In situ comparative measurements of the properties of aerosol droplets of different chemical composition

Aerosol optical tweezers can be used to manipulate multiple aerosol particles simultaneously. When coupled with spontaneous and stimulated Raman scattering, the composition, size and phase partitioning of different chemical components within a liquid droplet can be investigated. In combination, these two techniques suggest the possibility of a new strategy for characterising the thermodynamic behaviour of aerosols and the kinetics of mass transfer between the gas and condensed phases. We demonstrate here that two droplets can be characterised simultaneously, examining specifically the variation in wet particle size with relative humidity, recording the changes in size with nanometre accuracy. In a further demonstration, we use the size of a sodium chloride droplet to determine the relative humidity of the gas phase, allowing the variation in hygroscopicity of a second aqueous glutaric acid/ sodium chloride droplet to be studied. We suggest that such a comparative approach can provide new insights into aerosol dynamics.