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Global Aerosol Microphysics With TOMAS
Peter J. Adams
Acknowledgments: Win Trivitayanurak
GEOS-CHEM User’s Meeting
April 7, 2009
Center for Atmospheric Particle Studies (CAPS)
Motivation: CCN and Indirect Effect
Diameter
Aer
osol
Num
ber
Dis
trib
utio
n• Indirect effect of aerosols on clouds depends on number
concentration of cloud condensation nuclei (CCN)• Activation = conversion of a CCN particle to a cloud droplet• Kohler theory tells us that a CCN is a particle with enough solute
to overcome surface tension
CCN = number of particles larger than critical diameter
= shaded area
Critical diameter depends on:• Aerosol composition
(solubility)• Cloud supersaturation
→Need to predict size-resolved aerosol composition
TOMAS Algorithm
• TOMAS (TwO-Moment Aerosol Sectional microphysics algorithm)• Microphysics: condensation, coagulation, nucleation• Moments = 1) aerosol number and 2) aerosol mass• 30 bins segregated by dry mass per particle• Size range is about 10 nm – 10 μm
Dp
Number Size Distribution
N2 N3 N4 N5N6
N7
N30N1
…
Mass Size Distribution
Dp…
SO42-
NaCl
…
M2M3
M4M5
M6 M7
M30
M1
0.01 0.1 1 10 0.01 0.1 1 10 (m) (m)
GEOS-CHEM Implementation: Status• TOMAS is fully implemented in GEOS-CHEM (v. 7-04-11)• Size distribution
• 30 size sections; 10 nm to 10 m• Species
• Sulfate• Sea-salt (NaCl)• Organic Carbon (OC): hydrophobic and hydrophillic• Elemental Carbon (EC): externally mixed and internally mixed• Mineral Dust• Note this is 240 TOMAS-related tracers
• Processes• Coagulation• Condensational growth (H2SO4 and SOA condensation)• Cloud processing (in-cloud oxidation of SO2 to sulfate)• Nucleation: binary (Vehkamaki) and ternary (Napari); ion-induced
(MODGIL) easily implemented• Size-resolved deposition and primary emissions
cm-3
Sample model result
0
1000
2000
3000
4000
5000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
dN/d
logD
p (c
m-3)
0.01 0.1 1 10Diameter (m)
cm-3
dM/d
logD
p (
g m
-3)
0
50
100
150
200
250
300
1 3 5 7 9 11 13 15 17 19 21 23 25 27 290.01 0.1 1 10
Diameter (m)
0
50
100
150
200
250
300
1 12 23
Dust
OM2
OM1
Mixed EC
Pure EC
SeaSalt
SO4
Regional nucleation events: ACE-Asia
Ron Brown ship
Gosan site
Obs.BNUCTNUC
Ternary nucleation…• captures regional event• too frequent
Date
Date
1213
~400 km away
~600 km away
Gosan
Ron Brown
Co
nce
ntr
atio
n (
cm-3)
Co
nce
ntr
atio
n (
cm-3)
Timing and Other Options
• TOMAS is fast enough to run in a 3D model:• One month simulation on
Intel Xeon (2.66 GHz, 4 GB RAM)
TOMAS-30
10 µm1 µm0.1 µm0.01 µm
5 bins 5 bins 2 bins
5 bins
10 bins 10 bins 10 bins
5 bins 5 binsTOMAS-15
TOMAS-12
Lumping size bins
Std. GEOS-CHEM
With TOMAS
Tracers 54 12 hours
Wall Clock 310 3 days
• Other size resolutions developed in GISS GCM:
Conclusions• Fully functional TOMAS implemented in our version of
GEOS-CHEM• All major aerosol species• Reasonable description of all microphysical processes• 14 papers published or in development
• Ready to discuss implementation as an option in “standard” GEOS-CHEM
• TOMAS recommended for some problems• Nucleation, number of ultrafine particles, CCN
• Inefficient for other problems where aerosol mass is sufficient
• Discussion items:• Nucleation options• SOA options• Size bin options