Measurement of water activity of atmospheric aerosols
by Zheng Liang
M.Phil. Chemical Engineering
xi, 89 leaves : ill. ; 30 cm
In this research, a fast approach for studying the hygroscopic properties of atmospheric aerosols using an electrodynamic balance (EDB) was developed. The water activity of multicomponent seasalt aerosols was studied using this new approach....[ Read more ]
In this research, a fast approach for studying the hygroscopic properties of atmospheric aerosols using an electrodynamic balance (EDB) was developed. The water activity of multicomponent seasalt aerosols was studied using this new approach.
The electrodynamic balance is well suited for studying the compositional effect of water activity of aqueous droplets. In this research, a fast technique for measuring water activity and the percentage relative humidity of deliquescence (%RHD) using an EDB was developed. This method is based on the in-situ monitoring of an evaporating droplet upon a step change in the relative humidity (RH) of the feed to the EDB. It can reduce the time of measurement of water activity and the %RHD of aerosols from several hours as needed by corresponding conventional measurements in an EDB to within an hour. The measured data were found to be in good agreement with literature data. Application of this technique for measuring water activities of droplets containing volatile solute was also demonstrated.
Seasalt aerosols are hygroscopic aerosols which can be commonly found in urban atmosphere. Water activity data of seasalt aerosols were measured using the fast approach. They were also used to evaluate the performance of three commonly used mixed electrolyte solution models: the Zdanovskii-Strokes-Robinson (ZSR) model, the Kusik and Meissner (K-M) model and the Pitzer model. The composition-water activity data will be useful for future modeling of the thermodynamic and transport properties of atmospheric aerosols.
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