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Email: marcelo.guzman uky.edu. Third Workshop on Air-Ice Chemical Interactions Columbia University, New York, June 6, 2011. A Photochemical Mechanism of Model Organic Matter in Ice. Marcelo I. Guzman 1 and Michael Hoffmann 2 - PowerPoint PPT Presentation
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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]
Guzman et al. (2006) J. Phys. Chem. A, 110, 931
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
Guzman et al. (2007) J. Geophys. Res., 112, D10123
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)
Guzman et al. (2007) J. Geophys. Res., 112, D10123
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
Guzman et al. (2006) J. Phys. Chem. A, 110, 3619
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
Guzman et al. (2006) J. Phys. Chem. A, 110, 3619
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