SENSITIVITY TESTS WITH GEOS-Chem AEROSOL OPTICAL

PROPERTIES: THE ROLE OF BLACK CARBON

Gabriele Curci

CETEMPS Dept. Physical and Chemical Sciences

University of L’Aquila

gabriele.curci@aquila.infn.it

6th International GEOS-Chem Meeting, 6-9 May 2013, Harvard, USA

τ(λ), ω(λ), g(λ), m(λ), dV/d log(r), …

STANDARD GEOS-Chem CALCULATION: EXTERNAL MIXING

Bulk aerosol (mass only) chemistry-transport model Need to assign RH-dependent size distributions and species densities

ln r

dN

/ d

ln r

rm

σg

Species 1

RH

Species 2

Species N . . .

If external mixing and spherical particles are

assumed:

Mie parameters averaged over size distributions may be pre-tabulated as a function of RH, and then used to calculate e.g. AOD at each time step and grid cell:

N

i

i

ieffi

iextM

RHr

RHQAOD

1 ,

,

)(

)(

4

3

INTERNAL MIXING OPTIONS

homogeneous mixing core/shell mixing

Species 1

Species 2

Species N

. . .

Species combine in a new size distribution at each time step and grid cell

Distribution average Mie parameters are not useful anymore

Radius-by-radius calculations using Mie parameters tabulated as a function of size and refractive index (CPU time x 10-20 w.r.t. external mixing)

SENSITIVITY TESTS ON MIXING AND BLACK CARBON

Name Description

EXT GEOS-Chem external mixing

CS Core-Shell Core with all insoluble species: BC, DUST, POC

BCPICORE Core-Shell Core with soluble BC only

BCHI Core-Shell Core same as CS, but BC refractive index from Bond and Bergstrom (2006)

AERONET AEROSOL OPTICAL DEPTH 2008 @ 443 nm

NA

SA

EU

AF

WA EA

AERONET AEROSOL OPTICAL DEPTH @ 443 nm

• General overestimation where anthropogenic and fire sources are large (NA, SA, EU, China) • Not bad over desert and sea

AERONET AEROSOL OPTICAL DEPTH @ 443 nm

• Small effect on AOD

EXT CS BCPICORE BCHI

AERONET SINGLE SCATTERING ALBEDO

AERONET SINGLE SCATTERING ALBEDO

• Overestimated • Model display very low variability with respect to observations

AERONET SINGLE SCATTERING ALBEDO

• Very sensitive to mixing assumption • Core-Shell assumption enhance variability • BC-only core unrealistic

EXT CS BCPICORE BCHI

AERONET ASYMMETRY PARAMETER

AERONET ASYMMETRY PARAMETER

• Overestimation where anthropogenic sources are large (NA, EU, China) • Consistent with Reff positive bias (not shown): if Reff is too large, g is expected to be overestimated

AERONET ASYMMETRY PARAMETER

• Core-Shell with large core seems to be the more realistic assumption

EXT CS BCPICORE BCHI

INPUT TO RADIATIVE TRANSFER MODEL (LIBRADTRAN)

• Mixing assumption may thus have a large effect on radiative forcing calculations …

FUTURE DEVELOPMENTS

• Complete debugging and release version with internal mixing option and AERONET-like output

• Extensive sensitivity tests on size distributions, refractive indices against AERONET

• Extension to sectional and modal aerosol models

• Definition of a general input format. Also useful to input idealized profiles

• Parallelization

• Online coupling with libRadTran?

• Online coupling with GEOS-Chem?

A long way ahead …

SPARE SLIDES

FlexAOD WORKING DIAGRAM

Size Distributions

Refractive Indices

Hygroscopic Growth Factors

Mixing Assumption

FlexAOD

Look-up Tables: • Mie Single Sphere • Mie Coated Sphere

Aerosol Optical Depth

Single Scattering Albedo

Asymmetry Parameter and Phase Function

Aggregated: • Effective radius • Volume Conc. • Refr. index

Satellites, Sunphotometers,

RTM, …

INPUT OUTPUT

USE

Aerosol Species Mass

RADIATION-AEROSOL OPTICAL SIMULATION

Species Densities

AVERAGE AEROSOL BURDEN SIMULATED AT 4°x5° IN 2008

MISR AEROSOL OPTICAL DEPTH 2008 @ 443

AERONET EFFECTIVE RADIUS

AERONET EFFECTIVE RADIUS

• Overestimation +30 % where anthropogenic sources are large (NA, EU, China) • Underestimation over desert • Over sea large overestimation (AERONET only sensitive to fine fraction?)