The Effect of Titanium Dioxide on Secondary Organic Aerosol Formation

Subscriber access provided by Kaohsiung Medical University

Environmental Processes

The Effect of Titanium Dioxide on Secondary Organic Aerosol Formation Yi Chen, Shengrui Tong, Jing Wang, Chao Peng, Maofa Ge, Xiaofeng Xie, and Jing Sun Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b02466 • Publication Date (Web): 20 Sep 2018 Downloaded from http://pubs.acs.org on September 20, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

Environmental Science & Technology

The Effect of Titanium Dioxide on Secondary Organic Aerosol Formation Yi Chen a, b, c, Shengrui Tong a, *, Jing Wang a, Chao Peng a, b, Maofa Ge a, b, d, *, Xiaofeng Xie e, Jing Sun e

a

State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

b

c

University of Chinese Academy of Sciences,Beijing 100049, China

State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Peking University, Beijing 100871, China

d

Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China

e

Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

ACS Paragon Plus Environment


1

ABSTRACT

2

Secondary organic aerosol (SOA), a dominant air pollutant in many countries,

3

threatens the lives of millions of people. Extensive efforts have been invested in studying

4

the formation mechanisms and influence factors of SOA. As promising materials in

5

eliminating air pollutants, the role of photocatalytic materials in SOA formation is

6

unclear. In this study, TiO2 was employed to explore its impact on SOA formation during

7

the photooxidation of m-xylene with NOx in a smog chamber. We found that the presence

8

of TiO2 strongly suppressed SOA formation. The yields of SOA in the photooxidation

9

experiments of m-xylene with NOx were 0.3-4%, while negligible SOA was formed when

10

TiO2 was added. When ((NH4)2SO4) was introduced as seed, the presence of TiO2

11

decreased the yields of SOA from 0.3-6% to 0.3-1.6%. The sharply decreased

12

concentrations of reactive carbonyl compounds were the direct cause of the suppression

13

effect of TiO2 on SOA formation. However, the suppression effect was influenced by the

14

addition of seed and the initial concentration of NOx. Reaction mechanisms of the

15

photocatalysis of m-xylene with and without NOx were proposed.

16


Page 2 of 35

Page 3 of 35


17

INTRODUCTION

18

Fine particulate matter (PM2.5), which emerges as a by-product during the rapid

19

progress of national industrialization and urbanization, severely reduces atmospheric

20

visibility, impacts local and global climate and threatens human health

21

have shown that secondary organic aerosol (SOA) contributes 30%-60% of PM2.5 during

22

pollution events involving severe haze 5, 6. Generation of SOA is driven by the oxidation

23

of gaseous organic compounds. In most of these oxidation processes, OH radical is

24

believed to be the uppermost oxidant, which could be produced by the photolysis of O3,

25

HONO, and the reaction of O3 with alkene, and so on

26

contributes 34%-42% of OH radical formation in daytime

27

of photochemical pollution, NOx is an important precursor of HONO

28

positive correlation was found between the concentration of NOx and PM2.5

29

areas, NOx emission is mainly contributed by vehicle exhaust and usually accompanied

30

by the release of aromatic hydrocarbons. Aromatic hydrocarbons account for 70-90% of

31

anthropogenic sources and 20-30% of non-methane hydrocarbons in urban air

32

Furthermore, aromatic hydrocarbons dominated 20%-70% of SOA formation in urban

33

areas

34

aromatic hydrocarbons in the presence of NOx is classified as a classical reaction in

35

laboratory research 20-24.

16, 18, 19

7, 8

9, 10

1-4

. Field studies

. Photolysis of HONO

. As the prime component 11, 12

. Moreover, a 13

. In urban

14-17

.

. Because of their contributions to SOA formation, photooxidation of



Page 4 of 35

36

Titanium dioxide (TiO2), a typical and commonly used photocatalytic material, has

37

attracted extensive interest owing to its high transformation efficiency and

38

cost-effectiveness and nontoxicity

39

could promote the elimination of gas phase pollutants, such as NOx, O3, formaldehyde

40

and aromatic hydrocarbons. NOx can be degraded by TiO2 under UV-light illumination to

41

produce NO3-, NO2- on the surface and gas phase products HONO and HNO3

42

degradation efficiency of O3 is related to the relative humidity and the content of TiO2 in

43

the matrix

44

formaldehyde to CO2 and H2O

45

hydrocarbons in the presence of TiO2, Debono and Sleiman studied the kinetics, reaction

46

intermediates and carbon balance of toluene 33, 34. Because of their desirable properties of

47

self-cleaning and degradation of pollutants, commercial TiO2-coated surfaces have

48

gradually been applied to road pavements, building exteriors, windows and indoor paint,

49

such as the surface of National Opera Hall in China, several thousand building in Japan

50

(MM Towers, Matsushita Denso building et al), Dives in Misericordia Church in Rome

51

and the roof of Dubai Sports City’s Cricket Stadium 35-38. When the coated TiO2 exposed

52

to real atmosphere environment, gas pollutants emitted by vehicles and industries are

53

expected to be adsorbed and eliminated by TiO2.

54 55

31

25

. It has been proved that the TiO2-coated surfaces

26-30

. The

. In the elimination of formaldehyde, TiO2 completely mineralizes 32

. Regarding the photodegradation of aromatic

However, in a recent report, Ourrad demonstrated that SOA was generated when limonene was eliminated by TiO2

39

. The SOA yield in Ourrad’s study was about 2.4%,


Page 5 of 35


56

which is lower than the SOA yields of limonene oxidized by OH radical, O3, NO3 in

57

atmosphere 40-42. This result suggests an adverse impact of photocatalytic materials. If the

58

adverse impact is ubiquitous, the role of photocatalytic materials in eliminating gas phase

59

pollutants should be reconsidered. Hence, the effects of photocatalytic materials on SOA

60

formation are worthy of further study. Moreover, most photocatalytic studies focused on

61

a single pollutant or several discrete components. In the real atmosphere, various

62

interactive pollutants coexist instead of a single component. Therefore, a more complex

63

situation should be studied in photocatalytic experiments.

64

Because of their emissions, BTEX (benzene, toluene, ethylbenzene, xylene) are thought

65

to be the most important aromatics hydrocarbon in atmosphere 14. Among BTEX, xylene

66

owns the fastest reaction rate toward OH radicals, which would dominate more SOA in

67

the same period 21. In this study, we chose m-xylene to represent aromatic hydrocarbons

68

to act as the precursor of SOA. NOx was injected as the source of OH radical to oxidize

69

m-xylene, generating SOA. TiO2 was introduced to study the influence of photocatalytic

70

materials on SOA formation. The gas phase and absorbed products were detected and

71

analyzed. The roles of TiO2 in the formation of SOA are discussed, and reasonable

72

reaction mechanisms are proposed.

73

MATERIALS AND METHODS

74

Smog Chamber Experiments To study the effect of TiO2 (P25, Acros) on SOA

75

formation, several reaction systems were designed: a ternary system, i.e., photocatalysis



76

of NOx and m-xylene (TiO2+NOx+m-xylene), and three binary systems, including

77

classical experiments (NOx+m-xylene) and photocatalysis of NOx/m-xylene (TiO2+NOx,

78

TiO2+m-xylene). All these reactions comprised the non-seed and seed experiments.

79

Because particles exist everywhere in real atmosphere, this setting is comprehensive for

80

describing the effect of TiO2 on SOA formation.

