九州大学大学院総合理工学府報告第 41 巻 第 1 号 1-7 頁 令和元年 9 月

Engineering Sciences Reports, Kyushu University
Vol. 41, No. 1, pp. 1-7, SEP, 2019

Simultaneous Removal of NO2 and C6H6 in an NO2/C6H6
Mixture in Air by 172-nm Xe2 Excimer Lamp
at Atmospheric Pressure
Masaharu TSUJI*1,2† Takashi KAWAHARA*3 Keiko UTO*1
Jun-Ichiro HAYASHI*1,2 and Takeshi TSUJI*4
E-mail of corresponding author: tsuji@cm.kyushu-u.ac.jp†(Received May 28, 2019, accepted July 12, 2019)
NO2 and C6H6 in an NO2(200 ppm)/C6H6(200 ppm) mixture were simultaneously removed in air at
atmospheric pressure using a 172-nm vacuum ultraviolet (VUV) Xe2 excimer lamp. Reactants andproducts before and after photoirradiation were analyzed using an FTIR spectrometer. Results showthat NO2 and C6H6 were finally converted to HNO3 and CO2, respectively, by 172-nm photolysis of the
NO2/C6H6 mixture. Although the removal rate of NO2 in the NO2/C6H6 mixture was nearly the sameas that of pure NO2 in air, the C6H6 removal delayed until a sufficient reduction of NOx (NO2, NO, andNO3) concentrations. In order to obtain information on these results, computer simulation of
decomposition processes was carried out. The delay of the C6H6 removal in the NO2/C6H6 mixture was
explained by 42–82 times larger reaction rate constants of the O(3P) + NOx reactions than that of theO(3P) + C6H6 reaction.
Key words: NOx, VOC, Excimer lamp, VUV photolysis, Air pollution

1.

Introduction

Nitrogen oxides (NOx = NO + NO2) andvolatile organic compounds (VOCs) are major
pollutants in the atmosphere, being a precursor
to photochemical smog, acid rain, and ozone
accumulation. The most general removal
methods of NOx are based on catalytic
reduction of NOx to elemental nitrogen bygaseous reducing agents, which are either
selective (ammonia or ammonium compounds)
or nonselective (NOx, carbon monoxide, andhydrocarbons).1-3) In the selective catalytic
reduction process, NOx is reduced by ammonia
over a catalyst to form harmless N2 and H2Ovapor without creating any secondary
pollutants. Non-selective catalytic reduction
requires injection of expensive NH3 or otherreducing agents without catalysts.
VOCs are recognized as major contributors to
air pollution, either through their toxic nature*1

Institute for Materials Chemistry and Engineering,and Research and Education Center of GreenTechnology*2 Department of Applied Science for Electronics andMaterials*3 Department of Applied Science for Electronics andMaterials, Graduate Student*4 Department of Materials Science, Shimane
Universityorasparticipantsinatmosphericphotochemical reactions. They are emitted
from different outdoor sources (motor vehicles,
incomplete combustion in industrial processes)
and from indoor sources.4,5) Current methods toremove VOC from indoor air include plasma
oxidation, photocatalytic oxidation, andadsorption by activated carbons.6-12)
The plasma discharge method is also used indomestic air cleaners for NOx and VOC
removal. Radicals formed by plasma discharge
act as major active species for NOx and VOC
removal.13) However, these radicals also oxidize
nitrogenandoxygensimultaneously,
respectively generating NOx and ozone.14)
Therefore, the development of a new effective
removal method of NOx and VOC is highly
anticipated.
Vacuum ultraviolet (VUV) photolysis of air
pollutants is a new promising method for NOx
and VOC removal. Advantages of the VUVphotolysis method are that it involves lowtemperature operation in air at atmosphericpressure using a simple apparatus and no
expensive catalysts. In general, when NOx and
VOCs are decomposed using electric discharge
in air, toxic NOx are formed because collisionsof fast electrons generated in discharges with

