Tandem configuration of differential mobility and centrifugal particle mass analysers for investigating aerosol hygroscopic properties

Abstract

A tandem arrangement of Differential Mobility Analyser and Humidified Centrifugal Particle Mass Analyser (DMA-HCPMA) was developed to measure the deliquescence and efflorescence thresholds and the water uptake of submicron particles over the relative humidity (RH) range from 10 to 95%. The hygroscopic growth curves obtained for ammonium sulfate and sodium chloride test aerosols are consistent with thermodynamic model predictions and literature data. The DMA-HCPMA system was applied to measure the hygroscopic properties of urban aerosol particles, and the kappa mass interaction model (KIM) was used to characterize and parameterize the concentration-dependent water uptake observed in the 50-95% RH range. For DMA-selected 160nm dry particles (modal mass of 3.5fg), we obtained a volume-based hygroscopicity parameter, Kv ≈ 0.2, which is consistent with literature data for freshly emitted urban aerosols. Overall, our results show that the DMA-HCPMA system can be used to measure size-resolved mass growth factors of atmospheric aerosol particles upon hydration and dehydration up to 95% RH. Direct measurements of particle mass avoid the typical complications associated with the commonly used mobility-diameter-based HTDMA technique (mainly due to poorly defined or unknown morphology and density).