effect of solute core curvature on solubility luz teresa padró april 26, 2004
TRANSCRIPT
Effect of Solute Core Curvature on Solubility
Luz Teresa PadróApril 26, 2004.
Introduction Aerosols are composed of:
Inorganic and organic matter
Implications of organics in cloud condensation nuclei (CCN) activity
Composition, structure and surface affect activation diameters at different supersaturations
Raymond and Pandis [2002] Studied cloud activation of single
component aerosol particles at 0.3% and 1% supersaturation 15 compounds
Hygroscopic secondary organics Hydrophobic primary organics
Compared results with classical Köhler theory and one that takes into account solubility
Results Theoretical and experimental
values do not agree Attributing this to the particles
solubility in water
More solute is being dissolved than that calculated by solubility studies Is the organic completely soluble?
0.3% Supersaturation
1% Supersaturation
Modification of Results
Assumed everything dissolved No core present
Theoretical and experimental values have better agreement Low solubility compounds activation
may be determined by the curvature or Kelvin effect alone
Complete Solubility Assumption
Köhler Theory
3
lnpp
o
pw
D
B
D
A
p
Dp
w
ws
w
ww
MnB
RT
MA
6
4
where:
pw(Dp) - water vapor pressure over the droplet diameter Dp
po - water vapor pressure over a flat surface at the same temperature
Mw - molecular weight of water
σw - surface tension of water
R - ideal gas constant
T – temperature
ρw - density of water
ns - moles of solute
Köhler Curves
Critical Parameters Dpc and Sc
Critical Droplet Diameter, Dpc
Critical Saturation, Sc
21
3
A
BDpc
21
3
27
4ln
B
ASc
Sc : Accounting for Solute
s
sss M
dn
6
3
21
3
3
27
4ln
sws
swc dM
MAS
where:
ν - van’t Hoff factor
ds - dry particle diameter
ρs - density of the solute
Ms - molecular weight of the solute
Compounds Studied Adipic acid Glutamic acid Glutaric acid Norpinic acid Pinic acid Pinonic acid
Method
Theory calculations: ns required by theory Dpc required for ns
mass of water in Dpc
nsolubility in mass of water
Ratio of ns/nsolubility for each compound
Theory to Solubility
ns/nA ns/nGR ns/nGM ns/nN ns/nPI ns/nPO
a 0.500 0.007 1.321 0.229 0.137 1.703
b 18.317 0.245 48.422 8.379 5.035 62.432
where:
A – adipic acid
GR – glutaric acid
GM – glutamic acid
N – norpinic acid
PI – pinic acid
PO – pinonic acid
Table 1. Theory to solubility ratio for (a) 0.3% supersaturation and (b) 1% supersaturation.
Method II Experimental Calculations:
nexperimental
Core diameters
Kelvin effect greater than 1? curvature enhanced-solubility
Theory to Experimental
ns/nA ns/nGR ns/nGM ns/nN ns/nPI ns/nPO
a 0.137 0.902 1.554 2.164 0.002 0.000
b 0.054 0.677 1.083 0.002 0.003 0.001
Table 2. Theory to experimental ratio for (a) 0.3% supersaturation and (b) 1% supersaturation.
Core diameter
dwA (cm) dwGR (cm) dwGM (cm) dwN (cm) dwPI (cm) dwPO (cm)
a1.57E-05 -4.56E-05 -4.21E-06 -1.79E-05 9.15E-05 1.14E-03
b1.06E-05 -1.43E-05 3.46E-06 4.20E-05 3.79E-05 5.00E-05
Table 3. Dry core diameter for (a) 0.3% supersaturation and (b) 1% supersaturation.
Mass Balance31
3 6
s
ssw
mdd
where:
dw – core diameter
ds – dry particle diameter
ms – mass of solute
Kelvin effect
Ccurved surface
/Cflat surfaceA
Ccurved surface
/Cflat surfaceGM
Ccurved surface
/Cflat surfaceN
Ccurved surface
/Cflat surfacePI
Ccurved surface
/Cflat surfacePO
a 1.0021 - - 1.0009 1.0001
b 1.0032 1.0180 1.0019 1.0021 1.0017
Table 4. Kelvin effect of compounds that have a core for (a) 0.3% supersaturation and (b) 1% supersaturation.
Summary of Results
Solubility shows no activation: at both supersaturations
glutamic acid and pinonic acid at 1% supersaturation
adipic acid, glutaric acid, norpinic acid and pinic acid
Summary of Results II Experiments shows no activation:
At both supersaturations glutamic acid
At 0.3% supersaturation norpinic acid
Kelvin effect > 1 Shows possibility of curvature-enhanced
solubility Will be studied using a dissolution kinetics model
Thank you!