APM aerosol microphysics

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This page describes the APM (Advanced Particle Microphysics) option in GEOS-Chem. APM is one of two microphysics packages being incorporated into GEOS-Chem, the other being TOMAS.


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 amounts of secondary species coated on primary particles (through condensation, coagulation, equilibrium uptake, and aqueous chemistry) are tracked.

Authors and collaborators

  • Fangqun Yu (SUNY Albany) -- Principal Investigator
  • Gan Luo (SUNY Albany)

APM User Groups

User Group Personnel Projects
SUNY Albany Fangqun Yu ...

Computational Information

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;
  5. The coating of primary particles by sulfate is tracked using one tracer (sulfate mass) for each type of primary particles;
  6. 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.

In the study reported in Yu and Luo [2009], all simulations are running on 8-CPU Linux workstations with the 2.2 Ghz Dual Quad-Core AMD Opteron Processor 2354. The model system is compiled using OpenMP for running in parallel. The original GEOS-Chem code has 54 tracers, and it takes 24.23 hours for one year full-chemistry simulations at 4x5 horizontal resolutions and 47 layers (GEOS-5 data). The GEOS-Chem with APM model incorporated has 127 tracers (73 additional tracers: 40 for sulfate, 20 for sea salt, one for H2SO4 gas, 4 tracers for BC/OC from fossil fuel, 4 tracers for BC/OC from biomass/bio-fuel, and 4 for sulfate attached to dust, BC, primary OC, and sea salt particles). With full size-resolved microphysics (nucleation, condensation, coagulation, deposition, and scavenging) and chemistry, it takes the model (127 tracers) 52.35 hours for the same year simulations on the same machine. In other words, the efficient schemes allow the increase in the computing cost per 100% increase in number of tracers (associated with particle size information) to (52.35/24.23-1)/(127/54-1) = 86%. Such a relatively small increase in the computing cost associated with full size-resolved microphysics is desirable and makes the future coupling of APM model with global climate model feasible.

Model Details

Particle Types and Representation

Aerosol types (mixing state):

 Semi- externally mixed: 
    Secondary particles (SP): sulfate, plus nitrate/ammonium/SOA in equilibrium
    Primary particles:  black carbon (BC), primary organic carbon (POC), dust, and sea salt 
                        + coated SP species on each type of primary particles.
 Size structures: 
    SP: 40 bins (1.2 nm - 12 μm)
    BC: two log-normal modes for hydrophobic BC and two log-normal modes for hydrophilic BC
    POC: two log-normal modes for hydrophobic OC and two log-normal modes for hydrophilic OC
    dust: 4 bins 
    sea salt: 20 bins (12 nm – 12 μm)



Ion-mediated nucleation (IMN) (Yu, 2010) and binary homogeneous nucleation (BHN) (Yu, 2008), in term of lookup tables.


To be added.


To be added.

Deposition and Scavenging

To be added.

Implementation notes

We have downloaded the recently released version of GEOS-Chem v8-03-01. We are looking into v8-03-01 to get ourselves familiar with the new code structure and designing best strategy to incorporate the APM. Our aim is to get the GEOS-chem + APM to the GEOS-Chem support team sometime in June.

Validation and Application

The first application of GEOS-Chem + APM focuses on predicting the number concentrations of particles in the troposphere. Significant amount of efforts have been devoted to validate the simulated global spatial distributions of particle number abundance, using a large amount of land-, ship-, and aircraft- based measurements. See following publications for details (full citations are given in the in the References section).

  1. Yu and Luo, ACP [2009]
  2. Yu et. al., JGR in press [2010]

The model has been applied in an number of other studies and results have been reported in the following papers:

  1. Luo and Yu, JGR submitted [2010]
  2. Luo and Yu, ACP [2010]


  1. Luo, G., and F. Yu, Particle formation and cloud condensation nuclei concentrations in the troposphere: A re-analysis of the impact of primary sulfate emission parameterizations, J. Geophys. Res., submitted, 2010.
  2. Luo, G., and F. Yu, A numerical evaluation of global oceanic emissions of alpha-pinene and isoprene, Atmos. Chem. Phys., 10, 2007-2015, 2010. PDF
  3. Yu, F., Updated H2SO4-H2O binary homogeneous nucleation rate look-up tables, J. Geophy. Res., 113, D24201, doi:10.1029/2008JD010527, 2008.
  4. Yu, F., Ion-mediated nucleation in the atmosphere: Key controlling parameters, implications, and look-up table, J. Geophys. Res., 115, D03206, doi:10.1029/2009JD012630, 2010.
  5. 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. PDF
  6. Yu, F., G. Luo, T. Bates, B. Anderson, A. Clarke, V. Kapustin, R. Yantosca, Y. Wang, S. Wu, Spatial distributions of particle number concentrations in the global troposphere: Simulations, observations, and implications for nucleation mechanisms, J. Geophys. Res., in press, 2010. PDF

Known issues

None at this time.