1.
Aromatic hydrocarbon
oxidation
2. Uncertainty analysis
Mike Pilling
University of Leeds, UK
2nd December 2004
MCM meeting Leeds
Oxidation mechanisms initiated by OH
• Most NMHCs:
– Abstraction or addition followed by addition of
O2 to form peroxy radical.
– Peroxy radical reacts with NO to form an
alkoxy, which reacts to form HO2. Reaction
with NO regenerates OH.
– NO  NO2 from peroxy reactions  O3
• Aromatics:
– HO-aromatic-O2 is short lived, regenerating
reactants. Adduct is too short lived to react
with NO under normal atmospheric conditions.
– Intermediates are generally short lived cf
parent
2nd December 2004
MCM meeting Leeds
2
Oxidation Routes for
Toluene
+ OH/O2
O2
HO2
HO2
OH
O
OH
NO2
NO
HO2
O2
O
OH
O
O
O
b-Hydroxy
Peroxy
+ O2
O2
O
OH
O2
O
O2
HO2
NO2
HO2
O
O
O
O
O
O
O
+
+
O
OH
O
O
NO
O
O
O
Peroxide Bicyclic
2nd December 2004
O
Epoxy-Oxy
Products
Phenol
Products
Oxepin
Also routes to:
Benzaldehyde via abstraction
MeBenzoquinone via 1,4 addition
MCM1: Peroxide Bicyclic Route, predominantly
producing butenedial + methylglyoxal
MCM2: Oxepin Route, predominantly
producing muconaldehyde type products
MCM3.1 – latest mechanism
MCM meeting Leeds
3
Mechanism for toluene oxidation
• Reviewed up to ~2000 by Calvert et al.
• Main contributions to mechanism from the groups
of Atkinson, Becker and Seinfeld
• ~6% via abstraction from –CH3
• Rest via HO-toluene-O2 adduct:
– ~12% via retention of aromatic ring
– Addition of O2 to form bridged bicyclic
compound that leads to ring opening.
– Role of NO not clear
• Mass balance only ~50%
2nd December 2004
MCM meeting Leeds
4
Subsequent key results
from EUPHORE:
Spectroscopic expts
using DOAS
• Glyoxal, formed from the formation of the
bicyclic compound and ring opening is a primary
product only. (Volkamer et al, J Phys Chem, 2001,
105, 7865)
• Measurements of substituted phenol yields and
demonstration of the need to work at low NOx
(Volkamer et al , PCCP, 2002, 4, 1598)
2nd December 2004
MCM meeting Leeds
5
EXACT consortium
Effects of oxidation of aromatic compounds in
the troposphere (EU, Framework 5)
• Kinetics of elementary reactions in initial stages
(Bordeaux, Hanover)
• Kinetics and mechanisms of secondary chemistry
(Cork, Wuppertal)
• Development and testing of overall mechanism.
Design of EUPHORE experiments. (Leeds, Imperial
College)
• Synthesis of intermediates (Newcastle)
• Secondary aerosol formation (Wuppertal, Imperial
College)
• Photochemical chamber studies at EUPHORE
(Valencia, Wuppertal, Cork)
• Coordination (Leeds)
2nd December 2004
MCM meeting Leeds
6
Chamber measurements at Wuppertal
and Cork on kinetics of intermediates
ln([reactant]t /[reactant]t]-kwall,dill.t
0
OH
kOHa,b
kNO3b,c
Ortho
20.81.7
9.60.5
Meta
22.31.7 10.30.4
para
20.91.0
OH
1,0
CH3
OH
0,8
OH
0,6
CH3
OH
OH
0,4
0,2
0,0
0,0
tolualdehyde
0,1
0,2
0,3
ln([reference]t0/[reference]t) - kdillt
NO3 reactions, relative to
2,3 dimethyl 3 butene
(17, 15, 10)x10-11 cm3 s-1
9.60.4
0,4
a :10-12 cm3 molecule-1 s-1
vs butyl ether and 1,2,4 trimethylbenzene
b : 2s errors
c : 10-15 cm3 molecule-1 s-1
vs tetrahydrofuran
Also extensive measurements of products in reactions of intermediates,
especially of hydroxyarenes (Olariu et al)
Photolysis rates and mechanisms for g –dicarbonyls (Thuener et al)
2nd December 2004
MCM meeting Leeds
7
Toluene Oxidation Routes in MCMv3.1
+ OH
7%
18%
O2
HO2
OH
Low ozone
formation
route
HO
O2
O
O
65%
.
