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The principal foundations, specific features and application fields of the advanced highly sensitive method of gas impurities detection -molecular condensation nuclei (MCN) method are discussed. MCN method is based on the conversion of impurity molecules to condensation nuclei of much larger size followed by the nuclei enlargement in the supersaturated vapor of specially selected low-volatile organic substances and detection of produced aerosol particles using an optical (nephelometric) method. The light scattering properties of the aerosol particles and air in the photometer of an MCN detector as well as sensitivity of the photometer's photodetector are investigated. We have determined that the light scattering by aerosol particles is interferometric by nature and is comparable within an order of magnitude with light scattering by the air inside a photometer. The threshold sensitivity of fotointegrator was reduced a level where the detection limit for the gas analyzer target component is determined by the background level of spontaneous condensation and not by the sensitivity of the detector's photoreceiver.Keywords: Molecular condensation nuclei (MCN), light scattering by aerosol particles and air, nephelometric method, threshold sensitivity of fotointegrator, condensation nuclei detector, gas analyzers based on the molecular condensation nuclei method, aerosol photometer, calibration gas analyzer by air scattering.

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