Effects of temperature, pressure, and carrier gases on the performance of an aerosol particle mass analyser

Abstract

Effective density is a crucial parameter used to predict the transport behaviour and fate of particles in the atmosphere, and to measure instruments used ultimately in the human respiratory tract (Ristimäki et al., 2002). The aerosol particle mass analyser (APM) was first proposed by Ehara et al. (1996) and is used to determine the effective density of aerosol particles. A compact design (Kanomax APM-3601) was subsequently developed by Tajima et al. (2013). Recently, a growing number of field studies have reported application of the APM, and experimental schemes using the differential mobility analyser alongside the APM have been adopted extensively. However, environmental conditions such as ambient pressure and temperature vary with the experimental location, and this could affect the performance of the APM. Gas viscosity and Cunningham slip factors are parameters associated with temperature and pressure and are included in the APM's classification performance parameter: λ. In this study, the effects of temperature and pressure were analysed through theoretical calculation, and the influence of varying carrier gas was experimentally evaluated. The transfer function and APM operational region were further calculated and discussed to examine their applicability. Based on the theoretical analysis of the APM's operational region, the mass detection limits are changed with the properties of carrier gases under a chosen λ value. Moreover, the detection limit can be lowered when the pressure is reduced, which implies that performance may be affected during field study. In experimental evaluation, air, oxygen, and carbon dioxide were selected to atomize aerosols in the laboratory with the aim of evaluating the effect of gas viscosity on the APM's performance. Using monodisperse polystyrene latex (PSL) spheres with nominal diameters of 50 and 100 nm, the classification performance of the APM was slightly varied with carrier gases, while the classification accuracy was consistently within 10 %.