Monitoring pollution from ship power plants with laser technologies

When fuel burns in a ship engine, soot particles are formed that absorb flue gas toxic components. This absorption takes place on the surface of a particle. By solving an inverse problem involving light attenuation and diffraction on particles it is possible to obtain information on concentration and particle size distribution functions through space. An analysis has been complete on possibility of simultaneous assessment of concentration and particle size with a laser differential attenuation method. A four-wavelength laser system has been developed that allows measuring laser radiation attenuation signals using a differential extinction at three wavelengths and Mie scattering signal on aerosol particles at the fourth wavelength. From measured attenuated signals, an average volumetric-surface diameter of the aerosol particles was calculated. It has been shown that wavelengths of laser probing shall be selected depending on a soot particle size range. Application of the differential laser attenuation method to soot particles in ship power plant exhausts at several wavelengths allows simultaneously assess their concentration and size distribution. At that, laser wavelengths shall be selected depending on an expected range of variation of the Sauter mean diameter of the particles.