Differential Optical Absorption Spectroscopy (DOAS) has become a very powerful tool to observe chemical composition of the atmosphere.

Its versatility permits to observe the atmosphere in a large variety of configurations and platforms providing information of different molecules in different layers of the atmosphere and even the evolution of some natural processes as the monitorization of volcanic plumes.

The observation of a particular layer of the atmosphere using DOAS requires the use of different instrumental configurations and posterior radiative transfer modelling due that this spectroscopic technique obtains information along the path that the radiation follows through the atmosphere.

DOAS zenith-sky viewing during the twilight provides information mainly from stratosphere whereas Multi Axis DOAS (MAX-DOAS) may obtain vertical information about vertical distribution of different molecules in the troposphere.

Halogens in the Troposphere are currently species of high interest due to its importance in the tropospheric equilibrium of ozone. This talk is focused in the obtention of bromine monoxide using zenith-sky DOAS, and the indirect determination of the existence of BrO in the Marine Boundary Layer by comparison with satellite measurements and in the recently detection and measurement of iodine monoxide in the Free Troposphere of North Subtropical regions using MAX-DOAS technique.