2

Simultaneous Removal of NO2 and C6H6 by VUV light

N2 give active N atoms, which provide NOx bycollisions with O2. In this respect, an additional
advantage of 172-nm photochemical method isthat no NOx are emitted because active
nitrogen is not generated under 172-nm
photoirradiation of N2.
We have studied removal of such typical NOx
and VOC as NO2 and C6H6 in air using a sideon type of 172-nm excimer lamp.15,16) NO2 wasdominantly converted to HNO3 after photolysis,
whereas C6H6 was converted to CO2 via
HCOOH and CO intermediates. Photochemical
oxidants are the product of chemical reactions
that occur between NOx and VOCs. Typicalphotochemical oxidants are ozone (O3),hydrogen peroxide (H2O2), and peroxyacetyl
nitrate (PAN). These photochemical oxidants
are cause for concern, as they can have negative
effects on human, plant, and animal health.
Therefore, simultaneous removal techniques ofNOx and VOCs in air at atmospheric conditions
are required.
In this study we attempted simultaneous
removal of NO2 and C6H6 in an NO2/C6H6
mixture in air by 172-nm photolysis. Air
dominantly consists of N2(80%) and O2(20%).
Although 172-nm photons are not absorbed by
N2, they are absorbed by O2 throughSchumann–Runge
continuum.17)
Afterphotoabsorption, O2 is selectively dissociatedinto the ground-state O(3P) atom and themetastable-state O(1D) atom: O2 + h (172 nm)→ O(3P) + (1D).19) O3 molecules are generated
by the subsequent three-body reactions: O(3P)+ O2 + N2 (or O2) → O3 + N2 (or O2). Therefore,
in addition to direct VUV photodegradation,
reactions of O(3P,1D) and O3 can participate inremoval of an NO2/C6H6 mixture. On the basisof our precious studies,15,16) most important
active species in the 172-nm photolysis of pure

Turbo pumpRotary pumpRotary pumpPressure
gauge
N222
N

O
O22

NC2O/
6H6
C6H6

FT-IR

NO2 and C6H6 were found to be OH + NO2 andO(3P) + C6H6 are major pathways for theformation of HNO3 and CO2 in the initial step.
In the present study, removal mechanisms are
discussed on the basis of computer simulationof reaction processes.

2.

Experimental

Fig. 1 portrays a schematic diagram of sideon type of 172-nm excimer lamp used for thisstudy. Table 1 presents the major performanceof the side-on lamp (SL). The input power of the
SL was 20 W. Experiments were conductedusing the SL at a chamber volume of 235.5 cm3or 39.3 cm3 where the chamber thicknesses was
3 cm or 0.5 cm, respectively.
Light from an unfocused 172-nm Xe2 lamp(155200 nm range, UER20H172; Ushio Inc.)
was irradiated into the photolysis chamber
through a quartz window. Experiments wereconducted using a closed batch chamber at
atmospheric pressure. The concentration of
NO2 and C6H6 diluted in an N2/O2 mixture (20%O2) was both 200 ppm (v/v). Outlet gases fromthe photolysis chamber were analyzed using a
gas analysis system (FG122-LS; Horiba Ltd.)equipped with an FTIR spectrometer. The
spectra in the 7004000 cm-1 region weremonitored. The concentrations of CO, CO2,HCOOH, and NO2 were calibrated using
standard gases. On the other hand, the HNO3,
N2O5, and O3 concentrations were evaluated byreference to standard spectral data supplied
from Horiba Ltd. Thereby, the residual
amounts of NO2 and C6H6, Ct/C0, were inferredfrom absorbance of FTIR peaks. Here, C0 is theinitial concentration of NO2 or C6H6.
The following gases were used: N2 (purity>99.9998%; Taiyo Nippon Sanso (TNS) Corp.)
O2 (purity >99.99995%; TNS Corp.), NO2 (2000ppm in high-purity N2; TNS Corp., and C6H6
(TNS.: 2000 ppm in high purity N2). FTIR data
indicated a small amount of H2O (300 ppm) is
Table 1. Performance of photolysis chamberusing a side-on lamp

QMS

Mass
flowmeter

VUV irradiation
172 nm Xe2 Excimer lamp

Pressure
gauge

Fig. 1. Side-on type of 172-nm photolysis
apparatus.

Input power
Irradiance
Window area
Photon numbers/s
Chamber volume

20 W
10 mW/cm2
78.5 cm2
6.83  1017 photons/s
235.5 or 39.3 cm3

3.1 Removal of NO2 and C6H6 in an NO2/C6H6
mixture by 172-nm photolysis in air

0.30

Absorbance

0.25

HNO3+ N2O5

HCOOH

0.15
0.10
0.05

CO
HNO3

C6H6

HCOOH
O3

HNO3
N2O5

CO2

0.00
4000

3500

3000

2500

2000

Wavenumbers / cm(a) NO2, C6H6

100
80
60
40

C6H6

20
0

NO2
0

600

50

1500

1000

-1

Fig. 2. FTIR spectra observed before (redline) and after 172-nm photolysis (blue line)of an NO2/C6H6 mixture in air (20% O2) for
15 s.

