June 7, 2004June 7, 2004

Laboratory Studies of Ice Laboratory Studies of Ice Initiation by Atmospheric Initiation by Atmospheric

Aerosol ParticlesAerosol Particles

Paul J. DeMottPaul J. DeMott

With acknowledgment to With acknowledgment to numerousnumerous contributors contributors

June 7, 2004June 7, 2004

Overview• Talk will concern itself only with primary ice initiation. Other

laboratory studies of relevance: Secondary ice formation, ice growth, instrumentation testing

• Ice formation mechanisms• Laboratory methodologies of old and new • What have we learned about about homogeneous freezing and

what remains?• What have we learned or not learned about heterogeneous ice

nucleation?– Mineral dust revisited: The major source of atmospheric IN?– Soot: Effective or not?– Organics aerosol components and ice nucleation– Real-time assessment of IN composition by mass spectrometry

• Need synergy with theory, modeling and field studies (will allude to)• The future

June 7, 2004June 7, 2004

Lab studies

Field Studies

theory

Numerical modeling

Science according to one “lab” person

June 7, 2004June 7, 2004

Ice nucleation mechanisms

A B C D E F G

RH

Homogeneous Heterogeneous

T

: dissolved solute (haze) : Ice particle

: non-dissolved solute particle

: Insoluble particle

Key:

June 7, 2004June 7, 2004

Some examples of ice nucleation studies instrumentation

Drop freezing devices Aerosol flow tubes (AFTIR)

June 7, 2004June 7, 2004

More instrumentation

Electrodynamic balance Diffusion chamber (filter processor)He

- Ne

lase

r

injector

positioncontrol

CCD -

trap electrodes

camera

CCD - line

Cloud Chamber (AIDA in this case)

230

232

234

236

238

240

Tem

pera

ture

(K)

0 5 10 15

Time (min)

800

850

900

950

1 000

Pre

ssur

e(h

Pa)

4 K/min 0.1 K/min

Moderate expansion cloud chamber:

T Range: 0 to –90 °C

P Range: 0.01 to 1000 hPa

Ice saturation by ice coated walls

AerosolChamber

HeatExchange

ThermostatedHousing

Vacuum Pump

Aerosol andTrace GasInstrumentation

Volume expansion at constant wall temperature:

• Cooling rates 0.1 to 4 K/min

• RHi increase up to 100 %/min

• RHi: > 160 %

• Duration of expansion 30 min

June 7, 2004June 7, 2004

Measuring ice formation by aerosols in the laboratory or Measuring ice formation by aerosols in the laboratory or atmosphere atmosphere [Continuous flow diffusion chamber (CFDC) – Rogers et al., JAOT, 2001; Now [Continuous flow diffusion chamber (CFDC) – Rogers et al., JAOT, 2001; Now

used in US, UK, Japan, Canada, Switzerland (soon)]used in US, UK, Japan, Canada, Switzerland (soon)]

1 -

1.5

m,

5 -

30 s

20

40

60

80

100

120

140

160

180

0.0 0.2 0.4 0.6 0.8 1.0

Fractional Distance from Cold Wall

Re

lati

ve

Hu

mid

ity

(%

)

-60

-50

-40

-30

-20

-10

0

Te

mp

(oC

); V

el

(cm

s-1)

RHw(%) RHi(%) Tx(C) Vel. (cm/s)

Ammonium sulfate

0.1

1

10

100

0 1 2 3 4 5 6 7 8

Diameter (m)

Co

nc

. (c

m-3

m

-1)

92% RH86% RH

or LCVI

June 7, 2004June 7, 2004

Homogeneous freezing: We believe we quantitatively understand spontaneous freezing of “pure” water, but…issue:

Surface vs. volume nucleation Surface crystallization of supercooled water in clouds

(A. Tabazadeh, Y. S. Djikaev, and H. Reiss; PNAS, 2002)

June 7, 2004June 7, 2004

Homogeneous freezing of solution drops: Dependence on water activity and freezing point depression - composition irrelevant?

• Water activity is defined by freezing point depression experiments (Robinson and Stokes, 1965), so stands to reason that both ideas work as parameterizations of homogeneous freezing nucleation. Both ideas can be formulated to predict nucleation rates (numerous authors).

Freezing temperatures of solute emulsion drops collapse onto constant water activity difference between solution and ice (Koop et al. 2000)

Freezing conditions of different solute drops is related to melting temperatures by a relatively constant factor (DeMott 2002, via Sassen via Rasmussen)

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Ice

Sat

urat

ion

Rat

ioS

ice

190 200 210 220 230 240

Temperature (K)

Exp A (180 hPa)

Exp B (1000 hPa)

Exp B (800 hPa)

Exp B (180 hPa)

Exp C (1000 hPa)

J=5x10 cm s8 -3 -1

J=1x10 cm s13 -3 -1

Water Saturation

Homogeneous freezing of sulphuric acid droplets (AIDA)

Based on Koop et al. 2000

June 7, 2004June 7, 2004

Water activity relation works for many substances, but…ammonium sulfate is a “bugger”

195

205

215

225

235

245

255

265

275

0.40.50.60.70.80.91

Water activity aw

Tem

per

atu

re (

K)

Koop et al. 2000

Bertram et al. 2000-emulsions

Prenni et al. 2000-AFTIR 100%

Chelf and Martin2000-AFTIR onset

Cziczo and Abbatt1999-AFTIR onset

Hung et al. 2002-AFTIR 50%

Chen et al. 2000-CFDC, F = 0.001

Chen et al. 2000-CFDC, F = 0.01

Mangold et al. 2004-AIDA (my guess)

aw(ice)

Need data as nucleation rate!

