Exploring the complexity of aerosol particle properties and processes using single particle techniques

Abstract

The complex interplay of processes that govern the size, composition, phase and morphology of aerosol particles in the atmosphere is challenging to understand and model. Measurements on single aerosol particles (2 to 100 μm in diameter) held in electrodynamic, optical and acoustic traps or deposited on a surface can allow the individual processes to be studied in isolation under controlled laboratory conditions. In particular, measurements can now be made of particle size with unprecedented accuracy (sub-nanometre) and over a wide range of timescales (spanning from milliseconds to many days). The physical state of a particle can be unambiguously identified and its composition and phase can be resolved with a high degree of spatial resolution. In this review, we describe the advances made in our understanding of aerosol properties and processes from measurements made of phase behaviour, hygroscopic growth, morphology, vapour pressure and the kinetics of water transport for single particles. We also show that studies of the oxidative aging of single particles, although limited in number, can allow the interplay of these properties to be investigated. We conclude by considering the contributions that single particle measurements can continue to make to our understanding of the properties and processes occurring in atmospheric aerosol.

A new electrodynamic balance (EDB) design for low-temperature studies: application to immersion freezing of pollen extract bioaerosols

“…As a robust methodology for the levitation of single particles which carry electric charge, the electrodynamic balance (EDB) technique has been applied in atmosphere science for several decades (see reviews by Davis, 1997;Krieger et al, 2012). On the base of such a strategy, numerous studies have been carried out on aerosol particles and droplets, including but not limited to contact ion pairs formation (e.g.…”

Deviations from Plane-Wave Mie Scattering and Precise Retrieval of Refractive Index for a Single Spherical Particle in an Optical Cavity

“…Studies on single particles, confined within optical or electrodynamic traps, now provide precise measurements of aerosol refractive indices and phases, hygroscopic growth, evaporation of semi-volatile components, and other properties of importance for their atmospheric behaviour. [2][3][4][5][6] These trapping-based techniques are most applicable to single particles with radii greater than 1 μm, but the smaller accumulation mode particles are of greater significance for atmospheric processes. 4 In a recent publication, we demonstrated that absolute extinction cross sections for single submicron radius spherical aerosol particles can be measured with high precision by combining optical confinement and levitation of a particle with cavity ring-down spectroscopy (CRDS).…”

“…[2][3][4][5][6] These trapping-based techniques are most applicable to single particles with radii greater than 1 μm, but the smaller accumulation mode particles are of greater significance for atmospheric processes. 4 In a recent publication, we demonstrated that absolute extinction cross sections for single submicron radius spherical aerosol particles can be measured with high precision by combining optical confinement and levitation of a particle with cavity ring-down spectroscopy (CRDS). 7 The change in ring-down time (RDT) when a particle is moved from well below the optical axis (z) of the ring-down cavity (RDT = 0) to the height of the centre axis of the Gaussian TEM00 cavity mode (RDT = ) is given by:…”

Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

“…23−25 To address the challenges in quantifying hygroscopicity for aerosols of complex composition, refinements in laboratory and field instrumentation, and improved frameworks for representing hygroscopicity, are required. 26,27 Hygroscopic growth measurements must be made up to water activities close to the dilute limit, ideally as high as 0.999. Such high water activities (a w ) are required for measurements to be directly relevant to CCN activation 28 and to place tighter constraints on the equilibrium solution compositions required to underpin the development of predictive models.…”