Are atmospheric halogen oxides "supposed to be" in the atmosphere? Where do they come from?
Classifying the presence of halogen oxides in the atmosphere as either natural, pollution or mixed bag, would result in mixed bag.

Natural sources of halogen oxides include the ocean and volcanoes. In 1963, Duce et al, 


  showed that bromine, like chlorine, was lost from the sea salt particles


Volcanoes are another source of halogen oxides,


  Halogens are emitted from volcanoes primarily as hydrogen halides (HCl, HF, HBr, and HI). Upon mixing with the atmosphere, chlorine and bromine species are partially converted to the halogen oxides OClO and BrO.


and


  Traditionally, emissions of volcanoes were regarded to be mainly of importance for the atmospheric sulfur cycle, acid deposition, and stratospheric effects from explosive eruptions. This view changed recently, mainly because of the observation of very high concentrations of bromine oxide, BrO, in the tropospheric, nonexplosive plume of Soufrière Hills, Montserrat. 


The Sun is a requirement for the ocean source of halogen oxides.

Salt lakes, such as the Great Salt Lake in Utah are also sources of halogen oxides.

Forest fires can be a source of fluorine. 

Pollution sources of halogen oxides includes: steel production, phosphate fertilizer production, burning coal, the manufacture of glass and ceramics.

Bromine and chlorine are used in cleaning products which are another source. Fire fighting chemicals such as PFAS (PolyFluoroAlkyl Substances) are another source.