Secondary Organic Aerosol
Formation: Ozonolysis of
Terpenes
George Marston, Yan Ma and Rachel
Porter
Department of Chemistry
© University of Reading 2006
www.reading.ac.
Ronald Reagan
"The
American
Petroleum
"A tree
is a tree.
How
Institute
many more filed
do yousuit
have
against
to look the
at?"EPA
'66[and]
charged that the agency
was suppressing a
"Trees
cause
morefor
scientific
study
pollution
thanbe
fear it might
automobiles
do.” ‘88
misinterpreted.
The
suppressed study
reveals that 80 percent
of air pollution comes
not from chimneys and
auto exhaust pipes, but
from plants and trees."
‘79
Uncertaintues in Ozone Terpene Mechanisms:
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Background
• The ozonolysis of alkenes is important
for atmospheric chemistry:
Oxidation of VOCs
Generation of radicals
Generation of oxygenated
products
Secondary Organic Aerosol
(SOA)
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SOA Formation
• Acid products from the
ozonolysis of terpenes are
components of SOA and may lead
to particle formation
• Health implications
• SOA can have direct and
indirect effects on climate
change
Uncertaintues in Ozone Terpene Mechanisms:
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4
Alkene Ozonolysis
*
POZ
O
O
O
O
+ O3
O
+
O
CI
Criegee
Intermediate
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OH Formation
H
H
O
O
O
O
O
O
+ OH
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Terpenes
pinene
3carene
pinene
terpinol
ene
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-Pinene Ozonolysis Products
O
O
OH
O
O
OH
HO
O
O
O
O
OH
OH
OH
Pinonic acid
O
Pinic acid
Norpinonic
acid
O
O
HO
OH
OH
OH
O
O
O
Pinalic acid
Norpinalic
acid
Norpinic
acid
O
OH
O
OH
OH-pinonic
acid
Uncertaintues in Ozone Terpene Mechanisms:
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OH-pinalic
acid
8
First step
O O
O
O
k 1
+ O3
O
O
CI1
POZ
O
(1  )k1
O
O
CI2
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Aims
• To develop mechanisms for acid formation
in terpene ozonolysis
• To model results to provide input of
rate constants and branching ratios for
the Master Chemical mechanism
 To determine which channel (CI) gives rise to
which product
 To determine branching ratios for
decomposition of primary
ozonides
 To compare product yields from different
terpenes
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Methodology
Enone
+ O3
O
O
O
O
CI1
Enal
+ O3
O
O
O
O
CI2
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Experimental
• Static reaction chamber coupled to gas
chromatography / mass spectrometry / flame
ionisation detection
• Acid products trapped on filters and
derivatised to methyl esters (BF3/Methanol)
• Enal and enone synthesised from ozonolysis
of a suitable terpene
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-Pinene Results
4
O
OH
O
Yield / %
3
OH
2
O
O
Pinonic acid
Pinonic acid (acetic acid added)
1
OH
Pinic acid
Pinic acid (acetic acid added)
0
0
20
40
60
80
100
Relative Hum idity / %
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Enal Results
O
5
O
OH
Yield / %
4
O
OH
Pinonic acid
Pinonic acid (acetic acid added)
Pinic acid
Pinic acid (acetic acid added)
3
2
O
O
1
OH
0
0
20
40
60
80
100
Relative Humidity / %
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14
Enone Results
O
• Only Pinonic Acid and
Norpinonic Acid are observed
O
O
O
O
OH
OH
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Enone Results
O
0.2
Norpinonic acid
O
O
Yield / %
0.15
OH
0.1
from the enone
0.05
from ?-pinene
0
0
20
40
60
80
100
Relative Humidity / %
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Branching Ratio
O
O
O
CI1
O
O
O
CI2
O
+ O3
O
O
O
H2COO
CI1
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Pinonic Acid Formation
5
Pinonic acid
Yield / %
4
O
from the enone
from the enal
from α-pinene
enone + enal
3
O
OH
2
1
0
0
20
40
60
80
100
Relative Humidity / %
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-Pinene Summary
50%
50 %
+ O3
+ O3
O
O
O
O
O
O
CI1
CI2
+H20
OH
OH
O
O
O
OH
O
norpinonic acid
OH
O
pinic acid OH
OH
O
OH
norpinic acid
Uncertaintues in Ozone Terpene Mechanisms:
OH
O
OH
O
pinalic acid
O
O
pinonic acid
O
O
O
OH-pinonic acid
O
OH
O
norpinalic acid
UC, Davis,
OH
OH
O
OH-pinalic acid
19
3-Carene Yields
3.5
-pinene product yield / %
3
O
2.5
O
OH
2
y = 1.2435x
R2 = 0.8898
1.5
0.3
1
0.2
0.1
0.5
0
0
0.1
0.2
0.3
0
0
0.5
1
1.5
2
2.5
3
3-carene product yield / %
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20
3-Carene, Enone and Enal
O
O
3-carene
OH
Enal
Enone
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O
O
3-Carene and Enone
OH
0.1
Yield / %
Nor-3-caronic acid
O
0.05
0
0
20
40
60
80
100
Relative hum idity / %
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3-Caronic Acid Mechanism
O
OH
O
O
Isom.
