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Published June 13, 2012 | public
Journal Article

Diffusion-Limited Versus Quasi-Equilibrium Aerosol Growth


Condensation of gas-phase material onto particulate matter is the predominant route by which atmospheric aerosols evolve. The traditional approach to representing formation of secondary organic aerosols (SOAs) is to assume instantaneous partitioning equilibrium of semivolatile organic compounds between gas and particle phases. Growth occurs as the vapor concentration of the species increases owing to gas-phase chemistry. The fundamental mathematical basis of such a condensation growth mechanism (quasi-equilibrium growth) has been lacking. Analytical solutions for the evolution of an organic aerosol size distribution undergoing quasi-equilibrium growth and irreversible diffusion-limited growth are obtained for open and closed systems. The quasi-equilibrium growth emerges as a limiting case for semivolatile species condensation when the rate of change of the ambient vapor concentration is slow compared with the rate of establishment of local gas-aerosol equilibrium. The results suggest that the growth mechanism in a particular situation might be inferred from the characteristics of the evolving size distribution. In certain conditions, a bimodal size distribution can occur during the condensation of a single species on an initially unimodal distribution.

Additional Information

© 2012 American Association for Aerosol Research. Received 29 November 2011; accepted 19 March 2012; Available online 13 Jun 2012. This work was supported by National Science Foundation grant AGS-1057183. The authors wish to acknowledge helpful discussions with Dr. Jeff Pierce.

Additional details

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