photochemistry of glyoxal and hydroxyl radicals Evolution of … · 2019-11-15 · 71 Glyoxal (40% wt in water, electrophoresis grade) and hydrogen peroxide (H2O2, 30% wt in water,

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Environmental Processes

Evolution of aqSOA from the air-liquid interfacialphotochemistry of glyoxal and hydroxyl radicals

Fei Zhang, Xiaofei Yu, Xiao Sui, Jianmin Chen, Zihua Zhu, and Xiao-Ying YuEnviron. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b03642 • Publication Date (Web): 30 Jul 2019

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Evolution of aqSOA from the air-liquid interfacial

photochemistry of glyoxal and hydroxyl radicals

Fei Zhang,†, ≠ Xiaofei Yu,§ Xiao Sui,≠ Jianmin Chen,†,＃,* Zihua Zhu,§,* and Xiao-Ying Yu≠,*

†Department of Environmental Science & Engineering, Shanghai Key Laboratory of Atmospheric Particle

Pollution and Prevention (LAP3), Fudan University, Shanghai, 200433, China

≠Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99354,

USA

§Environmental and Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland,

WA 99354, USA

＃Institute of Atmospheric Sciences, Fudan University, Shanghai, 200433, China

E-mail: [email protected]. Phone: 1-509-372-4524. E-mail: [email protected]. Phone: 021-

6564-2298. E-mail: [email protected]. Phone: 1-509-371-6240.

RECEIVED DATE

Running Title: Evolution of aqSOA at the air-liquid interface

1 ABSTRACT. The effect of photochemical reaction time on glyoxal and hydrogen peroxide at the air-

2 liquid (a-l) interface is investigated using in situ time-of-flight secondary ion mass spectrometry (ToF-

3 SIMS) enabled by a system for analysis at the liquid vacuum interface (SALVI) microreactor. Carboxylic

4 acids are formed mainly by reaction with hydroxyl radicals in the initial reactions. Oligomers, cluster

5 ions, and water clusters formed due to longer photochemistry. Our results provide direct molecular

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6 evidence that water clusters are associated with proton transfer and the formation of oligomers and cluster

7 ions at the a-l interface. The oligomer formation is facilitated by water cluster and cluster ion formation

8 over time. Formation of higher m/z oligomer and cluster ions indicates the possibility of highly

9 oxygenated organic components formation at the a-l interface. Furthermore, new chemical reaction

10 pathways, such as surface organic cluster, hydration shell and water cluster formation, are proposed based

11 on SIMS spectral observations and the existing understanding of glyoxal photochemistry is expanded.

12 Our in situ findings verify that the a-l interfacial reactions are important pathways for aqueous secondary

13 organic aerosol (aqSOA) formation.

14 KEYWORDS. in situ liquid SIMS; aqueous SOA; glyoxal; surface mixing state; cluster ions; water

15 clusters

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16 1. Introduction

17 Secondary organic aerosols (SOAs) are important components in aerosols, which can further affect the

18 air quality, climate forcing, and human health.1 Recently, SOA formation has been intensely

19 investigated.2, 3 Particularly, the multiphase nature of SOA formation poses significant experimental

20 challenges where air-liquid (a-l), solid-liquid (s-l), and liquid-liquid (l-l) interfaces are often

21 encountered.4-6 This work focuses on the interfacial reactions that occur at the a-l interface that is

22 approximated using a vacuum-liquid interfacial analysis in a microfluidic reactor. The surface layer of

23 atmospheric water (i.e., cloud, fog, and aerosol liquid water) is ubiquitous and provides a unique

24 microenvironment for chemical reactions.7 Many organic compounds form a monomolecular film at the

25 droplet surface,8 leading to a higher surface concentration and reactivity of molecules than in the bulk

26 liquid phase.9 The organic monolayer formed on the surface affects the physical-chemical properties of

27 droplets, such as surface tension, extinction coefficient, and reactivity, which influence cloud

28 condensation nucleation (CCN) and hygroscopic activity.10

29 Due to the large surface area of atmospheric water-containing particles (i.e., cloud droplets), volatile

30 organic compounds (VOCs) with moderately high Henry’s law constants can easily partition into the

31 aqueous phase to form aqSOA by photochemistry.11 In the presence of adequate solar radiation,

32 photochemistry of VOCs produces oligomers and polymers with other oxidants (i.e., hydroxyl radicals,

33 sulfate, nitrate) in the bulk of the droplets but also on the droplet surface, resulting in SOA formation. In

34 addition, chemical reactions can affect the effective Henry’s law constant and salting constant of VOCs,

35 representing their ability to transport onto the aqueous phase.12, 13

36 Glyoxal is the simplest dicarbonyl VOC with large natural and anthropogenic source.14 It has been

37 intensely investigated as a model for SOA formation.15 Glyoxal is known to participate in oxidation,

38 hydration, oligomerization, polymerization, esterification, and acetal/hemiacetal reactions to form low

39 volatility species in the aqueous phase, resulting in SOA formation after water evaporation.16, 17 Glyoxal

40 contributes 2.6 Tg C yr-1 to global SOA formation (11 Tg C yr-1)14 via the aforementioned pathways,

41 which predominantly occur during cloud water processing. The global mean lifetime of glyoxal uptake

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42 and SOA formation is about 20 h.14 Therefore, it is important to improve the mechanistic understanding

43 of aqueous SOA (aqSOA) formation using systematic experiments to support process model development

44 and improve model predictability.

45 Glyoxal aqueous photochemistry has been an intensively discussed topic.15, 18 Hydroxyl radical

46 oxidation is a main sink, which has a large contribution to aqSOA formation,19 where bulk approaches

47 including ion chromatography-electrospray ionization-tandem mass spectrometry (IC-ESI-MS),20 high

48 performance liquid chromatography (HPLC),21 and chemical ionization-mass spectrometry (CIMS) 22

49 were used. Earlier experimental results were the base of models 23-25 to predict aqSOA yields from glyoxal

50 aqueous phase oxidation. However, such model predictions showed a large gap compared with field

51 measurements due to lack of more detailed understanding of the effect of time on photochemical aging

52 and lack of understanding of reactions at the surface and a-l interface. For example, high molecular weight

53 compounds observed are still under debate. Limitations in detection techniques including surface

54 oligomer and organic cluster identification, reaction intermediate detection, and direct observation of the

55 surface properties of hydrophilicity and solvation shell formation remain great scientific challenges in

56 atmospheric process studies at the a-l interface.26

57 Recently, Yu et al. developed an in situ molecular imaging technique using a vacuum compatible

58 microfluidic reactor, namely System for Analysis at the Liquid Vacuum Interface (SALVI).27-30 SALVI

59 enables time-of-flight secondary ion mass spectrometry (ToF-SIMS), a vacuum surface technique to study

60 liquid surfaces, the vacuum-liquid interface, the a-l, l-l, and s-l interface.27, 31-34 Liquid SIMS has shown

61 suitability to study a variety of environmental and biological surfaces and interfaces.31, 32, 35, 36 This unique

62 approach was recently used to study glyoxal oxidation by hydrogen peroxide at the aqueous surface,27

63 demonstrating its feasibility in probing complex reaction products in a-l interfacial chemistry. This study

64 builds upon our earlier work and investigates the effect of photochemical reaction time on oligomer

65 formation, surface oxidation, and hydrophobicity at the a-l interface. We aim to elucidate the effect of

66 glyoxal photochemical oxidation aging time at the liquid surface and a-l interface using in situ liquid

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67 SIMS. Specifically, we investigated the evolution of glyoxal and hydrogen peroxide in the presence of

68 UV light up to 8 hrs., corresponding to an average time of sun radiation.

69 2. Experimental Section

70 2.1 Solution preparations

71 Glyoxal (40% wt in water, electrophoresis grade) and hydrogen peroxide (H2O2, 30% wt in water,

72 certified ACS grade) solutions were acquired from Sigma-Aldrich (St. Louis, MO, USA). Photochemical

73 reactions of glyoxal (5 mM) and H2O2 (20 mM) solutions were performed in the microchannel,37 under a

74 Hg-Ar UV lamp (Oriel lamp model 6035, power supply model 6060, USA). The wavelength of the lamp

75 is 253.65 nm, and it is estimated to provide 10-13-10-12 M of OH radicals (OH) in the reactor.38 Excess

76 oxidant was used in this study in order to approximate pseudo first-order kinetics with glyoxal.

