Effects of Aqueous-Phase and Photochemical Processing on

Dec 30, 2016 - Case study of spring haze in Beijing: Characteristics, formation ... Francesco Canonaco , André S. H. Prévôt , Pingqing Fu , Zifa Wang ...
0 downloads 0 Views 1MB Size
Subscriber access provided by Fudan University

Article

Effects of Aqueous-phase and Photochemical Processing on Secondary Organic Aerosol Formation and Evolution in Beijing, China Weiqi Xu, Tingting Han, Wei Du, Qingqing Wang, Chen Chen, Jian Zhao, Yingjie Zhang, Jie Li, Pingqing Fu, Zifa Wang, Douglas R. Worsnop, and Yele Sun Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04498 • Publication Date (Web): 30 Dec 2016 Downloaded from http://pubs.acs.org on December 31, 2016

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 free 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 accessible to all readers and 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.

Environmental Science & Technology 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 32

Environmental Science & Technology

1

Effects of Aqueous-phase and Photochemical Processing on Secondary

2

Organic Aerosol Formation and Evolution in Beijing, China

3 4

Weiqi Xu1,3, Tingting Han1,3, Wei Du1,3, Qingqing Wang1, Chen Chen1, Jian Zhao1,3,

5

Yingjie Zhang1,4, Jie Li1, Pingqing Fu1, Zifa Wang1, Douglas R. Worsnop5, Yele

6

Sun1,2,4*

7 1

8

State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric

9

Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing

10

100029, China 2

11

Center for Excellence in Regional Atmospheric Environment, Institute of Urban

12

Environment, Chinese Academy of Sciences, Xiamen 361021, China

13

3

4

14

University of Chinese Academy of Sciences, Beijing 100049, China

Collaborative Innovation Center on Forecast and Evaluation of Meteorological

15

Disasters, Nanjing University of Information Science & Technology, Nanjing 210044,

16

China 5

17

Aerodyne Research, Inc., Billerica, Massachusetts 01821, USA

18

19 20

*

To whom correspondence should be addressed: Yele Sun ([email protected]) 40 Huayanli, Chaoyang District, Beijing 100029, China. Tel.: +86-10-82021255

1

ACS Paragon Plus Environment

Environmental Science & Technology

21

Abstract

22

Secondary organic aerosol (SOA) constitutes a large fraction of OA, yet remains

23

a source of significant uncertainties in climate models due to incomplete

24

understanding of its formation mechanisms and evolutionary processes. Here we

25

evaluated the effects of photochemical and aqueous-phase processing on SOA

26

composition and oxidation degrees in three seasons in Beijing, China, using

27

high-resolution aerosol mass spectrometer measurements along with positive matrix

28

factorization. Our results show that aqueous-phase processing has a dominant impact

29

on the formation of more oxidized SOA (MO-OOA), and the contribution of

30

MO-OOA to OA increases substantially as a function of relative humidity or liquid

31

water content. In contrast, photochemical processing plays a major role in the

32

formation of less oxidized SOA (LO-OOA), as indicated by the strong correlations

33

between LO-OOA and odd oxygen (Ox = O3 +NO2) during periods of photochemical

34

production (R2=0.59-0.80). Higher oxygen-to-carbon ratios of SOA during periods

35

with higher RH were also found indicating a major role of aqueous-phase processing

36

in changing the oxidation degree of SOA in Beijing. Episodes analyses further

37

highlight that LO-OOA plays a more important role during the early stage of the

38

formation of autumn/winter haze episodes while MO-OOA is more significant during

39

the later evolution period.

2

ACS Paragon Plus Environment

Page 2 of 32

Page 3 of 32

Environmental Science & Technology

40

1. Introduction

41

Organic aerosols (OA) comprising plenty of compounds with vastly different

42

properties such as volatilities, oxidation states and hygroscopicity, account for a

43

substantial mass fraction of submicron aerosols (20-90%).1-3 OA can be either primary

44

from direct emissions or secondary from oxidation of biogenic and anthropogenic

45

volatile organic compounds (VOCs). While primary OA (POA) is relatively well

46

understood, our understanding of the formation mechanisms and evolutionary

47

processes of secondary OA (SOA) is not complete, especially in highly polluted

48

environments. As a result, traditional models often show substantial discrepancies in

49

simulating SOA mass concentrations 4, 5 and oxidation states. 6

50

SOA can be formed through gas-phase photochemical reactions with oxidants

51

(e.g., hydroxyl radical (OH) and ozone (O3))7 followed by gas-particle partitioning

52

that is affected by various factors, e.g., temperature (T), relative humidity (RH), and

53

total organic aerosol mass loadings.8-10 While direct quantification of SOA in ambient

54

environments is challenging, recent studies have shown that oxygenated OA (OOA)

55

determined from positive matrix factorization (PMF) analysis of OA that is measured

56

by aerosol mass spectrometers is a good surrogate of SOA.11,12 Therefore, OOA is

57

widely used to study the formation mechanisms and evolutionary processes of SOA.

58

For example, Herndon et al.

59

(Ox = O3 + nitrogen dioxide (NO2)) during photochemical processing, and the

60

relationship between OOA and Ox can be used as a metric to characterize SOA

13

found that OOA was well correlated with odd oxygen

3

ACS Paragon Plus Environment

Environmental Science & Technology

61

formation mechanisms associated with ozone production chemistry. OOA vs. Ox

62

shows different slopes ranging from 0.03 to 0.16 µg m-3 ppb-1 in different megacities,

63

e.g., Pasadena, Paris, Mexico City and New York City,14-17 which are all lower than

64

that in Beijing, China (0.49-1.07 µg m-3 ppb-1).18,

65

photochemical production of SOA and Ox in Beijing are different from other

66

megacities in Europe and North America. The reasons are not clear yet, but likely due

67

to different VOCs precursors and much higher NOx (= nitrogen monoxide (NO) +

68

NO2) levels in Beijing. SOA can also be formed through aqueous reactions in wet

69

aerosols, clouds and fogs, and has been widely observed in both ambient studies and

70

lab simulations.20-23 For example, Sorooshian et al. 24 found an important dual role of

71

both ambient RH and hygroscopicity in leading to an enrichment of oxygenated

72

organics, and Duplissy et al.

73

organics (κorg) in oxidized organics with high f44 (fraction of m/z 44 in OA) in Mexico

74

City, while such a trend is not observed in CalNex.26

25

19

These results indicate that

showed an enhanced hygroscopicity parameter of

75

However, Sun et al. 27 and Elser et al. 28 found that the OOA production in winter

76

in Beijing and Xi’an seemed to be independent of RH, suggesting that aqueous-phase

77

processing was likely not an important formation mechanism for SOA in winter. Such

78

a conclusion was different from previous studies that showed an enhanced SOA

79

formation at elevated RH levels (RH>70%) due to water uptake in summer in Atlanta,

80

U.S.21, 29 These results likely indicate a largely different impact of aerosol liquid water

81

on processing different types of SOA. In fact, Sun et al.

30

4

ACS Paragon Plus Environment

found that aqueous-phase

Page 4 of 32

Page 5 of 32

Environmental Science & Technology

82

processing has a different impact on highly oxidized OOA and freshly oxidized OOA

83

in winter in Beijing. While particle liquid water exerts strong influences on the

84

formation of highly oxidized OOA, it has minor impacts on freshly oxidized OOA. In

85

addition, the different meteorology (RH, T) and precursors between summer (e.g.,

86

U.S.) and winter (e.g., China) might also be potential factors affecting aqueous-phase

87

processing SOA. Therefore, it is of vital importance to evaluate the role of

88

aqueous-phase processing in the formation of SOA in different seasons in China.