81

These designed experiments were performed in a smog chamber. The detail

82

information of the smog chamber and the equipped instruments in our study was

83

illustrated in Figure S1. The main experimental procedures contained the pretreatment of

84

TiO2, the injection of reactants and the detection of the evolution of reactants and

85

products. To remove the adsorbed compounds, TiO2 was pretreated before the reaction.

86

First, TiO2 was calcined at 673 K for 10 h. Second, 200±1 mg of TiO2 was dispersed in

87

water (5 mL) under ultrasonic vibration for 10 min. Third, the dispersion was coated on

88

one side of the glass plate (250 mm*300 mm*2.5 mm) and dried by zero air blowing

89

mildly for approximately 30 min. Then, the glass plate was placed in the smog chamber.

90

The devices used to fix the glass plate were passivated before putting them into the

91

Teflon bag. Thereafter, the smog chamber was cleaned and filled with zero air. Finally,

92

the UV-lights were turned on for approximately 11 h to eliminate distractions. After the

93

pretreatment of TiO2, the reaction chamber was cleaned again. Then, certain amount of

94

m-xylene was injected into a three-way tube and was carried into smog chamber by zero

95

air. The volume of zero air was controlled by a mass flow controller. Thereafter, certain


Page 6 of 35

Page 7 of 35


96

amount of NOx was introduced in the chamber via controlling the flow rate and injection

97

time. In seed experiments, (NH4)2SO4 was added as seed, via atomizing (NH4)2SO4

98

aqueous solution (1 mg/g) at high pressure, which was dried by a silicone tube. In

99

classical experiments, blank glass plate was putted into the Teflon bag to exclude the

100

disturbance of glass plate. The lights were turned on to start the reactions after the

101

injected reactants were balanced for approximately 30 min.

102

The initial concentration of NOx was in the range of 0-220 ppb. NOx and the generated

103

O3 were continuously monitored by an NOx analyzer (T200, API) and an O3 analyzer

104

(T400, API), respectively. The concentration of m-xylene was set at 100 and 200 ppb;

105

100 ppb to simulate the low pollution level and 200 ppb to simulate severe pollution with

106

seed added. The concentration of m-xylene was quantified by gas chromatography-mass

107

spectrometry (GC-MS) (7890B-5977B, Agilent Technology) coupled with a Model 7100

108

Preconcentrator (Entech Instruments Inc.). The initial number concentration of

109

(NH4)2SO4 was approximately 104 m-3 in seed experiments. The concentration of SOA

110

was monitored with a scanning mobility particle sizer (SMPS). The flow rates of

111

collecting sample and sheath gas were 0.3 L/min and 3 L/min, respectively. The SOA

112

yields were calculated according to the mass ratio between the formed aerosol (∆M) and

113

the reacted m-xylene (∆CH). The formed SOA was corrected with wall loss.

114

Detection of Gaseous Products Because reactive oxygenated compounds were

115

believed to dominate the formation of SOA, analysis of gas products focused on reactive



Page 8 of 35

43, 44

116

carbonyl compounds (RCCs), which were detected via a derivation method

. In this

117

study, 2,4-dinitrophenylhydrazine (DNPH) was used to derive RCCs to form hydrazines

118

45-47

119

which was linked to smog chamber. Because the concentrations of products were low,

120

every sample was collected for 4 hours at a flow of 300 mL/min, and two samples were

121

collected for each experiment. Derivatives were extracted with 5 mL of acetonitrile and

122

then measured with high performance liquid mass spectrometry (HPLC-MS) (Waters,

123

Vion). The initial concentrations of NOx and m-xylene were consistent in all experiments

124

for the detection of gaseous products.

. A DNPH-Silica cartridge (350 mg, 1 mL) was connected to an ozone destructor,

125

A Nicolet FTIR Spectrometer 6700 combined with a mercury-cadmium-telluride

126

(MCT) detector and a 33 m Permanently Aligned Long Path Gas Cell (PIKE

127

Technology) were used to detect the changes of gas phase products by recording the

128

spectra in the range from 4000 to 750 cm−1. The spectra were obtained from the average

129

of 50 scans with a resolution of 2 cm-1. The experiments were conducted in the smog

130

chamber with the initial condition of 5 ppm m-xylene and 3 ppm NOx. For each

131

detection, the gas cell was vacuumized first, and then, the reaction gas from the smog

132

chamber was introduced into the gas cell by pressure differentials. The spectrum of zero

133

air was collected as the background, and the components in these reactions were detected

134

intermittently.


Page 9 of 35


135

Detection of the Adsorbed Products To better understand the reaction mechanisms,

136

the adsorbed products on TiO2 were measured via diffuse reflectance infrared Fourier

137

transform spectroscopy (DRIFTS). About 24 mg of preheated TiO2 was placed in the

138

sample holder with a flow of 400 mL/min zero air. After reaching steady state, the

139

background spectrum of TiO2 was collected. Then, m-xylene (50 ppm) and NOx (50 ppm)

140

were introduced into the reaction cell. Meanwhile, the xenon lamp (CHF-XM-500W)

141

with a 365 nm optical filter was turned on to irradiate the reaction cell. The software

142

(Omnic) started to collect series of spectra with an average of 100 scans and resolution of

143

4 cm-1.

144

GC-MS was combined to analyze the adsorbed products on TiO2. The samples after

145

terminating reactions were dispersed in acetonitrile to form suspension, followed by

146

treatment with ultrasonic wave for 20 minutes. Then, the filtered solution was condensed

147

via N2 bubbling to 0.5 mL. Thereafter, the condensed solution was taken to run GC-MS

148

test.

149

RESULTS AND DISCUSSION

150

Classical Experiments After turning the lights on, NO2 started to convert to NO,

151

accompanied by the formation of OH radical, O3 and gradual consumption of m-xylene

152

(Figure S3). Oxidation of m-xylene was started with the addition of OH radical to form

153

OH-aromatic adducts (>90%)

154

primary peroxy radicals via O2 addition, or generated dimethylphenols and HO2 by

48-50

. OH-aromatic adducts reacted with O2 to produce



Page 10 of 35

155

H-abstraction 49. Primary peroxy radicals underwent cyclization to form bicyclic radicals

156

and then combined with O2 to form bicyclic peroxy radicals

157

radicals were formed by the reaction of bicyclic peroxy radicals with NO

158

bicyclic alkoxyl radicals underwent a ring cleavage reaction to form RCCs (glyoxal,

159

methylglyoxal and the related unsaturated dicarbonyl compounds), and RCCs

160

participated in further reactions

161

confirmed that RCCs can partition onto particles and generate oligomers via accretion

162

reactions, such as hemiacetal and aldol addition

163

closely related to RCCs. The whole reaction process was complicated, but all of the steps

164

were linked with OH, peroxy radicals (RO2), alkoxyl radicals (RO), HO2, NO and O2, as

165

discussed by Kroll

166

the process. When the concentrations of low volatility products reached a critical value,

167

nucleation occurred and SOA grew. The products with lower volatility was more

168

favorable to SOA formation. In Table 1, the yields of SOA increased and then decreased

169

with the increase of the NOx concentration, consistent with the observation of

170

Sarrafzadeh and Song et al 57, 58. This phenomenon was caused by two roles of NOx in the

171

process. If the concentration of NOx increased, the generated NO would increase, and the

172

formation of OH radical would increase first and then decrease

173

competed with HO2 to react with RO2. The volatility of the compounds generated by

174

NO+RO2 is higher than the volatility of the compounds generated by HO2+RO2

56

49, 52, 53

49, 51

. Bicyclic alkoxyl 51

. Then,

. Both field and laboratory investigations

54-56

. Hence, the formation of SOA was

. Both low volatility and high volatility products were produced in


57

. The presence of NO

56

.