June 7, 2004June 7, 2004

• Organics appear to impact kinetics of homogeneous freezing or are preferentially delayed in freezing compared to sulfates (DeMott et al. 2003, Cziczo et al. 2004) – Talk by D. Cziczo tomorrow

• Soluble diacids seem not to be the answer (next slide)• Organic carbon fraction delays ice formation (Mohler et

al. 2004) – see later

Another issue: Impacts on homogeneous freezing associated with presence of organics

June 7, 2004June 7, 2004

CFDC lab studies of ammonium sulfate-dicarboxylic acid mixtures – phase state changes are more important than composition

100 nm particles (1% frozen)

130

135

140

145

150

155

160

165

170

175

180

-65 -60 -55 -50 -45 -40

Temperature (oC)

RH

ice (

%)

Pure ammonium sulfate1:1 malonic/sulfatePure malonic acid strongly driedpure malonic acid pre-deliquesced

RHw = 100%

90%

S. Brooks and A. Prenni

June 7, 2004June 7, 2004

Homogeneous and heterogeneous nucleation at low Homogeneous and heterogeneous nucleation at low temperatures on ambient tropospheric aerosol particles and temperatures on ambient tropospheric aerosol particles and

suggested impacts on cirrus (“take the lab to the field”)suggested impacts on cirrus (“take the lab to the field”)

Gierens (2003): “critical” concentration of heterogeneous IN triggering a switch of predominant mechanism from homogeneous freezing to heterogeneous nucleation, as a function of T and updraft speed

Synoptic lifting and Subvisual cirrus

Smaller scale wave forcing and anvil cirrus

w

DeMott et al. 2003, PNAS

Homogeneous freezing

Heterogeneous nucleation

June 7, 2004June 7, 2004

Homogeneous freezing on natural aerosol particles Homogeneous freezing on natural aerosol particles compared to laboratory surrogatescompared to laboratory surrogates

Homogeneous freezing of pure sulfates from Chen et al. (2000) or Koop et al. (2000)

NASA-SUCCESS RHi inside/outside cirrus, |w|<|1m/s (Jensen et al., JGR, 2001)

water saturation

Ice saturation

June 7, 2004June 7, 2004

What is the dominant composition of What is the dominant composition of heterogeneous ice nuclei?heterogeneous ice nuclei?

Statistics of PALMS cluster analyses of particle types

20% industrial20% industrial80% mineral dust (1/4 80% mineral dust (1/4 with any detectable S)with any detectable S)

June 7, 2004June 7, 2004

Laboratory studies of ice formation by mineral dust Laboratory studies of ice formation by mineral dust type particlestype particles (Archuleta et al. 2004) (Archuleta et al. 2004)

120

125

130

135

140

145

150

155

160

165

170

175

180

-65 -60 -55 -50 -45 -40

Temperature (°C)

RH

i(%)

50 nm100 nm200 nm

RHw = 100%

FeFe22OO33

120

125

130

135

140

145

150

155

160

165

170

175

180

-65 -60 -55 -50 -45 -40

Temperature (°C)

RH

i (%

)

50 nm + H2SO4100 nm + H2SO4200 nm + H2SO4

RHw = 100%

FeFe22OO33 + H + H22SOSO44

H2SO4

“shell” freezes

Pure H2SO4 homogeneously freezes

June 7, 2004June 7, 2004

Can heterogeneous freezing be parameterized using Can heterogeneous freezing be parameterized using concepts applied to homogeneous freezing? – concepts applied to homogeneous freezing? –

Seems so.Seems so.

200

210

220

230

240

250

260

270

0.40.60.81

Water Activity (aw)

Te

mp

era

ture

(K

)Treated Al2O3

(200 nm)Thet0

ΔTm

ΔTm

aiw

Bulk Freezing T

Δaw

200

210

220

230

240

250

260

270

0.40.60.81

Water Activity (aw)

Te

mp

era

ture

(K

)Treated

Al2O3

(200 nm)Thet0

ΔTm

ΔTm

aiw

Bulk Freezing T

Δaw

Coating freezing homogeneously

June 7, 2004June 7, 2004

Ice nucleation size effects versus classical theory. Active site theory may do better.

