Why are atmospheric BrO and ClO important to measure by satellite? The announcement Arianespace orbits two satellites – JCSAT-17 and GEO-KOMPSAT-2B – to support connectivity and environmental monitoring in Asia mentions GEO-KOMPSAT-2B which hosts the Geostationary Environmental Monitoring Spectrometer or GEMS UV/Vis (300-500 nm) imaging spectrometer for hyperspectral imaging of Earth's atmosphere.

The instrument's purpose is given as


  Ozone profile and total-column or gross profile of other species. Tracked species: BrO, NO2, O3, OClO, SO2 and aerosol


and its primary mission objectives are listed as


BrO Mole Fraction
ClO Mole Fraction
H2O Mole Fraction
HC3Br Mole Fraction
HCHO Mole Fraction


with the following as other mission objectives


HCHO Total Column
NO Mole Fraction
NO2 Total Column
NO2 Mole Fraction
O3 Mole Fraction
O3 Total Column
SO2 Mole Fraction
SO2 Total Column


I think that "Mole fraction" is a relative concentration and "Total column" is absolute? 

I see that some of the species listed in the instrument's purpose are not in its primary objectives, but oh well.

Question: Why exactly are atmospheric BrO and ClO so important to measure, and measure by satellite, and what is the difference between ClO in the "objectives" and OClO in the "purpose"?
BrO and ClO significantly deplete ozone from the atmosphere.

Researchers at Harvard University state:


  It is a remarkable fact that perhaps the most important observation coupling climate forcing to UV dosage levels at the surface at mid-latitudes is the observation of high (e.g. > 10 ppmv) water vapor and low temperatures (&lt; 210 K) with the simultaneous determination of BrO and ClO in the lower stratosphere at mid-latitudes.


Similarly, Science magazine states:


  Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O3; reactions involving BrO account for one-half of this loss. 


Additonally,


  ... where the chlorine and bromine thus released participate in the catalytic destruction of ozone.


Kinetic studies of the BrO plus ClO cross-reaction over the range T=246-314 K