77 2.2 In situ liquid SIMS

78 The mass spectral and image measurements were conducted on a ToF-SIMS 5 instrument (IONTOF

79 GmbH, Münster, Germany, Figure S1a). The liquid was sealed in a SALVI device underneath a 100 nm

80 thick SiN membrane. The primary ion beam was a 25 keV Bi3+ primary ion beam. Dynamic profiling

81 drilled an aperture with 2 µm in diameter through the SiN membrane. The liquid in the microchannel

82 membrane was withheld by its surface tension across the aperture.31, 32 Secondary ions could be then

83 emitted at an energy range of 0 to 10 eV from the aperture. A detailed schematic is shown in Figure S1.

84 More experimental details are described in SI and our previous publications.27, 37

85 3. Results and Discussion

86 Recently we demonstrated the feasibility of the in situ liquid SIMS to detect the a-l interfacial reactions

87 of glyoxal and hydrogen peroxide,27 and this study focuses on the time effect on the a-l interfacial

88 reactions and provides more scientific understanding and improved mechanistic information of the

89 aqSOA formation from UV aging of glyoxal and hydrogen peroxide. Compared to the surface sensitive

90 optical techniques such as vibrational spectroscopy including sum frequency generation (SFG) and second

91 harmonic generation (SHG) that have been widely used in atmospheric chemistry,39 in situ liquid SIMS

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92 offers molecular insight complementary to chemical bond, shift, and molecular orientation information at

93 the interface.40 Moreover, much larger and complicated cluster ions including water clusters can be easily

94 observed using liquid SIMS with 2D and 3D spatial distribution.

95 3.1 Photochemical Aging Products

96 Fig. 1 depicts the reaction flow chart highlighting new products identified in this work. Compared to

97 previous findings,18, 41-43 a number of reactions pathways are confirmed by our direct interfacial study. In

98 addition, several new reaction paths are discovered, for instance, formation of organic hydration shell,

99 water clusters, and organic-water cluster ions at the interface.

100 Carboxylic acids (i.e., glyoxylic acid, tartaric acid, glycolic acid) formed via glyoxal and OH oxidation

101 are confirmed.44 Hydration products were also formed in the UV aging, i.e., m/z- 121 C3H5O5- and m/z-

102 135 C4H7O5-. The carbonyl group can be hydrated to form two hydroxyl groups in the aqueous phase,

103 hydration can occur in the aqueous phase.45, 46 More oligomers (i.e., m/z- 285 (C8H13O11-), m/z- 329

104 (C9H13O13-), m/z- 347 (C9H15O14

-)) are observed at the aqueous interface, especially from the

105 photochemical reactions of 3 hr. or longer. Furthermore, oligomers with hydrophilic functional groups

106 could form cluster ions (i.e., m/z+ 165 (C2H3O4···C2H2O4)+, m/z+ 331 (C9H13O12···H2O)+, m/z+ 349

107 (C9H13O12···2H2O)+, m/z+ 367 (C9H13O12···3H2O)+) with water molecules as photochemistry persists.

108 The cluster ion formation indicates that the organic ion cluster can grow larger by absorbing water

109 molecules or other organic molecules at the surfaces. Our finding suggests that clusters formed primarily

110 from organic molecules can serve as the nucleus and provides evidence for subsequent nucleation in the

111 aqueous phase as a result of multiphase chemistry. The cluster ion formation can sometimes affect the

112 water uptake at the aqueous interface. Water clusters are known to play an important role in nucleation

113 in atmospheric water like cloud or fog.47 Our results have shed new lights in this aspect. In the following,

114 we discuss the photochemical aging products and processes.

115 3.2. Initial Oxidation

116 Spectral analysis shows that various types of oxidation products are formed as a result of the glyoxal

117 and OH radical reactions (Figs. 2, S2, S3a & S3b). Glyoxal is strongly oxidized in the presence of OH,

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118 and the formation of carboxylic acids is observed in the negative ion mode, including formic acid (m/z-

119 45), glyoxylic acid (m/z- 73), glycolic acid (m/z- 75), oxalic acid (m/z- 89), malonic acid (m/z- 103),

120 succinic acid (m/z- 117) and tartaric acid (m/z- 149) for < 3 hr. reactions (see Table S3). Tartaric acid is

121 formed by radical reactions in the presence of glyoxal radicals.16 Glyoxylic acid is known to be formed

122 from aldehyde reaction with OH, followed by the oxidation of another aldehyde group in glyoxylic acid

123 to form oxalic acid.48 Formic acid is an abundant product. It is formed either from the oxidation of

124 glyoxylic acid and dihydrated glyoxal with H2O2,43 or the oxidation of the 2-hydroxy-2-

125 hydroperoxyethanal (HHPE) with OH.49 HHPE was an intermediate product, which could be produced

126 via the addition of H2O2 to the aldehyde group in the aqueous phase without UV.50 Malonic acid (m/z-

127 103) is attributed to two potential pathways: (1) the decarboxylation from succinic acid51 and (2) the

128 dehydration from the hydration product (m/z- 121 C3H5O5-). Dehydration products are formed by radical

129 reactions.16 The carboxylic acids observed in our study are consistent with previous studies from ESI-

130 MS 20, 52 and AMS 43. Similar oxidation products such as glyoxylic acid (m/z+ 75), glycolic acid (m/z+

131 77), oxalic acid (m/z+ 91), malonic acid (m/z+ 105), succinic acid (m/z+ 119) are observed in the positive

132 spectra (Figs. S3a & b). These carboxylic acids are produced in an acidic environment in the aqueous

133 phase (Table S1) and could react with other inorganic pollutant oxidants, such as nitrite,20 sulfate,42 amino

134 acid 53, to form aqSOA in cloud drops. The in situ liquid SIMS observation is in agreement with the

135 earlier ESI-MS results using a bulk approach, both suggesting fast consumption of carboxylic acids during

136 UV aging.48

137 3.3. Oligomers Leading to aqSOA Formation

138 As the reaction time continues, many oligomers and cluster ions are observed (Tables 1, S2 & S3). In

139 the negative ion mode (Figs. 2 & S2), radical reactions are an important pathway to form oligomers. For

140 example, m/z- 185 (C4H9O8-) is observed in 6 h and 8 h of UV aging, which could be a combination of a

141 monohydrated glyoxylic acid radical (C2H3O4·) and dihydrated glyoxal radical (C2H5O4·), m/z- 241

142 (C6H9O10-) can form by the radical reaction from glyoxylic acid m/z- 73 (C2H3O4·) and tartaric acid m/z-

143 149 (C4H5O6·). As mentioned previously, H atom abstraction occurs easily for the dihydrated glyoxal.

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144 Other oligomers, such as m/z- 285 (C8H13O11-), m/z- 329 (C9H13O13

-), m/z- 347 (C9H15O14-), m/z- 365

145 (C12H13O13-), m/z- 383 (C12H15O14

-), m/z- 401 (C12H17O15-), and m/z- 419 (C12H19O16

-), can be produced

146 by radical reactions, acetal/hemiacetal formation, showing a significant contribution to the products in

147 reactions over 4 hr. Some of the oligomers were also found in cloud water and river water samples, such

148 as m/z- 121 C3H5O5-, 185 C4H9O8

- and 285 C8H13O11-,54 some of them were observed from laboratory

149 simulations of glyoxal and OH radical photochemistry.52

150 The compound of m/z- 285 (C8H13O11-) is proposed to be a tetramer formed by the acetal reaction of 4

151 hydrated glyoxal molecules. The peak of m/z- 329 is likely generated from the anhydride and radical

152 reaction, containing an oxalic acid anhydride and tartaric acid radical. Two oxalic acids could form an

153 anhydride (m/z- 161, C5H5O6-) in the presence of H+. The large oligomers with m/z- 347, 365, 383, 401,

154 and 419 are all glyoxal related species, since glyoxal could undergo hemiacetal and hydration reactions

155 in acidic conditions.41 The mass difference (Δm/z=18) of the oligomers indicates potential hydration

156 shells are formed at the interface, implying the change of surface water environment. Spectra from the

157 glyoxal and H2O2 control experiments shown in Fig. S5 provide the evidence that continued aging of

158 glyoxal does not lead to the same products as seen in Fig. 2.

