aerosols and climate :

uncertainties

and 

the need for standardization

Frank Raes, Jean-Philippe Putaud, Annette Borowiak
• Set the stage for Workshop that aims at developing a 

cross academic, industry, public stakeholder and 

government outlook on key aerosol metrology issues 

critical to furthering our understanding of aerosols in the 

climate theatre

From the letter of invitation:
- We are more aware of the importance of a range of aerosol 

characteristics and processes in the climate system. 

- Quantifying the climate impact of changing the concention of 

individual chemical components of the atmospheric aerosol is 

still very uncertain.

- Quanitying the climate impact of indivicual human activities ,

incl. policy measures, is even more uncertain (emissions & 

their chemical fingerprint are uncertain), but the sign is usually 

known.

- Deal with uncertainty by adopting a multi-pollutant /multieffect approach (not just aerosol emissions, not just climate 

impacts)

OUTLINE
- Standardization doesn’t reduce uncertainty of measurements 

or assessements but improves their comparability.

- Policy making and policy implementation is about comparing 

(e.g. comparing climate effects with and without a policy, 

comparing PM values with target /limit values)

- Polices often affect markets, or are themselves market based: 

standarization contributes to creating a level playing field.

(BC emissions tradeble like CO2 emissions?)

OUTLINE
size, chemical composition, morphology

ATMOSPHERIC AEROSOL PARTICLES

or: Particulate Matter

Diameter (micrometer)

0.01 0.1 1 10
PM2.5, Central Europe, regional background

SO4

23%

NH4

11%

NO3

10%

unacc.

19%

OM

24%

EC

8% sea salt

1%

dust

4%

PM2.5, Eastern USA, urban background

dust

20%

seasalt

2%

SO4

23%

NO3

8%

NH4

11%

unacc.

7%

OM

21%

EC

8%

PM2.5, Central Europe, urban background

SO4

18%

NH4

10%

NO3

12% unacc.

18%

OM

24%

EC

13%

dust

4% sea salt

1%

PM2.5, Shanghai, China, urban background

dust

13%

sea salt

2%

SO4

22%

NO3

9% NH4

9%

unacc.

3%

OM

32%

EC

10%

PM2.5, Eastern India (Kolkata), urban backgroung

dust

3% seasalt

10%

SO4

13%

NO3

7%

NH4

2%

OM

55%

EC

10%

PM2.5, Northern India (Gual Pahari), regional background

dust

5% sea salt

5%

SO4

16%

NO3

7%

OM

48%

EC

9%

NH4

7%

unacc

3%

PM2.5, Eastern USA, regional background

dust

20%

seasalt

1%

SO4

31%

NO3

5%

NH4

13%

unacc.

8%

OM

19%

EC

3%

regional

background

urban

background

Central

Europe

Eastern

USA

China

Shanghai

Northern

India

Elemental carbon

Organic Matter

Unaccounted

Ammonium

Nitrate

Sulfate

Seasalt

Dust

Source, J.P. Putaud, JRC

chemical composition of PM2.5, worldwide 

(2000 – 2010)

11 μg/m3 20 μg/m3

10 μg/m3

68 μg/m3

10 μg/m3

122 μg/m3

87 μg/m3
Posfai et al. JGR 1999
TOA Radiative Forcing for components IPCC 4AR, 2007
(1 ){ (1 ) 2(1 ) }( ) 2

1 2 2 ∆Eaer,direct = FTT − Ac ωβ − Rs − −ω Rs δ −δ pre

Solar constant

Atmosphere 

transmissivity

(w/o aerosols) 

Cloudiness

Single Scattering 

Albedo

Surface Albedo

Aerosol Optical 

Depth 

Backscatter 

fraction

δ pre≈ δ nat

Haywood and Shine,GRL, 1995
Chung et al., JGR, 2005

Aerosol Optical Depth: MODIS vs. AERONET
Annual average: - 0,35 Wm-2 (range: - 0,6 to – 0,1 Wm-2)

Uncertainty due to

- absorption properties of the aerosol (single scattering albedo)

- vertical distribution of the aerosol

Chung et al., JGR, 2005

TOA Direct Radiative Forcing by Aerosols
Size 

Distribution,

Chemical 

Composition,

Hygroscopic 

Growth,

(Mixing)

