Update on vinoxy radical work

1. Direct Measurements of Vinoxy Radicals
From Ozonolysis of cis- and trans-2-Butene
Using Cavity Ring-down Spectroscopy
Mixtli Campos-Pineda and Jingsong Zhang
Department of Chemistry
University of California
Riverside
Group Meeting, Summer 2018

2. Outline
 Motivation
 Ozonolysis
 2-butene ozonolysis
 Experimental Setup
 CRDS
 Measurement of ∙CH2CHO and HCHO
 Results
 Summary
 Current Work

3. O 2
R, alkyl radical
RH, hydrocarbon
HONO +hn OH
OH
NO
RO 2
RO
HO2
NO 2
ROONO 2
RONO 2
RO 2
carbonyl
+
alcohol
ROOH
NO 2
O3
O2
hn
OH
Alkenes
OH production
mechanism in
alkene + O3 reactions
SOA
Motivation

4. Oxidation
Organic acid,
ester, etc.
Secondary
Organic
Aerosol
(SOA)
Stabilized CI  oxidation
Pollutant in Atmosphere (SO2)
Aerosol Nucleation
R1
C
O
R2
O +
-
R1
C
O
R2
O
+ -
+ H2O
 The Importance of Criegee Intermediates

5.  The ozonolysis reaction is highly exothermic. The
primary ozonide is formed with high internal energy.
Olzmann et al. JPCA. 101, 9421–9429 (1997).
“hot” CI
“stabilized” CI

6. 0 20 40 60 80 100 120 140
0.0
0.1
0.2
0.3
0.4
0.5
This work
Drozd et al.
Hakala et al.
ysCI
Pressure (Torr)
• Acetone oxide from 2,3-
dimethyl-2-butene
ozonolysis:
• Nascent yield ≠ 0
• Undergoes bimolecular
reactions
• Undergoes decomposition
 “stabilized” Criegee intermediates (sCIs) can undergo
bimolecular reactions and unimolecular dissociation.
Hakala & Donahue. JPCA. 120 (2016) 2173.
Drozd et al. JPCA. 115 (2011) 161.
Campos-Pineda & Zhang. Chem Phys Lett. 2017.

7. 2-butene ozonolysis:
• Nascent yield of sCI close to 0.
• Most CI produced as “hot” CI and
undergoes decomposition/isomerization.
• Small amount of sCI is depleted by
decomposition and bimolecular
reactions.
• Can look at early products of ozonolysis
Hatakeyama et al, JPC. 88 (1984) 4736
Campos-Pineda & Zhang. Chem Phys Lett. 2017.
0 4 8 12 16 20 24
0.00
0.05
0.10
0.15
0.20
0.25
0.30
ysCI
Pressure (Torr)
cis-2-butene
0 4 8 12 16 20 24
0.00
0.05
0.10
0.15
0.20
0.25
0.30
This work
Hatakeyama et al.
ysCI
Pressure (Torr)
trans-2-butene

8. O3
+
+
1- a a
1- b b
anti-CI and syn-CI
branching
2-butene ozonolysis
+ OH
OH + CH3CO
• Vinoxy radical is a unique indicator of syn-CI
• Measurements help elucidate OH production
pathway and syn-CI branching ratio
• Measurements of HCHO
offer constraints to improve
the kinetic model.

9. Experimental Setup
Ozonolysis of alkenes is done using a flow reactor:
Reaction products are measured using cavity ring-down
spectroscopy (CRDS).
Dye Laser PMT
To pump
Purge Purge
O3
trap
FM
N2 inFM
O2 in
FMalkene
in
FM

10. CRDS:
Suitable for atmospheric measurements due to:
Long sample path (high sensitivity).
Real time measurements.
Portability (in situ measurements).

