Potentially Important Contribution of Gas-Phase Oxidation of

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Environmental Processes

The Potentially Important Contribution of Gas-phase Oxidation of Naphthalene and Methylnaphthalene to Secondary Organic Aerosol during Haze Events in Beijing Guancong Huang, Ying Liu, Min Shao, Yue Li, Qi Chen, Yan Zheng, Zhijun Wu, Yuechen Liu, Yusheng Wu, Min Hu, Xin Li, Sihua Lu, Chenjing Wang, Junyi Liu, Mei Zheng, and Tong Zhu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b04523 • Publication Date (Web): 09 Jan 2019 Downloaded from http://pubs.acs.org on January 10, 2019

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Environmental Science & Technology

ACS Paragon Plus Environment


The Potentially Important Contribution of Gas-phase Oxidation of Naphthalene and Methylnaphthalene to Secondary Organic Aerosol during Haze Events in Beijing Authors: Guancong Huang1, Ying Liu1*, Min Shao1,2, Yue Li1, Qi Chen1, Yan Zheng1, Zhijun Wu1, Yuechen Liu1, Yusheng Wu1†, Min Hu1, Xin Li1, Sihua Lu1, Chenjing Wang1, Junyi Liu1, Mei Zheng1, Tong Zhu1*

Affiliations: 1

SKL-ESPC and BIC-ESAT, College of Environmental Science and Engineering, Peking University, Beijing 100871, China

2

Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China

† Now

at Department of Physics, University of Helsinki, Helsinki 00014, Finland.

*Correspondence to: Dr. Ying LIU SKL-ESPC and BIC-ESAT, College of Environmental Science and Engineering, Peking University, Beijing 100871, China Email: [email protected] Prof. Tong ZHU SKL-ESPC and BIC-ESAT, College of Environmental Science and Engineering, Peking University, Beijing 100871, China Email: [email protected]


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1

ABSTRACT

2

Naphthalene (Nap) and methylnaphthalene (MN) are the most abundant polycyclic

3

aromatic hydrocarbons (PAHs) in atmosphere, and have been proposed to be important

4

precursors of anthropogenic secondary organic aerosol (SOA) derived from laboratory

5

chamber experiments. In this study, atmospheric Nap/MN and their gas-phase

6

photooxidation products were quantified by a Proton Transfer Reaction-Quadrupole

7

interface Time of Flight Mass Spectrometer (PTR-QiTOF) during the 2016 winter in

8

Beijing. Phthalic anhydride, a late generation product from Nap under high-NOx

9

conditions, appeared to be more prominent than 2-formylcinnamaldehyde (early

10

generation product), possibly due to more sufficient oxidation during the haze. 1,2-

11

phthalic acid (1,2-PhA), the hydrated form of phthalic anhydride, was capable of

12

partitioning into aerosol phase and served as a tracer to explore the contribution of Nap

13

to ambient SOA. The measured fraction in particle phase (Fp) of 1,2-PhA averaged at

14

73±13% with OA mass loadings of 52.5–87.8 μg/m3, lower than the value predicted by

15

the absorptive partitioning model (100%). Using tracer product-based and precursor

16

consumption-based methods, 2-ring PAHs (Nap and MN) were estimated to produce

17

14.9% (an upper limit) of the SOA formed in the afternoon during the wintertime haze,

18

suggesting a comparable contribution of Nap and MN with monocyclic-aromatics on

19

urban SOA formation.

20

21



22

TOC Art:

23 24

INTRODUCTION

25

Severe haze pollution in China has drawn public attention due to its impacts on

26

regional air quality and human health. Secondary organic aerosol (SOA) is a major

27

component of organic aerosol (OA) in most regions of China1 and accounts for more

28

than 40% of OA mass concentrations in PM1 (particulate matter with a diameter of less

29

than 1 µm) in winter Beijing2, 3. However, modeling studies indicated that the observed

30

SOA cannot be fully explained by known mechanisms of measured volatile organic

31

compounds (VOCs, usually as C2–C8 hydrocarbons)4. Laboratory studies have found

32

that intermediate- and semi-volatile organic compounds (I/SVOCs), such as long-chain

33

(C10–C19) alkanes and polycyclic aromatic hydrocarbons (PAHs), are additional SOA

34

precursors with high yields (up to 75%). Gas-phase C6–C19 alkanes and small PAHs

35

were predicted to explain 20–30% of anthropogenic SOA formation, when primary

36

emission and oxidation processes of I/SVOCs were implemented in regional model5.

37

Naphthalene (Nap) and methylnaphthalene (MN) have the largest portion of gaseous

38

PAHs (fewer than 4 rings). The gas- and particle-phase products from Nap reactions

39

with hydroxyl radical (OH) have been identified at molecular level in chamber studies.


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40

Ring-opening products, such as 2-formylcinnamaldehyde, are regarded as the major

41

gaseous products under high-NOx conditions, while ring-retaining products like 1,4-

42

naphthaquinone appear to be primary under low-NOx conditions6-9. With high-NOx

43

present, further oxidation of 2-formylcinnamaldehyde generates highly oxygenated

44

compounds (e.g., phthaldialdehyde, phthalic anhydride, and 1,2-phthalic acid), which

45

can condense onto existing aerosol depending on their vapor pressures. Some products

46

have been used as molecular markers to represent the SOA produced by Nap oxidation.

47

For example, particle-phase 1,2-phthalic acid (1,2-PhA(p)) correlated with SOA formed

48

in Nap chamber experiments10.