100 150 200 250 300
Irradiation time / s(b) HCOOH, CO, CO2
CO2

500
400

CO

300
200
HCOOH

100
0

200

0

50

100 150 200 250 300
Iraddiation time / s(c) N2O5, HNO3, O3

35000
30000

HNO3

150

O3
100

25000
20000
15000
10000

50
N2O5

NO2

0.20

3

0

0

50

5000

Ozone concentration / ppm

Fig. 2 shows FTIR spectra observed before
and after 172-nm photolysis of an NO2/C6H6
mixture in air (20% O2) for 15 s at a chamber
depth of 3 cm. Before photolysis, a strong NO2
peak at about 1600 cm-1 and a weaker C6H6
peak at about 3200 cm-1 are observed. After 15s photoirradiation, although the NO2 peak
disappears, the C6H6 peak becomes slightly
weak. In addition, N2O5, HNO3, HCOOH, CO,
CO2, and O3 peaks appear. All of these productpeaks have been observed by photolysis ofeither pure NO2 or C6H615,16) so that no new
product peaks, arising from the reactions
between NO2 and C6H6, were observed.
In Fig 3 is shown the dependence ofconcentrations of (a) NO2 and C6H6, (b)HCOOH, CO, and CO2, and (c) N2O5, HNO3,
and O3 on the irradiation time. NO2 isdecomposed completely within 5 s, whereas thedecomposition of C6H6 occurs more slowly andit takes about 50 s until its complete
decomposition. The HCOOH and CO
concentrations have peaks at 5060 s, whereas
the CO2 concentration increases withincreasing the irradiation time. These results
indicate that HCOOH and CO intermediates
are finally converted to CO2. The N2O5
concentration has a peak at 5 s and decreases
rapidly above that. On the other hand, the
HNO3 concentration increases until about 100s and then levels off above thereafter. It istherefore reasonable to assume that N2O5 isefficiently converted to HNO3 under ourcondition. The O3 concentration increases from

Residual amount of NO2 and C6H6 / %Results and discussion

第1号

zero to 31,000 ppm with increasing theirradiation time from zero to 300 s.

Concentrations / ppm

involved in the photolysis chamber as animpurity.

3.

第 41 巻九州大学大学院総合理工学報告

Concentrations / ppm

令和元年度

0

100 150 200 250 300
Iraddiation time / s

Fig. 3. Dependence of (a) residual amountsof NO2 and C6H6, (b) concentrations of
HCOOH, CO, and CO2, and (c)concentrations of N2O5, HNO3, and O3 on
the irradiation time in removal of NO2 andC6H6 in an NO2/C6H6 mixture by 172-nm
excimer lamp in air (20% O2). The chamber
depth was 3 cm.

Simultaneous Removal of NO2 and C6H6 by VUV light

100
80

C6H6 200 ppm with NO2 200 ppm

60

Only C6H6 200 ppm

40
20

NO2 200 ppm
with C6H6 200 ppm
Only NO2 200 ppm

0
0

10

20 30 40 50
Irradiation time / s

60

Fig. 4. Dependence of residual amounts of
NO2 and C6H6 on the irradiation time inpure NO2 or C6H6 and NO2/C6H6 mixture
under 172-nm photolysis in air (20% O2).
The chamber depth was 3.0 cm.
In order to examine effects of mixing NO2
with C6H6, dependence of residual amounts of
NO2 and C6H6 on the irradiation time in the
NO2/C6H6 mixture was compared with that inpure NO2 and C6H6 (Fig. 4). It should be notedthat the removal rate of NO2 in the NO2/C6H6
mixture is nearly identical to that of pure NO2.
On the other hand, the removal rate of C6H6 in
the NO2/C6H6 mixture is slower than that ofpure C6H6, so that the removal curve of C6H6 in
the NO2/C6H6 mixture shifts to longer
irradiation time in comparison with that ofpure C6H6 by about 10 s.