159 3.4. Surface Uptake and Its Implications in Nucleation

160 Water clusters were observed in the glyoxal and OH oxidation reactions in liquid in our previous

161 paper,27, 37 and they were only simulated or predicted in other studies.55-57 In this work, water clusters

162 ((H2O)nH+,1≤ n ≤ 44 and (H2O)nOH-,1 ≤ n ≤ 43) are observed among all photochemically aged samples

163 (Figs. 2, S2, S3a & S3b). Especially in the higher m/z range (m/z > 300), water clusters give predominant

164 signals in longer time periods in the positive ion mode (i.e., 4 hr., 6 hr., 8 hr.) in Fig. S3b, indicating that

165 the aqueous surface becomes more hydrophobic after photochemical aging. Water clusters may facilitate

166 the proton transfer and surface proton reaction of glyoxal at the a-l interface,58 thus promote glyoxal

167 uptake on the surface.58-60 The effective Henry’s law constant of glyoxal at the interface was determined

168 to be facilitated by hydrogen bonding and proton transfer of water clusters and organic-water clusters

169 previously.12 Moreover, we propose the “salting in” effect of glyoxal could take place at the a-l interface

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170 by forming more oligomers and organic-water clusters along with the photochemistry. The enhanced

171 effective Henry’s law constant and “salting in” effect was an important step for glyoxal to partition onto

172 the aqueous surface and its contribution to SOAs according to field observations.58, 61

173 In the positive mode (Figs. S3a & S3b), a series of high-intensity peaks are observed in the mass spectra,

174 with the m/z consistently increasing at an increment of m/z 18 (i.e., m/z+ 331 (C9H13O12···H2O)+, m/z+

175 349 (C9H13O12···2H2O)+, m/z+ 367 (C9H13O12···3H2O)+, m/z+ 385 (C9H13O12···4H2O)+), indicating water

176 could be attracted to organics, forming cluster ions. The hydroxyl, carbonyl, and carboxyl groups are

177 hydrophilic. Other types of cluster ions like m/z+ 165 (C2H3O4···C2H2O4)+ are also observed in the

178 positive ion mode (Fig. S3). These cluster ions indicate the occurrence of heteromolecular nucleation,

179 followed by the insoluble organics reaction on the organic cluster surfaces.62 Compounds containing such

180 functional groups have a high potential to attract water molecules via weak intermolecular force (i.e.,

181 hydrogen bonding, Van der Waals force).27, 63 From the SIMS spectra, cluster ions appear in the presence

182 of water clusters, demonstrating the effect of water clusters on hydrated cluster ion formation and

183 suggesting that water clusters play a role in changing the solvent and solute structure in liquid. As the

184 aging time continues, water molecules are condensed on the initial organic compounds (i.e., dimers,

185 trimmers and tetramers’ surfaces), reflected by the increased m/z of organics.

186 The liquid SIMS spectral results suggest glyoxal can participate in radical reactions, hemiacetal,

187 oligomerization, polymerization, esterification, and anhydride reactions to form higher molecular weight

188 species (i.e., m/z+ 225 C6H9O9+, m/z+ 313 C9H13O12

+, m/z- 165 C4H5O7-, m/z- 299 C8H11O12

-) after initial

189 oxidation. Different types of cluster ions (i.e., m/z+ 165 (C2H3O4···C2H2O4)+, m/z+ 367

190 (C9H13O12···3H2O)+, m/z+ 369 (C9H15O12···4H2O)+ and m/z- 635 (C18H21O20···C2H4O2···H2O)-) are also

191 observed, especially in the longer UV aging time. Our measurements support the hypothesis that water

192 in the aqueous phase plays an important role in oligomer and cluster ion formation due to proton transfer

193 and surface proton reaction.64

194 3.5 Progression of SOA Formation

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195 Spectral PCA (Figs. S8 & S9) is performed to determine the key peaks differentiating short vs. long

196 reaction times. PCA is a powerful statistical method to process ToF-SIMS data and reduce Poisson

197 noise.65 Three principle components (PCs) are extracted from PCA (Figs. 3a-c), and the loading plots

198 (Figs. 3d-f) are used to explain the main products of each PCs. Two sets of spectral PCA are done. In

199 the first round of spectral PCA, only known interference peaks such as PDMS are removed. In the second

200 round of spectral PCA, peaks are selected according to specific criteria detailed in SI.

201 Principal components (PC) PC1, PC2, and PC3 explain 68.02%, 9.99%, and 7.47% of the data (Fig. 3).

202 PC1 positive peaks are dominant within the first 30 min. of photochemistry (Fig. 3a), confirming that

203 more carboxylic acids (i.e., glyoxylic acid, oxalic acid) are produced and suggesting the importance of

204 photochemical oxidation in the initial stage. As the photochemistry continues from 30 min. to 1 hr., the

205 PC1 score continuously increases, suggesting that more carboxylic acids and large water clusters are

206 formed under the photochemistry according to the positive PC1 loadings. From positive PC1 and PC3

207 loadings, a pronounced peak of m/z- 45 formic acid is observed. Formic acid is not a first-generation

208 product, thus it does not contribute to the initial reaction products in 15 min and 30 min.

209 Compared to 1 hr., the 2 hr. aging sample is located in negative PC3 and negative PC1 (Fig. 3b). Key

210 contributions are from small water clusters (i.e., (H2O)nOH-, 1 ≤ n ≤ 14) and oxidation products (i.e., m/z-

211 45 CHO2- formic acid, m/z- 73 C2HO3

- glyoxylic acid, m/z- 75 C2H3O3- glycolic acid) according to the

212 PC1 and PC3 loading plots (Figs. 3d-e). The decrease of the PC1 and PC3 scores is attributed to reactions

213 consuming carboxylic acids (i.e., m/z- 73 C2HO2- glyoxylic acid) and forming cluster ion (i.e., m/z- 77

214 C2H5O3-), for instance, occurring in the esterification reaction under acidic conditions.

215 The PC2 score of the 3 hr. sample decreases largely from 2 hr. (Fig. 3a). Carboxylic acids (m/z- 45

216 formic acid, m/z- 87 C3H3O3-) and cluster ion (m/z- 77 C2H5O3

-) contribute to the continued photochemical

217 reaction as supported in the loading plots (Figs. 3d-e). These compounds participate in the radical

218 reactions, esterification and hemiacetal formation to form medium molecular weight compounds (i.e.,

219 m/z- 149 C4H5O6- tartaric acid, m/z- 165 C4H5O7

-, m/z- 223 C6H7O9- and m/z- 225 C6H9O9

-) in the 3 hr.

220 photochemical reaction.

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221 The 3 hr. and 4 hr. samples have a transition during the aging process as shown in the discreteness in

222 PC3. The products transform from carboxylic acids and small water clusters (i.e., (H2O)nOH-, 1 ≤ n ≤

223 14) to large water clusters (i.e., (H2O)nOH-, 15 ≤ n ≤ 44, Fig. 3c) and oligomers (i.e., m/z- 165 C4H5O7-,

224 m/z- 185 C9H15O14- and m/z- 419 C12H19O16

-) according to PC3 loadings. The 3 hr. and 4 hr. samples

225 contribute largely to positive PC3, negative PC1, and negative PC2 (Fig. 3a), carboxylic acids (i.e.,

226 glyoxylic acid m/z- 73 C2H3O4-, malic acid m/z- 133 C4H5O5

-, tartaric acid m/z- 149 C4H5O6-) may

227 participate reactions and generate oligomers with lower molecular weight (i.e., m/z- 223 C6H7O9-, m/z-

228 225 C6H9O9-, m/z- 237 C6H5O10

- and m/z- 241 C6H9O10-) in this transition. The increased dominance of

229 larger water clusters indicative of water cluster size growth (e.g., < 3 h, (H2O)nH+, 1≤n≤16; ≥ 3 h,

230 (H2O)nH+, 17≤n≤44) is another key feature during this period, implying that the occurrence of water

231 solvation shells at the surface is highly likely.

232 Positive PC3 loadings mainly attribute to the 6 hr. and 8 hr. UV aging (Fig. 3). The PC3 score increases

233 when the photochemical time increases passing 4 hr. of photochemical aging, which indicates more high

234 molecular weight compounds are formed (i.e., m/z- 311 C9H11O12-, m/z- 317 C8H13O13

-, m/z- 329

235 C9H13O13-, m/z- 343 C10H15O13

-, m/z- 357 C10H13O14-, m/z- 359 C10H15O14

- and m/z- 377 C13H13O13-). This

236 indicates that the highly oxidized organic compounds may contribute to nucleation. Additionally, water

237 clusters with m/z- > 300 are the main components in the positive PC3 loading, contributing more to 8 hr.