89

Previous studies suggested that fog and cloud processing with high RH levels

90

enhanced the oxidation degree of OA,31-33 while f44, a surrogate of oxidation degree,34

91

remained fairly constant at RH>50% in winter in Beijing.27 The reasons for such

92

differences are not clear yet. Therefore, photochemical and aqueous-phase formation

93

of SOA and its impacts on oxidation degree are far from being clearly understood,

94

particularly under the heavily polluted environments found in the megacities of China.

95

Owing to the high time resolution and capability in characterization of

96

non-refractory submicron aerosols (NR-PM1) composition,1 Aerodyne aerosol mass

97

spectrometers (AMS) are widely used to investigate the effects of photochemical and

98

aqueous-phase processing on SOA formation and evolution. For instance, Zhang et al.

99

33

found that aqueous-phase aging dominated the oxidation of OA in winter 2013 in

100

Beijing, while photochemical aging also played a role in winter 2014. In Hong Kong,

101

the degree of oxygenation and composition of OA were compared between foggy and

102

hazy periods to explore the effects of aqueous-phase or photochemical processing.31 5

ACS Paragon Plus Environment

Environmental Science & Technology

35

further found different slopes in the Van Krevelen diagram

Page 6 of 32

36

103

Chakraborty et al.

104

between foggy and non-foggy periods, suggesting the different aging mechanisms

105

between fog processing and photochemical oxidation. Although these studies provide

106

important insights into the effects of aqueous-phase or photochemical processing on

107

OA properties, significant uncertainties of relative importance for these two pathways

108

still exist,20, 37 for instance, the impacts on the transformation of less oxidized OOA to

109

highly oxidized OOA, and the oxidation degree of SOA in different seasons.

110

The frequent severe pollution in Beijing that is characterized by high

111

contributions of secondary particles38, 39 has been widely investigated using the AMS.

112

While the properties of inorganic species have been relatively well characterized,

113

those of OA have mainly focused on sources, elemental ratios and mass

114

concentrations, and therefore photochemical and/or aqueous-phase processing of SOA

115

and its role in severe haze formation remain relatively uncertain.40-44 Moreover, few

116

studies have been conducted in seasons other than winter to evaluate the different

117

roles of photochemical and/or aqueous-phase processing in the formation of SOA

118

during severe pollution episodes,18,

119

understanding of the evolutionary processes of haze pollution in different seasons.

45, 46

preventing us from having a better

120

In this study, we evaluate the impacts of photochemical and aqueous-phase

121

processing on SOA composition and oxidation degree of OA in three different seasons,

122

i.e., summer, autumn and winter in Beijing using High-Resolution Time-of-Flight

123

AMS (HR-ToF-AMS) measurements along with PMF. A more detailed evolution of 6

ACS Paragon Plus Environment

Page 7 of 32

Environmental Science & Technology

124

SOA composition and oxidation degree during pollution episodes is elucidated in four

125

case studies in different seasons with substantially different meteorological

126

parameters and precursors.

127

2. Experimental methods

128

Sampling and instrumentation

129

All measurements took place at the Tower branch of the Institute of Atmospheric

130

Physics, Chinese Academy of Sciences, a typical urban site in Beijing. The

131

measurements were conducted during three seasons, i.e., winter (December 16, 2013

132

– January 17, 2014), summer (June 3 – July 11, 2014) and autumn (October 14 –

133

November 12, 2014) using HR-ToF-AMS. The set up and operation of the HR-ToF-AMS is similar to our previous studies.30,

134 135

44

136

(model URG-2000-30EN) mounted in front of the sampling line. Ambient air

137

containing the remaining particles was drawn into the sampling room and then dried

138

by a diffusion silica-gel dryer, and finally was isokinetically sampled into the

139

HR-ToF-AMS at a flow rate of ~0.1 L/min. The mass-sensitive V-mode alternated

140

with the high mass resolution W-mode in the operation of the HR-ToF-AMS by 2 min,

141

5 min and 5 min in winter, autumn and summer, respectively.

Briefly, coarse particles larger than 2.5 µm were removed by a PM2.5 cyclone

142

Collocated measurements in each campaign included black carbon (BC), gaseous

143

NO2, and gaseous species (carbon monoxide (CO), O3, NO/NO2, and sulfur dioxide

144

(SO2)), which were measured by a two-wavelength Aethalometer (model AE22, 7

ACS Paragon Plus Environment

Environmental Science & Technology

Page 8 of 32

145

Magee Scientific Corp.), a cavity attenuated phase shift NO2 monitor (CAPS-NO2,

146

Aerodyne Research Inc.), and a series of gas analyzers from Thermo Scientific,

147

respectively. The meteorological parameters (wind, T and RH) were obtained from the

148

Beijing 325 m meteorological tower, which is approximately 30 m from the sampling

149

site. Data collected in this study are presented in Beijing local time.

150

HR-ToF-AMS data analysis

151

The AMS data including mass concentrations and elemental ratios were analyzed

152

using software SQUIRREL V 1.56 and PIKA V 1.15D written in Igor Pro 6.12 A

153

(Wavemetrics,

154

(http://cires1.colorado.edu/jimenez-group/ToFAMSResources/ToFSoftware/index.htm

155

l). The ionization efficiency (IE) was calibrated using pure ammonium nitrate

156

particles following the standard protocols.47-49 The relative ionization efficiency (RIE)

157

of ammonium was determined from pure ammonium nitrate and the default RIEs

158

were applied to other species. A collection efficiency (CE) of 0.5 was applied to the

159

three datasets for the following reasons (Table S1): (1) particles were dry; and (2)

160

slightly acidic as indicated by NH4+measured/NH4+predicted;50 and (3) the contribution of

161

ammonium nitrate was below 40%, a threshold value affecting the CE significantly.51

162

The elemental ratios of OA including organic-mass-to-organic carbon (OM/OC),

163

oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios were determined with

164

the approach recommended by Canagaratna et al.,52 which was referred to as

165

Improved Ambient (I-A). The elemental ratios were also calculated using the

Lake

Oswego,

8

ACS Paragon Plus Environment

OR,

USA)

Page 9 of 32

Environmental Science & Technology

166

approach proposed by Aiken et al. 34 for a comparison (Table S2), which was referred

167

to as Aiken Ambient (A-A).

168

OA factors representing specific sources were identified using the PMF2.exe

169

algorithm (v4.2)53 applied to the high-resolution mass spectra (HRMS). The detailed

170

PMF analysis and evaluation in autumn and winter have been given in Xu et al. 40 and

171

Sun et al.,26 respectively, and those in summer were detailed in supplementary

172

(Figures S1–S3). In this study, we use the sum of less oxidized oxygenated OA

173

(LO-OOA) and more oxidized oxygenated OA (MO-OOA) as a surrogate of SOA,

174

and other OA factors, e.g., cooking OA (COA), hydrocarbon-like OA (HOA), coal

175

combustion OA (CCOA), and biomass burning OA (BBOA) as POA. The O/C of

176

SOA was then calculated as: [LO − OOA] [MO − OOA] [LO − OOA] [MO − OOA] O/Cୗ୓୅ = ൤ × O/C୐୓ି୓୓୅ + × O/C୑୓ି୓୓୅ ൨ / ൤ + ൨ ሺOM/OCሻ୐୓ି୓୓୅ × 12 ሺOM/OCሻ୑୓ି୓୓୅ × 12 ሺOM/OCሻ୐୓ି୓୓୅ × 12 ሺOM/OCሻ୑୓ି୓୓୅ × 12