of the NO2/C6H6 mixture at 0.5 cm with a small
reaction volume (39.3 mL), where the above
assumption is expected to be well established.
The obtained experimental data for NO2, C6H6,and HNO3 are presented in Fig. 5(a). The
concentration of NO2 decreases to zero below 5s, whereas that of C6H6 decreases to zero at 10s. The HNO3 concentration increases from zero
to about 200 ppm after about 30 s.
Table 2 shows elementary reactions used forthe simulation. They consist of 172-nm
photolysis of O2 leading to O(1D) + O(3P) atoms(1),18) relaxation of O(1D) to O(3P) (2a)(2b),three-body reactions leading to O3 (3a)(3b),
VUV photolysis of O3 (4a)(4b), dissociation ofO3 (5)(7), three-body recombination of O(3P)(8a)(8b), VUV photolysis of NO2, (9), NOx + O3
reactions (10)(12), NOx + O(3P) reactions(13)(17), other NOx reactions (18)(21), and200
Concentrations / ppm

Residual amounts of NO2 and C6H6 / %

4

150

HNO3

C6H6

100

50

0
0

NO2
5

10

15

20

25

30

4
6
8
Irradiation Time / s

10

Irradiation time / s(b) Simulation

3.2 Simulation of removal processes of NO2
and C6H6 in an NO2/C6H6 mixture by 172-nm
photolysis in air

200
Concentrations / ppm

In our previous studies on 172-nm photolysis
of pure NO2 and C6H6, we succeeded in
reproducing dependence of their removal
amounts on the irradiation time by model
calculations.15,16) In this study, removal of an
NO2/C6H6 mixture is kinetically simulated bysolving simultaneous differential equations
using Runge–Kutta methods. Table A1(Appendix) gives experimental parameters
used for the simulation. For the simulation, we
assumed that such active species as 172-nm
photons, O(3P), and O3 were distributed
uniformly within the reaction chamber. At ashort chamber length of 0.5 cm, incident lightis attenuated by only 7.23% at 20% O2.15,16)
Therefore, we conducted removal experiments(a) Experiment

C6H6

HNO3

150

100

NO2
NO3
N2O5

50

00

NO
2

Fig. 5. Dependence of reagents andproducts on the irradiation time obtainedby (a) experiment and (b) simulation. The
chamber depth was 0.5 cm.

令和元年度

九州大学大学院総合理工学報告

Table 2

Reactions considered for the simulation ofsimultaneous removal of NO2 and C6H6 in the
NO2/C6H6 mixture by 172-nm photolysis in air.
Chemical equations

第 41 巻第1号

VUV photolysis of H2O (22), and other NOx
reactions (23)(25). 172-nm photolysis of C6H6(26) and reactions of C6H6 (27)(28) were also
considered.
In the simulation, we used the same reaction
rate constants and spectroscopic data as thoseused in our previous studies.15,16) Most of
kinetic and spectroscopic data were obtained
from Refs. 17–19. The temperature rise of 0.026
K/s in the photolysis chamber after
photoirradiation was assumed for thesimulation of simultaneous removal of NO2 andC6H6 in the NO2/C6H6 mixture because thetemperature of the reaction chamber increases
concomitantly with increasing photoirradiation
time. The validity of this assumption was
confirmed from the time evolution of O3 in air
in our photolysis chamber.15) Fig. 5(b) shows
simulation data for NO2, NO, NO3, N2O5, HNO3,
and C6H6 in the NO2/C6H6 mixture.
In our removal model of NO2, NO2 molecules
are oxidized to NO3 by collisions with O3,
whereas NO3 molecules are reduced to NO2 bycollisions with O3 and O(3P).

O2 + h → O(3P) + O(1D)

1

(1)

O(1D) + O2 → O(3P) + O2

k2a

(2a)

O(1D) + N2 → O(3P) + N2

k2b

(2b)

O(3P) + O2 + O2 → O3 + O2

k3a

(3a)

O(3P) + O2 + N2 → O3 + N2

k3b

(3b)

O3 + h→ O(3P) + O2

4a

(4a)

O3 + h → 3O(3P)

4b

(4b)

O3 → O2 + O(3P)

k5

(5)

O3 + O3 → 3O2(6)

2O(3P) + N2 → O2 + N2

k6
k7
k8a
k8b

NO2 + h→ NO + O(3P)

9

(9)

NO2 + O3 → NO3 + O2

k10

(10)

NO + O3 → NO2 + O2

k11

(11)

NO3 + O3 → NO2 + 2O2

k12

(12)

NO2 + O(3P) → NO3

k13

(13)

k14a

(14a)

k14b

(14b)

k15

(15)

NO + O(3P) → NO2

k16

(16)

NO3 + O(3P) → NO2 + O2

k17

(17)

NO2 + NO3 → N2O5

k18

(18)

NO2 + NO3
→ NO + NO2 + O2

k19

(19)

H2O + h (172 nm) → OH + H

NO + NO3 → 2NO2

k20

(20)

The NO2 + OH reaction gives HNO3.

