AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Kinetics of Water Transport in Amorphous Aerosol
JAMES F. DAVIES, Allen E. Haddrell, Rachael E.H. Miles, Jonathan P. Reid, University of Bristol
Abstract Number: 370 Working Group: Aerosols, Clouds, and Climate
Abstract Aerosol particles are often assumed to establish an instantaneous equilibrium composition with the surrounding gas phase. However, the kinetics of water transport can be limited by diffusion in the gas phase, in the particle bulk or by surface accommodation. For example, the slow transport of water within glassy or amorphous aerosol particles can lead to particles that approach an equilibrium state over timescales that are much longer than is accessible to most analytical instruments. Studies of water transport in single particles using optical or electrodynamic traps over timescales in excess of 10,000 seconds can provide robust methods for investigating the kinetics of water transport in amorphous states and for benchmarking models.
Measurements made using a new electrodynamic balance technique will be described, comparing the timescales for water transport during evaporation or condensation from solution droplets, surfactant coated droplets, glassy aerosol and aerosol consisting of a two-phase gel. Aerosol particles are injected into a gas flow which can be rapidly cycled (second timescale) between high and low relative humidity (dry and >90 % RH). Droplet sizes are recorded from elastic light scattering with a time-resolution of as low as 2.5 ms. Droplets of two different compositions can be studied in sequence, monitoring the time-dependence of one and then the second in quick succession, allowing the kinetics of water transport in amorphous aerosol to be compared precisely to inorganic aerosol.
The kinetics of water transport limited by bulk and surface transport processes will be reported and the influence of amorphous phases on the timescale for equilibration of water in atmospheric aerosol assessed.