Abstract
Abstract. Interactions with water are crucial for the properties, transformation, and climate effects of atmospheric aerosols. Here we present the high-humidity tandem differential hygroscopicity analyzer (HHTDMA) and a new method to measure the hygroscopic growth of aerosol particles with in situ restructuring to minimize the influence of particle shape. With this approach, growth factors can be measured with an uncertainty of 0.3 %–0.9 % over a relative humidity (RH) range of 2 %–99.6 % and with an RH measurement accuracy better than 0.4 %. The HHTDMA instrument can be used in hydration, dehydration, and restructuring modes of operation. The restructuring mode allows us to investigate the effects of drying conditions on the initial microstructure of aerosol particles and specifies the optimal parameters that provide their rearrangements into compact structures with a nearly spherical shape. These optimal parameters were used in hygroscopic growth experiments by combining the restructuring mode with a conventional hydration or dehydration mode. The tandem of two modes allowed us to measure the particle growth factors with high precision as well as to determine the thickness of the water adsorption layer on the surface of compact crystalline particles. To verify the HHTDMA instrument we compared the measured ammonium sulfate growth factors with those obtained from the E-AIM-based Köhler model (E-AIM: Extended Aerosol Inorganics Model). Averaged over the range of 38 %–96 % RH, the mean relative deviations between measurements and model results is less than 0.5 %. We demonstrate this precision by presenting data for glucose, for which bulk thermodynamic coefficients are available. The HHTDMA-derived activity coefficients of water and glucose were obtained for both dilute and supersaturated solutions and are in good agreement with those reported in the literature. The average deviation between the measured activity coefficients and those obtained by the bulk method is less than 4 %. For dilute solution in water with an activity range of 0.98–0.99, the hygroscopicity parameter of glucose and the molal osmotic coefficient were obtained with an uncertainty of 0.4 % and 2.5 %, respectively.
Highlights
The hydration and dehydration (H&D) high-humidity tandem differential mobility analyzers (HHTDMAs) operation mode was first used to study the effect of drying conditions on aerosol particle restructuring
In the range of 2 %–60 % relative humidity (RH) the mobility diameter gradually decreases, and when RH is more than 70 % RH it becomes almost constant with Db,H&D,min observed at 80 %–90 % RH
The maximum reduction of the initial DMA1 selected particles is observed when only silica gel diffusion dryer (SDD) is used as a desiccant, for which Db,H&D,min = 93.2 and 93.5 nm
Summary
The hygroscopic properties of atmospheric aerosol particles are vital for a proper description of their direct and indirect effect on the radiative budget of the Earth’s atmosphere (Hänel, 1976; Rader and McMurry, 1986; Pöschl, 2005; McFiggans et al, 2006; Andreae and Rosenfeld, 2008; Swietlicki et al, 2008; Cheng et al, 2008; Zieger et al, 2013; Rastak et al, 2014, and references therein). The response of aerosol particles to changes in relative humidity (RH) can be obtained by determining the growth factor of aerosol particles under enhanced RH conditions The latter is possible by means of a hygroscopicity tandem differential mobility analyzer (HTDMA). The irregular structure of the initial dry particles, leading to discrepancy between the mobility equivalent and mass equivalent particle diameters, is an additional source of growth factor uncertainty (Mikhailov et al, 2004; Kreidenweis et al, 2005). The role of these sources of uncertainties increases significantly at RH > 90 %
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
