Modelling the evolution of the key properties controlling SSA from near sources to regional scales

Maria Grazia FrontosoK. Carslaw, G. Mann, D. Spracklen

Institute for Climate & Atmospheric Science (ICAS)University of Leeds

ADIENT meeting, 02 April 2009, Manchester

OBJECTIVES

Quantifying the level of complexity required to capture observed temporal/spatial changes in SSA and what is lost by simplification

in a climate model.

Test of the UKCA model VS more complex size-resolved bin models.

• Black Carbon: mass, size distr, mixing state from SP2

• Single Scatter Albedo

BENCHMARK DATASETS

GLOMAP

GLObal Model of Aerosol Processes

GLOMAP

GLOMAP-bin & GLOMAP-mode

dNdlogr

log(r)

log(r)

dN dlogr

BOTH MODELS HAVE COMPARABLE AEROSOL PROCESSES

• Size & composition-resolved in 2-moment multi-component bin scheme• Species: SU, SS, BC, OC into 2 distributions (insoluble & soluble)• Include boundary layer nucleation

GLOMAP bin

GLOMAP mode

• Size & composition-resolved in 2-moment multi-component modal scheme• Species: SU, SS, BC, OC in 7 modes (HAM/M7 scheme)• Implementing dissolution module for NH3, HNO3 (NO3 & NH4 components in soluble modes)

BLACK CARBON in GLOMAP (1)

• EMISSIONS - anthropogenic sources (fossil fuel & biofuel BC/OC, Bond et al. 2004)

- wildfire sources (BC/OC following GFED emissions in Van Der Werf 2003)

• BC is treated as externally mixed

• BC in GLOMAP-bin is 2 distributions with 20 size bins: - insoluble - soluble/mixed

• BC in GLOMAP-mode is in 4 modes: - insoluble Aitken - soluble Aitken - soluble accumulation - coarse accumulation

BLACK CARBON in GLOMAP (2)

Solubledistribution

Insolubledistribution

BC emitted in insoluble distribution

Ageing is treated by transferring number and mass of insoluble

particles to the soluble distribution at a rate given by 1 molecule coating

of H2SO4

Amount of BC: Insoluble VS Soluble

Soluble BC is more efficiently removed by dry and wet deposition processes, and have a shorter residence time

Aircraft observations & global models???

Not a winning combination RESOLUTION

0

50

100

150

200

250

300

350

400

9.00 10.00 11.00 12.00 13.00 14.00Time (hour)

BC

mas

s

SP2 dataGLOMAP binGLOMAP mode

• Vertical variability• Horizontal variability

Aircraft observations & global models???

0

1000

2000

3000

4000

5000

0 50 100 150 200 250 300BC mass

Hei

gh

t (m

)

GLOMAP-binGLOMAP-modeSP2 data

More reasonable averaging data taking into account the vertical variability

BC mass: good agreement BIN & MODE

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500

BC - BIN

BC

- M

OD

E

B362

B363

B365

B366

B367

B368

B369

B370

B371

B373

B374

B379

Line 1:1

Slope = 1.01R = 0.99

BC mass - BIN

BC

mas

s -

MO

DE

BC mass < 0.1 g/m3

GLOMAP-bin GLOMAP-mode

BC mass against SP2 observations

Slope = 1.76R = 0.66 A general overestimation

Gavin McMeeking, SP2 data

Two different trends?• A underestimation• B overestimation

A

B

FLEXTRA: BC agespectrum Andreas Stohl, FLEXTRA products

• Emissions based mostly on EDGAR 2000 plus better North American emissions plus a few other modifications• Four anthropogenic tracers:

CO – passiveNOx – passiveSOx – dry and wet depositionBC – dry and wet deposition

• Two biomass burning tracers: CO and BC (latter again dry and wet deposition)• Output resolution: 0.25 degree over Europe

• BC agespectrum (purely passive and aerosol-like tracers) interpolated along the flight-path• Mass of BC in 20 bins (1 day, 2 days, ..... 20 days)

0

2

4

6

8

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0 2 4 6 8 10 12

BC age aer (days)

BC

ag

e tr

(d

ays)

FLEXTRASerie2

Y = 2.6 + 1.1 X R = 0.92

FLEXTRA: BC agespectrum

BC age as been calculated as average of BC aerosol and BC tracers age

Andreas Stohl, FLEXTRA products

FLEXTRA: BC agespectrum

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20Age (days)

Fra

cti

on

of

BC

FLEXTRA

Fresh BC

more than 60% of BC mass has less than 1 day

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20Age (days)

Fra

cti

on

of

BC

FLEXTRA

FLEXTRA: BC agespectrum

Aged BC

more than 50% of BC mass has more than 13 days

0,1

1

10

100

1000

0 2 4 6 8 10

BC age (days)

BC

mea

s/B

Cm

od

BCmeas/BCmod against BC age

• Model overestimate BC mass when BC age < 7 days

• Model underestimate BC mass when BC age > 7 days

too strong emissions of fresh BC?

too strong removal of aged BC?

