احمد محمدی اسلامی

Optical Absorption Spectroscopy” We introduce a software tool for calculating gas concentration in atmosphere from data obtained by employing Differential Optical Absorption Spectroscopy (DOAS) method. By considering the generalized Lambert-Beer’s law and as it is impossible to remove the absorber from light path for determining reference intensity spectrum, applying DOAS method is an appropriate selection. DOAS is being considered as a modern method in the open atmosphere spectroscopy. The final purpose of DOAS method is studying trace gases in open atmosphere, which have differential absorption in ultra-violet and visible spectral region, from long distance. In this technique, one can use light sources including sun, moon and appropriate lamps like xenon lamp. Important features of this method involve measuring several gases and contaminants such as O3, NO2 and SO2 simultaneously, continuity in measurements, high sensitivity in part per billion (ppb) range and determining light path proportional to necessity. DOAS method uses this fundamental fact that the effect of turbulence and optical system, Rayleigh and Mie scattering and also many trace gases absorption show very broad or even smooth spectral characteristics, whereas certain trace gases exhibit narrow band absorption structures. Thus DOAS separates broad- and narrow band spectral structures in an absorption spectrum. The broad band is then used as a new reference spectrum and the differential form of Lambert-Beer’s law can again be applied to the narrow band trace gas absorption. The designed software tool is capable of modeling recorded spectrum in computer via computing the convolution effect on the data relating to differential absorption cross-section of the mentioned trace gases. After that, the software tool calculate the trace gases concentration in open atmosphere, which have differential absorption, by possessing the recorded spectrum receiving from the spectrometer, as input data and extracting th