11. 346.8 347.2 347.6 348.0 348.4
0
1x10-19
2x10-19
3x10-19
4x10-19
5x10-19
6x10-19
7x10-19
8x10-19
9x10-19
1x10-18
1x10-18
Abs.cross-section
Wavelength
Vinoxy radical reference spectrum
347.0 347.5 348.0 348.5
0.0
4.0x10-22
8.0x10-22
1.2x10-21
1.6x10-21
2.0x10-21
2.4x10-21
2.8x10-21
3.2x10-21
3.6x10-21
4.0x10-21
Abs.cross-section
Wavelength
HCHO reference
Wang & Zhang. Chinese Journal of Chemical Physics. 17 (2004) 357
Cantrell et al. JPC, 94 (1990) 3902
Absorption features of ∙CH2CHO and HCHO in the 347-349 nm
range:

12.    
    )(
11
0


fNN
L
dc
formformvinoxyvinoxy 






Single Value Decomposition fitting:

13. Measurement of ∙CH2CHO and HCHO:
346.8 347.2 347.6 348.0 348.4
0.050
0.055
0.060
0.065
0.070
0.075
0.080
[]

Experiment
Fit
   
    )(
11
0


fNN
L
dc
formformvinoxyvinoxy 






Vinoxy
radical
HCHO

14. 4.0x1015
6.0x1015
8.0x1015
1.0x1016
1.2x1016
1.4x1016
8.0x1011
1.0x1012
1.2x1012
1.4x1012
1.6x1012
1.8x1012
2.0x1012
2.2x1012
N(molecule/cc)
Ozone (molecule/cc)
trans-2-butene
cis-2-butene
Vinoxy radical yield
Vinoxy “yield” ratio of
c2b/t2b ~ 0.6
Consistent with yOH ratio c2b/t2b
~ 0.55 (Tuazon et al.)
[𝑠𝑦𝑛−CI] 𝑐2𝑏
[𝑠𝑦𝑛−CI] 𝑡2𝑏
= 0.6
Yield ratio of vinoxy radical from c2b and t2b corresponds to the
yield ratio of OH.
Both OH and vinoxy are co-products from syn-CI.
Results

15. 2.0x1015
4.0x1015
6.0x1015
8.0x1015
1.0x1016
4x1014
5x1014
6x1014
7x1014
8x1014
9x1014
1x1015
trans-2-butene
cis-2-butene
N(molecule/cc)
Ozone (molecule/cc)
HCHO yield
 yield of HCHO ~0.11
 compare with Tuazon et
al.: yHCHO = 0.166
 yHCHO ratio of
c2b/t2b ~ 1
Results
Larger than the vinoxy
yield ratio (~0.6)

16. O3
+
+
1- a a
1- b b
anti-CI and syn-CI
branching
2-butene ozonolysis
+ OH
OH + CH3CO
HCHO
anti-CI produces HCHO
HCHO Additional HCHO
production pathway
from syn-CI

17. “hot” ester channel
HCHO
hydroxyacetaldehyde channel
+OH
HCO + OCH3 HCHO
HCHO , (CHO)2 , OH
O2
Martinez & Herron, JPC,1988, 92,4644
Kuwata et al., JPCA, 2003, 107, 11525

18. Simulation of the reaction in a flow reactor.
The system of ODEs is solved using
an approximation method by
KINTECUS.

19. HCHO from mechanism
2.0x1015
4.0x1015
6.0x1015
8.0x1015
1.0x1016
4x1014
5x1014
6x1014
7x1014
8x1014
9x1014
1x1015
trans-2-butene
Experiment
Simulation
N(molecule/cc)
Ozone (molecule/cc)
2.0x1015
4.0x1015
6.0x1015
8.0x1015
1.0x1016
4x1014
5x1014
6x1014
7x1014
8x1014
9x1014
1x1015
cis-2-butene
Experiment
Simulation
N(molecule/cc)
Ozone (molecule/cc)

20. 4.0x1015
6.0x1015
8.0x1015
1.0x1016
1.2x1016
8.0x1011
1.2x1012
1.6x1012
2.0x1012
2.4x1012
cis-2-butene
Experiment
Simulation
Experiment
Simulation
trans-2-butene
N(molecule/cc)
Ozone (molecule/cc)
Vinoxy radical from mechanism
 Kinetic model adequately
estimates HCHO and
vinoxy radical for c2b and
t2b ozonolysis.
 Vinoxy radical reaction
with oxygen not the only
source of HCHO

21. Summary
Direct measurements of vinoxy radical from ozonolysis of 2-butene
confirm syn-CI decomposition and vinoxy reactions as main OH
formation channel.
Production of HCHO from anti-CI via “hot” ester channel and
production of HCHO from syn-CI via hydroxyacetaldehyde channel
need further study.
Additional HCHO pathways reconcile HCHO and vinoxy (and OH)
yield ratios.

