Measurements of the boundary layer (bottom) of the atmosphere of the atmospheric trace gases NO2, O3, OClO and BrO

The experimental set up of the 'off axis' UV/visible wavelength diode array spectrometer was compared with a small portable field instrument. The diode array uses sunlight and moonlight to measure levels of ozone (O3), nitrogen dioxide (NO2), chlorine dioxide (OClO) and bromine oxide (BrO). The spectrometer works in the near ultraviolet and visible wavelengths and enables different viewing directions, including off axis measurements and moonlight measurements with the aid of a tracker. Raw data is times and recorded spectra of scattered light for several viewing directions. The derived data are column amounts of NO2, OClO, BrO and O3, which can be split into troposheric and stratosperic parts. An additional viewing direction was added to the instrument, only 2 degrees above horizontal, which gives enhanced sensitivity near to the boundary layer (bottom) of the atmosphere. Initial measurements with this new viewing direction clearly show a sensitivity to gases near to the ground, such as O4. This should provide additional information on the events where enhanced tropospheric BrO (bromine oxide) is observed, in which 'frost flowers' on young sea ice are thought to play a role.