Aerosol Microphysics Plans for GEOSCHEM Peter J Adams

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Aerosol Microphysics: Plans for GEOS-CHEM Peter J. Adams Carnegie Mellon University Civil and Environmental

Aerosol Microphysics: Plans for GEOS-CHEM Peter J. Adams Carnegie Mellon University Civil and Environmental Engineering

GEOS-CHEM Activities at CMU n n Comprehensive aerosol microphysics scheme implemented in GISS GCM

GEOS-CHEM Activities at CMU n n Comprehensive aerosol microphysics scheme implemented in GISS GCM For details, see following publications u Adams, P. J. , and J. H. Seinfeld, Predicting global aerosol size distributions in general circulation models, J. Geophys. Res. , 10. 1029/2001 JD 001010, 2002. u Adams, P. J. , and J. H. Seinfeld, Disproportionate impact of particulate emissions on global cloud condensation nuclei concentrations, Geophysical Research Letters, 10. 1029/2002 GL 016303, 2003. n Same aerosol microphysics will be implemented in GEOS-CHEM – this process is just beginning

Aerosol activation is a competition between solute and surface tension effects Number Aerosol Activation

Aerosol activation is a competition between solute and surface tension effects Number Aerosol Activation Particle Size Surface tension term Solute (Raoult) term Only largest particles activate to become cloud droplets: Dp>80 nm S=0. 2%

Particle Size Mechanistic: number of cloud drops depends on number of particles large enough

Particle Size Mechanistic: number of cloud drops depends on number of particles large enough to activate Cloud Droplets (cm-3) Number Mechanistic vs. Empirical Models Boucher & Lohmann, 1995 Sulfate Mass (mg m-3) Empirical: number of cloud drops correlated with sulfate mass based on observations

Cloud Droplets (cm-3) Kiehl et al. [2000] I: Martin et al. [1994]: -0. 68

Cloud Droplets (cm-3) Kiehl et al. [2000] I: Martin et al. [1994]: -0. 68 W/m 2 II: Martin et al. with background CCN: -0. 40 W/m 2 III: Jones et al. [1994]: -0. 80 W/m 2 IV: Boucher and Lohmann [1995]: 1. 78 W/m 2 - Sulfate Mass (mg m-3) “It is argued that a less empirical and more physically based approach is required…”

Two-Moment Sectional Algorithm n n n M 1 M 2. . . Two moments

Two-Moment Sectional Algorithm n n n M 1 M 2. . . Two moments of the size N 1 N 2. . . distribution (mass and number) are tracked for each size bin. The average size of particles in a given section is not constant with time mo 2 mo … Mass Two-moment method conserves both mass and number precisely Prevents numerical diffusion present in single-moment methods Excellent size resolution: 30 sections from. 01 mm to 10 mm

Aerosol Microphysics General Dynamic Equation n Coagulation: Condensation: ~30, 000 grid cells 1 year

Aerosol Microphysics General Dynamic Equation n Coagulation: Condensation: ~30, 000 grid cells 1 year Adaptive time steps

Aerosol Microphysics n Aerosol Types u Sulfate / sea-salt implemented in GISS GCM u

Aerosol Microphysics n Aerosol Types u Sulfate / sea-salt implemented in GISS GCM u Carbonaceous and dust in development n Processes u Emissions u Chemistry u Microphysics u Cloud processing u Size-resolved dry / wet deposition

Cloud Condensation Nuclei

Cloud Condensation Nuclei

Uncertainties n Particulate Emissions u Most sulfate aerosols results from gas-phase SO 2 emissions

Uncertainties n Particulate Emissions u Most sulfate aerosols results from gas-phase SO 2 emissions u Particulate sulfate: <5% of anthropogenic sulfur emissions n Nucleation of new aerosol particles u Important n uncertainties in mechanism and rate Both processes contribute significant numbers of small particles u insignificant n contribution to sulfate mass u important contribution to aerosol number concentrations and size distributions Must quantify sensitivity to these uncertainties

Sensitivity Scenarios n Base Case u 1985 sulfur emissions u all emissions as gas-phase

Sensitivity Scenarios n Base Case u 1985 sulfur emissions u all emissions as gas-phase SO 2 u nucleation based on critical concentration from binary (H 2 SO 4 -H 2 O) theory n Primary Emissions u 3% n of sulfur emissions as sulfate Enhanced Nucleation u critical n H 2 SO 4 concentration factor of 10 lower Pre-industrial u no anthropogenic emissions (but no sea salt)

Vertical Profiles

Vertical Profiles

Impact of Particulate Emissions

Impact of Particulate Emissions

Summary and Conclusions n n n Aerosol microphysical simulations developed in general circulation model

Summary and Conclusions n n n Aerosol microphysical simulations developed in general circulation model Results for sulfate / sea-salt are promising Allow mechanistic simulations of indirect climate forcing Require better knowledge of sources of particle number Indicate impact of primary particles on CCN concentrations This microphysical simulation will be incorporated into GEOS-CHEM

Future Work n Include other aerosol types Organic carbon u Elemental carbon u Mineral

Future Work n Include other aerosol types Organic carbon u Elemental carbon u Mineral dust u n n Couple size-resolved aerosol model to GCM clouds Model evaluation u Real world meteorologies GEOS CHEM (assimilated winds) F Nudged version of GISS model F Field campaigns u Satellite u F MODIS / MISR will provide more size and chemically resolved observations than previous satellite instruments