22. 347.0 347.5 348.0 348.5
0.16
0.17
0.18
0.19
0.20
0.21
0.22
0.23


347.0 347.5 348.0 348.5
0.16
0.17
0.18
0.19
0.20
0.21
0.22
0.23


O2 ~ 1x1015 molecule/cm3
O2 ~ 7x1016 molecule/cm3
 Modified apparatus for faster flows and
in situ oxygen measurements
 Short residence time experiments
(<0.5s)
 “Low” and “High” oxygen conditions
 ∆HCHO not explained by current
mechanism
Current Work

23. a
+ OH
HCHO Additional HCHO
production pathway?
Oxygen as constrain on
kinetic model

24. Experiments: fast (9 Torr) and slow (30 Torr)
 Ozone : Trap (<1E15) , 2E16 , 7E16
 Time/Pressure : 1s/30 Torr (original) , 0.35s/9 Torr
 Measurements of O2% by flowing O3/O2/N2 from trap through SS coil at
1atm and 150 °C into AMIO2 detector

25. Avg. ozone in
(molecule/cc) Oxygen in (molecule/cc) HCHO (molecule/cc) Vinoxy (molecule/cc) yHCHO yVinoxy
cis 30Torr
5.5E+15 0 8E+14 9E+11 0.145455 0.00016
5.5E+15 0 7E+14 9E+11 0.127273 0.00016
4.85E+15 0 7.5E+14 9E+11 0.154639 0.00019
4.85E+15 0 7.5E+14 8E+11 0.154639 0.00016
5.5E+15 4.36965E+16 6.9E+14 7E+11 0.125455 0.00013
5.5E+15 4.36965E+16 6.3E+14 7E+11 0.114545 0.00013
4.85E+15 8.74224E+16 5.8E+14 4E+11 0.119588 8.2E-05
4.85E+15 8.74224E+16 5.2E+14 5E+11 0.107216 0.0001
9Torr
2.55E+15 0 4.7E+14 1.5E+12 0.184314 0.00059
2.55E+15 0 4.2E+14 1.4E+12 0.164706 0.00055
1.6E+15 0 3E+14 1.3E+12 0.1875 0.00081
1.6E+15 0 2.8E+14 1.3E+12 0.175 0.00081
1.6E+15 3.91204E+16 1.3E+14 6E+11 0.08125 0.00038
1.6E+15 3.91204E+16 1.1E+14 6E+11 0.06875 0.00038
2.55E+15 7.83193E+16 1.5E+14 7E+11 0.058824 0.00027
2.55E+15 7.83193E+16 1.5E+14 5.5E+11 0.058824 0.00022
trans 30Torr
2.42E+15 0 3.5E+14 1.4E+12 0.144628 0.00058
2.42E+15 0 3.5E+14 1.4E+12 0.144628 0.00058
4.4E+15 0 4.2E+14 1.4E+12 0.095455 0.00032
4.4E+15 0 4.4E+14 1.5E+12 0.1 0.00034
2.42E+15 4.36965E+16 3.5E+14 8E+11 0.144628 0.00033
2.42E+15 4.36965E+16 3E+14 1.1E+12 0.123967 0.00045
4.4E+15 8.74224E+16 4.4E+14 8E+11 0.1 0.00018
4.4E+15 8.74224E+16 4.4E+14 7E+11 0.1 0.00016
9Torr
3.2E+15 0 5.3E+14 2.7E+12 0.165625 0.00084
3.2E+15 0 5.3E+14 2.7E+12 0.165625 0.00084
2.5E+15 0 3.8E+14 2.6E+12 0.152 0.00104
2.5E+15 0 3.8E+14 2.6E+12 0.152 0.00104
2.5E+15 3.91204E+16 2.3E+14 1.4E+12 0.092 0.00056
2.5E+15 3.91204E+16 2.3E+14 1.4E+12 0.092 0.00056
3.2E+15 7.83193E+16 3.4E+14 1.6E+12 0.10625 0.0005
3.2E+15 7.83193E+16 3.4E+14 1.6E+12 0.10625 0.0005

