Aerosol analysis by cavity-ring-down laser spectroscopy

The cavity-ring-down technique was applied for aerosol detection. The experimental set-up was based on a pulsed dye laser pumped with the third harmonic of an Nd:YAG laser. Validation of the method was performed using calibrated aerosol flows, all under ambient conditions. The method was exemplified with non-absorbing aerosols, such as NaCl and CuCl2.2H(2)O, of various sizes and concentrations. The results were used for the evaluation of the corresponding aerosol extinction coefficients as a function of size, shape and index of refraction. The thus obtained aerosol extinction efficiencies were compared to theoretical models. Good agreement with theory was observed for NaCl aerosols, while the results for CUCl2.2H(2)O particulates required averaging over particle size and over the orientation dependent index of refraction. The actual sensitivity currently achieved was as low as an extinction coefficient of 8 x 10(-8) cm(-1), which means detection capability of about six water micro-particulates per cm(3). The ultimate theoretical performance of this method for aerosol detection was estimated as an extinction coefficient of 1.4 x 10(-12) cm(-1), corresponding to about 100 micro-particulates per m(3). These figures indicate that this method has the potential to become one of the most sensitive on-line analytical technique for aerosol detection and quantification. (C) 2002 Elsevier Science B.V. All rights reserved.