The absorption efficiency (the mass absorption coefficient) of radiation of wavelength 694.300 nm by the soot aerosol in air (3.36 ± 1.67 m2/g) is determined based on the results of synchronous measurements of the aerosol absorption coefficient, using an optoacoustic spectrometer with a pulse ruby laser, and the mass concentration of soot in air, using an aethalometer. A concentrator of acoustic pulse energy, consisting of two parabolic mirrors, was used as a part of the optoacoustic detector in order to gain the threshold sensitivity to the absorption coefficient kminl = 6.8 10-10 см-1 at the laser pulse energy 30 mJ and the air pressure 760 Torr in the cell.