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)