177

Where O/CSOA refers to the O/C of SOA, and [LO-OOA] and [MO-OOA] represent

178

the mass concentrations of LO-OOA and MO-OOA, respectively. In addition, aerosol

179

liquid water content that is associated with inorganic species was predicted with the

180

ISORROPIA-II model.54

181

3. Results and discussion

182

SOA composition and oxidation properties

183

Two SOA factors, i.e., MO-OOA and LO-OOA, were identified during all three

184

seasons. MO-OOA showed ubiquitously higher O/C ratios and f44 than LO-OOA,

185

indicating that MO-OOA is a more oxidized SOA than LO-OOA. The mass spectra of 9

ACS Paragon Plus Environment

Environmental Science & Technology

186

MO-OOA between summer and autumn are similar (R2=0.98), and the oxidation

187

degrees were also close (O/C = 1.15 vs. 1.23). However, MO-OOA in winter showed

188

a different spectral pattern compared with those in summer and autumn. Particularly,

189

the MO-OOA spectrum was characterized by high m/z 29 (mainly CHO+) and m/z 43

190

(mainly C2H3O+) peaks and low O/C (0.81), suggesting that MO-OOA in winter was

191

overall less aged than those in summer and autumn. Although the LO-OOA spectra

192

also resembled each other during all three seasons (R2=0.92-0.98), the O/C ratios and

193

mass spectra varied substantially. For instance, LO-OOA in autumn presented a much

194

lower O/C (0.58) and higher hydrocarbon-like ions (CxHy+) than the other two seasons,

195

indicating that LO-OOA was less aged in autumn. The differences in SOA spectral

196

patterns and oxidation degrees are not only due to different meteorological conditions

197

and photochemical activities, but also are related to different VOCs precursors.

198

SOA dominated OA in summer, on average accounting for 57%, consistent with

199

the results from previous AMS studies in Beijing.19, 40 Note that LO-OOA showed an

200

overall higher contribution to SOA than MO-OOA (61% vs. 39%), indicating a more

201

important role of LO-OOA in summer. The average contribution SOA to OA was

202

decreased to 37% in winter. Similar to summer, SOA was also dominated by LO-OOA

203

(66%) although periods with higher concentrations of MO-OOA than LO-OOA were

204

also observed (Table S3). In contrast, MO-OOA showed a comparable contribution to

205

LO-OOA (53% vs. 47%) in autumn. Our results showed that SOA composition and

206

oxidation properties can vary substantially in different seasons and in general, the 10

ACS Paragon Plus Environment

Page 10 of 32

Page 11 of 32

Environmental Science & Technology

207

SOA contributions and O/C ratios decreased from summer, autumn to winter.

208

Aqueous-phase processing of SOA

209

Figure 1 shows the variations of mass fractions of OA factors, oxidation degrees,

210

mass concentrations of OA, and liquid water content (LWC) as a function of RH. It is

211

clear that LWC showed a linear increase as a function of RH at RH > 60% during the

212

three seasons indicating the potential impacts of aqueous-phase processing at high RH

213

levels. The variations of OA mass concentrations as a function of RH were different

214

among the three seasons. While OA increased gradually as RH increased in autumn

215

(Figure 1h), they first showed large increases at RH < 60% in summer and winter

216

(Figures 1g and 1i), and then decreased instead as the RH increased. The increases of

217

OA at low RH levels (< 60%) were clearly associated with the decreases of wind

218

speed (Figures 1a-1c) that facilitated the accumulation of air pollutants.55 The

219

decrease of OA at high RH levels in summer was mainly caused by several

220

precipitation events that scavenged OA substantially, and in winter was due to two

221

high pollution episodes formed under moderately high RH. In fact, after excluding the

222

precipitation events in summer, MO-OOA and sulfate showed significant

223

enhancements at high RH levels while most primary species remained relatively

224

constant across different RH levels (Figures S4-S6). These results illustrated strong

225

impacts of aqueous-phase processing in the formation of MO-OOA and sulfate.

226

Figure 1 also shows that the contribution of MO-OOA to OA showed a large

227

increase from 20% to 40% as RH increased from 60% to > 80%, while LO-OOA 11

ACS Paragon Plus Environment

Environmental Science & Technology

228

remained relatively constant (e.g., autumn and winter) and even had a decrease (e.g.,

229

summer). Results here indicate that aqueous-phase processing appears to affect most

230

the formation of MO-OOA while it has minor impacts on LO-OOA. After excluding

231

the effects of planetary boundary layer height (PBL) using HOA as a surrogate,27

232

MO-OOA and LO-OOA also showed similar variations as a function of RH (Figures

233

S4-S6), further supporting our conclusion above. The conclusion that MO-OOA was

234

more affected by aqueous-phase processing was further supported by the correlations

235

between MO-OOA and specific fragment ions. As shown in Figure S7, MO-OOA was

236

well correlated with C2H2O2+, C2O2+ and CH2O2+, which are typical fragment ions of

237

methylglyoxal and glyoxal, that are precursors of SOA via cloud processing.56, 57 In

238

addition, MO-OOA also showed tight correlations with CH3SO+, CH2SO2+ and

239

CH3SO2+, three typical fragment ions of methanesulfonic acid (MSA), which are

240

products mainly from the oxidation of dimethyl sulfide (DMS)58 and can be strongly

241

enhanced by aqueous-phase processing.32,59

242

As a response to the changes in OA composition, the bulk O/C of OA showed

243

different variations at low and high RH levels. While O/C ratios remained small

244

changes by varying 70%.

24

These results supported that aqueous-phase processing can 12

ACS Paragon Plus Environment

Page 12 of 32

Page 13 of 32

Environmental Science & Technology

249

affect the oxidation degree of OA by changing OA composition.23,

60

250

illustrating the impacts of aqueous-phase processing on SOA, we further calculated

251

the O/C ratios of SOA across the three seasons. As shown in Figure 1, O/CSOA showed

252

clear increases as a function of RH, yet presented different increasing rates at low and

253

high RH levels. Overall, O/CSOA increased more rapidly at high RH levels than low

254

RH levels, which agrees well with the changes in MO-OOA contributions. Note that

255

the increase in MO-OOA contribution in summer was associated with a decrease in

256

LO-OOA contribution, likely indicating the transformation of LO-OOA into

257

MO-OOA. Together, our results suggest that aqueous-phase processing has a more

258

important impact on the formation of highly oxidized SOA during all seasons in

259

Beijing.

260

Photochemical production of SOA

For better

261

Ox has been shown to be a more conserved tracer to indicate photochemical

262

processing compared with O3 due to the reactions of NO with O3 to form NO2.13 It

263

should be noted that the air masses contained relatively more NO2 (> 90%) leading to

264

a vast decrease in fractional O3 contributions ( 70 ppb) in

265

autumn and winter (Figure S8). Hence using Ox as an indicator of photochemical

266

process13 might not be appropriate under such conditions (e.g., Ox >70 ppb).

267

The mass loadings of OA showed overall increasing trends as the increases of Ox,

268

in agreement with the variations of OA as a function of Ox in Hong Kong.61 However,

269

the increasing rates of OA factors as a function of Ox were substantially different 13

ACS Paragon Plus Environment

Environmental Science & Technology

270

among different seasons. In summer, LO-OOA presented a linear increase with an

271

increase in Ox, while other OA factors remain relatively constant, suggesting a

272

dominant role of photochemical processing in the formation of LO-OOA (Figure S9).

