In the Bain Aerosol Research group, we investigate the physical properties of aerosol droplets. We are particularly interested in developing a fundamental understanding of aerosol properties which impact our climate. Due to the small size, and large surface-area-to-volume ratio of aerosol, as well as their contactless environment, aerosol droplets can have distinct physical properties from their macroscopic counterparts. To investigate these unique properties, we utilize a combination of single particle spectroscopy and bulk phase techniques.
Developing instruments to confine and characterize aerosol on the single particle level.
Designing and building instrumentation provides freedom to take on new problems. I have worked with traditional and holographic optical tweezers, a dual-beam optical trap and a photophoretic trap. These variations allow for the confinement of different types of solid and liquid particles (absorbing and non-adsorbing) and even non-spherical particles, in a contactless environment mimicking atmospheric conditions. Confined particles can be characterized with angular Mie scattering, cavity-enhanced Raman scattering, broadband scattering and optical imaging to retrieve the physical (size and refractive index) as well as the chemical (Raman scattering) information. Often, how these properties change in response to a change in ambient conditions provides insight into aerosol properties. Find out more.
Aerosol Optical Properties
Measuring and modelling the complex refractive index of aqueous aerosol as a function of water content and optical wavelength.
Aerosol in the atmosphere scatters and absorbs solar radiation and impacts our climate. The refractive index is a complex number which relates to these two processes. Sea spray is weakly absorbing in the visible region and predominantly scatters. In contrast, brown carbon aerosol absorbs strongly in the near UV and into the short wavelength portion of the visible spectrum. The real and complex terms of the refractive index are causally linked through the Kramers-Kronig relation. We can model the wavelength dependent complex refractive index using this relation. Measuring the cavity-enhanced Raman spectra of weakly absorbing droplets while heating them with a laser or collecting broadband Mie scattering from absorbing particles with discrete absorption bands provides sufficient data to determine the complex refractive index over the visible region. Find out more.
Atmospheric Nano- and Microplastics
Aerosol Surface Tension
Understanding the impacts of atmospheric plastics on aerosol properties and processes.
Field studies have found nano- and microplastics in urban centre atmospheric fallout, remote terrestrial locations and aloft in the atmosphere. Evidence suggests that these plastics can undergo long range atmospheric transport, but their impact on aerosol properties and processes is not yet understood. Plastics have a range of densities, chemical properties, colours and morphologies, and environmental aging can alter these properties. New techniques are required to characterize droplets with plastic inclusions in order to understand the processes and chemistry that occur in mixed phase droplets. Find out more.
Due to the large surface to volume ratio in picoliter droplets compared to bulk solutions, surfactant from the droplet bulk must partition to the interface, decreasing the droplet bulk concentration and altering the surface tension. This partitioning depends on the properties of the surfactant as well as the co-solutes with which it interacts. The co-solute identity may affect the critical micelle concentration (CMC), the diffusion coefficient of the surfactant and thus the partitioning dynamics as well as its surface excess and molecular area on the surface.
Measuring the surface tension in droplets to understand the impacts of bulk to surface partitioning of surfactants in finite volume droplets.
Surfactants have been identified in sea water and sea spray aerosol where they interact with co-solutes and may lower the surface tension of aerosol droplets which decreases the barrier to cloud droplet activation.