26.  Yield measurements with
observations
 Experiments not designed to
measure yield ratios (no ozone
desorption profile)
cis/trans HCHO cis/trans Vinoxy
30 Torr
1.01 0.28
0.88 0.28
1.62 0.58
1.55 0.48
0.87 0.39
0.92 0.28
1.20 0.45
1.07 0.65
9 Torr
1.11 0.70
0.99 0.65
1.23 0.78
1.15 0.78
0.88 0.67
0.75 0.67
0.55 0.55
0.55 0.43
High [O3]0 differences
[O2] = 2E16
[O2] = 7E16
Similar [O3]0
 Data OK for kinetic modelling
Experiments: fast (9 Torr) and slow (30 Torr)

27. Oxygen detector
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
O2calculated(%)
O2 measured (%)
Equation y = a + b*x
Weight No Weighting
Residual Sum
of Squares
2.53063
Pearson's r 0.99768
Adj. R-Square 0.99478
Value Standard Error
O2 calculated
Intercept 0 --
Slope 1.17184 0.02829
 Calculated O2% assuming full
conversion of measured O3
 Calculated O2% is 1.17±0.03
times more than measured O2%
 No total ozone conversion
 Measurement/calculation error
• Literature suggest O2 trapped not
significant
• Literature doesn’t mention
products of SS coil denuder

28. Vinoxy + Ozone (?)
346.5 347.0 347.5 348.0 348.5 349.0
0.18
0.20
0.22
0.24
0.26
B
A
B
F
346.5 347.0 347.5 348.0 348.5 349.0
0.26
0.27
0.28
0.29
0.30
0.31
C
A
C
G
Low oxygen
High oxygen
 Average [O3] for low oxygen:
1.5 – 2E15 molecule/cc
 Average [O3] for high oxygen:
2E15 molecule/cc
HCHO HCHO
O3 O2
 No significant change of average
ozone by using excess oxygen

29. Travel time v reaction time
P (Torr) Travel time (s) Initial Alkene
Final Alkene
(Simulated) Initial O3
Average O3
remaining
Average O3 remaining
(Simulated)
30 1 1.80E+16 1.20E+16 5.00E+15 2.00E+15 2.10E+15
9 0.35 1.80E+16 1.60E+16 2.50E+15 1.50E+15 1.70E+15
 Model correctly estimates ozone with measured travel time
 Travel time  Reaction time
 Similar results with data from 12/22/2016
 No additional oxygen depletion
processes
HCHO HCHO
O3 O2

30. O3
+
+
1- a a
1- b b
+ OH
aHCHO
cHCHO
O2
bHCHO
?
Looking for processes and yields
 HCHO yield ratio is ~1 : a = b + c OR a = b (and trap has no oxygen)
 HCHO decreases with increasing oxygen : b > c

31. Vinoxy + Vinoxy (?)
 Correct trends, wrong
magnitudes
 k = 5 E -11 approaching
diffusion limit
HCHO HCHO
O2
O3 CH2CHO HCHO O2
k = 1 E -12
2.1E+15 1.2E+11 5.4E+14 9.3E+16
2.0E+15 4.0E+11 5.8E+14
2.1E+15 2.0E+12 5.4E+14 6.0E+15
2.0E+15 8.0E+11 7.5E+14
2.1E+15 1.7E+13 5.4E+14 5.0E+14
2.0E+15 8.0E+11 7.5E+14
k = 5 E -11
2.1E+15 1.2E+11 5.4E+14 9.3E+16
2.0E+15 4.0E+11 5.8E+14
2.1E+15 1.5E+12 5.4E+14 6.0E+15
2.0E+15 8.0E+11 7.5E+14
2.1E+15 3.1E+12 5.5E+14 5.0E+14
2.0E+15 8.0E+11 7.5E+14
O3 CH2CHO HCHO O2
1.7E+15 1.5E+11 1.6E+14 8.4E+16
1.5E+15 6.0E+11 1.5E+14
1.7E+15 2.2E+12 1.6E+14 3.0E+15
1.5E+15 1.5E+12 4.5E+14
1.7E+15 3.0E+12 1.6E+14 5.0E+14
1.5E+15 1.5E+12 4.5E+14
30 Torr
9 Torr
 Effect less significant at 9 Torr,
0.35s travel time (opposite of
what is observed)

32. New experiments at 9 Torr (fast and slow)
 Effect of oxygen on vinoxy radical
 Effect of oxygen on HCHO
 Effect of reaction time
 Glyoxal?

