Third Workshop on Air-Ice Chemical Interactions Columbia University, New York, June 6, 2011

A Photochemical Mechanism of Model Organic Matter in IceMarcelo I. Guzman1 and Michael Hoffmann2

1Department of Chemistry, University of Kentucky, Lexington, Kentucky, USA2Environmental Science & Engineering, Caltech, Pasadena, California, USAEmail: marcelo.guzman uky.edu

Third Workshop on Air-Ice Chemical Interactions Columbia University, New York, June 6, 2011

Relevant Processes in the Polar Environment

Organic Macromoleculesnatural waters

snowpacksatmospheric aerosol

Aromatic, ~ 450 Da

Aliphatic, <1000 Da

A Greenland Ice Core RecordDicarboxylic Acid: [Azelaic] (C9) 0.64 ng/g (MW: 188)a-Ketocarboxylic Acid: [Pyruvic] 0.23 ng/g (MW: 88)

What organics are found in in glacial ice?

Abundance in the fine (< 2 m) Arctic aerosol samples between January and April:

Kawamura et al. (2005) Atmos Environ 39, 599

oxalic acid26 ng/m3

OOH

OHO

pyruvic acid2 ng/m3

glyoxylic acid12 ng/m3

oxomalonic acid2 ng/m3

glyoxal2 ng/m3

OO

OOH

OOH

OOO

OHO

OOH

Goal: Photodecarboxylation mechanism in ice ice / fluid = ?

Boreal forest fires

Kawamura et al. (2001) JGR 106, 1331

Grannas (2007) Atmos Chem Phys 7, 4329

Organic Chromophores? Only dicarbonyl chromophores absorb at >300 nm…in the gas-phase However, in water most dicarbonyls exist as gem-diols… Certain carbonyls absorb in water in the UV, Pyruvic acid: 35% carbonyl

form at 300 K

UV Spectra of Organic Acids

Lund et al., Atmos. Chem. Phys. (2004), 4, 1759.

Marcelo I. Guzmán, University of Kentuckywww.guzmanlab.com

Frozen Aqueous Solutions

Menzel et al., (2000) J. Mag. Res.

> 99.9 % of the solutes accumulate in the unfrozen portion

selective incorporation of some ions

transient electrical potential

interfacial proton migration

NMR image of a sample of ice The sample diameter is 15 mm

Robinson et al. (2006) J. Phys Chem B, 110, 7613Grannas et al., (2007) J. Phys Chem A, 111, 11043Heger et al., (2004) J Phys Chem A, 109, 6702Guzman et al. (2006) J. Phys. Chem. A, 110, 931Kahan et al. (2007) J Phys Chem A, 111, 11006 Angell, C. A. In Water, a comprehensive treatise; Franks, F., Ed.; Plenum: New York, 1982; Vol. 7

Reaction rates and equilibrium in frozen solutionsconcentration effects

low temperatures

acidity changes

Aerosol-like Conditions

Assume 50% RH: 1 g NH4HSO4 / 0.6 g H2O

1 - 10 mg Pyruvic acid/g Sulfate

0.02 M to 0.2 M PAl > 300 nm

FLamp = 6 to 48 1014 photons cm-2 s-1

1 atm air or 1 atm N2 or 1 atm O2

Fsun 6 1015

Guzman et al. (2006) J. Phys. Chem. A, 110, 3619

This work: 5 to 200 mM

www.guzmanlab.com

Frozen Aqueous Pyruvic Acid Solutions:

Guzman et al. (2006) J. Am. Chem. Soc. 128, 10621

pyruvic acidPA

'carbonyl form'

2,2-dihydroxypropanoic acidPAH

'gem-diol form'

C C

O

CH3

O

HO

C C

OH

OHO

HO

CH3+ n H2O .(H2O)(n-1)kf

kr

www.guzmanlab.com

20% pyruvic acid is present as a carbonyl down to -35 ºC

QH = [PAH] / [PA]

3 2 HH

3

[CH C(OH) COOH] Q [PAH] K = [CH COCOOH] [PA] n n n

w w wa a a

Measurement Technique: Solid-State MAS NMR

Probe of water availability in frozen media

Number of water molecules involved at 293 K: n0 1 and n1 7

Reaction products?Mechanism?