273

As a comparison, LO-OOA showed synchronous increases as POA factors and

274

MO-OOA in autumn and winter (Figures S10 and S11). The increases of POA factors

275

as a function of Ox were likely due to the enhanced primary emissions that were

276

supported by the much higher NO2 fractions in Ox (Figure S8). However, the faster

277

increasing rates of LO-OOA than POA factors clearly indicate additional

278

photochemical production of SOA during all seasons. Note that LO-OOA presented

279

much faster increasing rates as a function of Ox than MO-OOA in summer and winter,

280

indicating that photochemical processing affects the formation of less oxidized SOA

281

in the two seasons. Comparatively, MO-OOA showed a comparable increasing rate

282

with LO-OOA in autumn, likely indicating the importance of both photochemical and

283

aqueous-phase processing in the formation of MO-OOA.

284

The relationship between O/C ratios and Ox varied among the three seasons. In

285

summer, O/C showed a clear increase as Ox increased. As shown in Figure 2a, such an

286

increase was mainly due to a significant enhancement of SOA associated with a

287

corresponding decrease in POA. Considering that the contribution of MO-OOA

288

showed a slight decrease, the increase in SOA contribution was mainly caused by

289

LO-OOA whose contribution increased from 26.4% to 63.1%. This result indicates

290

the dominant role of photochemical processing in the formation of LO-OOA and 14

ACS Paragon Plus Environment

Page 14 of 32

Page 15 of 32

Environmental Science & Technology

291

increasing oxidation degree of OA in summer. We also note that O/CSOA showed a

292

gradual decrease as a function of Ox. This can be explained by the enhanced

293

contribution of LO-OOA with lower O/C in SOA, and correspondingly a decrease in

294

the contribution of MO-OOA with higher O/C. Comparatively, SOA and O/C ratios

295

showed different relationship with Ox at low and high levels in autumn. While O/C,

296

O/CSOA, and SOA fraction all showed gradual increases at Ox < 70 ppb, they

297

decreased instead at Ox > 70 ppb. Such variations were tightly related to the dominant

298

increase in MO-OOA at low Ox levels (Figure 2b) and the increase in COA associated

299

with a decrease in MO-OOA at high Ox levels (Figure S10). These results suggest that

300

photochemical processing also played an important role in the formation of MO-OOA

301

and increasing the oxidation degree of OA at low Ox levels in autumn. Our results

302

agreed with Li et al.31 that an increase in MO-OOA on a hazy day in Hong Kong was

303

mainly due to photochemical processing. Note that the elevated LWC from 14.2 µg

304

m-3 to 28.7 µg m-3 as a function of Ox (Figure S10) might also play a role in elevating

305

MO-OOA. O/C and O/CSOA stayed relatively constant as a function of Ox in winter

306

despite the increase in LO-OOA contributions. These results supported the idea that

307

photochemical processing did not affect oxidation degree of OA substantially in

308

winter. Therefore, the role of photochemical processing in the formation of SOA and

309

changing O/C was significantly different among the three seasons. While

310

photochemical processing plays a dominant role in the formation of LO-OOA and

311

enhancing oxidation degree of OA in summer, it has much smaller impacts on SOA 15

ACS Paragon Plus Environment

Environmental Science & Technology

312

formation and evolution in winter. Such conclusions were further supported by the

313

correlations between LO-OOA and Ox. As shown in Figure S12, LO-OOA presented

314

the best correlation with ∆Ox (the difference of Ox and background Ox, i.e., the

315

average of the lowest 5% of the data) during 12:00-18:00 when photochemical

316

processing is the most intense in a day (R2=0.59-0.80). The regressions slopes of

317

LO-OOA vs. ∆Ox were 0.17 and 0.61 µg m-3 ppb-1 in summer and winter, respectively,

318

indicating that SOA was much more oxidized in summer than winter due to

319

photochemical processing.13 We also noticed a better correlation between LO-OOA

320

and ∆Ox in winter than summer (Figure S12). One explanation is that LO-OOA in

321

summer was much more affected by the gas-particle partitioning due to high T.

322

Combined effects of RH and Ox on SOA properties

323

The effects of photochemical and aqueous-phase processing on SOA composition

324

(LO-OOA vs. MO-OOA) and oxidation degrees during the three seasons are further

325

illustrated in Figure 3. The ratio of MO-OOA/LO-OOA in summer showed an evident

326

gradient as a function of RH and Ox, confirming the different impacts of

327

photochemical and aqueous-phase processing on SOA with different oxidation

328

degrees. The MO-OOA/LO-OOA presented the highest values on the left-top corner

329

in summer indicating the important role of aqueous-phase processing in the formation

330

of MO-OOA under low Ox conditions. Previous studies also showed that high RH in

331

summer facilitated the transformation of HNO3 into aqueous-phase and increased

332

nitrate concentrations substantially.55, 62 As a result, the ratio of NO3-/SO42- showed 16

ACS Paragon Plus Environment

Page 16 of 32

Page 17 of 32

Environmental Science & Technology

333

similar gradients as MO-OOA/LO-OOA in summer (Figure S13). These results might

334

indicate that the transformation of VOCs into the aqueous-phase is an important

335

source of MO-OOA in summer. The O/CSOA showed remarkably similar RH/Ox

336

dependence as MO-OOA/LO-OOA. This is rational because O/CSOA is mainly driven

337

by MO-OOA with higher O/C (1.15) than that of LO-OOA (0.78). This result suggests

338

that SOA produced via photochemical processing is generally less oxygenated than

339

that produced through aqueous-phase processing.20 Figure 3d also shows that the ratio

340

of O/CSOA experienced small changes as Ox increased when RH was less than 40%,

341

which is due to the dominance of LO-OOA in SOA (MO-OOA/LO-OOA < ~0.2).

342

This result further indicates that photochemical processing played a major role in the

343

formation of LO-OOA at low RH levels. Comparatively, the MO-OOA/LO-OOA

344

increased as Ox increased at RH=40-70%, corresponding to an increase in O/CSOA

345

from ~0.8 to ~0.9 on average. This result indicates an enhanced role of photochemical

346

processing in the formation of MO-OOA under moderately high RH levels, which is

347

also likely from the transformation of LO-OOA into MO-OOA.

348

In winter, the ratio of MO-OOA/LO-OOA and O/CSOA presented high values in

349

the left-top corner when RH was high and Ox low, which is similar to that observed in

350

summer. This result supports our conclusion that aqueous-phase reactions played a

351

more important role in processing MO-OOA than LO-OOA and affecting OA

352

oxidation degrees. As shown in Figure S13c, the RH/Ox dependence of NO3-/SO42-

353

presented the lowest values in the left-top corner, indicating much higher 17

ACS Paragon Plus Environment

Environmental Science & Technology

354

concentrations of SO42- than NO3- in this area. Previous studies have shown that high

355

concentrations of SO42- in winter were mainly formed from aqueous-phase production,

356

most likely fog processing.27, 63 In contrast, low MO-OOA/LO-OOA and O/CSOA were

357

generally observed at low RH levels where high NO3-/SO42- ratios was also presented

358

(Figure S13). This result indicates a more important role of photochemical processing

359

in the formation of LO-OOA and NO3- at low RH levels. Compared with summer,

360

MO-OOA/LO-OOA and O/CSOA showed gradual decreases as Ox increased at both

361

low and high RH levels in winter, which indicates a faster formation of LO-OOA than

362

MO-OOA that is associated with photochemical processing. We note that the mass

363

loading of organics presented a large increase from ~20 to > 100 µg m-3 as Ox

364

increased in winter. High mass loadings of organic particles might be another

365

important factor in contributing to the formation of LO-OOA by absorbing VOCs.29

366

Although the mass loadings of OA also presented increases as Ox increased in summer,

367

the role of OA as an absorbing phase appears to be much smaller than winter because

368

the concentration differences between low and high Ox levels are generally less than

369

15 µg m-3.

