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SURFACTANT BEHAVIOR IN ATMOSPHERIC AEROSOLS
Allison Schwier25 April 2013
2
The McNeill Group
McNeill Group
1 Postdoc2 Grad Students1 Fulbright Scholar1 Visiting Professor4 Undergrads
3
Aerosol-CIMS
4
Aerosol Chamber
Surfactants
N2O5 (g)
“Inverted micelle”Can also form other morphologies: lenses, crystals, oils or lamellar phases
hydrophilic
hydrophobic
5
Atmospheric Aerosols
Health EffectsAir Quality10 – 90% organic material
2 nm - 20 μm Aerosol composition can be solid, liquid, or complex
http://www.nytimes.com/2007/12/29/world/asia/29china.html?_r=1
6
MechanismPrimary
http://www.chem.wisc.edu/users/keutsch
Secondary
7
http://www.chem.wisc.edu/users/keutsch
8
1. Organic Films can depress surface tension
Cl-
H2
OH2O Na+
H2O
Cl-H2O
Na+
H2ONa+
Effects of Surfactants
3. Can affect trace gas uptake (N2O5, HO2, etc.)
2. Can affect water uptake
H2O
H2O
H2O
N2O5
N2O5
N2O5
Seinfeld & Pandis, 2006
3p p
A BS
D D 4 6
where and w s w
w w
M n MA B
RT
Kelvin/Curvature Effect:
Raoult/Solute Effect:
When Kelvin > Raoult
GROWTH
Köhler Theory- cloud condensation nuclei activity (CCN)
Unknowns:
• Complex systems
• Natural conditions untested (pH, salt, organics)
8
9
I. Under what aerosol conditions will an organic film
form?
Cl-
H2
OH2O Na+
H2O
Cl-H2O
Na+
H2ONa+Cl-H2O
Cl-
H2O
Na+
H2ONa+
Fatty acids
10
Oleic acid (OA) – C18H34O2
Stearic acid (SA) – C18H36O2
O
OH
O
OH
Oleic acid
Stearic acid
OH
O
Surface Tension Experimental Procedure
Bulk Solutions
Pendant Drop Tensiometry
11
2egd
H
Adamson & Gast,1997
e
density diff bt solution and gas phase
d equatorial diameter
H shape factor
Juza, 1997
.18 33 2 3 18 34 2 2
.18 35 2 3 18 36 2 2
C H O Na H O C H O H O Na 1
C H O Na H O C H O H O Na 2
Varying organic concentrations
12
Oleic Acid in 3.1 M AS, pH = 3
80
75
70
65
60
55
50
45
σ (
dyn
cm-1
)
0.080.060.040.020.00
C (mol C/kg water)
Stearic Acid in 3.1 M AS, pH = 3
80
70
60
50
40
30
σ (
dyn
cm-1
)
0.40.30.20.10.0
C (mol C/kg water)
Solution σo (dyn cm-1) a ×102 (K-1) b (kg water/mol carbon)
SA 78.5 2.4 ± 0.2 502.3 ± 128OA 78.5 0.92 ± 0.05 (7.3 ± 4.9) ×106
ln(1 )o aT bC
Varying salt concentration
13
1.7 mM Stearic Acid at pH 3
80
75
70
65
60
55
50
σ (
dyn
cm-1
)
543210
(NH4)2SO4 (M)
(NH4)2SO4
(NH4)2SO4 + SA
Varying pH of saturated solutions
14
80
70
60
50
40
30
20
σ (
dyn
cm-1
)
876543210
pH
NaCl(NH4)2SO4
H2OOA NaCl (NH4)2SO4
H2OSA H2O
Saturated oleic acid and stearic acid in saturated NaCl, (NH4)2SO4, and water with varying pH.
Long chain fatty acids form surface films at all
atmospherically relevant conditions.
Impact: Organic films could exist if surfactants are
present.
15Schwier, Mitroo, McNeill, Atmospheric Environment, 2012
IIa. Can we model surface tension and
light absorbing properties of complex
mixtures a priori ?