33. 346.5 347.0 347.5 348.0 348.5 349.0
0.104
0.106
0.108
0.110
0.112
0.114


1
2
7
8
13
14
19
20

34. 346.5 347.0 347.5 348.0 348.5 349.0
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24


13
14
15
16
17
18

35. 346 347 348 349
3.00E-021
4.00E-021
5.00E-021
6.00E-021
7.00E-021
8.00E-021
9.00E-021
1.00E-020


Glyoxal reference

36. 346.5 347.0 347.5 348.0 348.5 349.0
0.15
0.16
0.17
0.18
0.19


Experiment
Fit
t2b: 1s - 8x1016
Oxygen
346.5 347.0 347.5 348.0 348.5 349.0
0.13
0.14
0.15
0.16
0.17
t2b: 0.35s - 8x1016
Oxygen


Experiment
Fit
346.5 347.0 347.5 348.0 348.5 349.0
0.06
0.07
0.08
0.09
0.10
t2b: 1s - no Oxygen


Experiment
Fit
346.5 347.0 347.5 348.0 348.5 349.0
0.06
0.07
0.08
0.09
0.10
0.11
0.12
t2b: 0.35s - no Oxygen


Experiment
Fit

37. Residence
time (s)
Avg. ozone in
(molecule/cc)
Oxygen in
(molecule/cc)
HCHO
(molecule/cc)
Vinoxy
(molecule/cc)
O3 remaining
(molecule/cc)
Glyoxal
(molecule/cc)
1 3.04E+15 0 4.30E+14 1.40E+12 5.00E+14 0
1 3.06E+15 0 4.30E+14 1.40E+12 5.00E+14 0
1 3.24E+15 8.5E+16 4.80E+14 7.00E+11 1.00E+15 1.15E+14
1 3.18E+15 8.5E+16 4.80E+14 7.00E+11 1.00E+15 1.15E+14
0.35 3.03E+15 0 4.10E+14 2.50E+12 1.10E+15 0
0.35 3.10E+15 0 4.10E+14 2.50E+12 1.10E+15 0
0.35 2.95E+15 7.7E+16 2.30E+14 8.00E+11 1.30E+15 6.50E+13
0.35 2.70E+15 7.7E+16 2.30E+14 8.00E+11 1.30E+15 6.50E+13

38. Travel time v reaction time
P (Torr) Travel time (s) Initial Alkene
Final Alkene
(Simulated) Initial O3
Average O3
remaining
Average O3 remaining
(Simulated)
30 1 1.80E+16 1.20E+16 5.00E+15 2.00E+15 2.10E+15
9 0.35 1.80E+16 1.60E+16 2.50E+15 1.50E+15 1.70E+15
 Model correctly estimates ozone with measured travel time
 Travel time  Reaction time
 Similar results with data from 12/22/2016
 No additional oxygen depletion
processes
HCHO HCHO
O3 O2
Better measurements
indicate there might
be an ozone-related
process!

39. trans-2-butene
 1s no oxygen:
 yHCHO ~ 0.15
 Vinoxy = 1.4x1012 molecule/cc
 1s with 8x1016 molecule/cc Oxygen
 Some possible glyoxal (1x1014
molecule/cc)
 Slight increase in HCHO, O3
 50% decrease in vinoxy
 0.35s no oxygen:
 yHCHO ~ 0.15
 Vinoxy = 2.5x1012 molecule/cc
 0.35s with 8x1016 molecule/cc Oxygen
 Some possible glyoxal (6.5x1013
molecule/cc)
 Slight increase in O3
 50% decrease in HCHO
 70% decrease in vinoxy

40. 346.5 347.0 347.5 348.0 348.5 349.0
0.13
0.14
0.15
0.16
0.17

Experiment
Fit
c2b: 1s - 8x1016
Oxygen
346.5 347.0 347.5 348.0 348.5 349.0
0.080
0.085
0.090
0.095
0.100
0.105
c2b: 0.35s - 8x1016
Oxygen


Experiment
Fit
346.5 347.0 347.5 348.0 348.5 349.0
0.065
0.070
0.075
0.080
0.085
0.090
0.095
0.100
0.105 c2b: 1s - no Oxygen


Experiment
Fit
346.5 347.0 347.5 348.0 348.5 349.0
0.060
0.065
0.070
0.075
0.080
0.085
0.090
0.095
0.100
0.105
c2b: 0.35s - no Oxygen