238 photochemical aging. This result suggests that the water molecules at the aqueous surface continue to

239 form by hydrogen bond. In addition, water clusters can promote proton transfer and facilitate the surface

240 proton reaction of glyoxal.58, 59

241 A large amount of cluster ions and oligomers are formed in the longer aging reactions (i.e., 4 hr., 6 hr.,

242 8 hr.) in positive spectral PCA (Fig. S10). Hydrated cluster ions indicative of particle growth such as

243 m/z+ 331 (C9H13O12···H2O)+, m/z+ 349 (C9H13O12···2H2O)+, m/z+ 351 (C9H15O12···2H2O)+, m/z+ 369

244 (C9H15O12···3H2O)+, m/z+ 385 (C9H13O12···4H2O)+, and m/z+ 387 (C9H15O12···4H2O)+) and oligomer

245 formation (i.e., m/z+ 315 C9H15O12+, m/z+ 327 C10H15O12

+, m/z+ 401 C12H17O15+, and m/z+ 435

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246 C13H23O16+) occur as the water cluster distribution shifts to larger size. This observation suggests highly

247 oxygenated molecules can grow larger via condensation of water molecules and water solvation shell

248 formation at the organic surfaces as the photochemical aging persist. Additionally, water is necessary for

249 oligomer and hydrated cluster ion formation. Previous work reported that aqSOA formation was

250 favorable in the presence of water,66 implying the significance of water clusters in the surface

251 microenvironment change. Our results reveal that water clusters promote the formation of cluster ions

252 and oligomers, potentially facilitating glyoxal uptake and reaction equilibrium at the surface.

253 3.6 Temporal and Spatial Evolution of Oxidation Products

254 To further illustrate the evolution of different key species, the temporal and spatial dependence of

255 selected species is depicted in Fig. 4. Organic aerosols are complex mixtures of thousands of organic

256 species that exist as internally mixed, externally mixed, or both.67 The SIMS 3D images of different

257 species (i.e., water clusters, oxidation products, oligomers, and cluster ions) show surface spatial

258 progression corresponding to the photochemical aging in Figs. 5 & S13. Since SIMS provides semi-

259 quantitative measurement, the products are normalized to the total selected ion intensities to illustrate the

260 trend via relative abundance.

261 Carboxylic acids (i.e., m/z- 45 HCOO- formic acid, m/z- 117 C4H5O4- succinic acid, m/z- 149 C4H5O6

-

262 tartaric acid) have a higher intensity on the surface than inside the bulk solution in the shorter UV

263 photochemical period (≤ 3 hr.). Especially for formic acid, it is quickly formed at 30 min. and 1 hr. They

264 are evenly distributed after 4 hr. (Fig. 5a). This indicates the oxidation products are initially formed at

265 the aqueous surface. This is not surprising because carboxylic acids are polar, capable of absorbing water

266 with weak intermolecular forces.

267 The average intensities of the oligomers in the shorter aging time are much lower than those in the

268 longer aging time (Figs. S6c & S7c). Oligomers (i.e., m/z- 323 C10H11O12-, m/z- 437 C12H21O17

-, m/z- 455

269 C6H7O6-) reach their maxima right after 3 hr. of UV aging process. As the photochemistry persists, smaller

270 oligomers (i.e., m/z- 161 C5H5O6-, m/z- 185 C4H9O8

-, m/z- 285 C8H13O11-, m/z+ 117 C4H5O4

+) are observed

271 at a higher intensity earlier than larger oligomers (Figs. 5, S6c & S13). The relative intensities of small

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272 oligomers decrease as large oligomers form, showing facilitated productions of large oligomer by smaller

273 ones. Our results provide detailed oligomer progression up to 8 hr. compared to previous studies.18

274 Although the larger oligomers have relatively lower intensities than the smaller ones partially due to the

275 lower ion yield of larger ions in SIMS,35, 68 larger oligomers (i.e., m/z- 209 C7H11O7-, m/z- 329 C9H13O13

-,

276 m/z- 421 C14H13O15-, m/z+ 227 C6H11O9

+, m/z+ 239 C7H11O9+) can be easily observed in longer aging (>

277 4 hr.). 3D images are consistent with the temporal aqSOA formation trend and PCA results.

278 Cluster ions, such as m/z- 269 (C4H3O3···C4H6O5···2H2O)-, m/z- 617 (C18H21O20···C2H4O2)-, m/z- 635

279 (C18H21O20···C2H4O2···H2O)-, reach maxima at 4 hr. (Figs. 4, 5d & S5d), indicating that photochemistry

280 promotes the cluster ion formation either between organic molecules or organic and water molecules.

281 Many cluster ions are found to coexist with large water clusters as hydrated clusters in the positive ion

282 mode. Cluster ions are believed to have an important effect on aerosol growth by attracting water

283 molecules69, 70; however, most previous works could not capture their presence due to lack of interfacial

284 measurements.71 Our approach provides direct observations of the cluster ion formation and the

285 possibility to study cluster ions relevant to water uptake at the aerosol surface on the molecular level.

286 Large water clusters (i.e., (H2O)22OH-, (H2O)24OH-, (H2O)28OH-, (H2O)31OH-, (H2O)36OH-) are found

287 to form efficiently in the longer aging time, with a peak at 4 hr. The increase of relative abundance of

288 larger water clusters suggests that photochemistry modifies the hydrophilicity of the aqueous phase.27, 72

289 In addition, the oligomer formation influences the enhancement of aqueous surface hydration shell. Due

290 to the polarity of glyoxal structure, it can easily react with water molecules by forming hydration shells

291 in UV aging. Moreover, potential “salting in” effect may occur at the surface in the presence of inorganic

292 salt (i.e., SO42-).13 Our findings suggest that the aqueous surface would (1) generate more oligomers with

293 more hygroscopicity, (2) form cluster ions between water molecules and oligomers (i.e., m/z- 269

294 (C4H3O3···C4H6O5···2H2O)-) or between oligomers (i.e., m/z- 617 (C18H21O20···C2H4O2)-), and (3) lead

295 to a more hydrophilic water environment at the aqueous surface as a result of photochemistry. Formation

296 of water clusters and cluster ions are important steps in nucleation growth in the atmosphere, promoting

297 the CCN number in ambient air.64 Knowledge of the mixing state progression as seen in Fig. 5 could

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298 provide more insight to the hygroscopic behavior of aerosols in a photochemical event. The growth of

299 cluster ions demonstrates that the organic compounds can condense on nucleated water clusters.

300 Moreover, these new physical understanding has important atmospheric implications. Solar radiation

301 often reaches its strongest intensity at around 1 pm.73 After morning traffic, the gaseous precursors (i.e.,

302 SO2, NOx) and fresh Aitken mode particles are emitted from vehicles, which could consume glyoxal and

303 OH in the presence of ultraviolet radiation. A previous study reported that the non-hygroscopic species

304 were first emitted during morning rush hours between 6 to 8 a.m., externally mixed with particles

305 containing hygroscopic species (i.e., nitrate, sulfate, other hydrophilic aqSOAs) to produce the aqSOAs

306 in Mexico City.74

307 In situ liquid SIMS has provided direct chemical mapping of the temporal dependence of water clusters

308 and cluster ions besides other products. The presence and dominance of larger water clusters at the longer

309 time (>4 hr.) suggests that photochemical aging is associated with water cluster formation, and hydrogen

310 bonding has a vital effect on the oligomer and cluster ion formation. Hydrophilicity and enhanced surface

311 uptake as a result of water cluster and oligomer evolution at the aqueous surface could be used to derive

312 the relationship between the CCN activation and hygroscopicity of aerosols with theoretical interpretation

313 and more systematic experiments. The organic oligomers and polymers (homomolecules and

314 heteromolecules) formed at the aqueous surface can participate in organic reactions with other insoluble

315 organic compounds, potentially leading to particle size growth and CCN number changes in the

316 atmospheric aqueous phase. Our in situ findings verify that the a-l interfacial reactions are important

317 pathways for aqSOA formation. Further, the formation of oligomers and cluster ions is facilitated by

318 proton transfer and surface proton reaction in the presence of water clusters over time. Glyoxal interfacial

319 photochemistry may elevate its uptake onto the aqueous surface, contributing to aqSOA formation,

320 surface activity, and aerosol nucleation as a result of multiphase chemistry. Our experimental observations

321 provide strong evidence of the evolution of aqSOA due to photochemistry in spectral analysis, PCA, and

322 2D/3D image analysis. In situ liquid SIMS offers a novel approach to study interfacial chemistry. Our

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323 results provide molecular level understanding of surface changes and interfacial reactions of importance

324 in multiphase chemistry leading to nucleation in the atmosphere.

