1

High Time-Resolution Size-Resolved Aerosol Predictions:

Learning about CCN from Aerosol Field Campaigns

Win TrivitayanurakGEOS-CHEM Meeting

Harvard University

April 4, 2005

2

Outline

ObjectiveModel Development StatusSample resultsFuture workConclusion

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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

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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 mo 2mo … Mass

M1

N1

M2

N2

...

...

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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 mass and number must go together ! Transport & convection

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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.

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Sample results – SO4 mass (L = 1)

Original GEOS-CHEM bulk SO4

Sum of 30 bins mass of sulfate

[g/m3][g/m3]

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Sample results – SO4 mass ( L = 10)

Original GEOS-CHEM bulk SO4

Sum of 30 bins mass of sulfate

[g/m3][g/m3]

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Sample results – Number Concentration( L=1 )

[no./cm3] [g/m3]

Sum of 30 bins mass of sulfateSum of 30 bins number of sulfate

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Sample results – Number Concentration( L= 10)

Sum of 30 bins mass of sulfate

[g/m3][no./cm3]

Sum of 30 bins number of sulfate

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Sample results – Size distribution

0

6

12

18

0.01 0.1 1 10

x 103

Sulfate number size distribution

dN

/dlo

gD

p

(cm

-3)

Dp(m)

0

30

60

90

0.01 0.1 1 10

-

Dp(m)

dM

/dlo

gD

p (g

cm

-3)

A snapshot at 7/31/2001 taken from grid box (61,31,1) ~ Shanghai, East China

Sulfate mass size distribution

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Model run time on Linux platform

Original

GEOS-CHEM

GEOS-CHEM w/ TOMAS

Transport Convection Convective Precip TOMAS Run time 13 hours 18 hours

1 month of GEOS-CHEM full chemistry run with 4x5 resolution and GEOS 3 meteorology

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Future work

Turning on transport & convectionIntroduce aqueous phase chemistry wrt

each size binIntroduce size-resolved dry depositionAdding more aerosol types (sea salt, dust,

OC, EC)Comparison to ACE-Asia

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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.

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QUESTIONS?

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Sulfate size distribution Snapshot at 7/1/2001 0.00HRS

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.01 0.1 1 10Dp (m)

dM

/dlo

gD

p

(g

m-3

)0

4

8

12

16

0.01 0.1 1 10

x 103

Dp (m)

dN

/dlo

gD

p (

cm-3

)

Sulfate number size distribution Sulfate mass size distribution

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Sulfate size distribution Snapshot at 7/1/2001 3.00HRS

0

0.05

0.1

0.15

0.2

0.25

0.3

0.01 0.1 1 10Dp (m)

dM

/dlo

gD

p

(g

m-3

)0

8

16

24

32

40

0.01 0.1 1 10

x 103

Dp (m)

dN

/dlo

gD

p (

cm-3

)

Sulfate number size distribution Sulfate mass size distribution

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Sulfate size distribution Snapshot at 7/17/2001

0

10

20

30

40

50

0.01 0.1 1 10Dp (m)

dM

/dlo

gD

p (

g m

-3)

0

12

24

36

48

0.01 0.1 1 10

x 103

Dp (m)

dN

/dlo

gD

p (

cm

-3)

Sulfate number size distribution Sulfate mass size distribution

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Binary nucleation model, H2SO4-H2O system [Jaecker-Voirol and Mirabel, 1989]

In each time step (1hr), first let gas-phase H2SO4

condense onto existing aerosol. At end of time step, if remaining H2SO4 concentration

exceeds critical concentration, then nucleation occurs. [Wexler et al., 1994]

Ccrit = 0.16exp(0.1T - 3.5RH - 27.7)

Nucleated particles are introduced to the smallest size bin

AerosolMicrophysics : Nucleation

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AerosolMicrophysics : NucleationNucleation events observed at H2SO4

concentrations below those required by binary nucleation model

Suggest other mechanisms are at work Ternary nucleation (H2SO4-NH3-H2O) Ion induced nucleation.

Shall test and see in GEOS-CHEM

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AerosolMicrophysics : 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]

0 .2 .4 .6 .8 .9 1.0 1.2 2 5

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AerosolMicrophysics : 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

0

0.1

0.2

0.3

0.01 0.1 1 10Dp (m)

Mass Size Distribution

Pro

babi

lity

OC/ECSulfate DustSea-salt

0

0.1

0.2

0.3

0.01 0.1 1 10Dp (m)

Number Size Distribution

Pro

babi

lity

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AerosolMicrophysics : 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?

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Field Campaign

TRACE-P Feb - Apr 2001 NW Pacific Asian Chemical outflow and

evolution Aircraft

ACE-Asia Late Mar - May 2001 Ground network: 2000-2003 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]

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ComparisonParameters? How to evaluate model? Nucleation:

SO2, H2SO4, 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/dlogDp(m2cm-3)

C-1

30

Alti

tude

(m

)

Temp (°C) Particle (# cm-3)

SO2 (ppbv)

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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?

0.01 0.1 1 10 Dp (um)

dN/d

logD

p (

cm-3)

[McNaughton et al., JGR 2004 in press]

Sulfuric acid or organic compound

Formed earlier w/ partial neutralization by NH3

Sulfuric acid with nearcomplete neutralizationOr ammoniated species

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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-1

30

Alti

tude

(m

)

Sulfate mass conc. (ug/m3)

Tw

in O

tter

Alti

tude

(m

)

[BAHREINI ET AL., 2003] [McNaughton et al., 2004 in press]