Construction And Automation Of The Data Acquisition System For A Multiaxial Differential Optical Absorption Spectrometer (Max-Doas)

Differential Optical Absorption Spectroscopy (DOAS) is a technique that allows detecting gas pollutant traces in the atmosphere. This technique uses the logarithmic difference between sunlight spectra; it determines changes in the optical path of the light or in local conditions. A multi-axial DOAS (MAX-DOAS) system takes advantage of the correlation between the elevation angle of the light receptor, the path taken by sunlight and the gas trace density to detect small and local variation of the absorption spectrum. Therefore a correct definition of the optical path and the slant column relies on an accurate setting of the elevation, polar angle and swept angle. Thus, an electro-mechanical system for developing a MAX-DOAS is presented and tested. The positioning system for the light collector (telescope) is developed a microcontroller unit, which controls two step motors, in the polar and azimuthal directions. Optical and technical characteristics are presented, as well as preliminary results of the first measurements of NO2 obtained with DOAS in Colombia, a discussion about the implemented solution are shown.