β

ω

σ scatσ abs

β

ω

δ tot −δ nat

TOA

direct 

global

RF

local

values

vertical

integration

horizontal

integration

closure experiments

( , ) ( ) 4 ( , , )

2

σ λ

π

λ p p sp

p

sca p n D m dmdD

D

Q D m = ∫∫

- The GAW – World Calibration Centre for Aerosol Physics

http://gaw.tropos.de/WCCAP/

- Intercomparisons

0

1

2

3

4

5

6

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Condensation Particle Counters

Dif. & Scan. Mobility Particle Sizers

Nephelometers

Absorption Spectrometers

Hygroscopicity-TDMA

Eu+NAm

Eu+NAm+Aus

Eu+NAm+Aus+Asia
Emissions

anthrop. &

natural

Size 

Distribution,

Chemical 

Composition,

Hygroscopic 

Growth,

(Mixing)

βωσ scat

σ abs

,

βωδ tot

δ nat

, TOA

direct 

global

RF

local

values

vertical

integration

horizontal

integration
Emissions of Black Carbon Aerosols

BC measured as - absorbing aerosol

- elemental carbon

- fraction of PM
Emissions

anthrop. &

natural

Size 

Distribution,

Chemical 

Composition,

Hygroscopic 

Growth,

(Mixing)

βωσ scat

σ abs

,

βωδ tot

δ nat

, TOA

direct 

global

RF

local

values

vertical

integration

horizontal

integration
same

emissions

TOA Direct Radiative Forcing by AerosolsIPCC 4AR ,2007
sensitivity analysis

with the same model

constrained by

observations

TOA 1st Indirect Radiative Forcing by AerosolsIPCC 4AR ,2007

IPCC 4AR, 2007

-0.5 0 0.5 1 1.5 Wm-2

BC direct effect

BC indirect effects

BC deposition

BC total

UNEP, 2011

O3,troposphere

0.25 - 0.45 Wm-2

0.0 - 1.0 Wm-2

TOA Radiative Forcing for emissions
Climate given at 2050, air quality benefits for 2030 and beyond

UNEP 2011
Climate given at 2050, air quality benefits for 2030 and beyond

UNEP 2011
CEN TC 264 – currently active WGs

WG 15: PM2.5 and PM10 (filter sampling & weighing)

WG 21: measurement of PAHs

WG 32: Particle number concentration

WG 35: EC/OC in PM

Published standards

EN 12341: PM10 filter sampling & weighing (required 

by2008 directive

EN 14907: PM2.5 filter sampling & weighing (required 

by2008 directive

EN 14902: Cd, As Ni, Pb in PM

EN 15549: BaP in PM

prEN 15980: PAHs in PM

Standardization activities in EU by CEN
• Deviations to reference cannot be explained by measurement inaccuracy (based on 

previous inter-comparisons)

• Large filter inhomogeneity

• No certified values for OC and EC (thermal protocol dependent)

TC amount measured in NIST RM 8785 by 13 labs in Europe

0

10

20

30

40

50

60

5 3 3 5 4 5 3 3 5 3 5 0 7 3

UoC NILU CHMI ISAC FMI ACUV IfT IfT ULund ITM JRC PSI CSIC LaMP

0

10

20

30

40

50

60

TC (μg/cm2) IMPROVE

TC (μg/cm2) NOSH

av. TC reported by participant (μg/cm2)

Fig. 1: TC amounts determined by the EUSAAR partners and reference values.

Also shown are the uncertainties of these values.

EU
- We are more aware of the importance of a range of aerosol 

characteristics and processes in the climate system.

-Quantifyingthe climate impactof changing the concentraion of 

individual chemical components of the atmospheric aerosol is 

still very uncertain.

-Quanitying the climate impact of indivicual human activities ,

incl. policy measures, is even more uncertain (emissions & 

their

chemical fingerprint are uncertain) but the sign is usually 

known.

-Deal with uncertainty by adopting a multi-pollutant /multieffect

approach (not just aerosol emissions, not just climate impacts)

CONCLUSIONS
- Standardization doesn’t reduce uncertainty of measurements 

or assessemnts but improves their comparability.