Page 11 of 35


175

Hence, the increased NO was unfavorable to SOA formation. For OH radical, it was a

176

determining factor of the oxidation of m-xylene to form SOA. The higher concentration

177

of OH radical was favorable to SOA formation

178

of NO and OH radical caused by the increase of NOx lead to that the SOA yield increased

179

first and then decrease. Finally, 0.3-4% SOA formed over the studied concentration range

180

of NOx in non-seed classical experiments.

57

. Therefore, the concentration changes

181

In the seed experiments, consumption of NOx and m-xylene, and the formation of O3

182

were like those of the non-seed experiments. Nonetheless, compared to the non-seed

183

experiments, the SOA yields increased to 0.3-6% due to the enhanced gas-solid partition

184

59, 60

185

deposition of semi-volatile organic compounds.

. In the seed experiment, (NH4)2SO4 acted as the nucleus and facilitated the

186

The results of RCCs measured by HPLC-MS are shown in Table S1, and the relative

187

intensities of these compounds calculated from the ratio of Ii/Ii-max are shown in Figure 1,

188

where Ii and Ii-max represent the intensity of compound i and the maximal intensity of i in

189

the three reaction systems, respectively. As expected, glyoxal and methylglyoxal were

190

identified. In addition, formaldehyde, acetaldehyde, propionaldehyde, hydroxyethanal

191

and m-tolualdehyde were also detected. For glyoxal and methylglyoxal, the concentration

192

of sample collected at the first 4 hours was higher than that collected at the late 4 hours.

193

For RCCs in Figure 1b, the higher concentrations were shown in the sample collected at

194

the late 4 hours. This phenomenon was corresponding to the transformation of glyoxal



Page 12 of 35

195

and methylglyoxal. Glyoxal, methylglyoxal and the related unsaturated dicarbonyl

196

compounds were the first-generation products of ring-open. They were further oxidized

197

to form low volatility products or compounds with small molecular weight such as

198

formaldehyde, acetaldehyde et al. Hence, the consumption of glyoxal, methylglyoxal

199

resulted in the decrease of concentration of themselves and the increase of concentration

200

of RCCs in Figure 1b. According to the IR experiments (Figure S4a), when reactants

201

were injected into the smog chamber, peaks were observed at 3032, 2935 and 2880 cm-1,

202

which were identified as the stretching vibration of νAr-CH

203

time, accompanied by the appearance of peaks from the gas phase products. The peaks at

204

2820 cm-1 and 2834 cm-1 were attributed to the aldehyde C-H stretch of methylglyoxal 62,

205

63

206

identified as the out-of-phase C-H stretch of glyoxal

207

2800-2850 cm-1 increased first and then decreased, revealing the generation and

208

consumption of glyoxal and methylglyoxal.

61 . These

peaks decreased over

. Near the peak of 2834 cm-1, there was a shoulder peak at 2839 cm-1, which was 62

. The absorption intensity at

209

Photocatalysis of m-Xylene or NOx on TiO2 Kinetic studies of the photocatalysis of

210

m-xylene or NOx on TiO2 were conducted in the smog chamber. Because conversion

211

occurred between NO and NO2, the total consumption rate of NO+NO2 (NOx) was

212

calculated to obtain the kinetic result. The kinetics of the photocatalysis of m-xylene or

213

NOx was treated as a pseudo first order reaction, which means the kinetic study of R1 can

214

be analyzed with Eq. (1). By integrating of Eq. (1), Eq. (2) was obtained, where k is the


Page 13 of 35


215

kinetic constant, t is the reaction time, [reactant]0 and [reactant]t are the concentration of

216

the reactant at 0 and t min, respectively. The natural logarithm of the ratio

217

[reactant]0/[reactant]t as a function of time is shown in Figure S5. The good linear

218

correlation validated the pseudo first order assumption. The kinetic constants obtained,

219

averaged from three experiments, were 0.58 ± 0.06 and 0.37 ± 0.04 h-1 for NOx and

220

m-xylene, respectively. TiO2

reactant products

221

d[reactant]

222

dt

ln

223

(R1)

= kreactant

[reactant]0 [reactant]t

(1)

= kt

(2)

224

During the photocatalysis of NOx with TiO2, NO and O3 were formed in gas phase.

225

However, all of them were converted after a period of photodegradation. In Figure S6,

226

the IR spectra collected by DRIFTS of NOx on the TiO2 surface with illumination were

227

exhibited, and the results are consistent with previous studies

228

NOx was closely relevant to the H-bonded hydroxyl groups on the surface of TiO2, as

229

revealed by the negative peaks at 3694, 3665, 3631 cm-1 28. With the consumption of OH

230

radical, several new peaks of products at 1488 and 1295 cm-1 (monodentate nitrate),

231

1605, 1584, 1568 and 1256 cm-1 (bidentate nitrate) and 1618 cm-1 (bridge nitrate) were

232

identified as the vibration of NO3-

233

increased first and then decreased over the exposure time, implying the formation and

234

transformation of NO2- 27. Finally, the adsorbed product of NOx was NO3-.

27, 29, 64

27-29

. The photocatalysis of

. The ν (NO) of bidentate nitrite at 1205 cm-1



Page 14 of 35

235

No SOA was detected in the photodegradation of m-xylene with or without seed added.

236

The measurements of RCCs show that the detected species were the same as those of the

237

classical experiments, but the signals were much lower, except for m-tolualdehyde (Table

238

S1 and Figure 1).

239

The adsorbed products in the photodegradation of m-xylene were studied via in situ

240

DRIFTS (Figure 2a). Reactive oxygen species (ROS) was generated on TiO2 to oxidize

241

the adsorbed compounds. Among the ROS generated by TiO2, OH (3694, 3665, 3631

242

cm-1) was detected and consumed during the reaction. The peaks at 1605 and 1588 cm-1

243

were identified as the ring skeletal vibration of benzene ring, while 1652 cm-1 was

244

assigned to the vibration of C=O of aromatic aldehyde

245

intermediates and the complexity of their structures, the collected IR spectra were

246

complicated. Hence, GC-MS was combined to analyze the absorbed products. As shown

247

in Figure S7, the total ion current (TIC) of the absorbed products in acetonitrile was

248

illustrated. m-Tolualdehyde was detected as the main adsorbed product, which confirmed

249

that the peaks at 1690 and 1652 cm-1 were the vibration of C=O of m-tolualdehyde

250

Owing to the abundance of m-tolualdehyde adsorbed on the surface of TiO2, the

251

desorption of m-tolualdehyde occurred at the same time, but the quantity was still small

252

(1.0 ppt and 1.3 ppt in the first and late 4 hours, respectively) due to its high desorption

253

activation energy

254

higher than that in classical experiment. The low concentration of m-tolualdehyde in

33

65

. Due to the multiple

65

.

. However, the concentration of gaseous m-tolualdehyde was still


Page 15 of 35


255

classical experiment was attributed by the portion of reaction channel, where

256

H-abstraction channel to form 3-methylbenzyl radical was 2%-4%

257

m-tolualdehyde was formed from 3-methylbenzyl peroxy radical (RmO2), which was

258

generated by 3-methylbenzyl radical reacting with O2 56. The existence of competing

259

reactions (NO+RmO2, HO2+RmO2) for RmO2 to form m-tolualdehyde and the

260

consumption of m-tolualdehyde also resulted in the low concentration of m-tolualdehyde

261

in classical experiment

262

adsorbed again on the surface of TiO2, resulting in a maximum in the process. The higher

263

concentration of m-tolualdehyde in the late 4 hours indicated that the maximum of

264

gaseous m-tolualdehyde was more likely to show in the late 4 hours. The decreased

265

concentration of m-tolualdehyde in classical experiment suggested that the consumption

266

of m-tolualdehyde was faster than the generation of it in the late 4 hours.

