Atmospheric Chemistry Cloud multiphase processes and their impact on climate Maria Cristina Facchini Istituto di Scienze dell’Atmosfera e del Clima - C.N.R.

Atmospheric ChemistryAtmospheric Chemistry

Cloud multiphase processes and their impact on climate

Maria Cristina Facchini Maria Cristina Facchini

Istituto di Scienze dell’Atmosfera e del Clima - C.N.R.Istituto di Scienze dell’Atmosfera e del Clima - C.N.R.

Bologna, ItalyBologna, Italy


AcknowledgementsAcknowledgements

M. Mircea, S. Fuzzi, S. Decesari, E. MattaM. Mircea, S. Fuzzi, S. Decesari, E. Matta ISAC-CNR, Bologna, ItalyISAC-CNR, Bologna, Italy

R.J. CharlsonR.J. CharlsonUniversity of Washington, Seattle, USAUniversity of Washington, Seattle, USA

A. Nenes, J.A. SeinfeldA. Nenes, J.A. Seinfeld California Institute of Technology, Pasadena, USACalifornia Institute of Technology, Pasadena, USA

S.L. CleggS.L. CleggUniversity of East Anglia, Norwich, UKUniversity of East Anglia, Norwich, UK

M. KulmalaM. KulmalaUniversity of Helsinki, Helsinki, FinlandUniversity of Helsinki, Helsinki, Finland

E. TagliaviniE. TagliaviniUniversity of Bologna, ItalyUniversity of Bologna, Italy


Clouds and climateClouds and climate Clouds are the most important factor Clouds are the most important factor

controlling the Earth albedo and hence the controlling the Earth albedo and hence the temperature of our planet temperature of our planet

Cloud optical properties are controlled by Cloud optical properties are controlled by size/number of droplets which in turn are size/number of droplets which in turn are governed by the “availability “ of aerosol governed by the “availability “ of aerosol particles to serve as CCNparticles to serve as CCN


Clouds and climate 2Clouds and climate 2 Changes in cloud optical properties induced by man’s Changes in cloud optical properties induced by man’s

activity are at the moment highly uncertainactivity are at the moment highly uncertain


Parameters influencing CDNParameters influencing CDN Many years ago, Twomey suggested that the Many years ago, Twomey suggested that the

most important parameter influencing cloud most important parameter influencing cloud droplet number (CDN) is aerosol number droplet number (CDN) is aerosol number concentration, while aerosol chemical concentration, while aerosol chemical composition has a relatively minor effectcomposition has a relatively minor effect

Recently, model and experimental results Recently, model and experimental results have induced to revisit this assumption and to have induced to revisit this assumption and to re-examine the relative importance of the re-examine the relative importance of the different factors influencing CDN distributiondifferent factors influencing CDN distribution


CDN and aerosol number CDN and aerosol number

The number of CDN is The number of CDN is not a “linear” function of not a “linear” function of aerosol number aerosol number (Ramanathan et (Ramanathan et alal., ., ScienceScience, 2001), 2001)

The large degree of The large degree of variation suggests that variation suggests that cloud properties are cloud properties are controlled by many controlled by many different factors different factors


The issue The issue

how does the chemistry of the cloud how does the chemistry of the cloud multiphase system influence multiphase system influence formation and evolution of the formation and evolution of the cloud droplet population ?cloud droplet population ?


RH

Dry particlewet aerosol

Cloud droplet

gas phase

R R

……an intuitive picture of cloud an intuitive picture of cloud chemistrychemistry

Absorbing material

Soluble fraction chemical composition


Cloud formationCloud formation

Atmospheric thermodynamic Atmospheric thermodynamic parameters (moisture availability, parameters (moisture availability, updraft velocity, temperature, etc.)updraft velocity, temperature, etc.)

