A Sample Extraction Diluter for Ultrafine Aerosol Sampling

Abstract

A diluter that was designed for sampling high concentrations (∼ 10¹⁰ cm⁻³) of ultrafine aerosols (particle diameter smaller than 0.02 μm) is described. Particular care was taken to minimize the effects of coagulation and diffusional deposition within the diluter. Furthermore, the diluter was designed so that the effects of these processes on the size distribution of the sampled aerosol can be calculated. Provision was made to monitor continuously flow rates of the aerosol sample and dilution air. With these flow measurements, dilution ratios can be calculated without recourse to empirical calibrations that may change with time. In its present configuration, it can achieve dilution ratios ranging from 300 to 4000; this range could be extended with minor modifications. In this paper the procedure that was used in designing the diluter is described, and the performance of the diluter is compared with design expectations.