NO
O2
NO2
HO2
10%
HO
Products
O2
+O2
PHENOL
O2
O
O
O
Little ring opening
along phenol route
Successive addition of OH,
NO3. Leads to formation of
nitrophenols
O
HO
HO
H-ABSTACTION
O
NO
O2
O2
NO2
Ring opening routes are
most active photochemically
and dominate ozone formation
HO2
HO2
O
O
O
O
O
O
+
O O
O
O
+
O O
EPOXY-OXY
PEROXIDE BICYCLIC
2nd December 2004
MCM meeting Leeds
8
CEAM Labs, Valencia
FTIR: Aromatics, O3, HCO2H,HCHO, HNO3
Absorption spectroscopy: O3
Chemiluminescence: NO
DOAS: NO2, Glyoxal
LIF: OH, HO2
GC-ECD: PAN, Methylglyoxal, PAN
GC-FID: Aromatics
HPLC/UV: Cresols, Benzaldehyde
2nd December 2004
CO-Monitor: CO
2D-GC: carbonyls
PFBHA: intermediates
Derivatisation: Oxepin (Triazolin)
Glyoxal, Methylglyoxal
(Diaminobenzol)
Filterradiometer:J(NO2)
SMPS:
Particle size distribution
MCM meeting Leeds
9
Quantitative GCxGC of Toluene Oxidation Products
27/09/01 TOLUENE - LOW NOx EXPERIMENT
Difficult to detect
appropriate amounts of
coproducts of glyoxal and
Meglyoxal
0.18
6
Concentration (ppb)
Concentration (ppb)- PROVISIONAL
0.20
8
Benzaldehyde
4
0.16
Angelica/oxopentenal
0.14
0.12
0.10
0.08
0.06
2
0.04
0.02
0
0.00
Chamber opened
Chamber opened
-0.02
9
10
11
13
14
15
9
10
Time at end of sampling (hrs)
1.0
11
12
13
14
15
Measurements also made by
GC/ECD
Time at end of sampling (hrs zulu)
600
0.8
Tolueneconc
Me-benzoquinone
Concentration (ppb)
Concentration (ppb)- PROVISIONAL
12
0.6
0.4
0.2
500
400
Chamber opened
300
0.0
Chamber opened
9
10
11
12
200
13
14
15
Time at end of sampling (hrs)
9
10
11
12
13
Time at end of sampling (hrs)
14
15
Angelica lactone
/oxopentanal
Benzaldehyde
Me-benzoquinone
0.0
0.5
1.0
Toluene
row
1.5
2.0
unknown
2.5
3.0
Maleic anhydride
3.5
2nd December 2004
0
5
MCM meeting Leeds
10
15
col
20
25
10
5
1400
4
1200
3
1000
2
800
1
600
0
400
10
Measured [OH]
(LIF)
12
13
14
15
16
17
-1
200
-2
0
Time / hrs UT
5
R ( = [OH]LIF / [OH]Hydrocarbon Decay )
Test of [OH]
LIF calibration
11
Benzene vmr / ppbv
7
Inferred [OH]
Guggenheim (1926)
k' = ln (c2 / c1) / (t2 - t1)
[OH]HC = (k' - kdil) / kOH+HC
[OH] / 10 molecule cm
-3
Hydrocarbon
concentration
4
3
2
1
0
(1) Toluene
(2) 1,3,5-TMB
(3) Toluene
(4) Ethene
(5a) o-Cresol
FTIR
(5b) o-Cresol
HPLC
(6) p-Xylene
(7) Benzene
(8) Benzene
(9) p-Xylene
Hydrocarbon Species
2nd
December 2004
MCM meeting Leeds
11
Test of HO2 calibration
HO2 concentration evolution in the dark and
second-order decay analysis
5.E+09
5.E-09
[HO2]
1/[HO2]
Regression
4.E+09
4.E-09
-1
1/[HO2] /molec cm
[HO2] /molec cm
-3
3
UV Light
3.E+09
3.E-09
HCHO photolysis
No NOx
2.E+09
2.E-09
1.E+09
1.E-09
0.E+00
0.E+00
0
200
400
600
800
1000
Time / s
From decay analysis k(HO2+HO2) = 3.0 x 10-12 molecule-1cm3s-1
Literature (JPL 97-4) k(HO2+HO2) = 2.8 x 10-12 molecule-1cm3s-1
2nd December 2004
MCM meeting Leeds
12
Toluene Oxidation Routes in MCMv3.1
+ OH
7%
18%
O2
HO2
OH
Low ozone
formation
route
HO
O2
O
O
65%
.