16
O
O
Methylglyoxal
Glyoxal
O
O
Glyoxal
O
O
Methylglyoxal
Glyoxal
O
O
Methylglyoxal
Aerosol-CIMS
Aerosol CIMS = Chemical Ionization Mass Spectrometer with a volatilization inlet flow
tube (VFT)
Low fragmentationHigh sensitivity (O~ppt)
17
Cross products make up to 55(±5%) product mass
HO
OH
OH
OH
OHO
O
HO
OH O
OHOH
O
O
OHOH
OH
HO
O
OH
OHO
OH OH
O
O
OH
OH
OHOH
HO
OH
OH
OH
OHO
O
HO
OH O
OHOH
O
O
OHOH
OH
HO
O
OH
OHO
OH OH
O
O
OH
OH
OHOH
OHO
HO O
OH
OH
CIMS Data
18
O
O
OH
O
S
O
OH
O
Hydrated G
Hydrated MG
MG - Sulfate
MG - MG
MG – MGMG -GG – G
MG -G
MG – MGMG -G
Hydrated MG
19
70
60
50
40
(d
yn c
m-1
)
86420
CMG (mol C/kg water)
MG + G Sareen et al. (2010)
ln(1 )o i ii
aT bC
Glyoxal Methylglyoxal
Glyoxal-Methylglyoxa
l
a 0 0.0185±0.0008
0.0189±0.0006
b 0 140±34 83±13a= (dyn cm-1 K-1); b= kg H2O (mol C)-1
Surface Tension
O
O
O
O
O
OH
OH
O
OH
OH
HO
OH
OH
HO
OH
OH
HO
HO
OH
OHO
20
Varying concentrations (1:1 G:MG) in 3.1 M AS
[ ] [ ]G MG
dAbs d G d MGl
dt dt dt
4 3
[ ][ ][ ] [ ][ ]II II
A B
d MGk MG NH k MG H O
dt
4 3
[ ][ ][ ] [ ][ ]II II
C D
d Gk G NH k G H O
dt
44 4
[ ][ ][ ] [ ][ ]II II
A C
d NHk MG NH k G NH
dt
33 3
[ ][ ][ ] [ ][ ]II II
B D
d H Ok MG H O k G H O
dt
Light absorbing products
21
2.0
1.5
1.0
0.5
0.0Abs
orba
nce
at 3
45 n
m (
AU
)
0.01 0.1 1 10 100Time (h)
A
B
2.0
1.8
1.6
1.4
1.2
1.0
0.8Abs
orba
nce
at 2
80 n
m (
AU
)
1.00.80.60.40.20.0
Time (h)
kAII 5 × 10-6
kBII 1 × 10-3
kCII 3.25 × 10-5
kDII 0.15
εG 750
εMG 7500
Self- and cross-reactions have the same rate-limiting step (protonation of the carbonyl)
Kinetic Model
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
353025201510Total organics concentration (mM)
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
3.02.01.00.0Salt Concentration (M)
C
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
43210
[H+] Concentration (mM)
A
B
2.0
1.5
1.0
0.5
0.0
Absorbance (A
U)
353025201510Total organics concentration (mM)
2.0
1.5
1.0
0.5
0.0
Absorbance (A
U)
3.02.01.00.0Salt Concentration (M)
C
2.0
1.5
1.0
0.5
0.0
Absorbance (A
U)
43210
[H+] Concentration (mM)
A
B
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
353025201510Total organics concentration (mM)
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
3.02.01.00.0Salt Concentration (M)
C
2.0
1.5
1.0
0.5
0.0
Ab
so
rb
an
ce
(A
U)
43210
[H+] Concentration (mM)
A
B
2.5
2.0
1.5
1.0Abs
orba
nce
(AU
)
1.00.80.60.40.20.0
Mole fraction glyoxal
1.0 0.8 0.6 0.4 0.2 0.0Mole fraction methylglyoxal
A B
C D
Cross-reaction products make up a
large fraction of product mass.
Absorption kinetics and surface tension can be modeled in
parallel.
Impact: Knowledge of reaction products might not be required to accurately
describe an aerosol system.Schwier, Sareen, Mitroo, Shapiro, McNeill, Environmental Science & Technology, 2010
22
23
IIb. Can we model surface tension of complex
reactive mixtures (up to 6 organics) a priori ?
ln(1 )o aT bC
24
( ) ( ) ln(1 )o i i ii
T T aT bC
( ) ( ) ln(1 )o i i ii
T T aT bC
2( ) ( ) ln(1 ) ln(1 )H O salt salt
salt
T T c aT bC kc bCc
2( ) ( ) ln(1 ) ln(1 )H O salt i i i salt i i
i isalt
T T c aT bC kc bCc
Henning et al. 2005
Schwier et al. 2010
How do we account for salt?
2 ways:Explicitly and ImplicitlyTuckermann et al. 2007
25
Complex Organic Mixture
OO
Methylglyoxal
Glyoxal
O O
Glyoxal
OO
Methylglyoxal
Glyoxal
O O
Methylglyoxal
Oxalic Acid
Succinic Acid
Acetaldehyde
Formaldehyde
26
Leucine + Acetaldehyde
What is the model missing??
~Structurally dissimilar molecule reaction pathways
27
Modeling structurally similar molecules is possible.
However, we are still missing key information about structurally
dissimilar molecules.