56

49,

51,

66

.

. In photocatalysis of m-xylene, the released products could be

267

Photocatalysis of m-xylene and NOx on TiO2 As discussed above, we obtained the

268

kinetic parameters of the photocatalysis of NOx and photocatalysis of m-xylene via a

269

pseudo first order assumption. However, we did not obtain a specific kinetic parameter in

270

classical photooxidation experiment because of the unstable OH radical concentration

271

caused by the diminishing NOx or in ternary system due to the complex reactions. Hence,

272

for comparison between the ternary system and binary systems, the natural logarithm of

273

[reactant]0/[reactant]t was calculated and plotted. As shown in Figure S5, the

274

consumption rates of NOx and m-xylene in ternary system were higher than the



Page 16 of 35

275

consumption rates in binary systems, suggesting that the consumption of NOx and

276

m-xylene in ternary system could not be explained by the single role of the photocatalysis

277

reactions (R2), (R3) or classical photooxidation reaction (R4). Moreover, the

278

consumption rates of NOx and m-xylene in their respective binary systems were close,

279

which means that R2 and R4, R3 and R4 could take place simultaneously in kinetics.

280

These results suggest that R2, R3, R4 should coexist in ternary system. Furthermore,

281

more complex reactions, such as R5, may also exist in ternary system. These interactions

282

in ternary system accelerate the consumption of m-xylene and NOx, in contrast with the

283

report of Palau

284

m-xylene and n-butyl acetate in their binary or ternary mixtures were depressed. Because

285

no interaction but only competition existed among toluene, m-xylene and n-butyl acetate,

286

the single degradation rates of toluene, m-xylene or n-butyl acetate decreased. Hence, the

287

kinetics of the system with interactive compounds is different from that of discrete

288

compounds system.

67

, which showed that the photodegradation efficiencies of toluene,

TiO2

289

m-xylene products

290

NOx products

(R3)

291

NOx + m-xylene → products

(R4)

292

NOx + -xylene products

TiO2

TiO2

(R2)

(R5)

293

In ternary system, the concentration of NOx and O3 decreased gradually via the

294

photocatalysis of TiO2 rather than trending to a stable value as shown in Figure S3a. For


Page 17 of 35


295

the species of RCCs, the detected result in ternary system was the same as the results in

296

photocatalysis of m-xylene and in classical experiments. The only difference in these

297

results was the signal intensities. As shown in Figure 1, for most of the RCCs, the highest

298

concentrations were presented in classical experiments, while the concentrations in

299

ternary system were in the middle. The detection of RCCs also suggested the coexistence

300

of R2, R3 and R4. Compared to the first 4 hours, the concentrations of glyoxal and

301

methylglyoxal in the late 4 hours decreased about 30% in the classical experiment, while

302

decreased about 70% in the ternary system. For the detected RCCs in Figure 1b, the

303

concentrations of them increased in classical experiment, while decreased in ternary

304

system. These phenomena suggest that the presence of TiO2 photodegraded the generated

305

RCCs in the process.

306

As analyzed by DRIFTS and GC-MS (Figure 2b, Figure S7, Table S1), NO3- and

307

m-tolualdehyde were the main identified adsorbed products and increased over time until

308

reaching the steady state. Similar to the photocatalysis of NOx, NO2- was formed in the

309

ternary reaction system, and the signal intensity first increased and then decreased. In

310

addition to the formation of m-tolualdehyde, nitric acid-(3-methyl-benzyl ester) was also

311

formed in the reaction, as shown in Figure S7. In the collected IR spectra, 1284 cm-1 was

312

attributed to the symmetrical stretching vibration of the N=O bonds of nitric

313

acid-(3-methyl-benzyl ester)

314

m-xylene in the classical experiments. However, the reported yields of nitric

68, 69

. The ester was analyzed as one of the products of



50, 56, 70

315

acid-(3-methyl-benzyl ester) were less than 1%

. From the detection results, nitric

316

acid-(3-methyl-benzyl ester) was a main component in the adsorbed products, revealing

317

that new reaction channels must exist in ternary system.

318

As shown in Table 2 and Figure 3a, the mass concentrations of SOA were so low that

319

SOA could be neglected in non-seed experiments, indicating that TiO2 could dramatically

320

suppress SOA formation. However, considerable amounts of SOA were formed when

321

seed was introduced (Figure 3b). The SOA yields varied from 0.3% to 1.6% among the

322

concentration range of NOx studied. The yields were higher than those in the ternary

323

system without seed added, but lower than the yields in the classical experiments with

324

seed. We found that the SOA yields increased first and then decreased with the increase

325

of NOx concentration, consistent with the classical experiments. In the single

326

photocatalysis of m-xylene with seed added, no SOA formed. Hence, the SOA generated

327

in ternary system with seed added should be related to the addition of NOx, i.e., the

328

reaction of m-xylene with NOx (R4). Because R4 was the reaction in classical

329

experiment, the roles of NO and OH radical on SOA formation were the same as that in

330

classical experiment. In addition, the photodegradation role of TiO2 was another factor to

331

affect SOA formation. The adsorption and photodegradation of NOx and m-xylene by

332

TiO2 decreased the generation of NO, affected the formation of OH radicals in gas phase

333

and decreased the concentration of RCCs from R4. The formed RCCs would be further

334

photodegraded by TiO2, suppressing SOA formation. Though the decrease of NO was


Page 18 of 35

Page 19 of 35


335

favored to SOA formation, the suppression effect to SOA formation caused by the

336

decrease of RCCs was stronger. Owing to the presence of TiO2, the critical value of NOx

337

for the highest concentration of OH radical changed compared with classical experiment.

338

Therefore, the change of OH radical, NO and RCCs caused by the photodegradation role

339

of TiO2 ultimately lead to the suppression of SOA formation and made a change about

340

the critical value of ppbC/NOx for the highest SOA yield.

341

Reaction Mechanisms and the Role of TiO2 in the Formation of SOA During the

342

photocatalysis of m-xylene, photocatalytic processes mainly occurred on the surface of

343

TiO2, so the products initially formed on the surface. According to the high yield of

344

m-tolualdehyde in the adsorbed products, the initial step on TiO2 should be dominated by

345

the oxidation of the methyl group of m-xylene to produce 3-methylbenzyl radical

346

deduced from the results of DRIFTS, OH radical should be the dominant oxidant in this

347

process. As shown in Schematic 1, m-methylbenzyl radical would react with O2 to form

348

peroxy radical. Then, peroxy radical was reduced by electrons to generate

349

m-tolualdehyde, which was further oxidized to m-toluic acid. m-Toluic acid underwent

350

the Photo-Kolbe reaction to form CO2 and toluene. Then, the photocatalysis of toluene

351

proceeded as previous studies

352

reactions. m-Tolualdehyde, benzaldehyde and other RCCs tended to be adsorbed on the

353

surface and further oxidized by ROS rather than desorbed into the gas phase, as

354

suggested by Debono

33

34

71

. As

. Other RCCs could be formed via the ring open

. For this reason, the concentration of RCCs in gas phase was



Page 20 of 35

355

low, leading to no formation of SOA in the process. The suppression effect of TiO2 on

356

SOA formation during the photocatalysis of m-xylene is conspicuous.