Aerosol properties: Aerosol properties: classically, the classically, the controlling chemical variables are controlling chemical variables are CCN size distribution and water CCN size distribution and water soluble masssoluble mass


Theory of cloud formationTheory of cloud formation

TrR

vas

g

ww

2exp

aw = water activity = surface tensionw = water molar volume


Water activityWater activity

1000exp

mww

Ma

orginorgorgorginorginorga

orginorgorgorginorginorg

wgas

waer

wgaswaerw

a

aaa

? ?for inorganic aqueouselectrolytic solutions

Only one paper:Clegg et al.,J. Aerosol Sci.,2001


Modified Köhler equationModified Köhler equation

norginorg jj

jj

ii

ii

Ns

sw

w

ws

M

m

Mm

rr

MrRT

Ms

)(4

321 33

Kelvin term

Raoult term


Chemical factors controlling cloud Chemical factors controlling cloud formationformation

Not simply inorganic soluble salts Not simply inorganic soluble salts influence cloud formationinfluence cloud formation

Soluble or slightly soluble organics Soluble or slightly soluble organics influence equilibrium water vapor influence equilibrium water vapor pressure and decrease surface tension pressure and decrease surface tension of the dropletsof the droplets

Soluble gases condensation Soluble gases condensation ((Charlson et al., Charlson et al., Science 2001Science 2001))


Aerosol chemical compositionAerosol chemical composition

Spring - Summer

SO414%

other ions9%

NO311%

NH47%

WSOC18%

WINC19%

unk22%


Organic aerosols andOrganic aerosols andKöhler theoryKöhler theory

Organic aerosols influence Organic aerosols influence equilibrium supersaturation by:equilibrium supersaturation by:““adding” soluble materialadding” soluble materialdecreasing surface tension with respect to pure decreasing surface tension with respect to pure

water or an inorganic salt solutionwater or an inorganic salt solution


Speciation of organic aerosolSpeciation of organic aerosol

The traditional analytical approach has The traditional analytical approach has usually been individual compound usually been individual compound speciation, but less than 10% of OC mass speciation, but less than 10% of OC mass has been accounted forhas been accounted for

A new method using functional group A new method using functional group analysis has been developed which accounts analysis has been developed which accounts for up to 90% of OC mass for up to 90% of OC mass (Decesari et (Decesari et alal., ., J. Geophys. ResJ. Geophys. Res., 2000)., 2000)


Organic solutes in cloudsOrganic solutes in clouds WSOC are a complex mixture of highly oxidised, WSOC are a complex mixture of highly oxidised,

multifunctional compounds with residual aromatic multifunctional compounds with residual aromatic nuclei and aliphatic chainsnuclei and aliphatic chainsNeutral compoundsNeutral compounds: mainly aliphatic polyols, polyethers, : mainly aliphatic polyols, polyethers,

sugars;sugars;Mono-/di-acidsMono-/di-acids: hydroxylated aliphatic acidic compounds;: hydroxylated aliphatic acidic compounds;PolyacidsPolyacids: unsaturated polyacidic compounds both : unsaturated polyacidic compounds both

aliphatic and aromatic with a minor content of hydroxyl aliphatic and aromatic with a minor content of hydroxyl groupsgroups

This information can be used to construct a set of This information can be used to construct a set of model compoundsmodel compounds


Why model compounds?Why model compounds?

Too often the physical and chemical Too often the physical and chemical properties of atmospheric OC are simulated properties of atmospheric OC are simulated in models using compounds which are not in models using compounds which are not representative of the physical realityrepresentative of the physical reality

Modellers need a synthetic information of a Modellers need a synthetic information of a few model compounds which can be used to few model compounds which can be used to simulate in a quantitative way the whole simulate in a quantitative way the whole OC of aerosol and cloudsOC of aerosol and clouds


CHCH22 CHCH33

38 %38 %

CHCH

OHOH

31 %31 %9 %9 %OO

CC CHCH22CHCH22

21 %21 %

ArAr

8 %8 %

CHCH

HOHO

9 %9 %

CHCH22 CHCH22

42 %42 %

CHCH22

OHOH

OO

41 %41 %

ArAr

50 %50 %

CHCH

HOHO

5 %5 %

CHCH22 CHCH22

23 %23 %

CHCH22OHOH

OO

23 %23 %

ArAr

neutral fractionneutral fraction

mono-/di-acidsmono-/di-acids

polyacidspolyacids

(Fuzzi et al., GRL, 2001)


Modified Köhler equationModified Köhler equation

norginorg jj

jj

ii

ii

Ns

sw

w

ws

M

m

Mm

rr

MrRT

Ms

)(4

321 33

Kelvin term


C(mol l-1)

1e-4 1e-3 1e-2 1e-1

(m

N m

-1)

50

55

60

65

70

75

Surface tension measurements Surface tension measurements

cloudTenerifeACE-2

fogPo Valley

cloud ACE-ASIA

= K - T ln (1+ C)