325 ACKNOWLEDGEMENTS. This work was supported by the funding from Pacific Northwest National

326 Laboratory (PNNL) Materials Synthesis and Simulation across Scales (MS3) Initiative Laboratory

327 Directed Research and Development (LDRD) and the Earth and Biological Sciences Directorate (EBSD)

328 Mission Seed LDRD, National Natural Science Foundation of China (No. 21527814), the Ministry of

329 Science and Technology of China (No. 2016YFC0202700, 2016YFE0112200, 2014BAC22B01), and

330 Marie Skłodowska-Curie Actions (690958-MARSU-RISE-2015). The research was conducted at W. R.

331 Wiley Environmental Molecular Sciences Laboratory (EMSL), a national Science User Facility sponsored

332 by the office of Biological and Environmental Research (OBER). Fei Zhang (ZF) is grateful for the

333 support from the China Scholarship Council (CSC) and Xiao Sui thanks the PNNL Alternate Sponsored

334 Fellowship (ASF). ZF thanks Rachel Komorek for editing and Prof. Hartmut Herrmann for comments

335 and discussions.

336 SUPPORTING INFORMATION. Additional experimental details, figures and tables are provided in

337 the supporting information. This material is available free of charge via the Internet at http://pubs.acs.org.

338 Seven texts, 4 tables, 28 figures and 1 scheme about the experimental operation procedures and additional

339 experimental data.

340

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341 REFERENCES

342 1. Zhang, X.; McVay, R. C.; Huang, D. D.; Dalleska, N. F.; Aumont, B.; Flagan, R. C.; Seinfeld, J. H., 343 Formation and evolution of molecular products in α-pinene secondary organic aerosol. Proc. Natl. Acad. 344 Sci. 2015, 112, (46), 14168-14173.345 2. Jimenez, J. L.; Canagaratna, M. R.; Donahue, N. M.; Prevot, A. S. H.; Zhang, Q.; Kroll, J. H.; DeCarlo, 346 P. F.; Allan, J. D.; Coe, H.; Ng, N. L.; Aiken, A. C.; Docherty, K. S.; Ulbrich, I. M.; Grieshop, A. P.; 347 Robinson, A. L.; Duplissy, J.; Smith, J. D.; Wilson, K. R.; Lanz, V. A.; Hueglin, C.; Sun, Y. L.; Tian, J.; 348 Laaksonen, A.; Raatikainen, T.; Rautiainen, J.; Vaattovaara, P.; Ehn, M.; Kulmala, M.; Tomlinson, J. M.; 349 Collins, D. R.; Cubison, M. J.; Dunlea, E. J.; Huffman, J. A.; Onasch, T. B.; Alfarra, M. R.; Williams, P. 350 I.; Bower, K.; Kondo, Y.; Schneider, J.; Drewnick, F.; Borrmann, S.; Weimer, S.; Demerjian, K.; Salcedo, 351 D.; Cottrell, L.; Griffin, R.; Takami, A.; Miyoshi, T.; Hatakeyama, S.; Shimono, A.; Sun, J. Y.; Zhang, 352 Y. M.; Dzepina, K.; Kimmel, J. R.; Sueper, D.; Jayne, J. T.; Herndon, S. C.; Trimborn, A. M.; Williams, 353 L. R.; Wood, E. C.; Middlebrook, A. M.; Kolb, C. E.; Baltensperger, U.; Worsnop, D. R., Evolution of 354 Organic Aerosols in the Atmosphere. Science 2009, 326, (5959), 1525-1529.355 3. Huang, R. J.; Zhang, Y. L.; Bozzetti, C.; Ho, K. F.; Cao, J. J.; Han, Y. M.; Daellenbach, K. R.; Slowik, 356 J. G.; Platt, S. M.; Canonaco, F.; Zotter, P.; Wolf, R.; Pieber, S. M.; Bruns, E. A.; Crippa, M.; Ciarelli, 357 G.; Piazzalunga, A.; Schwikowski, M.; Abbaszade, G.; Schnelle-Kreis, J.; Zimmermann, R.; An, Z. S.; 358 Szidat, S.; Baltensperger, U.; El Haddad, I.; Prevot, A. S. H., High secondary aerosol contribution to 359 particulate pollution during haze events in China. Nature 2014, 514, (7521), 218-222.360 4. Ciuraru, R.; Fine, L.; Van Pinxteren, M.; D’Anna, B.; Herrmann, H.; George, C., Photosensitized 361 production of functionalized and unsaturated organic compounds at the air-sea interface. Sci. Rep. 2015, 362 5, 12741.363 5. Donaldson, D. J.; George, C., Sea-surface chemistry and its impact on the marine boundary layer. 364 Environ. Sci. Technol. 2012, 46, (19), 10385-10389.365 6. Laskin, A.; Gaspar, D. J.; Wang, W.; Hunt, S. W.; Cowin, J. P.; Colson, S. D.; Finlayson-Pitts, B. J., 366 Reactions at interfaces as a source of sulfate formation in sea-salt particles. Science 2003, 301, (5631), 367 340-344.368 7. Donaldson, D. J.; Valsaraj, K. T., Adsorption and Reaction of Trace Gas-Phase Organic Compounds 369 on Atmospheric Water Film Surfaces: A Critical Review. Environ. Sci. Technol. 2010, 44, (3), 865-873.370 8. Fu, H.; Ciuraru, R.; Dupart, Y.; Passananti, M.; Tinel, L.; Rossignol, S.; Perrier, S.; Donaldson, D. J.; 371 Chen, J.; George, C., Photosensitized Production of Atmospherically Reactive Organic Compounds at the 372 Air/Aqueous Interface. J. Am. Chem. Soc. 2015, 137, (26), 8348-51.373 9. Garrett, B. C., Ions at the air/water interface. Science 2004, 303, (5661), 1146-1147.374 10. Yakobi-Hancock, J. D.; Ladino, L. A.; Bertram, A. K.; Huffman, J. A.; Jones, K.; Leaitch, W. R.; 375 Mason, R. H.; Schiller, C. L.; Toom-Sauntry, D.; Wong, J. P. S.; Abbatt, J. P. D., CCN activity of size-376 selected aerosol at a Pacific coastal location. Atmos. Chem. Phys. 2014, 14, (22), 12307-12317.377 11. Mellouki, A.; Wallington, T.; Chen, J., Atmospheric chemistry of oxygenated volatile organic 378 compounds: Impacts on air quality and climate. Chem. Rev. 2015, 115, (10), 3984-4014.379 12. Ip, H. S. S.; Huang, X. H. H.; Yu, J. Z., Effective Henry's law constants of glyoxal, glyoxylic acid, 380 and glycolic acid. Geophys. Res. Lett. 2009, 36, L01802.381 13. Kampf, C. J.; Waxman, E. M.; Slowik, J. G.; Dommen, J.; Pfaffenberger, L.; Praplan, A. P.; Prevot, 382 A. S. H.; Baltensperger, U.; Hoffmann, T.; Volkamer, R., Effective Henry's Law Partitioning and the 383 Salting Constant of Glyoxal in Aerosols Containing Sulfate. Environ. Sci. Technol. 2013, 47, (9), 4236-384 4244.385 14. Fu, T. M.; Jacob, D. J.; Wittrock, F.; Burrows, J. P.; Vrekoussis, M.; Henze, D. K., Global budgets of 386 atmospheric glyoxal and methylglyoxal, and implications for formation of secondary organic aerosols. J. 387 Geophys. Res. Atmos. 2008, 113, (D15), D15303.388 15. Ervens, B.; Volkamer, R., Glyoxal processing by aerosol multiphase chemistry: towards a kinetic 389 modeling framework of secondary organic aerosol formation in aqueous particles. Atmos. Chem. Phys. 390 2010, 10, (17), 8219-8244.