- Policy making and policy implementation about camparing 

(e.g. climate effect with and without a policy, comparing PM 

values with target /limit values)

- Polices often affect markets, or are themselves market based: 

standarization contributes to creating a level playing field.

(BC emissions tradeble like CO2 emissions?)

- Aerosol & Climate science has become relevant!

CONCLUSIONS
thanks
AeroCom (Schultz et al., 2006) 

compared instantaneous direct radiative forcing due to anthropogenic aerosols 

produced by 9 different global models (from Europe, Japan and the USA) with detailed 

aerosol modules,USING THE SAME EMISSIONS

Differences in computed direct aerosol forcing (range +0.04 to −0.41Wm−2) are due to:

• diversity in simulated aerosol residence times

• mass extinction coefficients

• forcing efficiencies (forcing per unit optical depth)

+

• in clear-sky conditions: aerosol absorption, size, and surface albedo

• in cloud-sky conditions: cloud fields and relative altitudes of absorbing aerosol 

and clouds

TOA Direct Radiative Forcing by Aerosols
Global 

TOA

Direct

Radiative 

Forcing

Global 

TOA

Indirect

Radiative 

Forcing

Charlson et al., Science, 1992
Snow, Ice

Albedo

Global 

TOA

Direct

Radiative 

Forcing

Global 

Radiative 

Forcing

Regional

Climate 

Impacts

Global 

TOA

Indirect

Radiative 

Forcing

Regional

Climate 

Impacts

Global &

Regional

Climate 

Impacts

Global

Climate 

Impacts

Global

Climate 

Impacts

Charlson et al., Science, 1992
Emissions

anthrop.

&

natural

Size 

Distribution,

Chemical 

Composition,

Hygroscopic 

Growth,

(Mixing)

β

ω

σ scat σ abs ,

β

ω

δ tot δ nat , TOA

direct 

global

RF

Cloud

Climatology

TOA

indirect 

global

RF

local

values

vertical

integration

horizontal

integration

CCN, CCNnat

Cloud

Droplet

Number

local

values

integration
( ) ( ) pre

out

pre RF = Ein − Eout − Ein − E
( ) ( ) pre

out

pre RF = Ein − Eout − Ein − E

( ) ( ) pre

out out

pre RF = Ein − Ein − E − E

RF = ∆Ein − ∆Eout

RF = ∆Ein,solar − ∆Eout,GHG − ∆Eout,aerosols − ∆Eout,surface _ albedo

Radiative Forcing: bottom-up

ATMOSPHERIC OZONE
Computing future aerosol radiative forcing:

scenarios → emissions → concentration fields → climate forcing

- Model validation (against measured aerosol constituents’ concentrations too)

- Model inter-comparisons

AeroCom (Schultz et al., 2006) compared instantaneous direct radiative forcing due to 

anthropogenic aerosols produced by 9 different global models (from Europe, Japan and the 

USA) with detailed aerosol modules.

Differences in computed direct aerosol forcing (range +0.04 to −0.41Wm−2) are due to:

• diversity in simulated aerosol residence times

• mass extinction coefficients

• forcing efficiencies (forcing per unit optical depth)

+

• in clear-sky conditions: aerosol absorption, size, and surface albedo

• in cloud-sky conditions: cloud fields and relative altitudes of absorbing aerosol and clouds
Reduced from 6.4 measured to 0,9

To match GCMs 
Computing current aerosol direct radiative forcing:

- E.g. Haywood and Shine’s approximation (1995) for a given WL:

Solar constant

Atmosphere 

transmissivity

(w/o aerosols 

Cloudiness

Single Scattering 

Albedo 

Surface Albedo Aerosol Optical 

Depth 

Backscastter 

fraction

- Radiative transfer modules (e.g. Modtran) need:

- extinction vertical profile

- extinction, absorption, and asymmetry factor WL dependence

Computing current aerosol indirect radiative forcing:

- mainly (?) remote sensing

- CCN number ↔ CN number size distribution, hygroscopicity

Is total present forcing, not 

Bar = average over solar an

In Charlsons work, optical depth is that of anthro 

If you use measurements you have natural + ant
Measurements of aerosol characteristics relevant to climate forcing

are currently performed for research (rather than regulation) purposes

⇒ they are done with conscience and awareness

Different flow rates in Nephelometer give same scattering measurements

Different ΔT in CPCs give same number of particles with Dp>50nm

go back to a basic physical principle

⇒ they aim at getting true (and not only “comparable”) values

No need for standardisation if several methods can measure the same truth

E.g. - aerosol absorption from photoacoustic spectrometer =

- extinction cell (extinction – scattering)

In contrast with PM mass concentration (gravimetric methods) which give wrong data because of 

sampling artifacts and analytical artifacts (aerosol water uptake at 45-50% RH), and then errors 

have to be the same everywhere.

⇒ continuous closure checks used as strigent data quality check

Still a lot has been done regarding standardisation in the field of aerosol metrology for 

climate over the past decade ( GAW SAG, GAW-WCCAP, ...,EMEP) Very often payed by 

European Commission
2003 WMO-GAW Guidelines (72 p.)

2011 WMO-GAW SOPs (76 p.)
- The GAW – World Calibration Centre for Aerosol Physics

http://gaw.tropos.de/WCCAP/

- Intercomparisons

- Audits (on-site check of sampling configuration, instruments, etc...)

Tamanrasset/Assekrem Algeria 2003

Hohenpeissenberg Germany 2003

Anmyeon South-Korea 2004

Pallas Finland 2004

Danum Valley Malaysia 2004

Mace Head Ireland 2004

Waliguan-Beijing China 2005

Danum Valley Malaysia 2005

Danum Valley Malaysia 2006

Cape Point South Africa 2006

Ny-Alesund Norway 2006

Beo-Moussala Bulgaria 2006

Izana Tenerife, Spain 2006

Point Barrow Alaska, USA 2007

Monte Cimone Italy 2007

Harwell UK 2007

Mauna Loa Hawaii, USA 2007

Finokalia Crete, Greece 2007

Cabauw The Netherlands 2008

Bukit Koto Tabang Indonesia 2008

Vavihill Sweden 2008

Cape Grim Australia 2008

Shangdianzi China 2009

Danum Valley Malaysia 2009

Hyytiälä Finland 2009

Birkenes Norway 2009

Finokalia Crete, Greece 2009

Preila Lithuania 2009

Aspvreten Sweden 2009

Melpitz Germany 2009

Ispra Italy 2010

JFJ, PdD, Kosetice, K-Puszta 2010 ?

I can make a GANTT-like diagram with 

this too, highlighting stations from the 

5 continents
Computing future aerosol radiative forcing:

scenarios → emissions → concentration fields → climate forcing

- Model validation (against measured aerosol constituents’ concentrations too)

- inorganics: nitrate, sulfate, (ammonium), etc...

- ∃ reference materials (NIST SRM 2694, IRMM xxx, ...)

- ∃ yearly or twice yearly regular inter-comparisons

GAW - QA/SAC-Americas: 78 labs worldwide 

(http://qasac-americas.org/)

EMEP- CCC: 51 labs worldwide 

(http://tarantula.nilu.no/projects/ccc/)

- carbonaceous aerosol

- reference material (NIST RM 8785) ?

- yearly inter-comparison with EUSSAR project (18 Eu labs)

- punctual inter-continental inter-comparison

EnvCan, IMPROVE, EUSAAR
• Deviations to reference cannot be explained by measurement inaccuracy (based on 

previous inter-comparisons)

• Large filter inhomogeneity

• No certified values for OC and EC (thermal protocol dependent)

TC amount measured in NIST RM 8785 by 13 labs in Europe

0

10

20

30

40

50

60

5 3 3 5 4 5 3 3 5 3 5 0 7 3

UoC NILU CHMI ISAC FMI ACUV IfT IfT ULund ITM JRC PSI CSIC LaMP

0

10

20

30

40

50

60

TC (μg/cm2) IMPROVE

TC (μg/cm2) NOSH

av. TC reported by participant (μg/cm2)

Fig. 1: TC amounts determined by the EUSAAR partners and reference values.

Also shown are the uncertainties of these values.