Wavenumber/cm-17501500225030003750

Tran

smita

nce/

%

40

50

60

70

80

90

100

CO2CO2

no CO

H2O

H2O

Experimental SetupPhotolysis Experiments

Photochemical reactor

a

e

d

c

b

FTIR

PC

CELL REACTOR

MICROPUMP

COOLING BATHPhotolysis Experiments

Photochemical reactor

a

e

d

c

b

FTIR

PC

CELL REACTOR

MICROPUMP

COOLING BATH

1

2

3

h

3

+H+3 3 3 2[CH C(O)C(O)OH] CH C(O)C(O)O CH C(O) + CO

33 3[CH C(O) CH C(OH)C(O)OH]


Photogeneration of Distant Radical Pairs in Frozen Pyruvic Acid Solutions

www.guzmanlab.com

Evolution of CO2 during the 313 nm photolysis of frozen PA solutions

t/min0 30 60 90 120 150 180 210

CO2/A

.U.

0.0

0.2

0.4

0.6

0.8

1.0

T/K

110

120

130

140

150

Recombination?Ruzicka at al. (2005) J. Phys. Chem. B, 109, 9346

1000/T3.8 4.0 4.2 4.4

log

([CO 2]

/ mM

)

-0.6

-0.4

-0.2

0.0

0.2

immediately after photolysisbefore thawingafter thawing

Photochemistry of Pyruvic Acid in Ice

[CO2] = A + B [1 - exp(- kD time)] Thermodynamics of CO2 Release

DH = 6.44 kJ/mol

CO2 evolves during & after irradiation. Post-irradiation CO2 increases with rate constants kD(T)

t/min0 240 480 720 960 1200 1440

[CO 2]/

mM

0.0

0.2

0.4

0.6

0.8

1.0

T/K

250

260

270

280

290

300

turn-off light

Guzman et al. (2007) J. Geophys. Res., 112, D10123

Post-irradiation CO2 Release

t/min-60 0 60 120 180 240 300

[CO

2]/[C

O2] to

tal

0.0

0.2

0.4

0.6

0.8

1.0

T/K

240

250

260

270

280

0.10 M PA0.01 M BF

turn-off light1) Photolysis at l = 313 nm:

PA 60 min h BF 15 min h

2) Turn-off light

3) Observe CO2 release vs. time

benzoylformic acidBF

OOH

O

h

benzaldehydeO

+ CO2


Pyruvic Acid (PA) photoproduct D thermally releases CO2 in a reaction impeded by the ice matrix

Ea,D = 22.8 kJ/mol in ice (96 kJ/mol @ 298 K) vs. H-bond in ice: ~21 kJ/mol

AD-factor = 12.1 s-1 (1.7 1013 s-1 @ 298 K)


Activation Energy (Ea,D) for Thermal CO2 Release of Species D

1) Photolysis of frozen 0.1 M PA at constant T and l = 313 nm

2) Turn-off light after 60 min

3) Measure kD for thermal CO2 release

4) Plot kD vs. 1/T between

227 K < T < 268 K1000/T(K )

3.8 4.0 4.2 4.4

log

(kD

/ s-1

)

-4.2

-4.0

-3.8

-3.6

-3.4

-3.2

log (kD/s-1) = 1.08 -1191/T

Photoproduct D thermally releases CO2 in a reaction impeded by the ice matrix

min5 10 15 20 25

0

100000

200000

300000

400000

500000

600000

C

B A

HPLC ESI MS (-)

PEAK A

PEAK B

CID 100 V

PA

Rela

tive

Abun

danc

e

0

1

0

1

0

1

0

1

0

1

0

1

0

1

m/z-

80 100 120 140 160 180 200 2200

1

A

B

C

D

E

F

G

H

12C-PA, 87

13C-PA, 90

13C-A

13C-B

12C-A

12C-B

177

183

175

182

12C-A, 100 V

12C-B, 100 V

13111587

87

177

175

ESI MS (-)

Product Analysis3 4 7

Retention time (min)

Inte

nsity

(a.u

.)