0.1 1 10

Sa

tura

tion

ra

tio

0.999

1.000

1.001

1.002

1.003

1.004

1.005

1.006

0.05 m

0.1 m

0.3 m

inorganic only

inorganic+organic

inorganic+organic+

Effect of organics on SEffect of organics on Scc

fromMircea et al.,Tellus, 2001


Trace gas dissolutionTrace gas dissolution

Laaksonen et al., JAS, 1998

HNO3


Modelling of chemical effectsModelling of chemical effects

marine case polluted case

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

Max

imum

alb

edo

chan

ge,

R*

10 cm/s

30 cm/s

100 cm/s

300 cm/s

insoluble

organicno

organicwith

5 ppbHNO3

2conc.

0.1 m s-1

0.3 m s-1

1.0 m s-1

3.0 m s-1

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

R*

10 cm/s

30 cm/s

100 cm/s

300 cm/s

insoluble

organicno

organicwith

5 ppbHNO3

2conc.

Max

imum

alb

edo

chan

ge,

R*

0.1 m s-1

0.3 m s-1

1.0 m s-1

3.0 m s-1

(Nenes et al., GRL in press)


0.1 m/s

1 m/s

10 m/s

CCN(m-3)

1e+8 1e+9

z(m

)

0

100

200

300

400

500

Effect of size segregated Effect of size segregated chemical compositionchemical composition

See poster Mircea et al., Session B

Dotted line: bulk compositionSolid line: size-segr. compostion


Water activity of Water activity of multicomponent solutionsmulticomponent solutions

data fromClegg et al.,J. Aerosol Sci.,2001r(m)

0.1 1 10

satu

ratio

n m

ixin

g ra

tio

1.000

1.002

1.004

1.006

1.008

1.01070% lectovicite+30% maleic acid

0.05 m

0.1 m

modifiedKoher theory

aw Cleggtreatment

as above +measured


Conclusions Conclusions

Dissolution of gases, dissolution of soluble Dissolution of gases, dissolution of soluble and slightly soluble organics and the and slightly soluble organics and the associated decrease of associated decrease of influence droplet influence droplet populationpopulation

There are many conditions in the There are many conditions in the atmosphere in which chemical factors atmosphere in which chemical factors influence/control cloud microphysics to the influence/control cloud microphysics to the same extent as cloud dynamics and/or same extent as cloud dynamics and/or aerosol number concentration aerosol number concentration


……still neededstill needed

data on physical and chemical properties of data on physical and chemical properties of aerosol are needed for different areas and aerosol are needed for different areas and aerosol typesaerosol types

thermodynamic data and models of thermodynamic data and models of aaww for for the complex cloud droplet solutions are the complex cloud droplet solutions are neededneeded


Model compounds molar Model compounds molar composition (%)composition (%)

pinonaldehyde 16pinonaldehyde 16levoglucosan 9levoglucosan 9catechol 2catechol 2azelaic acid 14azelaic acid 14hydroxy-benzoic acid 15hydroxy-benzoic acid 15-hydroxy-butyric acid 3-hydroxy-butyric acid 3fulvic acid 41fulvic acid 41

(Fuzzi et al., GRL, in press)


Models neutral compoundsModels neutral compounds

pinonaldehydepinonaldehydehydratedhydrated

levoglucosanlevoglucosan

cathecolcathecol

OH

OH

O

OHHO

OO

HO

HO

HO


Models mono-/di-acidsModels mono-/di-acids

azelaic acidazelaic acid

-hydroxy-butyric acid-hydroxy-butyric acidhydroxy-benzoic acidhydroxy-benzoic acid

HO

O

OH

O

HO O

OH

OH

OH

O


HO OO

OH

OH

O

OH

OOOHO

O

OOH

OH

O

Model polyacidsModel polyacids

fulvic acidfulvic acid


Surface tension depends onSurface tension depends onchemical composition chemical composition

0

0,1

0,2

0,3

0,4

NC MDA PA UNF

sp

ecif

ic (

dyn

e c

m-1 p

pm

C-1)

Atmospheric Chemistry Cloud multiphase processes and their impact on climate Maria Cristina Facchini Istituto di Scienze dell’Atmosfera e del Clima - C.N.R.

Documents

atmospheric chemistry

atmospheric chemistry

cloud properties

ccn slide

uncertain slide

cdn distribution slide

water soluble mass slide

cloud droplet number