1 High Time-Resolution Size- Resolved Aerosol Predictions: Learning about CCN from Aerosol Field Campaigns Win Trivitayanurak GEOS-CHEM Meeting Harvard University April 4, 2005

2 Outline Objective Model Development Status Sample results Future work Conclusion

3 Objectives To implement TOMAS aerosol microphysics in GEOS-CHEM. To evaluate the microphysics model by comparing aerosol model predictions against ACE Asia field campaign. Look for potential improvement to the microphysics model:  Nucleation model  Primary aerosol emission size-distributions  Vertical distribution

4 TOMAS Microphysics TOMAS (TwO-Moment Aerosol Sectional microphysics algorithm) [Adams and Seinfeld, 2002]  Conserve BOTH number and mass concentrations by tracking them for each size bin.  30 Bins – dry mass boundary  Processes include coagulation, condensation/ evaporation, dry deposition, wet deposition and nucleation m o 2m o … Mass M1N1M1N1 M2N2M2N2...

5 Model Development Status 30 size-bin sulfate aerosol tracers added to STT array  30 tracers for aerosol number of each size bin: Nk1, Nk2, Nk3, …., Nk30  30 tracers for aerosol mass of each size bin: SF1, SF2, SF3, …., SF30 Important : aerosol m ass and number must go together !  Transport & convection

6 Model Development Status … TOMAS microphysics integrated  Condensation + coagulation + nucleation – ON GEOS-CHEM processes  Transport – OFF  Convection – OFF  Convective precip. – OFF  LS precip. – ON  Aqueous oxidation – ON but not physical yet.  Dry deposition – ON but not size-dependent yet.

7 Sample results – SO4 mass (L = 1) Original GEOS-CHEM bulk SO4 Sum of 30 bins mass of sulfate [  g/m 3 ]

8 Sample results – SO4 mass ( L = 10) Original GEOS-CHEM bulk SO4 Sum of 30 bins mass of sulfate [  g/m 3 ]

9 Sample results – Number Concentration ( L=1 ) [no./cm 3 ] [  g/m 3 ] Sum of 30 bins mass of sulfate Sum of 30 bins number of sulfate

10 Sample results – Number Concentration ( L= 10) Sum of 30 bins mass of sulfate [  g/m 3 ] [no./cm 3 ] Sum of 30 bins number of sulfate

11 Sample results – Size distribution Sulfate number size distribution dN/dlogD p (cm -3 ) D p (  m) dM/dlogD p (  g cm -3 ) A snapshot at 7/31/2001 taken from grid box (61,31,1) ~ Shanghai, East China Sulfate mass size distribution

12 Model run time on Linux platform Original GEOS-CHEM GEOS-CHEM w/ TOMAS Transport  Convection  Convective Precip  TOMAS  Run time13 hours18 hours 1 month of GEOS-CHEM full chemistry run with 4x5 resolution and GEOS 3 meteorology

13 Future work Turning on transport & convection Introduce aqueous phase chemistry wrt each size bin Introduce size-resolved dry deposition Adding more aerosol types (sea salt, dust, OC, EC) Comparison to ACE-Asia

14 Conclusion Keeping the aerosol mass and number tracers consistent is crucial for TOMAS Early stage of TOMAS microphysics in GEOS-CHEM shows a promising future for high time-resolution size-resolved aerosol prediction.

15 QUESTIONS?

16 Sulfate size distribution Snapshot at 7/1/ HRS Sulfate number size distribution Sulfate mass size distribution

17 Sulfate size distribution Snapshot at 7/1/ HRS Sulfate number size distribution Sulfate mass size distribution

18 Sulfate size distribution Snapshot at 7/17/2001 Sulfate number size distribution Sulfate mass size distribution

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20 Binary nucleation model, H 2 SO 4 -H 2 O system [Jaecker-Voirol and Mirabel, 1989] In each time step (1hr), first let gas-phase H 2 SO 4 condense onto existing aerosol. At end of time step, if remaining H 2 SO 4 concentration exceeds critical concentration, then nucleation occurs. [Wexler et al., 1994] C crit = 0.16exp(0.1T - 3.5RH ) Nucleated particles are introduced to the smallest size bin Aerosol Microphysics : Nucleation

21 Aerosol Microphysics : Nucleation Nucleation events observed at H 2 SO 4 concentrations below those required by binary nucleation model Suggest other mechanisms are at work  Ternary nucleation (H 2 SO 4 -NH 3 -H 2 O)  Ion induced nucleation. Shall test and see in GEOS-CHEM

22 Aerosol Microphysics : Primary Aerosol Importance of primary ultrafine emissions  Particulate emissions are more efficient than gas- phase emissions at increasing CCN  indirect effects.  Need accurate size-distributions of primary aerosols. Ratio of CCN(0.2%) particulate emission scenario over gas-phase emission scenario [Adams and Seinfeld, GRL 2003]

23 Aerosol Microphysics : Primary Aerosol Current Primary Aerosol Size-Distributions  EC/OC: main source of ultrafine particles and aerosol number  Sulfate: also ultrafine  Dust: mostly coarse, some fine  Sea-salt: mostly coarse, some fine Dp (  m) Mass Size Distribution Probability OC/EC Sulfate Dust Sea-salt Dp (  m) Number Size Distribution Probability

24 Aerosol Microphysics : Vertical Distribution Vertical distribution of aerosols affects lifetime because lower aerosols are removed by rain more efficiently. How good is the vertical profile prediction? Examine how each process influences vertical distributions  sources vs. sinks  Gravitational settling = sink for large particles Enough settling?  Vertical mixing; how good?

25 Field Campaign TRACE-P  Feb - Apr 2001  NW Pacific  Asian Chemical outflow and evolution  Aircraft ACE-Asia  Late Mar - May 2001  Ground network:  Yellow Sea, Sea of Japan, Pacific and ground-based in China and Japan  Asian Aerosol, radiative effect, aerosol processes  Aircraft, R/V (ships), ground stations network [Huebert et al., 2003]

26 Comparison Parameters? How to evaluate model? Nucleation:  SO 2, H 2 SO 4, surface area, and number concentrations. Temp, RH.  Do observations agree with theory? [McNaughton et al., JGR 2004 in press] Observations during flight 7 of ACE-Asia. MBL Diameter (  m) dA/d log Dp (  m 2 cm -3 ) C-130 Altitude (m) Temp (°C) Particle (# cm -3 ) SO 2 (ppbv)

27 Comparison Primary Aerosol:  Size distribution measured on aircraft. Different volatility suggest aerosol types.  Do the input size distributions of primary aerosols produce accurate total number concentration and size distribution? Dp (um) dN/d log Dp (cm -3 ) [McNaughton et al., JGR 2004 in press] Sulfuric acid or organic compound Formed earlier w/ partial neutralization by NH3 Sulfuric acid with near complete neutralization Or ammoniated species

28 Comparison Vertical distribution:  Number profile, mass profile, size-resolved profile.  Compare model vs. observations  examine what is too high/low, e.g. production or loss.  Potential improvement? Is it in the aerosol model? Diameter (um) C-130 Altitude (m) Sulfate mass conc. (ug/m3) Twin Otter Altitude (m) [BAHREINI ET AL., 2003] [McNaughton et al., 2004 in press]