370

The RH/Ox dependence of MO-OOA/LO-OOA and O/CSOA in autumn was

371

different from those in summer and winter. As shown in Figure 3b, both

372

MO-OOA/LO-OOA and O/CSOA showed increases as RH and Ox increased and

373

reached its highest values in the central-top corner, indicating that both photochemical

374

and aqueous-phase processing contributed to the formation of MO-OOA and 18

ACS Paragon Plus Environment

Page 18 of 32

Page 19 of 32

Environmental Science & Technology

375

enhanced the oxidation degree of SOA in autumn. While the mass concentration of

376

MO-OOA was increased approximately by 6 µg m-3 as Ox increased from 30-40 ppb

377

to 60-70 ppb at RH levels of 30-40%, it was elevated by nearly 19 µg m-3 as RH

378

increased from 30-40% to > 90% at Ox levels of 30 -40 ppb. This result suggests that

379

aqueous-phase processing is still more important than photochemical processing in

380

the formation of MO-OOA in autumn.

381

Case studies of severe haze episodes

382

Figure 4 shows the evolution processes of SOA and the average bulk

383

composition of NR-PM1 and OA during four distinct episodes in the three seasons.

384

The first episode in summer (Ep1) was characterized by high humidity (~60-80%) and

385

temperature (> 25oC) that is commonly referred to as “Sauna days”, and also

386

consistently southerly winds (Figure 4a). SOA comprised the major fraction of OA,

387

on average accounting for 73% (Table S4), and the average O/CSOA was as high as

388

1.02 indicating highly oxidized SOA. Indeed, the MO-OOA concentration was more

389

than twice that of LO-OOA during this episode, highlighting the well processed SOA

390

observed under such meteorological conditions. We also note a strong diurnal cycle of

391

LO-OOA during Ep1 that is remarkably similar to that of Ox. The concentration of

392

LO-OOA showed a rapid increase after the photochemical processing started in early

393

morning, reached a maximum at noon time, and then presented a gradual decrease in

394

the late afternoon due to evaporative loss under high T. This result clearly indicates a

395

strong photochemical production of LO-OOA in “Sauna days” despite the dominance 19

ACS Paragon Plus Environment

Environmental Science & Technology

396

of MO-OOA. In contrast, Ep2 in summer showed substantially different SOA

397

composition from Ep1. Particularly, the contribution of LO-OOA (58%) was

398

significantly higher than MO-OOA (8%), indicating that photochemical processing

399

was the major formation mechanisms of SOA during this episode. This is consistent

400

with the extremely high Ox level (the daily maximum is 134 ppb and 150 ppb on 29

401

and 30 June, respectively), yet RH was relatively low (< 60%). The average O/CSOA

402

(0.82) was much smaller than that during Ep1, indicating that photochemical

403

processing in summer is subject to produce freshly oxidized SOA.

404

The evolution of MO-OOA and LO-OOA in autumn and winter was largely

405

different from that in summer. During the five-day episode in autumn (Ep3),

406

MO-OOA showed a continuous increase from a few µg m-3 to approximately 30 µg

407

m-3, associated with a gradual increase in RH. Such a temporal variation likely

408

illustrated a combined effect of aqueous-phase production and accumulation

409

processes from regional transport, consistent with the fact that MO-OOA is a well

410

processed and regional SOA. The temporal variation of LO-OOA was quite different

411

from that of MO-OOA. LO-OOA showed a rapid increase during the early stage of

412

Ep3 and then remained at relatively constant levels during the evolution stage except

413

two peaks on 17 and 18 October that were due to the photochemical production

414

associated with high Ox levels. The concentration of LO-OOA was much higher than

415

MO-OOA during the early period of Ep3, and MO-OOA gradually exceeded

416

LO-OOA during the later stage as RH increased gradually. Such changes in SOA 20

ACS Paragon Plus Environment

Page 20 of 32

Page 21 of 32

Environmental Science & Technology

417

composition were also observed in Ep4 in winter. As shown in Figure 4d, the

418

concentration of LO-OOA increased from 15 to 50 µg m-3 in approximately half hour

419

(17:00, 15 January) while that of MO-OOA only increased from 3 to 7 µg m-3. Such a

420

rapid increase in LO-OOA in the late afternoon was most likely due to air mass

421

changes and from the transport of air masses from nearby areas where LO-OOA was

422

photo-chemically formed during the daytime.30 This is also supported by the overall

423

similar trends between LO-OOA and Ox. LO-OOA then showed a gradual decrease at

424

nighttime associated with a corresponding increase in MO-OOA, indicating that

425

aqueous-phase processing played an enhanced role during the later evolution of SOA.

426

The two episodes in autumn and winter highlight different roles of LO-OOA and

427

MO-OOA in the evolution of haze episodes. While LO-OOA appears to be always

428

important at the early formation stage of haze episodes (e.g., ~80% of OOA),

429

MO-OOA becomes more important during the later stage due to aqueous-phase

430

production under high RH levels and continuous regional transport (e.g., ~60% of

431

OOA). Nevertheless, the four episode analyses together highlight the important roles

432

of SOA in the formation of haze episodes during all seasons (65-75% of OA in

433

summer and 51-56% in other two seasons), but SOA composition (LO-OOA vs.

434

MO-OOA) can vary substantially depending on meteorological parameters that affect

435

photochemical and aqueous-phase processing differently.

436

Acknowledgements

437

This work was supported by the National Natural Science Foundation of China 21

ACS Paragon Plus Environment

Environmental Science & Technology

438

(41575120), the National Key Basic Research Program of China (2014CB447900),

439

and the Strategic Priority Research Program (B) of the Chinese Academy of

440

Sciences (XDB05020501).

441 442

Supporting Information Available. The contents of Supporting Information provide

443

a detailed evaluation and selection of PMF solutions in summer, and 5 tables (Tables

444

S1-S5) and 13 figures (Figures S1–S13).

445 446

References

447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470

(1) Zhang, Q.; Jimenez, J.; Canagaratna, M.; Ulbrich, I.; Ng, N.; Worsnop, D.; Sun, Y. Understanding atmospheric organic aerosols via factor analysis of aerosol mass spectrometry: a review. Anal. Bioanal. Chem. 2011, 401, 3045-3067. (2) Jimenez, J. L.; Canagaratna, M. R.; Donahue, N. M.; Prévôt, A. S. H.; Zhang, Q.; Kroll, J. H.; DeCarlo, P. F.; Allan, J. D.; Coe, H.; Ng, N. L.; et al. Evolution of organic aerosols in the atmosphere. Science 2009, 326 (5959), 1525-1529. (3) Kanakidou, M.; Seinfeld, J. H.; Pandis, S. N.; Barnes, I.; Dentener, F. J.; Facchini, M. C.; Dingenen, R. V.; Ervens, B.; Nenes, A.; Nielsen, C. J.; et al. Organic aerosol and global climate modelling: a review. Atmos. Chem. Phys. 2005, 5, 1053-1123. (4) Matsui, H.; Koike, M.; Takegawa, N.; Kondo, Y.; Griffin, R. J.; Miyazaki, Y.; Yokouchi, Y.; Ohara, T. Secondary organic aerosol formation in urban air: Temporal variations and possible contributions from unidentified hydrocarbons. J. Geophys. Res.-Atmos. 2009, 114, D04201. (5) Kleinman, L. I.; Springston, S. R.; Daum, P. H.; Lee, Y.-N.; Nunnermacker, L. J.; Senum, G. I.; Wang, J.; Weinstein-Lloyd, J.; Alexander, M. L.; Hubbe, J.; et al. The time evolution of aerosol composition over the Mexico City plateau. Atmos. Chem. Phys. 2008, 8, 1559-1575. (6) Chen, Q.; Liu, Y.; Donahue, N. M.; Shilling, J. E.; Martin, S. T. Particle-Phase Chemistry of Secondary Organic Material: Modeled Compared to Measured O:C and H:C Elemental Ratios Provide Constraints. Environ. Sci. Technol. 2011, 45, 4763-4770. (7) Seinfeld, J. H.; Pankow, J. F. Organic atmospheric particulate material. Annu. Rev. Phys. Chem. 2003, 54, 121-140. 22

