The system is based on the method of Fourier-transform infrared spectroscopy (FT-IR). Infrared radiation is modulated by an interferometer and transmitted to an array of retroreflectors positioned at a distance of typically several hundred meters using a telescope. The reflected radiation is received by the same telescope and focused onto a detector. The large spectral range allows identification and quantification of a wide range of compounds. An important application of the system is air monitoring at industrial, construction or municipal sites. In addition, the OPS allows high-precision quantification of atmospheric gases.