Page 16 of 30



17

391 16. Lim, Y. B.; Tan, Y.; Perri, M. J.; Seitzinger, S. P.; Turpin, B. J., Aqueous chemistry and its role in 392 secondary organic aerosol (SOA) formation. Atmos. Chem. Phys. 2010, 10, (21), 10521-10539.393 17. McNeill, V. F., Aqueous Organic Chemistry in the Atmosphere: Sources and Chemical Processing of 394 Organic Aerosols. Environ. Sci. Technol. 2015, 49, (3), 1237-1244.395 18. Galloway, M. M.; Loza, C. L.; Chhabra, P. S.; Chan, A. W. H.; Yee, L. D.; Seinfeld, J. H.; Keutsch, 396 F. N., Analysis of photochemical and dark glyoxal uptake: Implications for SOA formation. Geophys. 397 Res. Lett. 2011, 38, (17), L17811.398 19. Mahajan, A. S.; Prados-Roman, C.; Hay, T. D.; Lampel, J.; Pohler, D.; Grossmann, K.; Tschritter, J.; 399 Friess, U.; Platt, U.; Johnston, P.; Kreher, K.; Wittrock, F.; Burrows, J. P.; Plane, J. M. C.; Saiz-Lopez, 400 A., Glyoxal observations in the global marine boundary layer. J. Geophys. Res. Atmos. 2014, 119, (10), 401 6160-6169.402 20. Kirkland, J. R.; Lim, Y. B.; Tan, Y.; Altieri, K. E.; Turpin, B. J., Glyoxal secondary organic aerosol 403 chemistry: effects of dilute nitrate and ammonium and support for organic radical?radical oligomer 404 formation. Environ. Chem. 2013, 10, (3), 158-166.405 21. Kampf, C. J.; Jakob, R.; Hoffmann, T., Identification and characterization of aging products in the 406 glyoxal/ammonium sulfate system-implications for light-absorbing material in atmospheric aerosols. 407 Atmos. Chem. Phys. 2012, 12, (14), 6323-6333.408 22. Wang, L.; Khalizov, A. F.; Zheng, J.; Xu, W.; Ma, Y.; Lal, V.; Zhang, R., Atmospheric nanoparticles 409 formed from heterogeneous reactions of organics. Nat. Geosci. 2010, 3, (4), 238-242.410 23. Knote, C.; Hodzic, A.; Jimenez, J. L.; Volkamer, R.; Orlando, J. J.; Baidar, S.; Brioude, J.; Fast, J.; 411 Gentner, D. R.; Goldstein, A. H.; Hayes, P. L.; Knighton, W. B.; Oetjen, H.; Setyan, A.; Stark, H.; 412 Thalman, R.; Tyndall, G.; Washenfelder, R.; Waxman, E.; Zhang, Q., Simulation of semi-explicit 413 mechanisms of SOA formation from glyoxal in aerosol in a 3-D model. Atmos. Chem. Phys. 2014, 14, 414 (12), 6213-6239.415 24. Waxman, E. M.; Dzepina, K.; Ervens, B.; Lee‐Taylor, J.; Aumont, B.; Jimenez, J. L.; Madronich, 416 S.; Volkamer, R., Secondary organic aerosol formation from semi‐and intermediate‐volatility organic 417 compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry. Geophys. Res. 418 Lett. 2013, 40, (5), 978-982.419 25. Chen, J.; Griffin, R.; Grini, A.; Tulet, P., Modeling secondary organic aerosol formation through cloud 420 processing of organic compounds. Atmos. Chem. Phys. 2007, 7, (20), 5343-5355.421 26. Trump, E. R.; Donahue, N. M., Oligomer formation within secondary organic aerosols: equilibrium 422 and dynamic considerations. Atmos. Chem. Phys. 2014, 14, (7), 3691-3701.423 27. Sui, X.; Zhou, Y.; Zhang, F.; Chen, J. M.; Zhu, Z.; Yu, X.-Y., Deciphering the Aqueous Chemistry of 424 Glyoxal Oxidation with Hydrogen Peroxide Using Molecular Imaging. Phys. Chem. Chem. Phys. 2017, 425 19, (31), 20357-20366.426 28. Yang, L.; Zhu, Z. H.; Yu, X. Y.; Thevuthasan, S.; Cowin, J. P., Performance of a microfluidic device 427 for in situ ToF-SIMS analysis of selected organic molecules at aqueous surfaces. Anal. Methods 2013, 5, 428 (10), 2515-2522.429 29. Yang, L.; Yu, X. Y.; Zhu, Z. H.; Iedema, M. J.; Cowin, J. P., Probing liquid surfaces under vacuum 430 using SEM and ToF-SIMS. Lab Chip 2011, 11, (15), 2481-2484.431 30. Yang, L.; Yu, X. Y.; Zhu, Z. H.; Thevuthasan, T.; Cowin, J. P., Making a hybrid microfluidic platform 432 compatible for in situ imaging by vacuum-based techniques. J. Vac. Sci. Technol. A 2011, 29, (6), 061101.433 31. Hua, X.; Szymanski, C.; Wang, Z.; Zhou, Y.; Ma, X.; Yu, J.; Evans, J.; Orr, G.; Liu, S.; Zhu, Z., 434 Chemical imaging of molecular changes in a hydrated single cell by dynamic secondary ion mass 435 spectrometry and super-resolution microscopy. Integr. Biol. 2016, 8, (5), 635-644.436 32. Yu, J.; Zhou, Y.; Hua, X.; Zhu, Z.; Yu, X.-Y., In situ characterization of hydrated proteins in water 437 by SALVI and ToF-SIMS. JOVE J. Vis. Exp. 2016, (108), e53708-e53708.438 33. Yu, X.-Y.; Yao, J.; Lao, D. B.; Heldebrant, D. J.; Zhu, Z.; Malhotra, D.; Nguyen, M.-T.; Glezakou, 439 V.-A.; Rousseau, R., Mesoscopic Structure Facilitates Rapid CO2 Transport and Reactivity in CO2 440 Capture Solvents. J. Phys. Chem. Lett. 2018, 9, (19), 5765-5771.

