5 $\times 10^{13}$ to 1.5 $\times10^{14}$ cm^-2. A background VCD was subtracted and the difference was assumed to reside in the PBL. The height of the PBL was taken to be 1 km, likely an upper limit. The enhanced BrO mixing ratios in the PBL varied between 0 and 30 pptv, which agreed well with satellite-based BrO measurements. The overall extent of this phenomena was found to be very large, on the order of 10³ km along the flight tracks and so perhaps as great as 10⁶ km² in area, much larger than previously expected. Even more remarkable were the results of the 26 April flight. Throughout this flight, BrO VCDs were found to be roughly 3 $\times10^{14}$ cm^-2, a factor of two larger than the other flights and much larger than in prior observations. A thorough examination of the spectroscopy indicated that these values were real. Factoring in the limited measurements of surface BrO, model calculations, and knowledge of Arctic meteorology, the only satisfactory explanation for the observed BrO was that a large fraction of it was present in the free troposphere, above the PBL. Concurrently, several other research groups hinted at similar findings although their results were not as definitive. One important result of these measurements is that they show the troposphere can be sensed using a nadir instrument, either aircraft-borne or from a satellite platform.