Abstract
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 160 nm dry particles (modal mass of 3.5 fg), we obtained a volume-based hygroscopicity parameter, κv ≈ 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).
Highlights
The interaction of atmospheric aerosol particles with water vapour results in size changes that strongly affect the optical properties of the aerosol particles and their direct radiative effect on the Earth’s energy budget (Waggoner et al, 1981; Rastak et al, 2014, and references therein)
The DMA-hygroscopicity centrifugal particle mass analyser (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 % relative humidity (RH) range
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
Summary
The interaction of atmospheric aerosol particles with water vapour results in size changes that strongly affect the optical properties of the aerosol particles and their direct radiative effect on the Earth’s energy budget (Waggoner et al, 1981; Rastak et al, 2014, and references therein). Many researchers employed humidity controlled nephelometers and estimated growth factors from the variation of aerosol light scattering coefficients with changing RH (Magi and Hobbs, 2003; Kim et al, 2006; Fierz-Schmidhauser et al, 2010a, b) All of these methods rely on certain assumptions (particle morphology, density, refractive index, etc.) to convert optical or mobility growth factor measurements into a mass-based scale. The single particle levitation technique is commonly used for the direct measurement of the water vapour uptake/release by particles due to RH variations (Tang and Munkelwitz, 1993, 1994; Peng and Chan, 2001) This technique enables high-precision measurements of the mass growth factor in hydration and dehydration mode, but it is applicable only to supermicron (typically 5–25 μm) particles and can be used only in laboratory conditions. Our work is mainly focused on the applicability of the tandem DMA-HCPMA set-up for investigating the hydration/dehydration of aerosol particles, including deliquescence/efflorescence phase transitions
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