organics and sea salts (human health)
TRANSCRIPT
Unusual oxidation mechanism for unsaturatedorganics on sea salt
Federico Karagulian
Department of Chemistry, University of California, Irvine, CA, 92697-2025
Newport Beach (USA), January 2008
Sea salts (NaCl) are an excellent medium for reactions of pollutants and organics susbtances
Why Sea Salts aerosols?
+ =+ + O3O3
aerosols medium(NaCl)
Organic membranes
Polluted atmosphere (ozone formation)
As organism die, they decompose and the hydrophobic cellular constituents rise toward the ocean’s surface.
Marine aerosol particles are formed by mechanical ejection from the ocean’s surface and, as they form, they acquire a coating of hydrocarbon surfactants.
Organic membranes and sea salts
more agglomeration
NaCl crystal
less agglomeration
NaCl coated with OPPC
Cl-Na+Cl-Cl-
N+OP =O
O-
Na+ Cl-
O
Na+ Cl-Na+
R2
=
H
OO
=O
=
O
R1
Coating with OPPC
Phosphocholines constitute the most abundant class of phospholipids
NaCl coated with 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC)
Cl-Na+Cl-Cl- Na+ Cl-Na+ Cl-Na+
N+OP=O
O-
O
R2
=
H
OO
=
O=
O
R1
NaCl coated with 1-oleoyl-2-palmitoyl-sn-glycero-3-
phosphocholine (OPPC)
Phosphocholines
Phosphocholines are common organics floating on the oceans and coming from
living organisms (also important constituents of human lungs)
the experiment:
double bond
salt
Organic membrane(OPPC)
Model of marine aerosols pictures them as inverted
micelles
CH3
CH3
CH3
CH3
CH3
NaCl/H2O
hydrophobic
A major source of this organic layer is the decomposition of marine organisms, which have biomembranes that are mixture of lipids, hydrophobic proteins and carbohydrates (B. Alberts et al., 1989; G.B. Ellison et al., 1999)
Phospholipids and fatty acids (mainly C12-18) are common products of biomembrane disintegration (R.B. Gagosian et al.,1981; J.C. Marty et al., 1979)
After reacting with OH, O3 and O2,the marine aerosol particle become
coated with alcohol, aldehyde,ketone, and carboxylic functional group
O2, OH, O3
CHOHOCH2
HOOCCH3
NaCl/H2O
hydrophilic
DRIFTSDiffuse Reflection Infrared Fourier Transform Spectroscopy
DRIFTS
O3 + He + H2O
1.5x10-2
1.0
0.5
0.0
abso
rban
ce
1800 1600 1400 1200 1000 wavenumber (cm
-1)
1708 (R-CHO)
1347 (C-H)
1210
1110
1385 (O-C-H)
1751 (R-COOH)
-10x10-3
-5
0
5
abso
rban
ce
3100 3050 3000 2950 2900 2850 2800 2750wavenumber (cm
-1)
2948 (-CH3-)
2850 (-CH2-)
2919 (-CH2-)
3008 (C=C)
Reaction of 2 ppm O3 with NaCl coated with OPPC at 0% RH
t
1.5x10-2
1.0
0.5
0.0
-0.5
abso
rban
ce
1800 1600 1400 1200 1000 wavenumber (cm
-1)
1708 (R-COH)
1347 (CH)
1261 (PO2)
-
1210 (C-O)
1110 (SOZ)
970 (-N(CH3)3
+
1385 (O-C-H)
1090 (PO2)
-
1751 (R-COOH)
0% RH 2% RH 10% RH 25% RH
Reaction of 2ppm O3 with NaCl/OPPC in the presence of water (100 min)
Classic Criegee mechanism
Hydroxyhydroperoxide(HHP)
R1-COOH
H2O2 + R1-CHO
PL carboxylic acid
H2O2 + R2-CHO
R2-COOH
2.0x10-2
1.5
1.0
0.5
0.0
abs(
SO
Z)
120100806040200time (min)
[O3] = 5.0 x 1013
cm-3
[O3] = 2.2 x 1013
cm-3
[O3] = 7.8 x 1012
cm-3
[O3] = 1.7 x 1012
cm-3
[O3] = 7.0 x 1013
cm-3
Kinetics
Unexpectedly, the final amount of SOZ increases with the O3 concentration
At high O3 concentration, SOZ converged to a common value (Karagulian et al., 2008)
Modified reaction mechanism
We found lifetime t for the primary ozonide (POZ) of ~ 100 ms, ([O3] ~ 100 ppb, ~ 50% RH)
Typical lifetime for the decomposition of POZ in solution is ~ 1 ms, (Mile et al., 1979)
POZ has as sufficiently long lifetime that can undergo further reaction with O3 and water vapor (F.Karagulian et al., 2008)
Summary
Secondary ozonide (SOZ) is not the only species formed on the surface, also primary ozonide (POZ) is sufficiently stable to undergo secondary reactions… …this is a very nice “interface” finding. POZ may react with O3 or H2O in addition to decomposition (F.Karagulian et al., 2008)
In polluted and dry areas such as Mexico City with O3 peaks of ~ 400 ppb and RH ~ 20 %, the lifetime of the POZ is about 90 ms for reaction with O3 and 5 ms for reaction with H2O.
Stable SOZ may be formed in the atmosphere at low RH or if the double bond is protected from water
John GreavesUCI MS facility
Acknowledgements
National Science Foundation
AirUCI
Barbara Finlayson-Pitts’s group
W.R. Wiley Environmental Molecular Science Laboratory Pacific Northwest National Laboratory (PNNL)