N2O5 + H2O → 2HNO3

k21

(21)

H2O + hν → OH + O(3P)

22

(22)

NO2 + OH → HNO3

k23

(23)

2N2O5 → 4NO2 +O2

k24
k25

(24)

N2O5 + O(3P) → 2NO2 + O2
C6H6 + h→ products

26

(26)

O(3P) + C6H6

k27

(27)

k28

(28)

O(3P) + O3 → 2O2
2O(3P) + O2 → O2 + O2

NO2 + O(3P) + N2
→ NO3 + N2
NO2 + O(3P) + O2
→ NO3 + O2
NO2 + O(3P) → NO + O2

→ Products

O3 + C6H6 → Products

(7)
(8a)
(8b)

(25)

5

NO2 + O3 → NO3 + O2
NO3 + O3 → NO2 + 2O2
NO3 + O(3P) → NO2 + O2

(10)
(12)
(17)

N2O5 molecules are formed by the NO2 + NO3
reaction.
NO2 + NO3 → N2O5

(18)

It was further converted to HNO3 by the N2O5
+ H2O reaction.
N2O5 + H2O → 2HNO3(21)

In addition, reactions of OH radicals, formed by
172-nm photolysis of H2O, are considered.

NO2 + OH → HNO3

(22)

(23)

N2O5 formed by the oxidation of NO2 is reduced
again to NO2 by the first-order reaction.
2N2O5 → 4NO2 + O2

(24)

N2O5 is also decomposed by the reaction with
O(3P).

Simultaneous Removal of NO2 and C6H6 by VUV light(a) Pure NO2
100
80

NO2

60

O2
N2O5

40

NO

20

NO3

0

0

O(3P)
O3

2

4

6

8

10

8

10

(b) Pure C6H6100

Consumption ratio of O(3P) / %Consumption ratio of O( 3P) / %Consumption ratio of O(3P) / %

6

O2

80
60
40

0

O(3P)

C6H6

20

0

100

2

4

O3
6

(c) NO2/C6H6 mixture

80
60
40
20
0

0

NO2

O2

NO

C6H6 N2O5
O(3P)

NO3

O3
2

4

6

8

10

Irradiation time / s

Fig. 6. Dependence of consumption ratio of
O(3P) in (a) pure NO2, (b) pure C6H6, and (c)NO2/C6H6 mixture on the irradiation time
under 172-nm photolysis. Data were obtainedby model calculations. The chamber depth was
0.5 cm.
N2O5 + O(3P) → 2NO2 + O2

(25)