Impact: Can we use this information in Köhler
Theory?Schwier, Viglione, Li, McNeill , Atmospheric Chemistry and Physics Discussion, 2012
28
III. If an organic film is oxidized, how does this change the CCN activity?
Cl-
H2
OCl-
H2O Na+
H2O
Cl-
H2O
Na+
H2ONa+
O3
O3
O3
28
Sodium Oleate and Oleic Acid
Azelaic Acid
Nonanaldehyde (nonanal)
Nonanoic Acid
9-oxononanoic Acid
+
OH
HO
OH
H
O
O
OH
O
O
H
O
O
OH
O
OH
HO
OH
H
O
O
OH
O
O
H
O
O
OH
O
OH
HO
OH
H
O
O
OH
O
O
H
O
O
OH
O
OH
HO
OH
H
O
O
OH
O
O
H
O
O
OH
O
Humid conditions
Humid conditions
+
29
OH
O
DMA = Differential Mobility AnalyzerCPC = Condensation Particle CounterCFSTGC = Continuous Flow Streamwise Thermal Gradient Cloud Condensation Nuclei Counter
Methodology 0.001 M and 0.01 M SO0.05 M NaCl
CFSTGC
O3 + N2
Flow Tube Reactor
CPC
DMA
Drier
AtomizerTSI 3076
Sodium Oleate (SO) Solutions
Humidified N2
tr = 3 min
Control Experiments:0.001 M SO0.06 M Na2SO4
Oxidation controls with salt
Acidified Experiments
730
CCN Data
2
3
4
5
6
7
8
91
Crit
ical
SS
[%
]
3 4 5 6 7 8 9100
Critical Dry Diameter [nm]
0.05 M NaCl0.001 M SO.NaCl0.01 M SO.NaCl0.001 M SO
831
Comparison of CCN activity Non-acidified and Acidified
32
2
3
4
5
6
7
8
91
Crit
ical
SS
[%]
3 4 5 6 7 8 9100
Critical Dry Diameter [nm]
0.05 M NaCl0.01 M OA-NaCl0.01 M OA-NaCl-1 ppm O3
2
3
4
5
6
7
8
91
Crit
ical
SS
[%]
3 4 5 6 7 8 9100
Critical Dry Diameter [nm]
0.05 M NaCl0.01 M OA-NaCl0.01 M OA-NaCl-1 ppm O3
2
3
4
5
6
7
8
91
Crit
ical
SS
[%]
3 4 5 6 7 8 9100
Critical Dry Diameter [nm]
0.05 M NaCl0.01 M SO-NaCl0.01 M SO-NaCl-1ppm O3
2
3
4
5
6
7
8
91
Crit
ical
SS
[%]
3 4 5 6 7 8 9100
Critical Dry Diameter [nm]
0.05 M NaCl0.01 M SO-NaCl0.01 M SO-NaCl-1ppm O3
Ozone oxidation of acidified particles slightly decreases CCN activity at higher critical SS
32
Power Law Fits
κ-Köhler
3
3 2
4κ
27 lnd c
A
D S
/4where s a w
w
MA
RT
Petters & Kreidenweis, 2007
10
Power Log Fit
κ (avg)
0.001 M SO, Water, (fit to NaCl SS%) -1.491 0.118 ± 0.004
NaCl -1.503 1.378 ± 0.025
0.001 M SO, NaCl -1.474 1.187 ± 0.034
0.001 M SO, NaCl, 1 ppm O3 -1.464 1.170 ± 0.027
0.01 M SO, NaCl, H2SO4 -1.271 0.971 ± 0.079
0.01 M SO, NaCl, H2SO4, 1 ppm O3 -1.449 0.786 ± 0.024
Na2SO4 -1.503 0.872 ± 0.016
0.001 M SO, Na2SO4 -1.475 0.708 ± 0.037
0.001 M SO, Na2SO4, 1 ppm O3 -1.460 0.708 ± 0.024
0.01 M SO, Na2SO4, H2SO4 -1.370 0.615 ± 0.029
0.01 M SO, Na2SO4, H2SO4, 1 ppm O3 -1.374 0.548 ± 0.024
33
32
cS x
Köhler Theory Analysis
Inferred surface tension for acidified aerosols, assuming in-particle concentrations of 0.176 or 1.76 M oleate in either 8.6 M NaCl or 10.6 M Na2SO4.
σ (mN/m) [0.176 M] σ (mN/m) [1.76 M]Before
OxidationAfter
Oxidation (1ppm)
Before Oxidation
After Oxidation
(1ppm)
NaCl 69.1 72.9 55.5 67.4
Na2SO4 72.4 74.8 66.1 74.8
2 33 2256 1
27
o o o
o w ii i
w i
M
M
RT M
3/2cS d
where
i
ii
i o
i o
m
m m
Padró et al. 2007
34
Oxidation depresses CCN activity, especially for acidic aerosols; it
also makes the organic film disappear.
