The MAXDOAS instrument measures halogen and other gases in the atmosphere. These halogen gases (bromine monoxide, BrO and iodine monoxide, IO) are catalysts that cause depletion of ozone near the ice surface and cause deposition of mercury to the snowpack. The raw data that the instrument measures are scattered skylight spectra (light intensities as a function of wavelength). Halogen gases absorb particular wavelengths (colors) of light, so we can analyze the spectra to identify what molecules are present in the atmosphere and how abundant they are. The instrument also measures other gases and the intensity of the sunlight in the ultraviolet region. By sending back complete spectra from the instrument, we can later reanalyze the spectra and retrieve more information. For details on the MAXDOAS method, see Hönninger et al., [2004].

The instrument consists of two portions:
1) the scan head, which resides above the ice to receive skylight, and 2) the computer/spectrometer, which resides deep below the ice for better temperature stability. The scan head orients a telescope to scan the sky for halogen gases and couples this skylight into a fiber optic that then brings the light below the ice for spectral analysis. The computer/spectrometer module consists of a low-power single-board computer, motor driver, interface electronics, and a miniature CCD-based spectrometer.

The raw data from the instrument are scattered skylight spectra. These data are then processed in our laboratory to produce a timeseries of halogen gas abundances and other data products. A sample of data from a similar instrument in 2005 is shown in the figure. In the top panel is ozone, measured with an instrument similar to the one that Professor Shepson’s group is using on the Obuoy. The middle top panel is BrO derived from MAXDOAS instruments. The lower two panels represent airmass histories. The lower middle panel is the contact with first year ice, and the lower panel is the contact with potential frost flowers (PFF). See Simpson et al., [2007] for details.