A Comparative Study of Different Methods for the Sampling of High Temperature Combustion Aerosols

Three different probes, respectively based on aerodynamic quenching, N₂ dilution, and thermophoresis, were used for particle sampling in biomass postcombustion gases from a laboratory reactor at different temperatures (from 1300 to 560°C). The different artifacts caused by the use of each probe were identified and compared. While the classical dilution sampling resulted in the formation (inside the probe) of particles comparable in size and composition to those already existing in the sampled gases, the aerodynamic quenching particle sampling (AQPS) probe always caused the nucleation of vapors into very small (15–20 nm) particles. The difference is attributed to the much higher cooling rate (∼ 10⁸ K/s) at the entrance of the probe. The preliminary results of the thermophoretic probe also reveal significant deviations between the collected sample and the actual particle population in the sampled gas. In general, the results shown here highlight the difficulties in obtaining representative samples in this type of systems, as well as the existence of a variety of possible sampling artifacts, whose interpretation is not straightforward. The AQPS probe is found to provide better results than the other methods considered, and its use might enable the study of both the condensed and vapor phase in hot gases containing important amounts of condensable inorganic vapours.