NO
O2
NO2
HO2
10%
HO
Products
O2
+O2
PHENOL
O2
O
O
O
Little ring opening
along phenol route
Successive addition of OH,
NO3. Leads to formation of
nitrophenols
O
HO
HO
H-ABSTACTION
O
NO
O2
O2
NO2
Ring opening routes are
most active photochemically
and dominate ozone formation
HO2
HO2
O
O
O
O
O
O
+
O O
O
O
+
O O
EPOXY-OXY
PEROXIDE BICYCLIC
2nd December 2004
MCM meeting Leeds
13
Design of chamber
experiments
Ozone Isopleth Plot for
Toluene Chamber Experiments
1000
Initial NOx [ppb]
800
3
600
0
2
24
560
400
120
200
450
340
230
0
0
200
400
600
800
1000
Initial Toluene [ppb]
2nd December 2004
MCM meeting Leeds
14
Comparison of MCM3.1 to
Toluene Chamber Experiment (27/09/01)
400
Experiment
MCM3.1
500
300
400
O3 [ppb]
Toluene [ppb]
450
350
300
200
100
250
200
0
150
9 10 11 12 13 14 15 16 17 18 19
9 10 11 12 13 14 15 16 17 18 19
Time [h]
Time [h]
100
140
120
100
NO [ppb]
NO2 [ppb]
75
50
25
80
60
40
20
0
0
9 10 11 12 13 14 15 16 17 18 19
9 10 11 12 13 14 15 16 17 18 19
Time [h]
Time [h]
2nd December 2004
MCM meeting Leeds
Conclusions:
- Ozone overpredicted
but OH is too low. Need
early OH source that
doesn’t produce O3
- NO2 is not rapidly
enough
- Co-products of glyoxal/
Me glyoxal not detected
in sufficient concn
15
g-dicarbonyls. Photolysis (NO = 0) and ‘photosmog’
experiments (with NO)(Cork, Valencia measurements)
experiment
MCMv3.1
200
600
150
100
50
400
250
400
200
0
11.0
11.2
200
300
150
200
O3 [ppb]
800
experiment
MCMv3
MCMv3.1
Butenedial (04/07/02)
Butenedial[ppb]
250
HO2 [ppt]
Butenedial [ppb]
Butenedial (16/07/02)
100
0
0
11.4
11.0
Time [h]
11.2
100
50
11.4
10
11
12
13
14
15
10
11
Time [h]
Time [h]
12
13
14
15
14
15
14
15
Time [h]
60
140
8
50
6
20
10
2
40
NO [ppb]
30
100
4
NO2 [ppb]
Glyoxal [ppb]
40
CO [ppb]
120
60
20
0
11.2
11.4
11.0
Time [h]
11.2
10
11.4
12
13
14
15
10
11
Time [h]
12
13
Time [h]
15
2(5H)-Furanone
8
1.0x10
Maleicanyhdride
250
7
20
-3
5
0
11.0
11.2
200
11.4
Time [h]
7
6.0x10
7
4.0x10
7
2.0x10
11.0
11.2
11.4
10
Time [h]
100
0
11
12
13
Time [h]
MCM meeting Leeds
150
50
0.0
photolysis
December 2004
HO2 [ppt]
40
8.0x10
10
OH[molecule cm ]
60
0
2nd
11
Time [h]
MALANHY [ppb]
BZFUONE [ppb]
80
40
0
-2
11.0
60
20
0
0
80
14
15
10
11
12
13
Time [h]
photosmog
16
Butenedial
O
O
hv
0.4
0.6
O O
O
O +
HO2
+ RO2
+ HO2
0.7
0.3
0.6
O
O
5H-Furan-2-one
CH3
0.4
O
O
O
+ HO2
maleic anhydride
glyoxal
O
0.29
O
O
0.71
O
OH
O O
OH
O
+ HO2 + CO
+ CO2
O
H
O
or
O
O
h
R
R
CO
O
ketene
+
O
C
R= H: acrolein
O
R= CH3: methylvinylketone
R
O
O
2(5H)furanone
R
O
O
O
2(3H)furanone
O
+
MCM v3.1 photolysis
mechanism vs
photolysis observations
HCHO
O
maleic anhydride
2nd December 2004
MCM meeting Leeds
17
Searching for an OH production route
• Alkyl peroxy radicals
isomerise / dissociate to
from OH only at high T
• Modification of the
peroxy can lead to low T
production of OH:
e.g.
