Characterization of multicomponent aerosols by raman spectroscopy

Abstract

In this work the feasibility of Raman spectroscopy, especially the detection limit of this technique for the chemical characterization of multicomponent aerosols, which appear in technical processes has been investigated. In such kind of aerosols high number concentrations (> 10 6 cm-3) can be observed whereas the range of the pollutant loading varies from 10-1000 mg/m3. For these purposes different type of aerosols have been investigated. Aerosols in which the pollutant can be found in the dispersed phase as well as in the gas phase (aqueous solutions of NH3 aerosols), those where the pollutant appears only in the dispersed phase (aqueous solutions containing SO42-/ NO3- salts) and aerosols where there is no Raman shift between the signals of the gas and the dispersed phase (toluene/ dodecane aerosols). Furthermore aerosols generated by the reaction between NH3 and HCl in nitrogen containing different amounts of vapor are also investigated. The characterization of the aerosols with Raman spectroscopy with respect to their gas phase is without any difficulty, whereas the analysis in the dispersed phase is partially marginal and in majority of cases almost not possible. Especially for the reaction aerosols rejection of elastically scattered light is the principle limitation in collecting Raman scattered light from particles in the Mie-scattering regime. Copyright © American Association for Aerosol Research.