OH
O
O
O
O
+ O2
OO
CI2
O
+ RO2
or HO2
O
O O
ester
channel
O
O
O
O
OH
CI1
stab.
+ H2O
3-Caron ic acid
O
O
OH
OH
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3-Carene Summary
32%
68%
+ O3
O
+ O3
O
O
O
O
O
CI2
CI1
decomp.
OH
stab.
+ H2 O
isom.
decomp.
OH
decomp.
OH
O
O
O
O
O
3-norcaronic acid
3-caronic acid
O
O
O
OH
OH
OH
OH
OH
O
O
OH
OH
3-caric acid
HO
3-caralic acid
O
O
O
3-OH-caronic acid
HO
OH
O
OH
O
OH
3-norcaric acid
O
3-norcaralic acid
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-pinene
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Mechanism
O
-pinene
O
O
O
O
+RO2
OO
-OH
+O2
O
OO
-H2CO
O
+O2
O
O
-pinene
O
O
OO
+O2
-OH
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O
+RO2
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O
Pinalic-4-acid
O
OH
O
O
O
92 % +
O
8 %
O
O
O
O
O
O
O2
OH
O
O
O
O2
Pinalic-3-acid
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OH
Pinalic-4-acid
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Terpinolene
93 %
+
O
O
O
O
7 %
O
O
OO
OO
O
O
O
O
OH
OH
Terpinolalic Acid Terpinolalic Acid
(a)
(b)
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Hydroperoxide Formation
80 %
+ O3
O
O
O
OO
OOH
OH
terpinolalic acid (a)
20 %
OOH
OH
O
O
terpinolalic acid (c)
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Hydroperoxide Formation
?
favoured over
O
O
O
O

O
Formation of
hydroperoxide directly
from quenching of nascent
Criegee Intermediates?
OH
M
O2
?
O
HO
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Summary
• Improvements in mechanisms
• Uncertainties:


O
Ring opening in pinene and
terpinolene
Intramolecular
Isom.
reactions
OH
O
O
O
O
Isomerisation
O
O
O
OH
O
O
+O2
OO
• Some quantitative data, but more
 Hydroperoxide
needed formation
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Acknowledgements
• Natural Environment Research Council
• University of Reading
• Dr Yan Ma
• Dr David Johnson
• Rachel Porter
• Dr Andy Russell
• Dr David Chappell
• Tim Wilcox
• Thomas Luciani
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Mechanisms
O O OH
+M
+ H2O
O
OH
H2O
O
O
O
O
CI1
Ester
Channel
O O
OH
Pinonic acid
O
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Mechanisms
O
O
Isom.
O
O
OH
O
OH
CI2
O
O
+ RO2
O
O
OH
Pinonic acid
or HO2
O
+ O2
O
OO
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O
OO
Mechanisms
O
O
.
Isom.
O
RO 2
O
OH
O
O
1
3
2
+ O2
Isom.
+O2
O
OH
O
OO
O
OH
5
O
8
OO
+ RO 2
+ RO2
or HO2
O
O
OH
OH
O
pinic acid
O
9
OH
O
CO 2
+ O2
O
+ RO 2
OH
+ O2
OO
10
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