357

In the ternary system, as analyzed from the kinetics and products, R2, R3, R4 and a

358

new reaction channel related to the formation of nitric acid-(3-methyl-benzyl ester)

359

should coexist. As discussed above, no SOA formed in the process of R2, and the

360

ultimate product of R3 was nitrate. R4 was the reaction in the classical experiments,

361

which led to the formation of SOA. The reaction mechanism of R4 to form SOA was

362

discussed above. Nitric acid-(3-methyl-benzyl ester) yielded in the ternary system was

363

considerable, which should not be formed by R4. In R4, the proportion of H-atom

364

abstraction from the methyl-substituent group was 2%-4%, which was the primary cause

365

for the low yield of nitric acid-(3-methyl-benzyl ester)

366

the 3-methylbenzyl radical generated by the oxidation of NO3 radical was a key

367

intermediate in the synthesis of nitric acid-(3-methyl-benzyl ester)

368

above, 3-methylbenzyl radical was the specific primary intermediate in the photocatalytic

369

process, which was distributed for the oxidation of OH radical in the ternary experiments

370

rather than NO3 radical. 3-Methylbenzyl radical further reacted with O2 and NO to form

371

nitric acid-(3-methyl-benzyl ester) 56. Then, compared with the classical experiments, the

372

enhanced formation of m-methylbenzyl radical greatly improved the yield of nitric

373

acid-(3-methyl-benzyl ester) adsorbed on the surface of TiO2 in the ternary system.

49, 51, 66


. Baciocch proposed that

72

. As mentioned

Page 21 of 35


374

Hence, the formation of nitric acid-(3-methyl-benzyl ester) occurred via R5, indicating

375

that the presence of NOx could impact the mechanism of the photocatalysis of m-xylene.

376

As deduced from the characteristics of the four reactions in the ternary system, the

377

SOA formed in the process should be dominated by R4. RCCs were mainly generated

378

from R4. The photocatalysis of TiO2 eliminated some of NOx and m-xylene (R2, R3, R5),

379

which decreased the amount of NOx and m-xylene that were available to react with each

380

other (R4). In addition, the intermediate products could also be photocatalyzed by TiO2.

381

Therefore, the concentrations of gaseous RCCs in the ternary system were lower than that

382

in the classical experiments, but higher than that in the photocatalysis of m-xylene. With

383

the formed RCCs in the ternary system, the detection of SOA formation was insignificant

384

when no seed was added. However, when seed was added, considerable SOA was

385

generated. These results reveal that the concentrations of gaseous RCCs formed in the

386

ternary system were too limited to nucleate in the non-seed reaction, but the

387

concentrations of RCCs were enough to gas-solid partition on the seed to grow. The SOA

388

yields in the seed ternary system were closely related to the initial concentration of NOx.

389

These results suggested that the effect of TiO2 on SOA formation in the ternary system

390

was still suppression. However, the efficiency of this suppression was influenced by

391

many factors, such as the addition of seed and the concentration of NOx. The addition of

392

seed would decrease the suppression effect of TiO2 on SOA formation.



393

In modern cities, vehicle emissions (NOx, aromatic hydrocarbon, long-chain alkene et

394

al) play a significant role in SOA formation. In severe pollution period, many cities take

395

measures to restrict the numbers of vehicle on the road to improve air quality. In our

396

study, we found that the presence of TiO2 could effectively suppress SOA formation from

397

the oxidation of m-xylene, which means that coating TiO2 on building surface and

398

pavement could be a potential way to abate fine particle pollution. However, since studies

399

on the influence of photocatalytic materials on SOA formation have rarely been reported

400

to date, more efforts should be made in this field to obtain a deep understanding of the

401

process and further improve the suppression efficiency of photocatalytic materials on

402

SOA formation 39.

403

Supporting Information

404

The list of chemicals, detected products (Table S1), diagram of the experimental setup

405

(Figure S1), Spectrum of light source in smog chamber (Figure S2), reaction profiles of

406

the classical experiments (Figure S3), collected IR spectra of the gas phase (Figure S4),

407

kinetics profiles (Figure S5), DRIFTS spectra (Figure S6), and TIC of the adsorbed

408

products (Figure S7)

409

Corresponding Authors

410

Shengrui Tong: Phone: +86-10-8261-2655; e-mail: [email protected].

411

Maofa Ge: Phone: +86-10-6255-4518; e-mail: [email protected].

412

ACKNOWLEDGMENTS


Page 22 of 35

Page 23 of 35


413

This work was supported by the National Key Research and Development Program of

414

China (2016YFC0202202, 2016YFA0203000), the National Natural Science Foundation

415

of China (41571130022, 91544223), and the International Partnership Program of

416

Chinese Academy of Sciences (GJHZ1656).

417 418

REFERENCE

419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446

1. Shrivastava, M.; Lou, S.; Zelenyuk, A.; Easter, R. C.; Corley, R. A.; Thrall, B. D.; Rasch, P. J.; Fast, J. D.; Simonich, S. L. M.; Shen, H.; Tao, S., Global long-range transport and lung cancer risk from polycyclic aromatic hydrocarbons shielded by coatings of organic aerosol. PNAS 2017, 114, (11), E2263. 2. Moise, T.; Flores, J. M.; Rudich, Y., Optical properties of secondary organic aerosols and their changes by chemical processes. Chem. Rev. 2015, 115, (10), 4400-4439. 3. von Schneidemesser, E.; Monks, P. S.; Allan, J. D.; Bruhwiler, L.; Forster, P.; Fowler, D.; Lauer, A.; Morgan, W. T.; Paasonen, P.; Righi, M.; Sindelarova, K.; Sutton, M. A., Chemistry and the linkages between air quality and climate change. Chem. Rev. 2015, 115, (10), 3856-3897. 4. Wang, Y.; Lee, K.-H.; Lin, Y.; Levy, M.; Zhang, R., Distinct effects of anthropogenic aerosols on tropical cyclones. Nat. Clim. Change 2014, 4, (5), 368-373. 5. Huang, R. J.; Zhang, Y.; Bozzetti, C.; Ho, K. F.; Cao, J. J.; Han, Y.; Daellenbach, K. R.; Slowik, J. G.; Platt, S. M.; Canonaco, F.; Zotter, P.; Wolf, R.; Pieber, S. M.; Bruns, E. A.; Crippa, M.; Ciarelli, G.; Piazzalunga, A.; Schwikowski, M.; Abbaszade, G.; Schnelle-Kreis, J.; Zimmermann, R.; An, Z.; Szidat, S.; Baltensperger, U.; El Haddad, I.; Prevot, A. S., High secondary aerosol contribution to particulate pollution during haze events in China. Nature 2014, 514, (7521), 218-222. 6. Guo, S.; Hu, M.; Zamora, M. L.; Peng, J.; Shang, D.; Zheng, J.; Du, Z.; Wu, Z.; Shao, M.; Zeng, L.; Molina, M. J.; Zhang, R., Elucidating severe urban haze formation in China. PNAS 2014, 111, (49), 17373-17378. 7. Atkinson, R.; Arey, J., Atmospheric degradation of volatile organic compounds. Chem. Rev. 2003, 103, 4605-4638. 8. Gligorovski, S.; Strekowski, R.; Barbati, S.; Vione, D., Environmental implications of hydroxyl radicals (OH). Chem. Rev. 2015, 115, (24), 13051-13092. 9. Su, H.; Cheng, Y.; Oswald, R.; Behrendt, T.; Trebs, I.; Meixner, F. X.; Andreae, M. O.; Cheng, P.; Zhang, Y.; Pöschl, U., Soil nitrite as a source of atmospheric hono and oh radicals. Science 2011, 333, (6049), 1616-1618.



