IN-SITU CHARACTERIZATION OF ULTRAFINE PARTICLES BY LASER-INDUCED INCANDESCENCE - SIZING AND PARTICLE STRUCTURE DETERMINATION

The laser-induced incandescence (LII) method is applied to the in situ size analysis of aerosol particles of different origin at room temper ature. A detailed theoretical model of the particle heating and coolin g for the different size fractions incorporating a solution of a Fredh olm integral equation of the first kind is used to retrieve the partic le size distribution from the time-dependent aerosol thermal emission detected after a ns laser pulse. The results are compared with TEM dat a of deposited aerosol particles along with online measurements employ ing a differential mobility analyzer (DMA). Besides the size distribut ion, the LII signal contains information on the internal structure of particle agglomerates, which can be obtained by analyzing the changes in the measured size distribution with the laser pulse energy. The obj ective of the paper is an evaluation of LII for its capability to meas ure the size distributions of various types of aerosols in the size ra nge about 5-200 nm and to determine the primary particle sizes in the case of agglomerated particles. (C) 1998 Elsevier Ltd. All rights rese rved.