ACS Paragon Plus Environment

Page 22 of 32

Page 23 of 32

Environmental Science & Technology

471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512

(8) Hennigan, C. J.; Bergin, M. H.; Russell, A. G.; Nenes, A.; Weber, R. J. Gas/particle partitioning of water-soluble organic aerosol in Atlanta. Atmos. Chem. Phys. 2009, 9 (11), 3613-3628. (9) Donahue, N. M.; Robinson, A. L.; Stanier, C. O.; Pandis, S. N. Coupled partitioning, dilution, and chemical aging of semivolatile organics. Environ. Sci. Technol. 2006, 40 (8), 2635-2643. (10) Shilling, J. E.; Chen, Q.; King, S. M.; Rosenoern, T.; Kroll, J. H.; Worsnop, D. R.; DeCarlo, P. F.; Aiken, A. C.; Sueper, D.; Jimenez, J. L.; et al. Loading-dependent elemental composition of α-pinene SOA particles. Atmos. Chem. Phys. 2009, 9 (3), 771-782. (11) Zhang, Q.; Jimenez, J. L.; Canagaratna, M. R.; Allan, J. D.; Coe, H.; Ulbrich, I.; Alfarra, M. R.; Takami, A.; Middlebrook, A. M.; Sun, Y. L.; et al. Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced northern hemisphere mid-latitudes. Geophys. Res. Lett. 2007, 34, L13801. (12) Kondo, Y.; Miyazaki, Y.; Takegawa, N.; Miyakawa, T.; Weber, R.; Jimenez, J.; Zhang, Q.; Worsnop, D. R. Oxygenated and water-soluble organic aerosols in Tokyo. J. Geophys. Res. 2007, 112, D01203, doi:10.1029/2006JD007056. (13) Herndon, S. C.; Onasch, T. B.; Wood, E. C.; Kroll, J. H.; Canagaratna, M. R.; Jayne, J. T.; Zavala, M. A.; Knighton, W. B.; Mazzoleni, C.; Dubey, M. K.; et al. Correlation of secondary organic aerosol with odd oxygen in Mexico City. Geophys. Res. Lett. 2008, 35, L15804. (14) Wood, E. C.; Canagaratna, M. R.; Herndon, S. C.; Onasch, T. B.; Kolb, C. E.; Worsnop, D. R.; Kroll, J. H.; Knighton, W. B.; Seila, R.; Zavala, M.; et al. Investigation of the correlation between odd oxygen and secondary organic aerosol in Mexico City and Houston. Atmos. Chem. Phys. 2010, 10 (18), 8947-8968. (15) Sun, Y. L.; Zhang, Q.; Schwab, J. J.; Demerjian, K. L.; Chen, W. N.; Bae, M. S.; Hung, H. M.; Hogrefe, O.; Frank, B.; Rattigan, O. V.; et al. Characterization of the sources and processes of organic and inorganic aerosols in New York City with a high-resolution time-of-flight aerosol mass spectrometer. Atmos. Chem. Phys. 2011, 11 (4), 1581-1602. (16) Hayes, P. L.; Ortega, A. M.; Cubison, M. J.; Froyd, K. D.; Zhao, Y.; Cliff, S. S.; Hu, W. W.; Toohey, D. W.; Flynn, J. H.; Lefer, B. L.; et al. Organic aerosol composition and sources in Pasadena, California, during the 2010 CalNex campaign. J. Geophys. Res.-Atmos. 2013, 118 (16), 9233-9257. (17) Zhang, Q. J.; Beekmann, M.; Freney, E.; Sellegri, K.; Pichon, J. M.; Schwarzenboeck, A.; Colomb, A.; Bourrianne, T.; Michoud, V.; Borbon, A. Formation of secondary organic aerosol in the Paris pollution plume and its impact on surrounding regions. Atmos. Chem. Phys. 2015, 15 (24), 13973-13992. (18) Sun, Y.; Jiang, Q.; Wang, Z.; Fu, P.; Li, J.; Yang, T.; Yin, Y. Investigation of the sources and evolution processes of severe haze pollution in Beijing in January 2013. J. Geophys. Res.-Atmos. 2014, 119 (7), 4380-4398. (19) Hu, W.; Hu, M.; Hu, W.; Jimenez, J. L.; Yuan, B.; Chen, W.; Wang, M.; Wu, 23

ACS Paragon Plus Environment

Environmental Science & Technology

513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554

Y.; Chen, C.; Wang, Z.; et al. Chemical composition, sources, and aging process of submicron aerosols in Beijing: Contrast between summer and winter. J. Geophys. Res.-Atmos. 2016, 121 (4), 1955-1977. (20) Ervens, B.; Turpin, B. J.; Weber, R. J. Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies. Atmos. Chem. Phys. 2011, 11 (21), 11069-11102. (21) Hennigan, C. J.; Bergin, M. H.; Dibb, J. E.; Weber, R. J. Enhanced secondary organic aerosol formation due to water uptake by fine particles. Geophys. Res. Lett. 2008, 35 (18), L18801. (22) Kaul, D. S.; Gupta, T.; Tripathi, S. N.; Tare, V.; Collett, J. L. Secondary Organic Aerosol: A Comparison between Foggy and Nonfoggy Days. Environ. Sci. Technol. 2011, 45 (17), 7307-7313. (23) Lim, Y. B.; Tan, Y.; Perri, M. J.; Seitzinger, S. P.; Turpin, B. J. Aqueous chemistry and its role in secondary organic aerosol (SOA) formation. Atmos. Chem. Phys. 2010, 10 (21), 10521-10539. (24) Sorooshian, A.; Murphy, S. M.; Hersey, S.; Bahreini, R.; Jonsson, H.; Flagan, R. C.; Seinfeld, J. H. Constraining the contribution of organic acids and AMS m/z 44 to the organic aerosol budget: On the importance of meteorology, aerosol hygroscopicity, and region. Geophys. Res. Lett. 2010, 37 (21), L21807. (25) Duplissy, J.; DeCarlo, P. F.; Dommen, J.; Alfarra, M. R.; Metzger, A.; Barmpadimos, I.; Prevot, A. S. H.; Weingartner, E.; Tritscher, T.; Gysel, M.; et al. Relating hygroscopicity and composition of organic aerosol particulate matter. Atmos. Chem. Phys. 2011, 11 (3), 1155-1165. (26) Hersey, S. P.; Craven, J. S.; Metcalf, A. R.; Lin, J.; Lathem, T.; Suski, K. J.; Cahill, J. F.; Duong, H. T.; Sorooshian, A.; Jonsson, H. H.; et al. Composition and hygroscopicity of the Los Angeles Aerosol: CalNex. J. Geophys. Res.-Atmos. 2013, 118 (7), 3016-3036. (27) Sun, Y.; Wang, Z.; Fu, P.; Jiang, Q.; Yang, T.; Li, J.; Ge, X. The impact of relative humidity on aerosol composition and evolution processes during wintertime in Beijing, China. Atmos. Environ. 2013, 77, 927-934. (28) Elser, M.; Huang, R.-J.; Wolf, R.; Slowik, J. G.; Wang, Q.; Canonaco, F.; Li, G.; Bozzetti, C.; Daellenbach, K. R.; Huang, Y.; et al. New insights into PM2.5 chemical composition and sources in two major cities in China during extreme haze events using aerosol mass spectrometry. Atmos. Chem. Phys. 2016, 16 (5), 3207-3225. (29) Zhang, X.; Liu, J.; Parker, E. T.; Hayes, P. L.; Jimenez, J. L.; de Gouw, J. A.; Flynn, J. H.; Grossberg, N.; Lefer, B. L.; Weber, R. J. On the gas-particle partitioning of soluble organic aerosol in two urban atmospheres with contrasting emissions: 1. Bulk water-soluble organic carbon. J. Geophys. Res. 2012, 117, D00V16. (30) Sun, Y.; Du, W.; Fu, P.; Wang, Q.; Li, J.; Ge, X.; Zhang, Q.; Zhu, C.; Ren, L.; Xu, W.; et al. Primary and secondary aerosols in Beijing in winter: sources, variations and processes. Atmos. Chem. Phys. 2016, 16 (13), 8309-8329. (31) Li, Y. J.; Lee, B. Y. L.; Yu, J. Z.; Ng, N. L.; Chan, C. K. Evaluating the 24