447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485

10. Acker, K.; Möller, D.; Wieprecht, W.; Meixner, F. X.; Bohn, B.; Gilge, S.; Plass-Dülmer, C.; Berresheim, H., Strong daytime production of OH from HNO2 at a rural mountain site. Geophys. Res. Lett. 2006, 33, (2), L02809. 11. Stemmler, K.; Ammann, M.; Donders, C.; Kleffmann, J.; George, C., Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid. Nature 2006, 440, (7081), 195-198. 12. Li, S.; Matthews, J.; Sinha, A., Atmospheric hydroxyl radical production from electronically excited NO2 and H2O. Science 2008, 319, (5870), 1657-1660. 13. Tao, M.; Chen, L.; Wang, Z.; Ma, P.; Tao, J.; Jia, S., A study of urban pollution and haze clouds over northern China during the dusty season based on satellite and surface observations. Atmos. Environ. 2014, 82, 183-192. 14. Liu, P. G.; Yao, Y.; Tsai, J.; Hsu, Y.; Chang, L.; Chang, K., Source impacts by volatile organic compounds in an industrial city of southern Taiwan. Sci. Total Environ. 2008, 398, 154-163. 15. Cai, C.; Geng, F.; Tie, X.; Yu, Q.; An, J., Characteristics and source apportionment of VOCs measured in Shanghai, China. Atmos. Environ. 2010, 44, (38), 5005-5014. 16. Guo, S.; Hu, M.; Guo, Q.; Zhang, X.; Zheng, M.; Zheng, J.; Chang, C. C.; Schauer, J. J.; Zhang, R., Primary sources and secondary formation of organic aerosols in Beijing, China. Environ. Sci. Technol. 2012, 46, (18), 9846-9853. 17. Ran, L.; Zhao, C. S.; Xu, W. Y.; Han, M.; Lu, X. Q.; Han, S. Q.; Lin, W. L.; Xu, X. B.; Gao, W.; Yu, Q.; Geng, F. H.; Ma, N.; Deng, Z. Z.; Chen, J., Ozone production in summer in the megacities of Tianjin and Shanghai, China: a comparative study. Atmos. Chem. Phys. 2012, 12, (16), 7531-7542. 18. Lü, Z. F.; Hao, J. M.; Duan, J. C.; Li, J. H., Estimate of the formation potential of secondary organic aerosol in Beijing summertime. Environ. Sci. 2009, 30, (4), 969-975. 19. Odum, J. R.; Jungkamp, T. P. W.; Griffin, R. J.; Flagan, R. C.; Seinfeld, J. H., The atmospheric aerosol-forming potential of whole gasoline vapor. Science 1997, 276, (5309), 96-99. 20. Ng, N. L.; Kroll, J. H.; Chan, A. W. H.; Chhabra, P. S.; Flagan, R. C.; Seinfeld, J. H., Secondary organic aerosol formation from m-xylene, toluene, and benzene. Atmos. Chem. Phys. 2007, 7, 3909–3922. 21. Li, K.; Wang, W.; Ge, M.; Li, J.; Wang, D., Optical properties of secondary organic aerosols generated by photooxidation of aromatic hydrocarbons. Sci. Rep. 2014, 4, 4922. 22. Li, L.; Tang, P.; Nakao, S.; Chen, C. L.; Cocker, D. R., Role of methyl group number on SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions. Atmos. Chem. Phys. 2016, 16, (4), 2255-2272. 23. Li, L.; Tang, P.; Nakao, S.; Cocker Iii, D. R., Impact of molecular structure on secondary organic aerosol formation from aromatic hydrocarbon photooxidation under low-NOx conditions. Atmos. Chem. Phys. 2016, 16, (17), 10793-10808.


Page 24 of 35

Page 25 of 35

486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524


24. Ji, Y.; Zhao, J.; Terazono, H.; Misawa, K.; Levitt, N. P.; Li, Y.; Lin, Y.; Peng, J.; Wang, Y.; Duan, L.; Pan, B.; Zhang, F.; Feng, X.; An, T.; Marrero-Ortiz, W.; Secrest, J.; Zhang, A. L.; Shibuya, K.; Molina, M. J.; Zhang, R., Reassessing the atmospheric oxidation mechanism of toluene. PNAS 2017, 114, (31), 8169-8174. 25. Fujishima, A.; Zhang, X.; Tryk, D., TiO2 photocatalysis and related surface phenomena. Surf. Sci. Rep. 2008, 63, (12), 515-582. 26. Monge, M. E.; George, C.; Anna, B. D.; Doussin, J.-F.; Jammoul, A.; Wang, J.; Eyglunent, G.; Solignac, G.; Daёle, V.; Mellouki, A., Ozone formation from illuminated Titanium J. Am. Chem. Soc. 2010, 132, 8234–8235. 27. Hadjiivanov, K.; Bushev, V.; Kantcheva, M.; Klissurski, D., Infrared spectroscopy study of the species arising during NO2 adsorption on TiO2 (anatase). Langmuir 1994, 10, 464-471. 28. Nanayakkara, C. E.; Larish, W. A.; Grassian, V. H., Titanium dioxide nanoparticle surface reactivity with atmospheric gases, CO2, SO2, and NO2: Roles of surface hydroxyl groups and adsorbed water in the formation and stability of adsorbed products. J. Phys. Chem. C 2014, 118, (40), 23011-23021. 29. Sivachandiran, L.; Thevenet, F.; Rousseau, A.; Bianchi, D., NO2 adsorption mechanism on TiO2: An in-situ transmission infrared spectroscopy study. Appl. Catal. B-Environ. 2016, 198, 411-419. 30. Ohko, Y.; Nakamura, Y.; Negishi, N.; Matsuzawa, S.; Takeuchi, K., Unexpected release of HNO3 and related species from UV-illuminated TiO2 surface into air in photocatalytic oxidation of NO2. Environ. Chem. Lett. 2010, 8, (3), 289-294. 31. Nicolas, M.; Ndour, M.; Ka, O.; D’anna, B.; George, C., Photochemistry of atmospheric dust: Ozone decomposition on illuminated Titanium dioxide. Environ. Sci. Technol. 2009, 43, 7437–7442. 32. Noguchi, T.; Fujishima, A., Photocatalytic degradation of gaseous Formaldehyde using TiO2 film. 1998, 32, (23), 3831-3833. 33. Debono, O.; Thevenet, F.; Gravejat, P.; Hequet, V.; Raillard, C.; Lecoq, L.; Locoge, N., Toluene photocatalytic oxidation at ppbv levels: Kinetic investigation and carbon balance determination. Appl. Catal. B-Environ. 2011, 106, (3-4), 600-608. 34. Sleiman, M.; Conchon, P.; Ferronato, C.; Chovelon, J.-M., Photocatalytic oxidation of toluene at indoor air levels (ppbv): Towards a better assessment of conversion, reaction intermediates and mineralization. Appl. Catal. B-Environ. 2009, 86, (3-4), 159-165. 35. Bai, C., Ascent of nanoscience in China. Science 2005, 309, (5731), 61-63. 36. Chen, H.; Nanayakkara, C. E.; Grassian, V. H., Titanium dioxide photocatalysis in atmospheric chemistry. Chem. Rev. 2012, 112, (11), 5919-5948. 37. Banerjee, S.; Dionysiou, D. D.; Pillai, S. C., Self-cleaning applications of TiO2 by photo-induced hydrophilicity and photocatalysis. Appl. Catal. B-Environ. 2015, 176-177, 396-428.