Experiment
Fit

41. Residence
time (s)
Avg. ozone in
(molecule/cc)
Oxygen in
(molecule/cc)
HCHO
(molecule/cc)
Vinoxy
(molecule/cc)
O3 remaining
(molecule/cc)
Glyoxal
(molecule/cc)
1 3.00E+15 0 4.30E+14 9.00E+11 5.00E+14 0
1 3.25E+15 0 4.30E+14 9.00E+11 5.00E+14 0
1 3.80E+15 8.5E+16 3.80E+14 4.50E+11 1.00E+15 6.50E+13
1 3.60E+15 8.5E+16 4.30E+14 4.00E+11 1.00E+15 6.50E+13
0.35 2.60E+15 0 4.00E+14 1.10E+12 5.00E+14 0
0.35 2.45E+15 0 4.30E+14 1.10E+12 5.00E+14 0
0.35 2.06E+15 7.7E+16 1.00E+14 3.30E+11 1.60E+15 1.50E+13
0.35 2.15E+15 7.7E+16 1.00E+14 3.30E+11 1.60E+15 1.50E+13

42. cis-2-butene
 1s no oxygen:
 yHCHO ~ 0.15
 Vinoxy = 9x1011 molecule/cc
 1s with 8x1016 molecule/cc Oxygen
 Maybe glyoxal (6.5x1013 molecule/cc)
 Increase in O3
 50% decrease in vinoxy
 Slight change in HCHO
 0.35s no oxygen:
 yHCHO ~ 0.15
 Vinoxy = 1.1x1012 molecule/cc
 0.35s with 8x1016 molecule/cc Oxygen
 Glyoxal <LOD (<1x1013 molecule/cc)
 Significant increase in O3
 > 50% decrease in HCHO
 ~70% decrease in vinoxy

43. Will vinoxy ever be completely scavenged?
 Adding 1.9x1017 molecule/cc of oxygen
347.0 347.5 348.0 348.5
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17


Experiment
Fit
t2b, 1 s, 9 Torr
No oxygen
347.0 347.5 348.0 348.5
0.18
0.19
0.20
0.21
0.22
0.23
t2b, 1 s, 9 Torr
1.9x1017
molecule/cc O2


Experiment
Model

44. Will vinoxy ever be completely scavenged?
 Adding 1.9x1017 molecule/cc of oxygen
Residence
time (s)
Avg. ozone in
(molecule/cc)
Oxygen in
(molecule/cc)
HCHO
(molecule/cc)
Vinoxy
(molecule/cc)
O3 remaining
(molecule/cc)
Glyoxal
(molecule/cc)
1 3.24E+15 8.5E+16 4.80E+14 7.00E+11 1.00E+15 1.15E+14
1 3.18E+15 8.5E+16 4.80E+14 7.00E+11 1.00E+15 1.15E+14
1 4.85E+15 1.9E+17 5.50E+14 5.00E+11 1.00E+15 2.00E+14
1 4.85E+15 1.9E+17 6.05E+14 4.00E+11 8.00E+14 2.00E+14
 Oxygen directly relates to glyoxal production
 Oxygen decreases vinoxy but cannot scavenge it completely
 Oxygen affects average ozone, but doubling oxygen does not

45. So far
 Long time trans-2-butene in agreement with previous observations
 Long time cis-2-butene close enough
 Yields and yield ratios without oxygen same as previously found
 Glyoxal seen in long time t2b ozonolysis with oxygen scavenging (upper
limit ~2x1014 molecule/cc (model estimates ~4x1013)
 Oxygen increases ozone average slightly, except for short time c2b
where it increases ozone significantly
 Might explain why HCHO decreases
 There might be differences in secondary processes between c2b and t2b

46. O3
+
+
1- a a
1- b b
+ OH
aHCHO
zHCHO
O2
bHCHO
?
Summary of new mechanistic findings
 HCHO yield ratio is ~1 : a ~ b (+c+…)+z OR a ~ b+c+… (trap has no oxygen)
 HCHO decreases with increasing oxygen : b+c > z
cHCHO
O3 ?

47. Acknowledgements
Prof. Jingsong Zhang
Prof. Liming Wang
Dr. Yingdi Liu
Ge Sun
Xinghua Liu
UCMEXUS Fellowship