ACS Paragon Plus Environment

Page 24 of 32

Page 25 of 32

Environmental Science & Technology

555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596

degree of oxygenation of organic aerosol during foggy and hazy days in Hong Kong using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). Atmos. Chem. Phys. 2013, 13 (17), 8739-8753. (32) Ge, X.; Zhang, Q.; Sun, Y.; Ruehl, C. R.; Setyan, A. Effect of aqueous-phase processing on aerosol chemistry and size distributions in Fresno, California, during wintertime. Environ. Chem. 2012, 9 (3), 221-235. (33) Zhang, J. K.; Ji, D. S.; Liu, Z. R.; Hu, B.; Wang, L. L.; Huang, X. J.; Wang, Y. S. New characteristics of submicron aerosols and factor analysis of combined organic and inorganic aerosol mass spectra during winter in Beijing. Atmos. Chem. Phys. Discuss. 2015, 2015, 18537-18576. (34) Aiken, A. C.; DeCarlo, P. F.; Kroll, J. H.; Worsnop, D. R.; Huffman, J. A.; Docherty, K. S.; Ulbrich, I. M.; Mohr, C.; Kimmel, J. R.; Sueper, D.; et al. O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with High-Resolution Time-of-Flight Aerosol Mass Spectrometry. Environ. Sci. Technol. 2008, 42 (12), 4478-4485. (35) Chakraborty, A.; Bhattu, D.; Gupta, T.; Tripathi, S. N.; Canagaratna, M. R. Real-time measurements of ambient aerosols in a polluted Indian city: Sources, characteristics, and processing of organic aerosols during foggy and nonfoggy periods. J. Geophys. Res.-Atmos. 2015, 120 (17), 9006-9019. (36) Heald, C. L.; Kroll, J. H.; Jimenez, J. L.; Docherty, K. S.; DeCarlo, P. F.; Aiken, A. C.; Chen, Q.; Martin, S. T.; Farmer, D. K.; Artaxo, P. A simplified description of the evolution of organic aerosol composition in the atmosphere. Geophys. Res. Lett. 2010, 37 (8), L08803. (37) Martin, S. T.; Andreae, M. O.; Artaxo, P.; Baumgardner, D.; Chen, Q.; Goldstein, A. H.; Guenther, A.; Heald, C. L.; Mayol-Bracero, O. L.; McMurry, P. H.; et al. Sources and properties of amazonian aerosol particles. Rev Geophys 2010, 48, 42. (38) Guo, S.; Hu, M.; Zamora, M. L.; Peng, J.; Shang, D.; Zheng, J.; Du, Z.; Wu, Z.; Shao, M.; Zeng, L.; et al. Elucidating severe urban haze formation in China. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (49), 17373-17378. (39) 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.; et al. High secondary aerosol contribution to particulate pollution during haze events in China. Nature 2014, 514, 218-222. (40) Sun, Y.; Wang, Z.; Dong, H.; Yang, T.; Li, J.; Pan, X.; Chen, P.; Jayne, J. T. Characterization of summer organic and inorganic aerosols in Beijing, China with an Aerosol Chemical Speciation Monitor. Atmos. Environ. 2012, 51, 250-259. (41) Sun, Y.; Jiang, Q.; Xu, Y.; Ma, Y.; Zhang, Y.; Liu, X.; Li, W.; Wang, F.; Li, J.; Wang, P.; et al. Aerosol Characterization over the North China Plain: Haze Life Cycle and Biomass Burning Impacts in Summer. J. Geophys. Res.-Atmos. 2016, 121 (5), 2508-2521. (42) Sun, Y.; Du, W.; Wang, Q.; Zhang, Q.; Chen, C.; Chen, Y.; Chen, Z.; Fu, P.; 25

ACS Paragon Plus Environment

Environmental Science & Technology

597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638

Wang, Z.; Gao, Z.; et al. Real-Time Characterization of Aerosol Particle Composition above the Urban Canopy in Beijing: Insights into the Interactions between the Atmospheric Boundary Layer and Aerosol Chemistry. Environ. Sci. Technol. 2015, 49 (19), 11340-11347. (43) Chen, C.; Sun, Y. L.; Xu, W. Q.; Du, W.; Zhou, L. B.; Han, T. T.; Wang, Q. Q.; Fu, P. Q.; Wang, Z. F.; Gao, Z. Q.; et al. Characteristics and sources of submicron aerosols above the urban canopy (260 m) in Beijing, China, during the 2014 APEC summit. Atmos. Chem. Phys. 2015, 15 (22), 12879-12895. (44) Xu, W. Q.; Sun, Y. L.; Chen, C.; Du, W.; Han, T. T.; Wang, Q. Q.; Fu, P. Q.; Wang, Z. F.; Zhao, X. J.; Zhou, L. B.; et al. Worsnop, D. R. Aerosol composition, oxidation properties, and sources in Beijing: results from the 2014 Asia-Pacific Economic Cooperation summit study. Atmos. Chem. Phys. 2015, 15 (23), 13681-13698. (45) Zhang, J. K.; Sun, Y.; Liu, Z. R.; Ji, D. S.; Hu, B.; Liu, Q.; Wang, Y. S. Characterization of submicron aerosols during a month of serious pollution in Beijing, 2013. Atmos. Chem. Phys. 2014, 14 (6), 2887-2903. (46) Sun, Y. L.; Chen, C.; Zhang, Y. J.; Xu, W. Q.; Zhou, L. B.; Cheng, X. L.; Zheng, H. T.; Ji, D. S.; Li, J.; Tang, X.; et al. Rapid formation and evolution of an extreme haze episode in Northern China during winter 2015. Scientific reports 2016, 6, 27151. (47) Jayne, J. T.; Leard, D. C.; Zhang, X.; Davidovits, P.; Smith, K. A.; Kolb, C. E.; Worsnop, D. R. Development of an aerosol mass spectrometer for size and composition analysis of submicron particles. Aerosol Sci. Tech. 2000, 33, 49-70. (48) Jimenez, J. L.; Jayne, J. T.; Shi, Q.; Kolb, C. E.; Worsnop, D. R.; Yourshaw, I.; Seinfeld, J. H.; Flagan, R. C.; Zhang, X. F.; Smith, K. A.; et al. Ambient aerosol sampling using the Aerodyne Aerosol Mass Spectrometer. J. Geophys. Res.-Atmos. 2003, 108 (D7), 13. (49) Drewnick, F.; Hings, S. S.; DeCarlo, P.; Jayne, J. T.; Gonin, M.; Fuhrer, K.; Weimer, S.; Jimenez, J. L.; Demerjian, K. L.; Borrmann, S.; et al. A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS)—Instrument Description and First Field Deployment. Aerosol Sci. Tech. 2005, 39 (7), 637-658. (50) Zhang, Q.; Jimenez, J. L.; Worsnop, D. R.; Canagaratna, M. A case study of urban particle acidity and its effect on secondary organic aerosol. Environ. Sci. Technol. 2007, 41, 3213-3219. (51) Matthew, B. M.; Middlebrook, A. M.; Onasch, T. B. Collection Efficiencies in an Aerodyne Aerosol Mass Spectrometer as a Function of Particle Phase for Laboratory Generated Aerosols. Aerosol Sci. Tech. 2008, 42, (11), 884-898. (52) Canagaratna, M. R.; Jimenez, J. L.; Kroll, J. H.; Chen, Q.; Kessler, S. H.; Massoli, P.; Hildebrandt Ruiz, L.; Fortner, E.; Williams, L. R.; Wilson, K. R.; et al. Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications. Atmos. Chem. Phys. 2015, 15 (1), 253-272. 26