Rel

ativ

e A

bund

ance

m/z-

lnm

250 300 350 400 450

0

1

2

3Abso

rban

ce/1

0-3

0

1

2

30

1

2

3

A

B

C

PA

4.1

6.9

UV SPECTRA

Pyruvic acid

Peak B

Peak A

/ppm

050100150200

A

B

C

13C NMR SPECTRA

UV SPECTRA

Ethers Kimura


Abs

orba

nce/

10-3

(ppm)

PA

O O

OHh O O

OH

1 O O

OH

3ISC

PA

O O

OH

O O

OH

3+

H+

H+

O O

OCO2+

HO O

OHK

K

OH

OH

O

HOO

OHA PA

O O

OH

HO O

OH

C

O O

OH

HO O

OH

D

C O

O

HO O

OH

C O

B

CO2

**

•C

O

TEMPO

N

O•

Reaction Mechanism

Guzman et al. (2006) J. Phys. Chem. A, 110, 3619; (2007) J. Geophys. Res., 112, D10123

5 to 200 mMB is favored in:1) higher [PA]o (fluid solutions), or2) the concentrated nanoscopic environments in ice

1000/T3.8 4.0 4.2 4.4

log

CO2

-0.1

0.0

0.1

Quantum Yields for the Overall CO2 Production in Fluid and Frozen Solutions

Solution @ 293 K:BFCOBF 2 2

CO2a

Rate of overall CO formation from BF0.38Rate of light absorption I

R

PACOPA 2 2

CO2a

Rate of overall CO formation from PA 0.78Rate of light absorption by BF I

R

Log (CO2) = 0.81 - 338/T @ T < 270 K

Frozen < 270 K:PA, < 270 K PA, 293 K0.7eff eff

extrapolatedCO2experimentalCO2

0.45For PA at 293 K: 0.60.78

Guzman et al. (2007), J. Geophys. Res., 112, D10123

date / years A.D.1000 1200 1400 1600 1800

DCO

2 / p

pmv

-5

0

5

10

15

20

D CO

/ ppb

v

0

20

40

60

80

100

S(CO2)/S(CO) ~ 200

(▼) DCO2 and (Δ) DCO mixing ratios between Greenland (GRIP and Eurocore) and Antarctic (Vostok) ice core records versus mean gas age

Photolysis of dissolved organic matter in surface ocean waters: (CO2)/(CO) ~ 50

A Natural Experiment for the Photo-productionof CO and CO2 in Ice

Guzman et al. (2007), J. Geophys. Res., 112, D10123

Photochemistry of Model Organic Matter

Rincon et al., (2009) J Phys Chem A, 113, 10512

stageI II III IV V VI

abun

danc

e (a

.u)

0

50

100

150

200

250

average mass (Da)

0

50

100

150

200

250

300

350

Total ion abundance & average ion mass

time/h0 10 20 30 40 50

TOC

%

0

20

40

60

80

100

A B C D

Excitation Wavelength (nm)250 300 350 400 450 500 550 600

Emis

sion

Are

a

0.0

0.5

1.0

1.5

2.0

2.5

ExcitationWavelenght (nm)

300 400 500

Emis

sion

Max

ima

(nm

)

360400440480520

Area under the fluorescenceemission curves peak at 350 nm

J. Phys. Chem Lett., 2010, 1, 368

Rincon, et al.,(2009) J Phys Chem A, 113, 10512(2010) J Phys Chem Lett, 1, 368

Ketyl AlkoxylAcetyl

Initial Processes During Photolysis, [Pyruvic Acid] > 4 mM

Mechanism of the Photochemical Free Radical Oligomerization of Aqueous Pyruvic Acid Solutions