Page 17 of 30



18

441 34. Yao, J.; Lao, D. B.; Sui, X.; Zhou, Y.; Nune, S. K.; Ma, X.; Troy, T. P.; Ahmed, M.; Zhu, Z.; 442 Heldebrant, D. J.; Yu, X.-Y., Two coexisting liquid phases in switchable ionic liquids. Phys. Chem. Chem. 443 Phys. 2017, 19, (34), 22627-22632.444 35. Zhou, Y. F.; Yao, J.; Ding, Y. Z.; Yu, J. C.; Hua, X.; Evans, J. E.; Yu, X. F.; Lao, D. B.; Heldebrant, 445 D. J.; Nune, S. K.; Cao, B.; Bowden, M. E.; Yu, X. Y.; Wang, X. L.; Zhu, Z. H., Improving the Molecular 446 Ion Signal Intensity for In Situ Liquid SIMS Analysis. J. Am. Soc. Mass. Spectrom. 2016, 27, (12), 2006-447 2013.448 36. Ding, Y.; Zhou, Y.; Yao, J.; Szymanski, C.; Fredrickson, J.; Shi, L.; Cao, B.; Zhu, Z.; Yu, X.-Y., In 449 Situ Molecular Imaging of the Biofilm and Its Matrix. Anal. Chem. 2016, 88, (22), 11244-11252.450 37. Sui, X.; Zhou, Y.; Zhang, F.; Zhang, Y.; Chen, J.; Zhu, Z.; Yu, X.-Y., ToF-SIMS characterization of 451 glyoxal surface oxidation products by hydrogen peroxide: a comparison between dry and liquid samples. 452 Surf. Interface Anal. 2018, 50, (10), 927-938.453 38. Lim, Y. B.; Turpin, B. J., Laboratory evidence of organic peroxide and peroxyhemiacetal formation 454 in the aqueous phase and implications for aqueous OH. Atmos. Chem. Phys. 2015, 15, (22), 12867-12877.455 39. Stephen, M. B.; Allen, H. C., Vibrational spectroscopy of gas-liquid interfaces. In Physical Chemsitry 456 of Gas-Liquid interfaces, Faust, J. A.; House, J. E., Eds. Elsevier: 2018; pp 105-133.457 40. Zhang, F.; Fu, Y.; Yu, X.-Y., Microfludics and interfacial chemistry in the atmosphere. In Physical 458 chemistry of gas-liquid interfaces, Jennifer A. Faust; House, J. E., Eds. Elsevier: 2018; pp 245-270.459 41. Loeffler, K. W.; Koehler, C. A.; Paul, N. M.; De Haan, D. O., Oligomer formation in evaporating 460 aqueous glyoxal and methyl glyoxal solutions. Environ. Sci. Technol. 2006, 40, (20), 6318-6323.461 42. Galloway, M.; Chhabra, P.; Chan, A.; Surratt, J. D.; Flagan, R.; Seinfeld, J.; Keutsch, F., Glyoxal 462 uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and 463 irradiated conditions. Atmos. Chem. Phys. 2009, 9, (10), 3331-3345.464 43. Lee, A. K.; Zhao, R.; Gao, S. S.; Abbatt, J. P., Aqueous-phase OH oxidation of glyoxal: application 465 of a novel analytical approach employing aerosol mass spectrometry and complementary off-line 466 techniques. J. Phys. Chem. A 2011, 115, (38), 10517-26.467 44. Ervens, B.; Sorooshian, A.; Lim, Y. B.; Turpin, B. J., Key parameters controlling OH-initiated 468 formation of secondary organic aerosol in the aqueous phase (aqSOA). J. Geophys. Res. Atmos. 2014, 469 119, (7), 3997-4016.470 45. Axson, J. L.; Takahashi, K.; De Haan, D. O.; Vaida, V., Gas-phase water-mediated equilibrium 471 between methylglyoxal and its geminal diol. Proc. Natl. Acad. Sci. 2010, 107, (15), 6687-6692.472 46. Liu, L.; Zhang, X. H.; Li, Z. S.; Zhang, Y. H.; Ge, M. F., Gas-phase hydration of glyoxylic acid: 473 Kinetics and atmospheric implications. Chemosphere 2017, 186, 430-437.474 47. Faust, J. A.; Wong, J. P. S.; Lee, A. K. Y.; Abbatt, J. P. D., Role of Aerosol Liquid Water in Secondary 475 Organic Aerosol Formation from Volatile Organic Compounds. Environ. Sci. Technol. 2017, 51, (3), 476 1405-1413.477 48. Carlton, A. G.; Turpin, B. J.; Altieri, K. E.; Seitzinger, S.; Reff, A.; Lim, H.-J.; Ervens, B., 478 Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation 479 experiments. Atmos. Environ. 2007, 41, (35), 7588-7602.480 49. Zhao, R.; Lee, A. K.; Abbatt, J. P., Investigation of aqueous-phase photooxidation of glyoxal and 481 methylglyoxal by aerosol chemical ionization mass spectrometry: observation of hydroxyhydroperoxide 482 formation. J. Phys. Chem. A 2012, 116, (24), 6253-63.483 50. Zhao, R.; Lee, A. K. Y.; Soong, R.; Simpson, A. J.; Abbatt, J. P. D., Formation of aqueous-phase α-484 hydroxyhydroperoxides (α-HHP): potential atmospheric impacts. Atmos. Chem. Phys. 2013, 13, (12), 485 5857-5872.486 51. Herrmann, H.; Tilgner, A.; Barzaghi, P.; Majdik, Z.; Gligorovski, S.; Poulain, L.; Monod, A., Towards 487 a more detailed description of tropospheric aqueous phase organic chemistry: CAPRAM 3.0. Atmos. 488 Environ. 2005, 39, (23), 4351-4363.489 52. Tan, Y.; Perri, M. J.; Seitzinger, S. P.; Turpin, B. J., Effects of precursor concentration and acidic 490 sulfate in aqueous glyoxal− OH radical oxidation and implications for secondary organic aerosol. Environ. 491 Sci. Technol. 2009, 43, (21), 8105-8112.

Page 18 of 30



19

492 53. De Haan, D. O.; Corrigan, A. L.; Smith, K. W.; Stroik, D. R.; Turley, J. J.; Lee, F. E.; Tolbert, M. A.; 493 Jimenez, J. L.; Cordova, K. E.; Ferrell, G. R., Secondary Organic Aerosol-Forming Reactions of Glyoxal 494 with Amino Acids. Environ. Sci. Technol. 2009, 43, (8), 2818-2824.495 54. Feng, J. S.; Moller, D., Characterization of water-soluble macromolecular substances in cloud water. 496 J. Atmos. Chem. 2004, 48, (3), 217-233.497 55. Darvas, M.; Picaud, S.; Jedlovszky, P., Molecular dynamics simulations of the water adsorption 498 around malonic acid aerosol models. Phys. Chem. Chem. Phys. 2013, 15, (26), 10942-10951.499 56. Vaida, V., Perspective: Water cluster mediated atmospheric chemistry. J. Chem. Phys. 2011, 135, (2), 500 020901.501 57. Brovchenko, I.; Geiger, A.; Oleinikova, A., Clustering of water molecules in aqueous solutions: Effect 502 of water-solute interaction. Phys. Chem. Chem. Phys. 2004, 6, (8), 1982-1987.503 58. Schweitzer, F.; Magi, L.; Mirabel, P.; George, C., Uptake rate measurements of methanesulfonic acid 504 and glyoxal by aqueous droplets. J. Phys. Chem. A 1998, 102, (3), 593-600.505 59. Garczarek, F.; Gerwert, K., Functional waters in intraprotein proton transfer monitored by FTIR 506 difference spectroscopy. Nature 2006, 439, (7072), 109-112.507 60. Buch, V.; Milet, A.; Vacha, R.; Jungwirth, P.; Devlin, J. P., Water surface is acidic. Proc. Natl. Acad. 508 Sci. 2007, 104, (18), 7342-7347.509 61. Schwartz, S. E. In Mass-Transport Considerations Pertinent to Aqueous Phase Reactions of Gases in 510 Liquid-Water Clouds, Berlin, Heidelberg, 1986; Springer Berlin Heidelberg: Berlin, Heidelberg, 1986; pp 511 415-471.512 62. Lee, S. H.; Reeves, J. M.; Wilson, J. C.; Hunton, D. E.; Viggiano, A. A.; Miller, T. M.; Ballenthin, J. 513 O.; Lait, L. R., Particle formation by ion nucleation in the upper troposphere and lower stratosphere. 514 Science 2003, 301, (5641), 1886-1889.515 63. Hsieh, C. S.; Okuno, M.; Hunger, J.; Backus, E. H. G.; Nagata, Y.; Bonn, M., Aqueous Heterogeneity 516 at the Air/Water Interface Revealed by 2D-HD-SFG Spectroscopy. Angew. Chem. Int. Ed. 2014, 53, (31), 517 8146-8149.518 64. Goken, E. G.; Castleman, A. W., Reactions of formic acid with protonated water clusters: Implications 519 of cluster growth in the atmosphere. J. Geophys. Res. Atmos. 2010, 115, (D16), D16203.520 65. Lu, H. B.; Campbell, C. T.; Graham, D. J.; Ratner, B. D., Surface characterization of hydroxyapatite 521 and related calcium phosphates by XPS and TOF-SIMS. Anal. Chem. 2000, 72, (13), 2886-2894.522 66. Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R. G.; Jenkin, M. 523 E.; Rossi, M. J.; Troe, J., Evaluated kinetic and photochemical data for atmospheric chemistry: Volume 524 II - gas phase reactions of organic species. Atmos. Chem. Phys. 2006, 6, 3625-4055.525 67. Easter, R. C.; Ghan, S. J.; Zhang, Y.; Saylor, R. D.; Chapman, E. G.; Laulainen, N. S.; Abdul-Razzak, 526 H.; Leung, L. R.; Bian, X. D.; Zaveri, R. A., MIRAGE: Model description and evaluation of aerosols and 527 trace gases. J. Geophys. Res. Atmos. 2004, 109, (D20), D20210.528 68. Benninghoven, A., Chemical-Analysis of Inorganic and Organic-Surfaces and Thin-Films by Static 529 Time-of-Flight Secondary-Ion Mass-Spectrometry (Tof-Sims). Angew. Chem. Int. Ed. 1994, 33, (10), 530 1023-1043.531 69. Zhang, R. Y.; Khalizov, A.; Wang, L.; Hu, M.; Xu, W., Nucleation and Growth of Nanoparticles in 532 the Atmosphere. Chem. Rev. 2012, 112, (3), 1957-2011.533 70. Zhang, R. Y., Getting to the Critical Nucleus of Aerosol Formation. Science 2010, 328, (5984), 1366-534 1367.535 71. Kulmala, M.; Kontkanen, J.; Junninen, H.; Lehtipalo, K.; Manninen, H. E.; Nieminen, T.; Petaja, T.; 536 Sipila, M.; Schobesberger, S.; Rantala, P.; Franchin, A.; Jokinen, T.; Jarvinen, E.; Aijala, M.; 537 Kangasluoma, J.; Hakala, J.; Aalto, P. P.; Paasonen, P.; Mikkila, J.; Vanhanen, J.; Aalto, J.; Hakola, H.; 538 Makkonen, U.; Ruuskanen, T.; Mauldin, R. L.; Duplissy, J.; Vehkamaki, H.; Back, J.; Kortelainen, A.; 539 Riipinen, I.; Kurten, T.; Johnston, M. V.; Smith, J. N.; Ehn, M.; Mentel, T. F.; Lehtinen, K. E. J.; 540 Laaksonen, A.; Kerminen, V. M.; Worsnop, D. R., Direct Observations of Atmospheric Aerosol 541 Nucleation. Science 2013, 339, (6122), 943-946.542 72. Vaida, V., Atmospheric radical chemistry revisited. Science 2016, 353, (6300), 650-650.