525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563

38. Cassar, L., Photocatalysis of cementitious materials: Clean buildings and clean air. MRS Bull. 2011, 29, (05), 328-331. 39. Ourrad, H.; Thevenet, F.; Gaudion, V.; Riffault, V., Limonene photocatalytic oxidation at ppb levels: assessment of gas phase reaction intermediates and secondary organic aerosol heterogeneous formation. Appl. Catal. B-Environ. 2015, 168-169, 183-194. 40. Peng, C.; Wang, W.; Li, K.; Li, J.; Zhou, L.; Wang, L.; Ge, M., The optical properties of limonene secondary organic aerosols: The role of NO3, OH, and O3 in the oxidation processes. J. Geophys. Res.-Atmos. 2018, 123, (6), 3292-3303. 41. Zhao, D. F.; Kaminski, M.; Schlag, P.; Fuchs, H.; Acir, I. H.; Bohn, B.; Häseler, R.; Kiendler-Scharr, A.; Rohrer, F.; Tillmann, R.; Wang, M. J.; Wegener, R.; Wildt, J.; Wahner, A.; Mentel, T. F., Secondary organic aerosol formation from hydroxyl radical oxidation and ozonolysis of monoterpenes. Atmos. Chem. Phys. 2015, 15, (2), 991-1012. 42. Fry, J. L.; Kiendler-Scharr, A.; Rollins, A. W.; Brauers, T.; Brown, S. S.; Dorn, H. P.; Dubé, W. P.; Fuchs, H.; Mensah, A.; Rohrer, F.; Tillmann, R.; Wahner, A.; Wooldridge, P. J.; Cohen, R. C., SOA from limonene: role of NO3 in its generation and degradation. Atmos. Chem. Phys. 2011, 11, (8), 3879-3894. 43. Kalberer, M.; Paulsen, D.; Sax, M.; Steinbacher, M.; Dommen, J.; Prevot, A. S. H.; Fisseha, R.; Weingartner, E.; Frankevich, V.; Zenobi, R.; Baltensperger, U., Identification of polymers as major components of atmospheric organic aerosols. Science 2004, 5664, (303), 1659-1662. 44. Berndt, T.; Richters, S.; Jokinen, T.; Hyttinen, N.; Kurten, T.; Otkjaer, R. V.; Kjaergaard, H. G.; Stratmann, F.; Herrmann, H.; Sipila, M.; Kulmala, M.; Ehn, M., Hydroxyl radical-induced formation of highly oxidized organic compounds. Nat. Commun. 2016, 7, 13677. 45. Bergh, V. V. d.; Vanhees, I.; Boer, R. D.; Compernolle, F.; Vinckier, C., Identification of the oxidation products of the reaction between a-pinene and hydroxyl radicals by gas and high-performance liquid chromatography with mass spectrometric detection. J. Chromatogr. A 2000, 896, 135-148. 46. Kolliker, S.; Oehme, M., Structure elucidation of 2,4-dinitrophenylhydrazone derivatives of carbonyl compounds in ambient air by HPLC/MS and multiple MS/MS using atmospheric chemical ionization in the negative ion mode. Anal. Chem. 1998, 70, (9), 1979-1985. 47. Mathew, S.; Grey, C.; Rumpunen, K.; Adlercreutz, P., Analysis of carbonyl compounds in sea buckthorn for the evaluation of triglyceride oxidation, by enzymatic hydrolysis and derivatisation methodology. Food Chem. 2011, 126, (3), 1399-1405. 48. Wang, H.; Ji, Y.; Gao, Y.; Li, G.; An, T., Theoretical model on the formation possibility of secondary organic aerosol from OH initialed oxidation reaction of styrene in the presence of O2/NO. Atmos. Environ. 2015, 101, 1-9.


Page 26 of 35

Page 27 of 35

564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602


49. Pan, S. S.; Wang, L. M., Atmospheric oxidation mechanism of m-xylene initiated by OH radical. J. Phys. Chem. A 2014, 118, (45), 10778-10787. 50. Kwok, E. S. C.; Aschmann, S. M.; Atkinson, R.; Arey, J., Products of the gas-phase reactions of o-,m- and p-xylene with the OH radical in the presence and absence of NOx J. Chem. Soc., Faraday Trans. 1997, 93, (16), 2847-2854. 51. Atkinson, R., Atmospheric chemistry of VOCs and NOx. Atmos. Environ. 2000, 34, 2063-2101. 52. Schwier, A. N.; Sareen, N.; Mitroo, D.; Shapiro, E. L.; Mcneill, V. F., Glyoxal-methylglyoxal cross-reactions in secondary organic aerosol formation. Environ. Sci. Technol. 2010, 44, 6174–6182. 53. Haan, D. O. D.; Corrigan, A. L.; Tolbert, M. A.; Jimenez, J. L.; Wood, S. E.; Turley, J. J., Secondary organic aerosol formation by self-reactions of methylglyoxal and glyoxal in evaporating droplets. Environ. Sci. Technol. 2009, 43, 8184–8190. 54. Kawamura, K.; Okuzawa, K.; Aggarwal, S. G.; Irie, H.; Kanaya, Y.; Wang, Z., Determination of gaseous and particulate carbonyls (glycolaldehyde, hydroxyacetone, glyoxal, methylglyoxal, nonanal and decanal) in the atmosphere at Mt. Tai. Atmos. Chem. Phys. 2013, 13, (10), 5369-5380. 55. Li, K.; Li, J.; Liggio, J.; Wang, W.; Ge, M.; Liu, Q.; Guo, Y.; Tong, S.; Li, J.; Peng, C.; Jing, B.; Wang, D.; Fu, P., Enhanced light scattering of secondary organic aerosols by multiphase reactions. Environ. Sci. Technol. 2017, 51, (3), 1285-1292. 56. Kroll, J. H.; Seinfeld, J. H., Chemistry of secondary organic aerosol: Formation and evolution of low-volatility organics in the atmosphere. Atmos. Environ. 2008, 42, (16), 3593-3624. 57. Sarrafzadeh, M.; Wildt, J.; Pullinen, I.; Springer, M.; Kleist, E.; Tillmann, R.; Schmitt, S. H.; Wu, C.; Mentel, T. F.; Zhao, D.; Hastie, D. R.; Kiendler-Scharr, A., Impact of NO2 and OH on secondary organic aerosol formation from β-pinene photooxidation. Atmos. Chem. Phys. 2016, 16, (17), 11237-11248. 58. Song, C.; Na, K.; Cocker, D. R., Impact of the hydrocarbon to NOx ratio on secondary organic aerosol formation. Environ. Sci. Technol. 2005, 39, 3143-3149. 59. Lambe, A. T.; Chhabra, P. S.; Onasch, T. B.; Brune, W. H.; Hunter, J. F.; Kroll, J. H.; Cummings, M. J.; Brogan, J. F.; Parmar, Y.; Worsnop, D. R.; Kolb, C. E.; Davidovits, P., Effect of oxidant concentration, exposure time, and seed particles on secondary organic aerosol chemical composition and yield. Atmos. Chem. Phys. 2015, 15, (6), 3063-3075. 60. Lu, Z.; Hao, J.; Takekawa, H.; Hu, L.; Li, J., Effect of high concentrations of inorganic seed aerosols on secondary organic aerosol formation in the m-xylene/NOx photooxidation system. Atmos. Environ. 2009, 43, (4), 897-904. 61. Hommel, E. L.; Allen, H. C., The air–liquid interface of benzene, toluene, m-xylene, and mesitylene: a sum frequency, Raman, and infrared spectroscopic study. Analyst 2003, 128, (6), 750-755.



