Under What Conditions Can Equilibrium Gas-Particle Partitioning Be Expected to Hold in the Atmosphere?
The prevailing treatment of secondary organic aerosol formation in atmospheric models is based on the assumption of instantaneous gas-particle equilibrium for the condensing species, yet compelling experimental evidence indicates that organic aerosols can exhibit the properties of highly viscous, semisolid particles, for which gas-particle equilibrium may be achieved slowly. The approach to gas-particle equilibrium partitioning is controlled by gas-phase diffusion, interfacial transport, and particle-phase diffusion. Here we evaluate the controlling processes and the time scale to achieve gas-particle equilibrium as a function of the volatility of the condensing species, its surface accommodation coefficient, and its particle-phase diffusivity. For particles in the size range of typical atmospheric organic aerosols (∼50-500 nm), the time scale to establish gas-particle equilibrium is generally governed either by interfacial accommodation or particle-phase diffusion. The rate of approach to equilibrium varies, depending on whether the bulk vapor concentration is constant, typical of an open system, or decreasing as a result of condensation into the particles, typical of a closed system.
Huajun
H
Mai
Multiphase Chemistry Department, Max Planck Institute for Chemistry , 55128 Mainz, Germany.
Manabu
M
Shiraiwa
Richard C
RC
Flagan
John H
JH
Seinfeld
D000336:Aerosols / Q000737:chemistry*; D001272:Atmosphere; D004058:Diffusion; D005740:Gases; D008962:Models, Theoretical; D010316:Particle Size; D014835:Volatilization
D000336:Aerosols; D005740:Gases