CH3CO + O2 → CH3CO3* →
OH + CH2CO2
CH3CO3* + M → CH3CO3
• Can such routes operate
in aromatic chemistry?
H O
H
O
H O
O
H
O
H OH
O
H
H
O
O
+ O2
OO
H O
H
OH
O
O
H
O
O
OH
O
H
O
O
O H
O
OH +
O
O
O
+ OH
O
O
2nd
December 2004
MCM meeting Leeds
18
EXACT-1 : Attempts to improve the model performance by
including an NO2 aerosol sink /HONO source and an early
source of OH
Alternative mechanisms are also feasible, e.g. Volkamer, O3 +
furanones
Toluene (27/09/01)
8
4.0x10
200
0.0
10
11
12
13
14
15
16
3
O3 [ppb]
Toluene [ppb]
8
8.0x10
300
experiment
MCMv3.1
NO2 conversion on aerosol
OH source in early stages
aerosol surface area
300
2
9
1.2x10
400
400
aerosol surface area [nm /cm ]
9
1.6x10
500
200
100
0
10
11
Time [h]
12
13
14
15
16
Time [h]
100
40
120
80
100
30
40
20
HONO [ppb]
80
NO [ppb]
NO2 [ppb]
60
60
40
20
0
0
10
11
12
13
Time [h]
2nd December 2004
14
15
16
20
10
0
10
11
12
13
14
15
16
Time [h]
MCM meeting Leeds
10
11
12
13
14
15
16
Time [h]
19
Current status of aromatic
mechanisms
•
•
•
•
•
•
•
•
Mechanism underestimates total radical production rates by a factor of
~2 at short and long times.
At the same time, mechanism overestimates O3 formation – need route
to radical formation that doesn’t give NO to NO2 conversion.
NOx removed from system more rapidly than mechanism indicates
Identification of glyoxal co-products ( g dicarbonyls) via GCxGC and
GC/ECD with synthesis of targets – yields very low.
Photochemistry and photosmog experiments on g dicarbonyls are
incompatible in terms of radical yields – need new chemistry.
Further extensive experiments on other aromatics – benzene, p-xylene,
1,3,5 trimethyl benzene, hydroxy aromatics, using both EUPHORE and
small chambers for kinetics. Provide detailed mechanistic and kinetic
data, but problems remain.
