Use of a Berner Low-Pressure Impactor at Low Inlet Pressures. Application to the Study of Aerosols and Vapors at High Temperature

The behavior of a Berner-type low-pressure impactor operated at low inlet pressures (down to 0.04 bar) has been studied both theoretically and experimentally. The stage cut diameters have been found to decrease with inlet pressure, the general behavior of the impactor being similar to that of the atmospheric case down to similar to 0.1 bar. At this inlet pressure, particles in the range 3-100 nm are classified along six different impactor stages, which offer the possibility of studying, e. g., freshly nucleated aerosols. The impactor so operated has been applied to the study of aerosol formation in biomass combustion, connected to the exit of a probe used in a previous work. The results presented in this article confirm and complement the conclusions of that work regarding submicron particle formation (i.e., nucleation of alkali sulfate occurs first and is followed by chloride condensation at lower temperatures) and also illustrate the possibilities of the impactor operated at low pressures. Finally, the relevance of diffusion on the collection efficiency of the successive stages is briefly discussed.