EU
∫∫ =

p p

p

sca sca p N D m r t dmdD

D

r t Q D m ( , , , ) 4 ( , , ) ( , , )

2 π

σ λ λ

effects on radiation balance: scattering and absorption
∫∫ c

=

p − p c c p d dDp CCN(S ,r,t) H[D D (S ,ε )]N(D ,ε,r,t) ε ,

effects on clouds: cloud condensation nuclei
The GAW – World Calibration Centre for Aerosol Physics

http://gaw.tropos.de/WCCAP/

- Intercomparisons

- Audits

- Travelling reference instruments (for especially remote stations)
Definitions

What is a Standard?

A standard is an established norm or requirement

It is usually a formal document that establishes uniform 

technical criteria, methods, processes and practices 

It may be developed privately or unilaterally, for example 

by a corporation, regulatory body, military

Simply They define how things should be done
∫∫ =

p p

p

sca sca p N D m r t dmdD

D

r t Q D m ( , , , ) 4 ( , , ) ( , , )

2 π

σ λ λ

effects on radiation balance: scattering and absorption
∫∫ c

=

p − p c c p d dDp CCN(S ,r,t) H[D D (S ,ε )]N(D ,ε,r,t) ε ,

effects on clouds: cloud condensation nuclei
“Black Carbon” or “Elemental Carbon” is:

- carbon-containing particulate matter, resulting from incomplete combustion

- it withstands high temperatures

- it is black, hence absorbs light 

- emitted together with CO2, CO, NMHC, organic particlate matter) 

BLACK CARBON PARTICLES
Anthropogenic forcing??


ng/m3

Observed Modeled 

Measuring and modeling BC surface concentrations

Koch et al., 2009
impacts of BC and tropospheric ozone

On air quality

Black carbon and ozone in the lower atmosphere are harmful air 

pollutants affecting health of humans and ecosystems

Black carbon, a component of particulate matter, and ozone both lead 

to premature deaths worldwide. (PM2.5: ∼2 million per year , WHO)

Ozone is also the most important air pollutant, responsible for reducing 

crop yields, and thus affects food security.

On global and regional climate ?
present impacts of BC and tropospheric ozone 

On global and regional climate

Changes in their burdens over the 20th Century result in an 

expected equilibrium global warming of 0.0-0.8 C due to BC 

and 0.1-0.4 C due to O3. (The equilibrium warming expected 

from CO2 is about 1.3 C.)

Atmospheric heating by BC disturbs tropical rainfall and regional 

circulation patterns such as the Asian monsoon.

Black carbon’s darkening of snow and ice surfaces increases 

their absorption of sunlight, which, along with atmospheric 

heating, exacerbates melting of snow and ice around the world, 

including in the Arctic, the Himalayas. 
UNEP, 2011

change in BC deposition: 2005 to 2030

reference scenario

%
expected impacts of BC and tropospheric ozone

ireference scenario: 2005 to 2030 

Avoidance of 0.2-1.8 million premature deaths per year , in North 

America, East Asia, SE Asia & Pacific, While in increase by 0.1-

2.0 million in South, West & Central Asia and Africa..

Decreasing production of wheat, rice corn and soy by 7 to 120 

million tonnes across Asia with an associated economic loss of 

US$ 1 – 20 billion. Increasing crop yields in US and Europe.

The compensating warming and cooling impacts of changes in 

BC, ozone and other aerosols lead to a small net warming of less 

than 0.1 C globally

Black carbon’s darkening of snow and ice and atmospheric 

heating, keeps exacerbating melting of snow and ice in the 

Himalayas
Conclusions so far:

based on our knowledge of the behaviour of BC and 

ozone in the atmosphere, and of their impacts on air quality,

And on lobal and regional climate in teh near term 

it makes a lot of sense to look for measures that specifically 

target the emissions of BC and ozone precursors in order 

to solve a range of important problems at once. 
thanks
calculation effects of aerosols 

∫∫ =

p p

p

sp sca p n D m dmdD

D

Q D m ( , ) 4 ( ) ( , , )

2 π

σ λ λ

∫∫ CCN Sc

= H Dp − Dp c Sc n Dp d dDp ( ) [ ( ,ε )] ( ,ε ) ε ,

∫ ∫ =

x

p p

p

x p n D d dD

D

PM D

0

3

( , ) 6 ( ) ρ ρ

π

ρ

( ,ε ) = ( )δ (ε −ε ) n Dp n Dp

assuming internal mixing of chemical species into an average one

assuming external mixing of i chemical species 

= ∑ − k

n Dp ni Dp i 1 ( ,ε ) ( )δ (ε ε )

with δ the Kronecker delta function

scattering, absorpttion

cloud activation:

particulate matter

Closure experiments
- We are more aware of the importance of a range of aerosol 

processes in the climate system.

