Table S1 – Photooxidation products from low-NOx
Structure
OOH
Name
Abbreviation
Molecular
Weight
Detected at
By CIMS
α-pinene
hydroperoxide
168.228
253
186.244
271
184.228
269
218.244
303
168.288
(+) 169
184.228
203, 269
APINENEOOH
OH
OOH
OH
α-pinene hydroxyl
hydroperoxide
APINENEOHOOH
OOH
α-pinene
hydroperoxy
carbonyl
O
APINENEOOHO
OOH
OOH
OH
a-pinene hydroxyl
dihydroperoxide
OOH
OH
O2
APINENEOHOOHOOH
OOH
Pinonaldehyde
O
O
PINON
Pinonic acid
O
O
PINON ACID
Ratio of 9:1 for 203:269
OH
Pinonic peracid
O
O
OOH
PINON PERACID
200.228
219, 285
Ratio 1:4 for 219:285
10-hydroxy pinonic
acid
O
HO
200.228
219, 285
172.218
257
154.202
(+) 155
O
10-OH PINON ACID
OH
O
C9OOH
OOH
Norpinonaldehyde
O
O
NORPINON
Table S2 – Kinetic model of low-NOx α-pinene photooxidation
Reaction
Rate constant /
photolysis ratea,b
Referencec
j1 = 2.25 x10−6
Sander, 2006
OH + H2O2 → HO2 + H2O
k1 = 1.8 x10−12
Sander, 2006
HO2 + HO2 → H2O2 + O2
k2 = 2.5 x10−12
Sander, 2006
OH + OH → H2O2
k3 = 6.28 x10−12
Sander, 2006
OH + HO2 → O2 + H2O
k4 = 1.1x10−10
Sander, 2006
APINENE + OH → APINENEOH
k5 = 4.8 x10−11
d
Atkinson, 2006
k6 = 5.4 x10−12
d
Atkinson, 2006
hν
H2O2 
→ 2 OH
→ APINENE + H2O
ktotal = 5.34 x10−11
APINENE + O2 → APINENEOO
Instantaneous
APINENEOO + HO2 → APINENEOOH + O2
→ Products
k7 = 1.2 x10−11
k8 = 8.0 x10−12
ktotal = 2.0 x10−11
APINENEOH + O2 → APINENEOHOO
Instantaneous
APINENEOHOO + HO2 → APINENEOHOOH
→ PINON + O2 + OH + HO2
→ APINENEOHOOHOOH
→ APINENEOH other products
k9 = 5.1x10−12
k10 = 4.0 x10−12
k11 = 4.2 x10−13
k12 = 1.05 x10−11
ktotal = 2.0 x10−11
APINENEOHOO + APINENEOHOO → Products
hν
APINENEOHOOH 
→ PINON + OH
APINENEOHOOH + OH → PINON
k13 = 2.0 x10−12
j2 = 1.46 x10−6
k14 = 1.2 x10−11
→ APINENEOHOO + H2O
k15 = 1.1x10−11
→ APINENEOHOOH
k16 = 2.4 x10−12
ktotal = 2.54 x10−11
APINENEOHOOH + O2 → APINENEOHOOHOO
Instantaneous
hν
PINON 
→ Products
j3 = 7.26 x10−6
Atkinson, 2006
PINON + OH → PINON + H2O
k17 = 3.7 x10−11
Atkinson, 2006
Davis, 2007
PINON + O2 → PINONOO
Instantaneous
PINONOO + HO2 → PINON ACID + O3
k18 = 5.0 x10−12
→ PINON PERACID + O2
k19 = 5.0 x10−12
→ C9OOH + CO2
→ NORPINON
k20 = 2.8 x10−12
k21 = 2.2 x10−12
→ Products
k22 = 5.0 x10−12
ktotal = 2.0 x10−11
APINENEOOH + OH → APINENEOOHOH
k23 = 4.0 x10−11
APINENEOOHOH + O2 → APINENEOHOOHOO
Instantaneous
APINENEOHOOHOO + HO2 → APINENEOHOOHOOH + O2
→ Products
k24 = 1.1x10−11
k25 = 9.0 x10−12
ktotal = 2.0 x10−11
APINENEOOHOHOOH + OH → Products
a
3
-1 -1
k26 = 4.0 x10−11
-1
Units: Rate constants cm molecule s , photolysis rates s
Photolysis rates calculated from absorption cross sections and the spectral radiance of the chamber lights
c
Reactions without a reference listed were determined here, see text for details
d
Total Rate constant for α-pinene + OH (k5 + K6) is from the Atkinson, 2006. Each individual rate constant
represents the branching ratio of the reaction between OH addition to the double bond and H-abstraction by
OH.
b
Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M.
J., and Troe, J.: Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II gas phase reactions of organic species, Atmos. Chem. Phys., 6, 3625-4055, 2006.
Davis, M. E., Talukdar, R. K., Notte, G., Ellison, G. B., and Burkholder, J. B.: Rate coefficients for the OH
plus pinonaldehyde (C10H16O2) reaction between 297 and 374 K, Environ. Sci. Technol., 41, 39593965, 2007.
Sander, S. P., Finlayson-Pitts, B. J., Friedl, R. R., Golden, D. M., Huie, R. E., Kolb, C. E., Kurylo, M. J.,
Molina, M. J., Moortgat, G. K., Orkin, V. L., and Ravishankara, A. R.: Chemical kinetics and
photochemical data for use in atmospheric studies, evaluation number 15, Jet Propulsion
Laboratory, Pasadena, CA, 2006.
Concentration (ppm)
4.5
A
4.0
3.5
3.0
2.5
0
5
10
15
B
Concentration (ppb)
10
1
0.1
0
2
4
6
8
10
12
Time (hours)
Figure S1 – Photolysis of H2O2 (A) by black lights in the Caltech environmental chamber and
Consumption of α-pinene by OH (B) during the same experiment. In each case the black squares are
the data and the red line is the simulation from the kinetic model from Table S2. The concentration of
α-pinene is plotted on a log scale to show the first order kinetics.
OH
H
OH
O
O
seven member
ring intermediate
O
O
OH
OH, O2
Isomerization
OOH
HO2
-O2
OO
OOH
OH
HOO
OOH
OH
OOH
OH
HO2
O2
seven member
ring intermediate
H
OH
OOH
O2
Isomerization
OH, O2
OH
OOH
-O2
OO
OOH
Isomerization
six member
ring intermediate
OOH
OH
OOH
O
O2
-HO2
OOH
OOH
Figure S2 – Proposed mechanism of peroxy radical isomerization from addition of OH to either the
tertiary or secondary carbon of the double bond of α-pinene.
CIMS Signal (AU)
10
1
0
2
4
6
Time (hours)
Figure S3 – Signal of pinonaldehyde from direct injection in the presence of 4 ppm H2O2 photolyzed by
black lights. The simulation (red line) incorporates both reaction with OH (kOH = 3.7 x 10-11 cm3
molecules-1 s-1) and photolysis (j = 7.26 x 10-6 s-1).