Transcript Laboratory results and future needs

Laboratory Studies of Ice
Initiation by Atmospheric
Aerosol Particles
Paul J. DeMott
With acknowledgment to numerous contributors
June 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, 2004
Science according to one “lab” person
theory
Lab studies
Numerical
modeling
Field Studies
June 7, 2004
Ice nucleation mechanisms
Key:
: dissolved solute (haze)
: Ice particle
: non-dissolved solute
particle
: Insoluble particle
Homogeneous
Heterogeneous
T
RH
A
B
C
D
E
F
G
June 7, 2004
Some examples of ice nucleation
studies instrumentation
Drop freezing devices
Aerosol flow tubes (AFTIR)
June 7, 2004
More instrumentation
Electrodynamic balance
Diffusion chamber (filter processor)
CCD - lni e
po s itoi n
con tro l
ni ej c to r
CCD cam e ra
H e -N e al se r
trap
e el c trode s
June 7, 2004
Cloud Chamber (AIDA in this case)
Thermostated
Housing
Pressure (hPa)
1 000
950
900
850
800
Aerosol
Chamber
Aerosol and
Trace Gas
Instrumentation
Heat
Exchange
Temperature (K)
240
238
236
234
4 K/min
0.1 K/min
232
230
0
5
10
15
Time (min)
Vacuum Pump
Volume expansion at constant wall
temperature:
• Cooling rates 0.1 to 4 K/min
Moderate expansion cloud chamber:
• RHi increase up to 100 %/min
T Range: 0 to –90 °C
• RHi: > 160 %
P Range: 0.01 to 1000 hPa
• Duration of expansion 30 min
Ice saturation by ice coated walls
Measuring ice formation by aerosols in the laboratory or
atmosphere [Continuous flow diffusion chamber (CFDC) – Rogers et al., JAOT, 2001; Now
1 - 1.5 m,
5 - 30 s
used in US, UK, Japan, Canada, Switzerland (soon)]
or LCVI
Ammonium sulfate
92% RH
86% RH
10
-3
Conc. (cm m-1)
100
1
0.1
0
1
2
3
4
5
6
7
8
Diameter (m)
June 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, 2004
Homogeneous freezing of solution drops: Dependence on water
activity and freezing point depression - composition irrelevant?
Freezing temperatures of solute emulsion drops collapse onto constant water activity
difference between solution and ice (Koop et al. 2000)
•
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 conditions of different solute drops is related to melting temperatures by a
relatively constant factor (DeMott 2002, via Sassen via Rasmussen)
June 7, 2004
Ice Saturation Ratio Sice
Homogeneous freezing of sulphuric acid droplets (AIDA)
2.2
Based on Koop et al. 2000
2.0
1.8
1.6
Exp A (180 hPa)
Exp B (1000 hPa)
Exp B (800 hPa)
Exp B (180 hPa)
Exp C (1000 hPa)
J=5x108 cm-3s-1
J=1x1013 cm-3s-1
Water Saturation
1.4
1.2
1.0
190
200
210
220
Temperature (K)
230
240
Water activity relation works for many substances,
but…ammonium sulfate is a “bugger”
Koop et al. 2000
275
Need data as
nucleation rate!
Temperature (K)
265
255
aw(ice)
245
235
225
215
205
195
1
0.9
0.8
0.7
0.6
0.5
0.4
Bertram et al. 2000emulsions
Prenni et al. 2000AFTIR 100%
Chelf and Martin
2000-AFTIR onset
Cziczo and Abbatt
1999-AFTIR onset
Hung et al. 2002AFTIR 50%
Chen et al. 2000CFDC, F = 0.001
Chen et al. 2000CFDC, F = 0.01
Mangold et al. 2004AIDA (my guess)
Water activity aw
June 7, 2004
Another issue: Impacts on homogeneous freezing
associated with presence of organics
• 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
June 7, 2004
CFDC lab studies of ammonium sulfate-dicarboxylic acid mixtures
– phase state changes are more important than composition
100 nm particles (1% frozen)
180
175
170
RHice (%)
165
RHw = 100%
160
155
150
145
Pure ammonium sulfate
1:1 malonic/sulfate
Pure malonic acid strongly dried
pure malonic acid pre-deliquesced
140
135
90%
130
-65
-60
-55
-50
-45
-40
Temperature (oC) S. Brooks and A. Prenni
June 7, 2004
Homogeneous and heterogeneous nucleation at low
temperatures on ambient tropospheric aerosol particles and
suggested impacts on cirrus (“take the lab to the field”)
DeMott et al. 2003, PNAS
Homogeneous
freezing
Smaller scale
wave forcing
and anvil cirrus
w
Heterogeneous
nucleation
Synoptic lifting and Subvisual
cirrus
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
June 7, 2004
Homogeneous freezing on natural aerosol particles
compared 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)
Ice saturation
June 7, 2004
What is the dominant composition of
heterogeneous ice nuclei?