-Quantifyingthe climate impactof changing the concentraion of 

individual chemical components of the atmospheric aerosol is 

still very uncertain.

-Quanitying the climate impact of indivicual human activities ,

incl. policy measures, is even more uncertain (emissions & 

their

chemical fingerprint are uncertain) but the sign is usually 

known.

-Deal with uncertainty by adopting a multi-pollutant /multieffect

approach (not just aerosol emissions, not just climate impacts)

conclusions
- Standardization doesn’t reduce uncertainty of measurements 

or assessemnts but improves their comparability.

- Policy making and policy implementation about camparing 

(e.g. climate effect with and without a policy, comparing PM 

values with target /limit values)

- Polices often affect markets, or are themselves market based: 

standarization contributes to creating a level playing field.

(BC emissions tradeble like CO2 emissions?)

- Aerosol & Climate science has become relevant!

conclusions
( ) ( ) ref

out

ref RF = Ein − Eout − Ein − E

reference = pre-industrial era

hence

and 

( − ) ≈ 0 ref

out

ref Ein E

( ) RF = Ein − Eout
ATMOSPHERIC AEROSOL: macroscopic view

MISR 

2006
AeroCom (Schultz et al., 2006) compared 

instantaneous direct radiative forcing due to anthropogenic 

aerosols produced by 9 different global models with 

detailed aerosol modules, using identical emissions.

Differences in computed direct aerosol forcing (range 

+0.04 to −0.41Wm−2) are due to:

• diversity in simulated aerosol residence times

• mass extinction coefficients

• forcing efficiencies (forcing per unit optical depth)

+

• in clear-sky conditions: aerosol absorption, size, and 

surface albedo

• in cloud-sky conditions: cloud fields and relative 

altitudes of absorbing aerosol and clouds
• For any statement that I going to make there is an expert in the room that can go much mre n depth, or even challenge it

• Steve: father if not grand-father: without a beard mor like a father

• When interest of standardization organizations > relevance!

• PM/healt already relevant: legislation > lavel playing field money (even though this community knows much less aerosol,but 

there is epidemiological evidence!) (do we havedirect evidence of impacts of aerosols on climate:, and that it is important?)

• How can we go from microscopic compexity to values regional or glonal impacts on radiation balece and climate?

• Do we need to consider all that complexity, to come to usefull values?

• Not yet legislation for aerosols and climate, scientific need (but e.g. BC in CDM is discussed ?) anyway relevance 

• Ozone vs PM, PM external internal mixing: onc you ave O3, RF easy to calculate.once you have PM dot easy to calculate

• TOA forcing, RF = delta(present) – delta (pre-industrial) > role of knowing pre-industrial values – Overall Earth radiation balance

– Delta aerosols, delta GHG.delat alsbedl

• - IPCC usual graph (not policy relevant), immediately show other IPCC (more relevant) > Shindell

• At this point usefull to make a distinction between – assessement of present day effects of PM on climate (relevant to 

monitor compliamce with legilation: standardization) – predicting future impacts of PM on climate (policy development)

• Paper Charlson et al. / Haywood & Shine

– based on secondary parameters: problem of pre-industrial

– Based on primar parameters related to emisioins

• What did we learn? Include TOA > TOA+ surface+atmospheric forcing >regional impacts

• We know a lot about aerosols, compared to what health people know or want to consider about PM. Still the latter made it 

to policy and hence standardization: research becomes different ...

• Ibe exampels of standardization work in air quality work

• Two communities are any way mergibg: e.g. UNEP assessement.

– RF of BC emissions (IGAC, telephone conference India, US, Nairobi, Europe)

– Effect on Climate, Health Crops. Integrated > uncertainties are less problematic.

• Conclusion?