Professor, Chemistry Department
Under the tutelage of J. Sloan at the University of Waterloo, Allan studied the freezing behaviour of aerosols for his Ph.D. research. As an NSERC Postdoctoral Fellow, he worked with Mario J. Molina at the Massachusetts Institute of Technology from 1998 to 2000. From 2001-2011 he was a Canada Research Chair in Environmental and Atmospheric Chemistry. Currently he is the director of the NSERC-CREATE-Atmospheric Aerosol Program (2010-present).
Current Group Members
Forested regions of the planet emit copious amounts of aerosols each year, which have important atmospheric implications such as their potential to affect cloud formation and scatter incoming radiation. Despite this the character and behaviour of these aerosols and their reaction products in the atmosphere remain poorly understood. James’ research involves the use of optical and fluorescence microscopy along with some relatively simple and novel experiments designed to probe these particles and determine their physical state, i.e., whether they are in the liquid, semi-solid, or solid phase.
Ice nuclei are aerosols that catalyze ice formation at temperatures approaching 0°C (pure water droplets freeze close to -40°C). As a result, these aerosols can influence cloud formation, lifetime and radiative forcing. Ryan’s work focuses on collecting aerosols from a variety of field sites, including oceans, coastal forests, and mountain summits. Experiments conducted in a flow cell are used to identify ice nuclei, quantify both ability and atmospheric concentration, and look for correlations between their abundance and prevailing weather conditions.
Ice nucleation is one of the most basic processes that lead to precipitation. At temperatures warmer than about -36ºC, ice crystals form in clouds by heterogeneous nucleation involving aerosol particles known as ice nuclei(IN). IN can have great influence on cloud microphysical and radiative properties. Meng’s research uses a flow cell combined with a microscope to study the IN properties of aerosols collected from some field sites.
Vickie studies aerosol particles that can act as ice nuclei. These particles are atmospherically important because they will affect the microphysics of clouds and thus the Earth’s radiative budget and hydrological cycle. Vickie’s work focuses on collecting aerosol particles in the field using impactors, she will be looking at ice nuclei found in the Arctic and how they may be related to the microlayer of the ocean. The concentration of aerosols acting as ice nuclei that are collected in the field can be quantified using a droplet freezing assay.
The freezing of water is one of the most common and least understood processes in the atmosphere, with the mechanisms underlying freezing at the molecular scale still unclear. Stephen’s research utilizes Molecular Dynamics modeling of water to observe the behavior of the molecules and their interaction with aerosol surfaces as they freeze.
The formation of ice in the atmosphere is poorly understood yet has a large impact on atmospheric processes. Kaitlin’s research uses nonlinear spectroscopy to investigate atmospherically relevant solutions at a molecular level to help understand fundamental questions about the process of ice nucleation.
Investigating properties of atmospheric particles is vital to understand the influence of atmospheric particles on the climate. A very important property of atmospheric particles is the viscosity. The viscosity of atmospheric particles and connected with it the diffusion coefficients dictate how fast reactions in particles occur. Dagny’s research project focuses on the determination of diffusion coefficients of fluorescent molecules in particles. To determine the diffusion coefficients Dagny is using the microscopy method FRAP (fluorescence recovery after photobleaching).
Aerosols play an important role in the formation of warm and cold clouds. At temperature warmer than about -36°C, certain types of aerosols termed ice nuclei (IN) have the ability to form ice crystals which are responsible of most precipitation in the mid-latitutes. Understanding the properties of these IN is crucial to better quantify climate feedback. Cédric’s work focuses on the identification of the IN nature at different places (e.g. Whistler peak) using an offline technique which consists of collecting aerosols with a multiple stages impactor and analyzing each stage in the laboratory to assess the thermodynamic conditions at which ice is forming.
Viscosity and diffusion influence the speed at which reactions take place in the atmosphere. Adrian is interested in the effect of low temperature on the viscosity and diffusion coefficients relating to aerosols.
The viscosity of secondary organic material (SOM) particles in the atmosphere, as well as molecular diffusivity within these particles can affect rates of growth, reaction with oxidants and other atmospheric processes. Erin’s research will involve measuring viscosity and diffusion in SOM at atmospherically relevant temperatures and humidity. Improved understanding of these properties of SOM will help improve climate modelling and lead to a greater understanding of the influence of aerosols on climate.