Statistics of PALMS cluster analyses of particle types
20% industrial
80% mineral dust (1/4
with any detectable S)
June 7, 2004
Laboratory studies of ice formation by mineral dust
type particles (Archuleta et al. 2004)
Fe2O3
Fe2O3 + H2SO4
180
180
175
170
Pure H2SO4
homogeneously
freezes
165
160
RHw = 100%
170
H2SO4
“shell”
freezes
165
160
155
RHi (%)
RHi(%)
175
RHw = 100%
150
145
155
150
145
140
140
135
135
130
130
50 nm
100 nm
200 nm
125
125
50 nm + H2SO4
100 nm + H2SO4
200 nm + H2SO4
120
120
-65
-60
-55
-50
-45
Temperature (°C)
-40
-65 -60 -55 -50 -45 -40
Temperature (°C)
June 7, 2004
Can heterogeneous freezing be parameterized using
concepts applied to homogeneous freezing? –
Seems so.
270
270
ΔT
ΔTmm
Bulk
T
Bulk Freezing
Freezing T
Treated
Treated
Al22OO33
Al
(200nm)
nm)
(200
Temperature
(K)
Temperature (K)
260
260
250
250
Thet0
het0
240
240
ΔT
ΔTmm
230
230
i
aaiww
220
220
Δaww
210
210
Coating freezing
homogeneously
200
200
11
0.8
0.6
0.6
0.4
0.4
Water Activity
Activity (a
(aww))
June 7, 2004
Ice nucleation size effects versus classical
theory. Active site theory may do better.
180
Fe2O3 coated
with H2SO4
170
RHice (%)
160
theory (m=-0.1)
theory (m = -0.1)
100 nm data
200 nm data
150
140
130
120
210
220
230
240
Temperature (degK)
June 7, 2004
Resuspending actual dust samples (Asian dust – Archuleta
et al. 2004)
Ca, Si, S, Mg
180
175
170
165
160
RHi(%)
Homogeneous
freezing points
of sulfuric acid
aerosols
RHw = 100%
200 nm
155
150
Si, Al, Fe
145
140
Heterogeneous
nucleation by
dust
135
130
50 nm
100 nm
200 nm
125
200 nm
120
-65
-60
-55
-50
-45
-40
Temperature (°C)
June 7, 2004
Natural dust samples (nucleation mechanism unknown)
•
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
180
AZ - 100 nm
170
AZ - 200 nm
RHi (%)
160
150
AZ-AIDA (d=350
nm, s=1.5)
140
Asian - 200 nm
130
RHw = 100%
120
110
100
-65
70%
-55
80%
-45
-35
-25
o
TEMPERATURE ( C)
90%
Asian - 100 nm
OL - 200 nm
-15
June 7, 2004
Combustion soot as an ice nucleus (AIDA studies).
Contrast with some other studies suggest morphology,
surface properties, chemistry are important.
2.2
pw,0/pice,0
Hom IN (a=0.303)
Soot
SA Coated Soot
SA (ACP 2003)
Ice Saturation Ratio
2.0
1.8
1.6
1.4
1.2
1.0
180
190
200
210
220
Temperature (K)
230
240
AIDA 2003
June 7, 2004
1 000
16% OC
40% OC
p (hPa)
950
900
850
800
212
Two expansions at identical
pumping speed and
temperature profiles
Tg (K)
210
208
206
202
200
RHi (%)
40% OC content:
Less ice particles
16% OC content:
Many ice particles
204
16% OC
40% OC
150
100
10 000
Iscatt (a.u.)
7 500
0.6
5 000
0.6
16 % OC
40 % OC
2 500
0.5
t = 20s
0.5
0.4
optical depth
500
0
300
FTIR
optical depth
0.4
200
t = 20s
CPC3010
1 000
Cn,ice (cm-3)
Cn,ae (cm-3)
0
1 500
0.3
0.3
0.2
0.2
0.1
0.1
0.0
6000 5000 4000 3000 2000 1000
0.0
6000 5000 4000 3000 2000 1000
100
PCS2000
0
0
200
400
Time (s)
600
800
1 000
wavenumber / cm
-1
June
7, 2004
wavenumber
/ cm
-1
AIDA Studies Summary (Möhler and colleagues)
Aerosol
Mixed Cloud
Cirrus
Spark generator soot
Immersion freezing
Deposition freezing
SIN ≈ 1.1 to 1.3
SA coated soot
Immersion freezing
Flame soot (-60 °C)
Arizona Test Dust (ATD)
SIN ≈ 1.4 to 1.6
Increasing OC content
suppresses IN
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)
June 7, 2004
Lab studies of processed natural ice nuclei suggest
need for parameterizations based on aerosol properties
rather than generalization of concentrations
1000
100
10
Series1
Series2
Series3
Meyers et al.
1
INSPECT (<-38C)
0.1
INSPECT (>-35C)
0.01
-35
-30
-25
-20
-15
-10
-5
0
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?
June 7, 2004