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543 73. Griffith, E. C.; Adams, E. M.; Allen, H. C.; Vaida, V., Hydrophobic collapse of a stearic acid film by 544 adsorbed l-phenylalanine at the air–water interface. J. Phys. Chem. B 2012, 116, (27), 7849-7857.545 74. Wang, Y. S.; Yao, L.; Wang, L. L.; Liu, Z. R.; Ji, D. S.; Tang, G. Q.; Zhang, J. K.; Sun, Y.; Hu, B.; 546 Xin, J. Y., Mechanism for the formation of the January 2013 heavy haze pollution episode over central 547 and eastern China. Sci China-Earth Sci 2014, 57, (1), 14-25.

548

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549 FIGURE CAPTIONS.

550 Figure 1. Flow chart of glyoxal and hydrogen peroxide photochemical aging with expanded reaction

551 pathways. Adapted from Ref. 27 with permission from the PCCP Owner Societies. Representative new

552 products are highlighted in red boxes. The 3D chemical structure represents water molecules.

553 Figure 2. Comparison of products in all UV aging in the negative ion mode (m/z- 1-300). Red color bars

554 depict the location of water clusters, green carboxylic acids, pink hydration products, and blue oligomers.

555 Figure 3. Spectral PCA results of selected peaks in the negative ion mode. Score plots of PC1 vs. PC2

556 (a), PC1 vs. PC3 (b), PC2 vs. PC3 (c) and loading plots of PC1, PC2 and PC3 in the range m/z- 1-300 (d),

557 m/z- 301-500 (e) and m/z- 501-800 (f). Red color bars represent water clusters, green color carboxylic

558 acids, pink hydration products, blue oligomers, and cyan cluster ions.

559 Figure 4. Temporal evolution of (a) carboxylic acids, (b) oligomers, (c) cluster ions, and (d) water

560 clusters in the negative ion mode. The error bars are the measurement standard deviations.

561 Figure 5. 3D reconstructed images of key species in the negative ion mode. (a) Carboxylic acids formic

562 acid m/z- 45 CHO2-, succinic acid m/z- 117 C4H5O4

-, tartaric acid m/z- 149 C4H5O6-, (b) oligomers m/z-

563 161 C5H5O6-, 185 C4H9O8

-, 209 C7H11O7-, (c) oligomers, m/z- 285 C8H13O11

-, 329 C9H13O13-; 421

564 C14H13O15-, (d) cluster ions m/z- 269 C7H9O11

-, 617 C19H21O23-, 635 C19H23O24

-, and (e) large water

565 clusters m/z- 467 (H2O)25OH-, 521 (H2O)28OH-, 611 (H2O)33OH-. 3D images were normalized to total

566 ion intensities excluding interference peaks. The darker color indicates higher intensity, and the brighter

567 color lower intensity.

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568 FIGURES

569

570 Figure 1. Flow chart of glyoxal and hydrogen peroxide photochemical aging with expanded reaction

571 pathways. Adapted from Ref. 27 with permission from the PCCP Owner Societies. Representative new

572 products are highlighted in red boxes. The 3D chemical structure represents water molecules.

573

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574

575 Figure 2. Comparison of products in all UV aging in the negative ion mode (m/z- 1-300). Red color bars

576 depict the location of water clusters, green carboxylic acids, pink hydration products, and blue oligomers.

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577

578

579 Figure 3. Spectral PCA results of selected peaks in the negative ion mode. Score plots of PC1 vs. PC2

580 (a), PC1 vs. PC3 (b), PC2 vs. PC3 (c) and loading plots of PC1, PC2 and PC3 in the range m/z- 1-300 (d),

581 m/z- 301-500 (e) and m/z- 501-800 (f). Red color bars represent water clusters, green color carboxylic

582 acids, pink hydration products, blue oligomers, and cyan cluster ions.

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583

584 Figure 4. Temporal evolution of (a) carboxylic acids, (b) oligomers, (c) cluster ions, and (d) water

585 clusters in the negative ion mode. The error bars represented the standard deviation of measurements.

586

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587

588 Figure 5. 3D reconstructed images of key species in the negative ion mode. (a) Carboxylic acids formic

589 acid m/z- 45 CHO2-, succinic acid m/z- 117 C4H5O4

-, tartaric acid m/z- 149 C4H5O6-, (b) oligomers m/z-

590 161 C5H5O6-, 185 C4H9O8

-, 209 C7H11O7-, (c) oligomers, m/z- 285 C8H13O11

-, 329 C9H13O13-; 421

591 C14H13O15-, (d) cluster ions m/z- 269 C7H9O11

-, 617 C19H21O23-, 635 C19H23O24

-, and (e) large water

592 clusters m/z- 467 (H2O)25OH-, 521 (H2O)28OH-, 611 (H2O)33OH-. 3D images were normalized to total

593 ion intensities excluding interference peaks. The darker color indicates higher intensity, and the brighter

594 color lower intensity.

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595 Table 1. Possible peak assignment in the negative ion mode.

m/z- [M-H]-‡ Possible assignment Ref.

185 C4H9O8- Hydrated glyoxylic acid…dihydrated glyoxal This work

223 C6H7O9- Hydrated glyoxylic acid + tartaric acid 16

225 C6H9O9- Dihydrated glyoxal + tartaric acid 16

237 C6H5O10- m/z- 165 + oxalic acid This work

241 C6H9O10- m/z- 223...H2O This work

285 C8H13O11- Dihydrated glyoxal trimer + glyoxal This work

311 C9H11O12- m/z- 237 + glyoxylic acid/m/z- 161 + tartaric acid This work

317 C8H13O13- Monohydrated glyoxal + glyoxylic acid + tartaric acid hydrate This work

329 C9H13O13- m/z- 311 + H2O This work

343 C10H15O13- Monohydrated tartaric acid+ monohydrated malic acid + acetic

acid This work

347 C9H15O14- 6 Glyoxal/m/z- 329 + H2O This work

357 C10H13O14- 2 Monohydrated glyoxal + glyoxylic acid+ monohydrated tartaric

acid16

359 C10H15O14- Malic acid + glycolic acid + tartaric acid…3H2O This work

365 C12H13O13- 6 Glyoxal monohydrate This work

377 C10H17O15- m/z- 359 + H2O This work

383 C12H15O14- 6 Glyoxal dihydrate This work

401 C12H17O15- 5 Glyoxal dihydrate + monohydrated glyoxal This work

419 C12H19O16- 4 Glyoxal dehydrate + 2 monohydrated glyoxal This work

596 Notes: ‡Peak identification uses the peak center to estimate the major component of a peak.

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597 SYNOPSIS TOC

598

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599 Highlights

600 1. More oligomers and cluster ions are formed at the aqueous surface in the longer UV aging reactions.

601 2. Higher relative distribution of larger water cluster shows water uptake ability of the aqueous surface

602 becomes stronger in the longer UV aging reactions.

603 3. Water clusters facilitate the proton transfer and further the surface proton reaction, contributing to

604 oligomer and cluster ion formation.

605 4. Heteromolecular and homomolecular nucleation may occur at the a-l interface as a result of multiphase

606 chemistry.

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For TOC art only

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Documents

photochemistry of glyoxal and hydroxyl radicals Evolution of … · 2019-11-15 · 71 Glyoxal (40% wt in water, electrophoresis grade) and hydrogen peroxide (H2O2, 30% wt in water,