Cavity Ring-Down Spectroscopy (CRDS) techniques belong to the most sensitive modern methods of absorption coe cient determination. So far they are applied for detection of trace amounts of various compounds in gases and liquids. This technique requires using of lasers which can be precisely tuned to absorption lines of requested matter. Such sources are fabricated due to recent progress in semiconductor lasers technology. Combination of both techniques provides opportunity to construct fully optoelectronic, very sensitive detectors of atmospheric impurities. During the lecture our recent solutions of such sensors will be presented. Water vapour can be very e ectively detected in near infrared spectral range. Here single mode diode lasers, which are tuned to selected lines of 936 or 1340 nm overtones of H20 molecule, were applied. Using CRDS techniques the sensitivity about 10 −5% (10 ppb) was achieved. Also nitride oxides can be e ectively registered with these methods. 0.1 ppb sensitivity of NO2 detection with blue and violet range was already demonstrated. However the observation of N2O and NO should be done in mid-infrared range. Quantum Cascade Lasers are the most promising sources of such radiation. In our preliminary experiment performed in 4.52 − 4.53μm range the detection limit of N2O about 1.3 ppb was achieved. The wavelength selection requires avoiding of the interferences by other atmospheric impurities like CO2 and H2O. The detection of NO can be performed in 5.26μm range. Here a very precise tuning of laser frequency to the vibronic transitions of NO molecule is necessary. Wavelength stability during cw laser operation should reach about 10−5 μm.