Mechanism of Polymerization

Guzman, et al.,(2006) J Phys Chem A, 110, 931(2006) J Phys Chem A, 110, 3619

www.guzmanlab.com

TEMPO

N

O•

Conclusions• Method to quantify carbonyl concentrations in ice

(20% for PA)• Carbonyl hydration in frozen solutions• Identification of radical pairs intermediates and

reaction products in water and ice• Reaction mechanism in ice• Quantum yields in ice• Ice core records implications• HULIS

AcknowledgmentsMichael Hoffmann

Caltech ESE

N. DalleskaCaltech Environmental

Analysis Center

S. HwangCaltech Solid State

NMR facility

A. J. ColussiCaltech ESE

Angela RinconUniversity of Cambridge

www.guzmanlab.com

• Paul Wennberg• John Seinfeld• Richard Flagan• Angelo Di Bilio

From Haan et al., Tellus (1998) 50 B, 253

CO production versus the time in liquid phase (solid line) or in solid phase at −20°C (dashed lines). Curves 1, 2, 3, 4 respectively correspond to the following samples: Eurocore (104 m); Eurocore (211.35 m); Vostok BH3 (108.6 m) and artificial gas-free ice. Curve 5 corresponds to the same test as curve 2 except that the meltwater was irradiated by UV for 1 hour 30.

CO, formaldehyde and acetaldehyde are produced upon irradiation of snow

Haan et al., (1998) Tellus 50 B 253Grannas and Shepson, (2004) BGC

Domine and Shepson (2002) Science, 297, 1506

• Previous studies: subM < [PA] < mM at pH 8.2

Ia = I0 [1 – exp(-2.303 l C)]

• For [PA] < 4 mM the formation rate of products

generated in the unimolecular decomposition of 3PA*

increase linearly with [PA] ( f[PA])

Kieber and Blough, (1990) Free Radical Res. Commun., 10, 109

Pyruvic Acid Concentration Effects

PA/mM0 20 40 60 80 100

0.0

0.1

0.2

0.3

0.4

0.5[PA]

K + [PA]A B


conditions: assume aw= 0.5

0.6 g H2O/1 g NH4HSO4

1 - 10 mg Pyruvic acid/g Sulfate 0.02 M to 0.2 M PA

Mechanism involves a bimolecular initiation process!

K = 158 mM

Pyruvic Acid Concentration Effects

CO2(g) released during irradiation of frozen, deareated aqueous PA (100 mM) doped with TEMPO at 253 K. (▲) without TEMPO; (▼) [TEMPO] = 0.25 mM;

(●) [TEMPO] = 1.00 mM; (■) [TEMPO] = 2.40 mM

t/min0 10 20 30 40 50 60

CO2/

mM

0.0

0.1

0.2

0.3

0.4 0.25 mM0.00 mM1.00 mM2.40 mM

Quantum Yields for the overall CO2 production in frozen solutions

Solution < 270 KBFCOBF 2 2

CO2a

Rate of overall CO formation from BF 0.38Rate of light absorption by BF I

R

Frozen: Log (CO2) = 0.81 – 338/T @ T < 269 K

PA PA PA PA BF BFCO CO CO COPA 2 2 2 2

CO PA PA PA2PA PAaa 0 a

BF BF

l CII I l C I l C 0.60.6 l Cl C

eff

eff effeff

eff

R R R R

400 BFPACOPA 2902

BF 400CO2 PACO2

290BFCO2

( ) ( )

( ) ( )0.6

lamp

lamp

A A dRR A A d

l l l

l l l

293 KH

< 270 KH

K 2.5 0.6K 4

PA, < 270 K PA, 293 K0.6eff eff

Third Workshop on Air-Ice Chemical Interactions Columbia University, New York, June 6, 2011

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Transcript of Third Workshop on Air-Ice Chemical Interactions Columbia University, New York, June 6, 2011