Impact: Can this change cloud nucleation?
Schwier, Sareen, Lathem, Nenes, McNeill, Journal of Geophysical Research, 2011
35
Surfactant systems in aerosols are incredibly complex
Organic films form at atmospherically relevant conditions
Modeling of reaction mixtures could be simplified depending on the organic species
Oxidation does not always increaseCCN activity
Conclusions
36
Cl-
H2
OH2O Na+
H2O
Cl-H2O
Na+
H2ONa+
Acknowledgements:
V. Faye McNeillDhruv Mitroo
Giuliana ViglioneNeha Sareen
McNeill GroupTerry Lathem
Athanasios NenesKoberstein Group
Funding:37
38
Back-up Slides
39
Impact
Direct Effect: scattering/absorbing solar radiation
Indirect Effect: cloud properties such as cloud lifetime and albedoAerosols mostly believed
to have a cooling effect
http://stratus.astr.ucl.ac.be/textbook/chapter4_node3_2.html
Global radiation budget and climate
Scientific Understanding is LOW
40
41
Taken from Isaksen et al. [2009], adapted from AR4 IPCC [2007]
Mechanisms(Hemi)acetal formation
Aldol Condensation
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
+
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
+
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
42
MechanismsImidazole Formation
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
OO
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
+
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2ONH
NHNH
NH
O
O
- H2ON
N
O
HN
N
O
4 2 3 32 2 2 2 NH H O NH H O
32 +NH22 H O
2 H O
O
O
OHO
HOHO O
O
O OH
O O
OHOH
O
O
O
O
O O
O O
OH O
OOH
O
2 NH4+ + 2 H2O 2 NH3 + 2 H3O+
2 NH3 +
O
O
-2 H2O NH
NHNH
NH
O
O
- H2O
N
N
OHN
N
O
43
Köhler Theory
21
32
4
4( ) 4
3
droplet purevapor
v l p T v
pl v p
l
G G G
G N g ng R N g
RG g g R
v
Consider the change of Gibbs free energy of formation of a single drop from a flat surface
Write in terms of vapor and liquid and curvatureRewrite and relate n to Rp
Evaluate gl-gv: Use Gibbs fundamental equation and laws of ideality, simplify, write in terms of pressure, integrate, and re-substitute
3 2
0
4ln 4
3
2exp
( ) 4exp
p pl
oA A
l p
w p w wo
w p
kTG R S R
v
Mp p
RT R
p D M
p RT D
Solve for maximum ΔG, then re-arrange in terms of saturation ratio
Kelvin Equation
Pure Water Droplet
Following Seinfeld & Pandis 44
Köhler Theory cont.Flat Water Solution
*
( ) ( )
exp ( )
w w
o os w w
w w
o os w w
g l
pK T
x RT
p x p
Write out chemical potential of gas phase and liquid phase in terms of partial pressures, activity coefficients, combine, simplify
Aqueous Solution Droplets
Combine these cases
3
3
( ) 4exp
( ) 4ln ln ln 1
( / 6)
( ) 4 6ln
w p w wo
w w p
w p w w s wwo
p p s s
w p w w s wo
w p p
p D v
p x RTD
p D v n v
p RTD D n v
p D M n v
p RT D D
Solve for molar volume, substitute, use dilute approximationSolve molar volume, write in terms of A and B 45
Empirical Model
( ) ln(1 )
( ) ln(1 )
w
w i i ii
T aT bC
T aT bC
Szyszkowski – Langmuir equation
Henning (2005) describes complex non reacting organic species by modifying the above equation:
σ and σw are the surface tension of solution and waterT is the temperatureC is the concentration of soluble carbon (mol C/kg water)a and b constants related to the organicχ Is the carbon content of each species (mol C/kg water)
46
“Salting Out”~ Salt ions surround themselves with a shell of water
Electrostriction~ Decreases amount of available water for organic~ “SALT IN” or “SALT OUT”
log log os s
o
SK C
S
γ and γo are activity coefficients of organic in salt and waterS and So are solubility of organic in salt and waterKs is Setschenow constantCs is salt concentration
Setschenow, 1889
Varies on factors such as polarity of the organic, and type of salt
47
Project 1
Control experiments:
At pH 1, ratio of dissociated vs. non-dissociated using pKa and pH, will remain mostly non dissociated at acidic conditions
Bulk depletion effects – used solid precipitate
Nitric acid effect on surface tension depression
48
Project 2
Time spent in aerosol form: 3.5 s, so oligomerization products were formed in bulk solutions
49
Project 3
Ozone concentration 0.2 & 1 ppm Particle concentration: 9 x 104 cm-3 , 200
nm diameter
Acidified aerosols, pH ~8 to pH ~0.4
Internally mixed aerosols: sum of components for κ-Köhler theory
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