Optical levitation measurement on hygroscopic behaviour and SVOC vapour pressure of single organic/inorganic aqueous aerosol

Publication date: September 2018
Source:Atmospheric Environment, Volume 189
Author(s): Chen Cai, Chunsheng Zhao
Quantifying the gas/particle partitioning of organic compounds is of great significance to the understanding of atmospheric aerosol indirect effect. Accurate determination of the hygroscopicities and vapour pressures of semi-volatile organic compounds (SVOC) is of crucial importance in studying their partitioning behaviour into atmospheric aerosol, as the influences on SVOCs evaporation from participation of inorganic species remains unclear. In this study we first present thermodynamic quantitative simulation and tweezed single particle measurement of hygroscopicity and volatility of single aerosol droplets. With thermodynamics simulation of the hygroscopicity, SVOC time dependent evaporation and potential chloride depletion reaction in a single trapped droplet, we illustrate influences from different process towards the trapped droplet. In optical tweezers measurement, the trapped droplet in the aerosol optical tweezers acts as a microcavity, which stimulates the cavity enhanced Raman spectroscopy (CERS) signal. Size and composition of the particle are calculated from Mie fit to the positions of the "whispering gallery modes" in the CERS fingerprint. Hygroscopic behaviours and SVOC saturated vapour pressure can then be extracted from the correlation between the changing droplet radius and solute concentration (derived from experimentally determined real part of refractive index (RI)) with good accuracy and reliability.

Graphical abstract

https://ift.tt/2zhqBUm