Aerosol Hygroscopicity on A Single Particle Level Using Microscopic and Spectroscopic Techniques: A Review

Abstract

Studies on the hygroscopic properties of aerosol particles can provide criti- cal insights into important aerosol properties such as (1) alteration of aerodynamic properties; (2) cloud-droplet nucleation efficiency; (3) optical properties; and (4) physicochemical changes through complex heterogeneous chemical reactions with atmospheric gas-phase species. Investigations of the hygroscopic properties have been carried out using various analytical techniques for individual or bulk aerosol particles with deviating chemical compositions. Solid information on the hygroscopic properties, morphology, and chemical composition of airborne particles on a micrometer scale can be achieved by using a single particle approach. In this short review, recent microscopic (such as optical microscope, atomic force microscopy, environmental SEM and TEM, and scanning transmission X-ray microscopy) and spectroscopic (including Raman microspectrometry, FTIR spectroscopy, and their combination with levitation techniques) studies of hygroscopicity of aerosol particles on a single particle level are provided.