603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633

62. Profeta, L. T.; Sams, R. L.; Johnson, T. J.; Williams, S. D., Quantitative infrared intensity studies of vapor-phase glyoxal, methylglyoxal, and 2,3-butanedione (diacetyl) with vibrational assignments. J. Phys. Chem. A 2011, 115, (35), 9886-9900. 63. Akagi, S. K.; Burling, I. R.; Mendoza, A.; Johnson, T. J.; Cameron, M.; Griffith, D. W. T.; Paton-Walsh, C.; Weise, D. R.; Reardon, J.; Yokelson, R. J., Field measurements of trace gases emitted by prescribed fires in southeastern US pine forests using an open-path FTIR system. Atmos. Chem. Phys. 2014, 14, (1), 199-215. 64. Wu, J.; Cheng, Y., In situ FTIR study of photocatalytic NO reaction on photocatalysts under UV irradiation. J. Catal. 2006, 237, (2), 393-404. 65. Niu, H.; Li, K.; Chu, B.; Su, W.; Li, J., Heterogeneous reactions between toluene and NO2 on mineral particles under simulated atmospheric conditions. Environ. Sci. Technol. 2017, 51, (17), 9596–9604. 66. Suh, I.; Zhang, R.; Molina, L. T.; Molina, M. J., Oxidation mechanism of aromatic peroxy and bicyclic radicals from OH-Toluene reactions. J. Am. Chem. Soc. 2003, 125, 12655-12665. 67. Palau, J.; Colomer, M.; Penya-Roja, J. M.; Martinez-Soria, V., Photodegradation of Toluene, m-Xylene, and n-Butyl Acetate and their mixtures over TiO2 catalyst on glass fibers. Ind. Eng. Chem. Res. 2012, 51, (17), 5986-5994. 68. Sulpizio, A.; Mella, M.; Albini, A., Hydrogen abstraction from the isomeric cymenes. Tetrahedron 1989, 45, (23), 7545-7552. 69. Korolevich, M. V.; Sivchik, V. V.; Zhbankov, R. G.; Lastochkina, V. A., Theoretical and experimental study of frequencies and absolute band intensities in IR spectrum of methyl nitrate. J. Appl. Spectrosc. 1986, 45, (6), 1275-1280. 70. Fan, J.; Zhang, R., Density functional theory study on OH-initiated atmospheric oxidation of m-xylene. J. Phys. Chem. A 2008, 112, 4314-4323. 71. Wang, H.; Ji, Y.; Chen, J.; Li, G.; An, T., Theoretical investigation on the adsorption configuration and OH-initiated photocatalytic degradation mechanism of typical atmospheric VOCs styrene onto (TiO2)n clusters. Sci. Rep. 2015, 5, 15059. 72. Baciocchi, E.; Giacco, T. D.; Rol, C.; Sebastiahi, G. V., The role of nitrate free radicals in the photochemical side-chain nitrooxylation of alkylbenzenes by cerium(IV) ammonium nitrate in acetonitrile. Tetrahedron Lett. 1985, 26, (4), 541-544.

634 635


Page 28 of 35

Page 29 of 35


636

Table 1 Initial conditions and data in classical photooxidation experiments Non-seed NOx

CH0

a

a

ppbC/ NOx

∆M b, c

Seed Yield

NOx

CH0

a

a

(%)

ppbC/ NOx d

∆M b, c

Yield (%)

46

135

23.4

4.8±0.1

1.0±0.1

56

259

37.1

13.7±0.8

1.4±0.1

50

139

22.2

10.9±0.2

2.1±0.2

58

274

37.8

27.1±1.1

2.7±0.3

61

132

17.4

11.3±0.2

2.5±0.2

78

245

25.1

25.5±1.1

2.8±0.3

69

94

11.0

7.8±0.3

2.0±0.3

82

261

25.5

29.0±0.9

2.9±0.3

78

95

9.7

15.0±0.4

3.7±0.4

86

252

23.4

31.7±1.1

3.2±0.3

78

130

13.3

12.5±0.2

2.4±0.2

127

197

12.4

35.3±1.1

4.5±0.4

79

127

12.8

11.2±0.2

2.1±0.2

130

211

13.0

33.7±1.1

4.0±0.4

116

127

8.8

4.0±0.2

0.8±0.1

164

155

7.6

25.3±1.0

4.2±0.4

121

112

7.4

1.5±0.1

≈ 0.3

180

193

8.6

42.0±1.0

5.7±0.6

124

107

6.9

1.8±0.1

≈ 0.3

221

185

6.7

2.31±0.3

≈ 0.26

a

: the unity is ppb. b: the unity is ug/m3. c: the density of SOA was assumed to be 1.4 g/cm3 and the stated uncertainties (1σ) were from scatter in particle volume measurements. d: the ratio between the carbon atom concentration of m-xylene and the concentration of NOx. 637 638



639

Page 30 of 35

Table 2 Initial conditions and data in the ternary experiments Non-seed

NOx

a

CH0

a

Seed

ppbC ∆M

b, c

NOx

a

CH0

/NOx

a

ppbC/ NOx d

∆M

b, c

Yield (%)

45

110

19.5

0.03

51

261

41.0

7.4±0.7

0.61±0.06

45

105

18.7

0.02

50

246

39.3

6.3±0.9

0.55±0.08

46

105

18.2

0.02

54

228

33.7

5.4±0.6

0.50±0.06

46

122

21.2

0.09

73

238

26.1

9.9±0.9

0.89±0.08

78

117

12.0

0.04

79

184

18.7

13.4±0.9

1.57±0.10

78

72

7.4

0.10

79

214

21.7

12.2±0.9

1.22±0.10

83

113

10.9

0.01

119

267

18.0

10.2±0.8

0.82±0.07

111

73

5.2

0.02

120

318

21.2

8.7±0.7

0.58±0.05

114

116

8.1

0.01

122

243

15.9

8.3±0.7

0.73±0.05

117

108

7.4

0.003

162

237

11.7

3.7±0.6

0.34±0.06

a

: the unity is ppb. b: the unity is ug/m3. c: the density of SOA was assumed to be 1.4 g/cm3 and the stated uncertainties (1σ) were from scatter in particle volume measurements. d: the ratio between the carbon atom concentration of m-xylene and the concentration of NOx. 640 641


Page 31 of 35


642

643 644

Figure 1 The relative intensities of the detected RCCs (glyoxal, methylglyoxal,

645

m-tolualdehyde in (a), hydroxyethanal, acetaldehyde, propionaldehyde and formaldehyde

646

in (b)) in the classical experiments, the ternary system and the photocatalysis of

647

m-xylene. 1 and 2 represent the sample of the first 4 hours and the late 4 hours in the

648

experiments, respectively.

649



650 651

Figure 2 DRIFTS spectra of adsorbed products of the m-xylene (a) and the m-xylene

652

with NOx (b) photocatalyzed by TiO2

653


Page 32 of 35

Page 33 of 35


654

655 656

Figure 3 Evolution of NOx, O3, m-xylene (∆CH) and SOA (∆M) along with the reaction

657

time in the non-seed (a) and seed (b) ternary system.

658



659

660 661

Schematic 1 The proposed mechanisms of the photooxidation of m-xylene.

662


Page 34 of 35

Page 35 of 35

663


Table of content

664 665


The Effect of Titanium Dioxide on Secondary Organic Aerosol Formation

Recommend Documents