Need new detailed experiments, e.g. by laser flash photolysis or
discharge flow on targeted intermediates:
– OH and HO2 formation
– O3 + g-dicarbonyls / furanones
Improved detection methods for glyoxal co-products
2nd December 2004
MCM meeting Leeds
20
Comparison of ethene measurements and simulations
1400
700
1200
600
1000
500
C2H4 [ppb]
C2H4 [ppb]
Ethene experiments used to refine the auxiliary chamber mechanism
800
600
400
300
200
200
0
10:00
400
100
11:00
12:00
13:00
14:00
15:00
16:00
0
10:00
Time [h]
11:00
12:00
13:00
14:00
15:00
16:00
Time [h]
2s measurement uncertainty (grey bands)
2s uncertainties from Monte-Carlo simulations (error bars)
2nd December 2004
MCM meeting Leeds
21
600
800
700
500
600
500
O3 [ppb]
O3 [ppb]
400
300
400
300
200
200
100
0
10:00
100
11:00
12:00
13:00
14:00
15:00
0
10:00
16:00
11:00
12:00
Time [h]
14:00
15:00
16:00
15:00
16:00
Time [h]
500
300
250
HCHO [ppb]
400
HCHO [ppb]
13:00
300
200
200
150
100
100
0
10:00
50
11:00
12:00
13:00
14:00
15:00
16:00
0
10:00
Time [h]
2nd December 2004
11:00
12:00
13:00
14:00
Time [h]
MCM meeting Leeds
22
Uncertainty contributions, ethene, low
and high NOx
OH + NO2 = HNO3
HOCH2CH2O2 + NO = HOCH2CH2O + NO2
OH + NO2 = HNO3
HCHO = CO + 2 HO2
NO2 = NO + O
HOCH2CHO + OH = HOCH2CO3
HOCH2CH2O2 + NO = HOCH2CH2O + NO2
HOCH2CH2O = HO2 + 2 HCHO
C2H4 + OH = HOCH2CH2O2
NO + O3 = NO2
HO2 + O3 = OH
NO2 = NO + O
C2H4 + O3 = HCHO + CH2OOA
NO + O3 = NO2
HO2 + NO = OH + NO2
HOCH2CH2O = HO2 + HOCH2CHO
HOCH2CH2O = HO2 + 2 HCHO
HOCH2CH2O2 + HO2 = HOCH2CH2O2H
C2H4 + OH = HOCH2CH2O2
HO2 + NO = OH + NO2
HOCH2C(O)O2NO2 = HOCH2CO3 + NO2
HOCH2CH2O = HO2 + HOCH2CHO
NO2 = HONO
HOCH2CO3 + NO = NO2 + HO2 + HCHO
HOCH2CH2O2 + HO2 = HOCH2CH2O2H
HOCH2CH2O2 + NO = HOCH2CH2NO3
HOCH2CO3 + NO2 = HOCH2C(O)O2NO2
HO2 + O3 = OH
HOCH2HC2O2H + OH = HOCH2CHO + OH
0
2
4
6
8
10
12
14
16
18
0
Contribution to the total uncertainty [%]
2nd December 2004
MCM meeting Leeds
10
20
30
40
50
Contribution to the total uncertainty [%]
23
Morris method – (MOAT analysis), high NOx
Effects of individual rate constants on peak O3 concentration
40
HOCH2CH2O2 + NO = HOCH2CH2O + NO2
OH + NO2 = HNO3
40
HCHO = CO + HO2 + HO2
35
HOCH2CHO + OH = HOCH2CO3
HOCH2CH2O = HO2 + 2 HCHO
30
HOCH2CH2O = HO2 + HCHO + HCHO
HOCH2CHO + OH = HOCH2CO3
25
HO2 + O3 = OH
20
Standard Deviation [ppb]
Standard Deviation [ppb]
HOCH2CH2O2 + NO = HOCH2CH2O + NO2
NO2 = HONO
C2H4 + OH = HOCH2CH2O2
HOCH2CH2O = HO2 + HOCH2CHO
HOCH2CH2O2 + NO = ETHOHNO3
HOCH2CO3 + NO = NO2 + HO2 + HCHO
HO2 + NO = OH + NO2
15
NO2 = NO + O
NO + O3 = NO2
HOCH2CH2O2 + HO2 = HYETHO2H
10
HCHO = H2 + CO
5
HOCH2CH2O = HO2 + HOCH2CHO
30
HO2 + O3 = OH
HOCH2C(O)O2NO2 = HOCH2CO3 + NO2
OH + NO2 = HNO3
20
HOCH2CH2O2 + NO = HOCH2CH2NO3
NO2 = NO + O
HOCH2CO3 + NO = NO2 + HO2 + HCHO
10
NO + O3 = NO2
HOCH2CH2O2 + HO2 = HOCH2CH2O2H
HOCH2CO3 + NO2 = HOCH2C(O)O2NO2
C2H4 + O3 = HCHO + CH2OOA
HO2 + NO = OH + NO2
C2H4 + OH = HOCH2CH2O2
NO2 = HONO
0
0
50
100
150
Mean [ppb]
200
250
0
0
10
20
30
40
50
60
70
80
90
Mean [ppb]
2nd December 2004
MCM meeting Leeds
24