HR: 1340h
AN: A13A-0873 [Abstracts]
TI: A computationally efficient aerosol nucleation/condensation method: Pseudo-steady state gas phase sulfuric acid
AU: Adams, P J
EM: petera@andrew.cmu.edu
AF: Department of Civil and Environmental Engineering, Department of Engineering and Public
Policy, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, United States
AU: * Pierce, J R
EM: jrpierce@andrew.cmu.edu
AF: Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave.,
Pittsburgh, PA 15213, United States
AB:
Aerosol nucleation and condensation are two processes that compete for gas phase sulfuric acid when it is
formed in the atmosphere. Without approximations, accurate numerical integration of aerosol microphysics
requires time steps on the order of seconds or less when nucleation is occurring, significantly shorter than the
time steps required by other processes governing aerosol microphysics. This computational burden makes the
explicit numerical simulation burdensome in 3-dimensional atmospheric models. We have developed an
efficient method for simulating nucleation/condensation by assuming that gas phase sulfuric acid is at a pseudo-
steady state (PSS) concentration determined by chemical generation and its loss by nucleation and
condensation. The time step for nucleation/condensation is then governed by 1) the change in the condensation
sink, 2) the change in the generation rate of sulfuric acid, 3) the coagulation timescale, or 4) a master time step in
the model. The PSS assumption fails only when the time for sulfuric acid to reach its PSS state concentration is
not significantly shorter than the four timescales above. This may occur when the following conditions are met 1)
the condensation sink is less than 10-3-10-4 s-1, 2) nucleation is not occurring, and 3) the gas
phase production rate is changing. These conditions are not frequently met for a long period of time in the
atmosphere. The PSS assumption allows for time step increases of two to three orders of magnitude during
nucleation events in typical atmospheric conditions and has been shown to reduce the nucleation/condensation
computational time by a factor of 10-100.
DE: 1610 Atmosphere (0315, 0325)
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting