APM aerosol microphysics

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This page describes the APM (Advanced Particle Microphysics) option in GEOS-Chem.


The Advanced Particle Microphysics (APM) package was developed for implementation into GEOS-Chem at State University of New York (SUNY) at Albany. In the present version of the APM module, size-resolved microphysics for secondary particles (i.e., those formed from gaseous species) and sea salt has been treated with 40 sectional bins to represent sulfate (or secondary) particles and 20 sectional bins to represent sea salt particles. The bin structure is chosen to have relatively high resolution for the size range important to the growth of nucleated particles (a few nanometers) to cloud condensation nuclei (CCN). The growth of nucleated particles through the condensation of sulfuric acid vapor and equilibrium uptake of nitrate, ammonium, and secondary organic aerosol is explicitly simulated, along with the scavenging of secondary particles by primary particles (dust, black carbon, organic carbon, and sea salt). The amount of secondary species coated on primary particles (through condensation, coagulation, equilibrium uptake, and aqueous chemistry) are tracked.

The APM model contains a number of computationally efficient schemes: (1) Usage of pre-calculated lookup tables for nucleation rates and coagulation kernels; (2) Variable size ranges for particles of different types; (3) Variable bin resolution; (4) Variable and optimized time steps for the coagulation calculations; (4) The coating of primary particles by sulfate is tracked using one tracer (sulfate mass) for each type of primary particles; (5) Nitrate, ammonium, and SOAs asso-ciated with sulfate are calculated based on the equilibrium partition. The above schemes enable the APM model to capture the main properties of atmospheric particles important for their direct and indirect radiative forcing while keeping the computational costs quite low. The computational time of the coupled model (127 tracers) with full microphysics and chemistry is only about 2.2 times longer than that of the model with full chemistry only (54 tracers). In the other words, the application of efficient schemes keeps the increase in computational costs as low as 86% at 100% increase in number of tracers associated with particle size and composition.

Authors and collaborators

  • Fangqun Yu (U. of Albany) -- Principal Investigator
  • Gan Luo (U. of Albany)

APM User Groups

User Group Personnel Projects
U. of Albany Fangqun Yu ...

Implementation notes



Yu, F., and G. Luo, Simulation of particle size distribution with a global aerosol model: Contribution of nucleation to aerosol and CCN number concentrations, Atmos. Chem. Phys., 9, 7691-7710, 2009.

Known issues