In our removal model for the NO2/C6H6
mixture (Fig. 5(b)), NO2 is decomposed below
about 3 s. NO3 and NO are formed below 2 s
and disappear at about 3 s. The N2O5
concentration increases to about 60 ppm at
about 2 s and decreases to 4 ppm at 10 s. On
the other hand, the concentration of HNO3,
which is the dominant product in this model,
increases gradually from zero to 190 ppm until
10 s. A reasonable agreement is found between
the calculated and experimental data for time
profiles of the NO2, HNO3, and N2O5
concentrations, indicating that NO2 removal
proceeds dominantly through our proposed
removal model.
Fig. 5(b) also shows removal profile of C6H6
calculated taking account of all reactions
processes given in Table 2. In our removal
model of C6H6, C6H6 molecules are decomposedby the O(3P) + C6H6 reaction. A satisfactory
agreement between the experimental andsimulation data is obtained for the C6H6
removal in the NO2/C6H6 mixture, implyingthat our simulation model is applicable toreproduce the removal profile of C6H6 in the
NO2/C6H6 mixture
Fig. 6 shows the dependence of theconsumption ratio of O(3P) on the irradiation
time in pure NO2 or C6H6, and NO2/C6H6
mixture obtained by simulations. Results showthat the time profile of consumption ratio of
O(3P) obtained from the NO2/C6H6 mixture isnearly identical to that obtained from pure NO2,
excpet for the time profile of consumption ratioof O(3P) by C6H6. Below about 3 s, O(3P) atoms
are dominantly consumed by NO2, NO, andNO3. Although the consumption ratio of O(3P)
by O2 is small below 2 s, it gradually increases
above 2 s and it becomes larger than those ofNO2, NO, and NO3 above about 3 s.
It should be noted that the time profile ofconsumption ratio of O(3P) by C6H6 in the
NO2/C6H6 mixture is different from that in pure
C6H6. The consumption ratio of the O(3P) +C6H6 reaction rapidly decreases from 14% to1.1% in the short 0–3 s range in pure C6H6,
whereas it occupies only 1.5–4.0 % in the 2–6 srange in the NO2/C6H6 mixture. On the basis ofabove facts, O(3P) atoms are initially consumed
by NOx in the NO2/C6H6 mixture, so that theconsumption of O(3P) by C6H6 delays by 4±2 s
in the NO2/C6H6 mixture.
We discuss below the reason why the time
profile of consumption ratio of O(3P) by C6H6 in
the NO2/C6H6 mixture is different from that inpure C6H6 using known reaction rate constantsof related reactions. Removal of NO2 and C6H6
occurs competitively in the NO2/C6H6 mixture.
The reaction rate constant of the O(3P) + C6H6
reaction (k27 = 4.04 ×10-14 cm3 s-1 molecule-1) issmaller than those of the O(3P) + NO2 reactions(k13 + k15 = 3.33 ×10-11 cm3 s-1 molecule-1) by afactor of 82.19) It is also smaller than those of
the O(3P) + NO reaction (k16 = 2.99 ×10-11 cm3 s1 molecule-1) and O(3P) + NO3 reaction (k17 =1.70 ×10-11 cm3 s-1 molecule-1) by factors of 74
and 42, respectively.19) Therefore, O(3P) atoms
are initially consumed by reactions with suchNOx as NO2, NO, and NO3. The O(3P) + C6H6
reaction occurs after the NO2, NO, and NO3
concentrations become low, where the initialNO2 concentration is reduced to about half. The
consumption of O(3P) by NOx in the initialstage is attributed to the main reason why the
C6H6 removal delayed until a sufficient
reduction of NOx.
For the practical use of our removal method,a flow system, by which continuous removal of
NO2/C6H6 is possible, is required. On the basisof the present results, a long reaction chamber

令和元年度

九州大学大学院総合理工学報告

is necessary for the simultaneous removal of
NO2 and C6H6 in the NO2/C6H6 mixture using aflow system, where NO2 must be removed tosome extent upstream and the C6H6 is removed
downstream at low NO2 concentrations.

4.

Summary and Conclusion

NO2 and C6H6 in an NO2/C6H6 mixture were
simultaneously removed in air at atmosphericpressure using a 172-nm Xe2 excimer lamp.
Reactants and products before and after
photoirradiation demonstrated that NO2 andC6H6 were finally converted to HNO3 and CO2,
respectively. Although the removal rate of NO2
in the NO2/C6H6 mixture was nearly the sameas that of pure NO2 in air, the C6H6 removal
delayed until the NO2 concentration is reduced
to about half. In order to obtain information onthese results, computer simulation of removal
processes of NO2 and C6H6 in the NO2/C6H6
mixture was carried out. The delay of the C6H6
removal in the NO2/C6H6 mixture was
explained by much larger reaction rate
constants of the O(3P) + NOx reactions thanthat of the O(3P) + C6H6 reaction. The present
results give fundamental information on thedevelopmentofphotochemical
removalapparatus of mixtures of NOx/VOC.
Acknowledgments
This work was supported by JSPS KAKENHI
Grant number 25550056 (20132014).
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Appendix
Parameters used for the simulationof simultaneous removal of NO2 and C6H6 in
the NO2/C6H6 mixture by 172-nm photolysis in
air.
Table A1.

Absorption cross section of
O2 at 172 nm
Absorption cross section of
O3 at 172 nm
Branching fraction ofphotolysis of O3 at 172 nm
O3 + h→ O(3P) + O2 (4a)→ 3O(3P)(4b)
Absorption cross section of
NO2 at 172 nm
Absorption cross section of
C6H6 at 172 nm
Absorption cross section of
H2O at 172 nm
Initial reaction
temperature
Initial concentration of N2
Initial concentration of O2
Initial concentration of
C6H6
Initial concentration of
NO2
Initial concentration of
H2O
The number of repetitions
per sec

σ1 = 4.63×10-19[cm2/molecule]
σ4 = 8.16×10-19[cm2/molecule]
4a : 4b =0.9 : 0.1
9 = 1.45×10-17[cm2/molecule]σ26 = 6.48×10-21[cm2/molecule]σ22 = 8.16×10−19[cm2/molecule]297.6 [K]80 [%]
20 [%]
200 [ppm]
200 [ppm]
300 [ppm]
1000 [times/s]