ACS Paragon Plus Environment

Page 26 of 32

Page 27 of 32

Environmental Science & Technology

639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676

(53) Paatero, P.; Tapper, U. Positive matrix factorization: A non-negative factor model with optimal utilization of error estimates of data values. Environmetrics 1994, 5, 111-126. (54) Fountoukis, C.; Nenes, A. ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosols. Atmos. Chem. Phys. 2007, 7 (17), 4639-4659. (55) Sun, Y. L.; Wang, Z. F.; Fu, P. Q.; Yang, T.; Jiang, Q.; Dong, H. B.; Li, J.; Jia, J. J. Aerosol composition, sources and processes during wintertime in Beijing, China. Atmos. Chem. Phys. 2013, 13, (9), 4577-4592. (56) Carlton, A. G.; Turpin, B. J.; Altieri, K. E.; Seitzinger, S.; Reff, A.; Lim, H.-J.; Ervens, B. Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments. Atmos. Environ. 2007, 41 (35), 7588-7602. (57) Altieri, K. E.; Seitzinger, S. P.; Carlton, A. G.; Turpin, B. J.; Klein, G. C.; Marshall, A. G. Oligomers formed through in-cloud methylglyoxal reactions: Chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR mass spectrometry. Atmos. Environ. 2008, 42 (7), 1476-1490. (58) Zorn, S. R.; Drewnick, F.; Schott, M.; Hoffmann, T.; Borrmann, S. Characterization of the South Atlantic marine boundary layer aerosol using an aerodyne aerosol mass spectrometer. Atmos. Chem. Phys. 2008, 8 (16), 4711-4728. (59) Barnes, I.; Hjorth, J.; Mihalopoulos, N. Dimethyl sulfide and dimethyl sulfoxide and their oxidation in the atmosphere. Chem Rev 2006, 106 (3), 940-975. (60) Chen, Q.; Farmer, D. K.; Rizzo, L. V.; Pauliquevis, T.; Kuwata, M.; Karl, T. G.; Guenther, A.; Allan, J. D.; Coe, H.; Andreae, M. O.; et al. Submicron particle mass concentrations and sources in the Amazonian wet season (AMAZE-08). Atmos. Chem. Phys. 2015, 15 (7), 3687-3701. (61) Sun, C.; Lee, B. P.; Huang, D.; Jie Li, Y.; Schurman, M. I.; Louie, P. K. K.; Luk, C.; Chan, C. K. Continuous measurements at the urban roadside in an Asian megacity by Aerosol Chemical Speciation Monitor (ACSM): particulate matter characteristics during fall and winter seasons in Hong Kong. Atmos. Chem. Phys. 2016, 16 (3), 1713-1728. (62) Sun, Y. L.; Wang, Z. F.; Du, W.; Zhang, Q.; Wang, Q. Q.; Fu, P. Q.; Pan, X. L.; Li, J.; Jayne, J.; Worsnop, D. R. Long-term real-time measurements of aerosol particle composition in Beijing, China: seasonal variations, meteorological effects, and source analysis. Atmos. Chem. Phys. 2015, 15 (17), 10149-10165. (63) Quan, J.; Liu, Q.; Li, X.; Gao, Y.; Jia, X.; Sheng, J.; Liu, Y. Effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events. Atmos. Environ. 2015, 122, 306-312.

27

ACS Paragon Plus Environment

Environmental Science & Technology

677 678 679

Figure 1. Variations of the mass fractions of MO-OOA, LO-OOA and POA in OA,

680

and the O/C, O/CSOA, WS, LWC and OA as a function of RH in (a,d,g) summer, (b,e,h)

681

autumn and (c,f,i) winter. The data were binned according to the RH (10% increment),

682

and mean (circle), median (horizontal line), 25th and 75th percentiles (lower and

683

upper box), and 10th and 90th percentiles (lower and upper whiskers) are shown for

684

each bin. Note that the LWC and mass concentrations of MO-OOA and SO42- during

685

the three seasons are scaled on the same right axis on the top and middle panel,

686

respectively.

28

ACS Paragon Plus Environment

Page 28 of 32

Page 29 of 32

Environmental Science & Technology

687

688 689 690

Figure 2. Variations of mass fractions of MO-OOA, LO-OOA, and POA in OA, and

691

the O/C, O/CSOA, LO-OOA, MO-OOA and OA as a function of Ox in (a,d) summer,

692

(b,e) autumn and (c,f) winter. The data were binned according to the Ox concentration

693

(10 ppb increment), and mean (circle), median (horizontal line), 25th and 75th

694

percentiles (lower and upper box), and 10th and 90th percentiles (lower and upper

695

whiskers) are shown for each bin.

29

ACS Paragon Plus Environment

Environmental Science & Technology

696

697 698 699

Figure 3. RH vs. Ox dependence of the ratio of MO-OOA/LO-OOA and O/CSOA in

700

(a,d) summer, (b,e) autumn and (c,f) winter. The lines are colored by the mass

701

concentrations of organics. Grids with the number of points less than five were

702

excluded.

30

ACS Paragon Plus Environment

Page 30 of 32

Page 31 of 32

Environmental Science & Technology

703

704 705 706 707

Figure 4. Time series of meteorological parameters (RH, T, WS, WD), mass

708

concentrations of MO-OOA, LO-OOA and Ox during four episodes, i.e., (a) Ep1 and

709

(b) Ep2 in summer, and (c) Ep3 and (d) Ep4 in autumn and winter, respectively.

710

Below panels show average mass concentrations (e,f) and mass fractions (g,h) of

711

NR-PM1 species and OA factors during the four episodes. Also shown in (f) are the

712

average O/C and O/CSOA for each episode.

31

ACS Paragon Plus Environment

Environmental Science & Technology

203x112mm (150 x 150 DPI)

ACS Paragon Plus Environment

Page 32 of 32