Sensitivity runs

Too strong emissions of fresh BC?

Too strong removal of aged BC?

BC is only emitted in insoluble Aitken mode

BC emitted in 80% as insoluble Aitken and 20% as isoluble Aitken

Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 1 molecule coating of H2SO4

Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 10 molecule coating of H2SO4

BC mass against SP2 observations

Slope = 1.76R = 0.66

Slope = 1.49R = 0.69

• BC mixing state?

• BC size distributions?

• SP2 Black Carbon Emissions Element. Carbon

Insoluble vs soluble/mixed BCFraction of Insoluble BC mass

Fresh BC

Aged BC

Standard runs New runs

50 27%

6 30%

decreasefactor 2

increasefactor 5

SSA: -bin, -mode against observations

0,85

0,9

0,95

1

0,85 0,9 0,95 1

SSA observations

SS

A m

od

el

B362

B363

B365

B366

B367

B368

B369

B370

B371

B373

B374

B379

Line 1:1

0,85

0,9

0,95

1

0,85 0,9 0,95 1

SSA - BIN

SS

A -

MO

DE

B362

B363

B365

B366

B367

B368

B369

B370

B371

B373

B374

B379

Line 1:1

GLOMAP-modevs

GLOMAP-bin

GLOMAP-binvs

observations

Megan Northway, SSA data

Slope = 1.00R = 1.00

Slope = 1.006R = -0.3

Which is the role of RH on SSA?

RH meas (%) RH mod (%)

56.4 50.3

59.2 47.3

62.7 48.2

58 47.4

62.8 49.4

46.7 48.7

43.6 54.4

35.3 47.3

43.6 47.6

10.1 48.3

SSA SSA+RHmeas

0.944 0.950

0.955 0.962

0.955 0.972

0.933 0.952

0.935 0.959

0.940 0.939

0.924 0.919

0.910 0.904

0.909 0.907

0.909 0.913

• In some cases, ECMWF RH is not correct • Sub-grid RH variations: resolution issue?• Increase in RH increase in SSA

0,1

1

10

0,9 1 1,1

SSAmeas/SSAmod

RH

mea

s/R

Hm

od

Which is the role of RH on SSA?

RH can constrain the calculation of SSA

Model underestimate SSA when underestimate RH

Model overestimate SSA when overestimate RH

0,85

0,9

0,95

1

0,85 0,9 0,95 1

SSA observations

SS

A m

od

el

B362

B363

B365

B366

B367

B368

B369

B370

B371

B373

B374

B379

Line 1:1

SSA forced with “real” RH

• RH plays a role on SSA…• … not enough to reduce the discrepancies

Y = 0.882 XR = 0.69

What controls SSA variations with RH?

SSA not linear with RH

SSA not linear with fraction of soluble BC

Future investigations

• How the model performs in case of high internally mixed BC? Does it affect SSA?

• How the model performs against the size distributions? Is the mass quite right but the size wrong? Can we tune the emissions also for the size? New parameterizazions needed?

• Looking at CO & BC identify BC sources Is the model resolution an issue for that?

• Look at SP2 measurements for mixing state & size distribution

• Runs at higher resolution: 1x1 degree

• Zoom over UK

• UKCA 1-year simulation to compare with GlobAerosol (2004)

• Domain: Europe

• Spatial resolution: 2.8x2.8 degrees

• Temporal resolution: daily & hourly resolutions

• SSA & AOD at 870 and 670 nm

• Aerosol composition/type

• Effective radius can be also provided

DELIVERABLE (W.P.4)

Conclusions

• The aerosol sectional bin scheme agrees well with the modal one for BC mass (slope = 1.01, R = 0.99) and SSA values (slope = 1.00, R = 0.99)

• BC age & ratio insol/sol BC influence the total amount of BC. Solubility is driven more by ageing than emissions

• General overestimation of BC over Europe predicted by GLOMAP. More investigations required looking at BC mixing state and size distributions

• RH plays an important role and can constrains the calculation of SSA

• Higher resolution required for the sug-grid RH variations