[en] The purpose of the Research Contract No. 1815 was to develop a new method of sodium chloride aerosol generation for filter efficiency testing in nuclear installations. The first phase of the study was devoted to the development of a suitable aerosol generator. The first NaCl aerosol generator enabled determination of the influence various parameters like nozzle diameter, air flow rate, NaCl concentration in solution, solution temperature, etc., on the generation capacity and aerosol characteristics. The drawbacks of this generator were removed by modifying the design. Sodium chloride aerosol concentration was measured by means of a portable sodium flame photometer, and the particle size distribution was determined by a six-stage Andersen cascade impactor. For particle shape analysis electron microscopy was used. By using the aerosols generated the efficiency of air filters was tested. The results showed that the optimum parameters for atomization of ²⁴NaCl solution are: Nozzle diameter 0.5x10^-3m; compressed air pressure 196.132kPa; air flow rate 6.1x10^-5m³/s. Under these conditions test aerosols of 0.335x10^-6m mass median diameter were obtained with a geometrical standard deviation, sigma=2.04. Preliminary high efficiency particulate air filter tests with the above ²⁴NaCl aerosols showed the minimum filter penetration of the order of 5x10^-5% with a relative standard deviation not exceeding 15%. This showed that the ²⁴NaCl aerosol generated from liquid phase can be successfully used for filter testing in nuclear installations