120

130

140

150

160

170

180

210 220 230 240

Temperature (degK)

RH

ice (

%) theory (m=-0.1)

theory (m = -0.1)100 nm data200 nm data

Fe2O3 coated

with H2SO4

June 7, 2004June 7, 2004

Resuspending actual dust samples (Asian dust – Archuleta Resuspending actual dust samples (Asian dust – Archuleta et al. 2004)et al. 2004)

200 nm

200 nm

Ca, Si, S, Mg

Si, Al, Fe

Homogeneous freezing points of sulfuric acid aerosols

Heterogeneous nucleation by dust

120

125

130

135

140

145

150

155

160

165

170

175

180

-65 -60 -55 -50 -45 -40

Temperature (°C)

RH

i(%)

50 nm100 nm200 nm

RHw = 100%

June 7, 2004June 7, 2004

Natural dust samples (nucleation mechanism unknown)

100

110

120

130

140

150

160

170

180

-65 -55 -45 -35 -25 -15TEMPERATURE (oC)

RH

i (%

)

AZ - 100 nm

AZ - 200 nm

AZ-AIDA (d=350nm, s=1.5)

Asian - 200 nm

Asian - 100 nm

OL - 200 nm

RHw = 100%

90%80%70%

• CFDC (K. Koehler) and AIDA (Mohler) studies of one test dust agree on sense of size effects

• Hygroscopic dusts (OL) are less effective in CFDC (insoluble size?)

• Unusual (?) uniformity of Arizona and Asian sample

June 7, 2004June 7, 2004

Combustion soot as an ice nucleus (AIDA studies). Contrast with some other studies suggest morphology,

surface properties, chemistry are important.

1.0

1.2

1.4

1.6

1.8

2.0

2.2Ic

eS

atur

atio

nR

atio

180 190 200 210 220 230 240

Temperature (K)

p /pw,0 ice,0

Hom IN ( a=0.303)Soot

SA Coated Soot

SA (ACP 2003)

AIDA 2003

June 7, 2004June 7, 2004

Two expansions at identical pumping speed and temperature profiles

0

100

200

300

C(c

m)

n,ic

e-3

0 200 400 600 800 1 000

Time (s)

202

204

206

208

210

212

T(K

)g

100

150

200

RH

i(%

)

16% OC

40% OC

0

2 500

5 000

7 500

10 000

I(a

.u.)

scat

t

0

500

1 000

1 500

C(c

m)

n,ae

-3

800

850

900

950

1 000p

(hP

a)16% OC

40% OC

FTIR

PCS2000

CPC3010

6000 5000 4000 3000 2000 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

6000 5000 4000 3000 2000 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

optic

al d

epth

wavenumber / cm-1

16 % OC

t = 20s t = 20s

optic

al d

epth

wavenumber / cm-1

40 % OC

16% OC content:Many ice particles

40% OC content:Less ice particles

June 7, 2004June 7, 2004

AIDA Studies Summary (Möhler and colleagues)

Aerosol Mixed Cloud CirrusSpark generator soot Immersion freezing Deposition freezing

SIN ≈ 1.1 to 1.3

SA coated soot Immersion freezing SIN ≈ 1.4 to 1.6

Flame soot (-60 °C) Increasing OC content suppresses IN

Arizona Test Dust (ATD) Deposition freezing, SIN ≈ 1.0 to 1.2.

Highest IN temperature: -15°C.

Large fraction of activated mineral particles.

Saharan Dust (SD2

Asian Dust (AD1)

Liquid activation and homogeneous freezing around -35°C.

Very few deposition nuclei.

Immersion freezing at higher T (up to -5°C).

Deposition nucleation starts at SIN ≈ 1.05 to 1.15.

Number of particles activated at low RHi increases with decreasing T.

Two IN modes at intermediate T (-50°C)

Lab studies of processed natural ice nuclei suggest Lab studies of processed natural ice nuclei suggest need for parameterizations based on aerosol properties need for parameterizations based on aerosol properties

rather than generalization of concentrationsrather than generalization of concentrations

0.01

0.1

1

10

100

1000

-35 -30 -25 -20 -15 -10 -5 0

Series1

Series2

Series3Meyers et al.

INSPECT (>-35C)

INSPECT (<-38C)

June 7, 2004June 7, 2004

Some thoughts on future studies• What are the fundamental ice nucleation mechanisms (e.g., Cantrell, Shaw talks tomorrow)?• Investigations of missing primary or secondary mechanisms• New and improved instruments needed, especially for examining the role of different ice nucleation mechanisms• Need for relatively portable instruments that have utility in both the laboratory or on aircraft• To what extent are we missing information with existing instrumentation due to kinetics of nucleation and influence of preactivation processes?• Continued studies of IN morphology, chemistry, and attempts to tie such properties explicitly to IN activity (e.g., no overarching

parameterizations that ignore aerosol properties)• What are the various influences of organic and inorganic carbon compounds on ice nucleation?

– Combustion byproducts, surface active types, biomass burning-related• Biological ice nuclei: Do they play a significant role?