Comparative study of the effect of the trapping method on the physical properties of single aerosols trapped with an electrodynamic balance or optical tweezers

Allen Haddrell (1), Jonathan Reid (1)

(1) University of Bristol, Bristol, UK

     Abstract Number: 653
     Last modified: May 14, 2010

Abstract
Numerous methods have been developed to study hygroscopicity, and various other properties and characteristics of aerosols. Two such instruments are the electrodynamic balance (EDB) and optical tweezers (OT). Given that the way in which these two instruments both trap and probe an aerosol droplet are fundamentally different, the goal of this work is to study a series of organic aerosols in both systems to characterize any effect that the trapping process has on the measured properties of the particle. The EDB uses an electric field coupled with a slight net charge imparted onto the aerosol to accurately weigh the mass of an aerosol whereas an OT uses a focused laser beam to both trap a liquid aerosol and use light scattering to measure its radius; aside from particle size, both techniques can also be used to study a single aerosol droplet in other ways. Like any instrument, both have their advantages and limitations; for instance there are challenges studying phase transitions with OT whereas absolute size cannot be measured with an EDB. That said, in many ways these two techniques are complimentary and as such the use of both of these techniques to study a similar aerosol is advantageous. It has been shown that the presence of a net charge on an aerosol affects both its evaporation and nucleation rates. Given that the presence of a significant net charge on an aerosol is necessary for particle levitation in an EDB, therein lies the potential for that charge to affect measured rates. Likewise, heating of the droplet by the laser in OT may also effect various rates. To study this, we trap charged aerosols in both the EDB and OT, and compare their evaporation rates with neutral aerosols trapped in an OT.