49

The SOA yields ranged between 19–30% for Nap and 19–45% for MN at OA mass

50

loadings of 8.0–27.7 µg/m3 under high-NOx conditions in laboratories; while the yields

51

of Nap and MN were almost stable at 73% and 63% for low-NOx conditions6,

52

respectively. The SOA formation tended to be less efficient in presence of NOx, because

53

of relatively higher volatilities of high-NOx products (i.e., ring-opening products from

54

decomposition and fragmentation of alkoxy radicals in oxidation processes of Nap/MN).

55

As a result, the mass of SOA formed under high-NOx conditions increased with OA

56

loadings, which facilitated more partitioning of semi-volatile products into aerosol. The

57

high-NOx SOA yields can be described as a funtion of OA based on the empirical gas-

58

particle equilibrium partitioning model. Under low-NOx conditions, ring-retaining

59

products with lower volatilities (generated from hydroperoxides and epoxides) were

60

dominant, resulting in higher SOA yields with constant values11. Thus, gas-particle

61

partitioning of oxidation products is one of the key processes controlling the formation



62

and yields of SOA. However, the atmospheric abundance and partitioning of NOx-

63

dependent Nap products in urban environments have remained unclear, mostly due to

64

the complexity of oxidation processes, OA compositions and aerosol acidity in the real

65

atmosphere.

66

As a major energy consumer in the world, China contributes 20% of the global PAH

67

emissions with an annual emission of 104–114 Gg/yr12, 13. Primary emissions of PAHs

68

are associated with incomplete combustions of fuels, including coal combustion,

69

vehicle exhaust, cooking, and biomass burning14-17. Ambient level of Nap in winter

70

Beijing was about three times higher than that in Southern California18. The

71

concentration of Nap in Beijing showed a seasonal variation with peaks (0.32±0.18

72

ppb) in Jan19 and minima (75 µg/m3) accompanied with increasing secondary pollutants (Figure S5).


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The haze episode of Dec 17–22 was chosen as an example to examine the chemical

171

evolution of Nap, MN, and their products under heavily polluted conditions (Figure 2),

172

because of complete data collection in both gas and particle phase. The PM2.5

173

concentration increased from 23 µg/m3 to >175 µg/m3 from the afternoon of Dec 16 to

174

the midnight of Dec 19 (defined as Haze1 in yellow shaded area). Then it quickly rose

175

up to its maximum (443 µg/m3) in the early morning on Dec 20. After a sudden drop,

176

PM2.5 stayed at higher levels of more than 320 µg/m3 (defined as Haze2 in pink shaded

177

area). Finally, pollutants were flushed away by strong northerly wind (>5 m/s) at dawn

178

of Dec 22 (Figure S5). Mixing ratios of Nap, MN, and their oxidation products were

179

observed to increase by one order of magnitude from clean to polluted conditions. A

180

good correlation (R=0.83) between 2-formylcinnamaldehyde and NO2 (which usually

181

forms from the reactions of NO with peroxy radicals (RO2) from VOC OH-oxidation)

182

was found in all haze periods (Figure S6), implying that 2-formylcinnamaldehyde may

183

be produced in the reactions of Nap peroxy intermediate with NO and this mechanism

184

also leads to the formation of NO2 and hydroperoxy (HO2) radicals.

185

The total oxidant Ox (O3+NO2) is frequently used as an indicator of photochemical

186

oxidation capacity in urban areas under high NO conditions. In such conditions, ozone

187

tends to be quickly titrated by NO, and NO2 becomes the most important oxidant29.

188

During the period of Haze1, PM2.5, OA, and Ox all showed afternoon peaks. And the

189

enhancement of PM2.5 coincided with the formation of dicarbonyl products from

190

Nap/MN in the afternoons (R=0.63, Figure S7c) and anti-correlated with Nap (R=-0.03,

191

Figure S7a), suggesting that the oxidation of anthropogenic precursors (Nap and other



192

VOCs) may contribute to the increase of OA and PM2.5 in Haze1. By contrast, PM2.5

193

showed a good correlation with naphthalene (R=0.73, Figure S7b) but poor correlation

194

with 2-formylcinnamaldehyde (R=0.07, Figure S7d), which suggests that the

195

contribution of primary urban emissions became more significant during the period of

196

Haze2. Both Nap oxidation products and their precursors accumulated during the

197

nighttime of Dec 21, Ox, OA and PM2.5 kept at high values in this episode. Thus,

198

compared to Haze1, higher OA in Haze2 was likely associated with enhanced primary

199

emission and less secondary production.

200

Diurnal Pattern and Evolution of Gas-phase Products from Nap and MN.

201

The diurnal variations of Nap and MN for all clean and haze periods during the

202

campaign are shown in Figure S8a and S8f, respectively. Nap and MN, mainly come

203

from vehicle exhaust and coal combustion in urban sites, exhibited high concentrations

204

in the morning and evening, and decreased to their minima at ~3:00 p.m. Possible

205

explanations include the fast photochemical removal of Nap and MN, reduced

206

emission, and increased dilution during the daytime. There are four oxygenated

207

compounds regarding Nap oxidation (i.e., 2-formylcinnamaldehyde, phthaldiadehyde,

208

phthalic anhydride, and 1,2-PhA) identified with PTR-QiTOF during haze events,

209

which are generally in accord with known high-NOx products of Nap in laboratories.

210

The distinct secondary formation of these products was observed in the afternoon

211

(12:00 p.m. to 5:00 p.m.) of haze episodes (in Figure S8b-e), when the ratios of the

212

products to their precursor (Nap) increased with the reaction time (Figure S9). 2-

213

formylcinnamaldehyde was suggested as a primary product from Nap oxidation in


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presence of NOx in chamber experiments. Other ring-opening products (including

215

phthaldialdehyde, phthalic anhydride, and 1,2-PhA) showed good correlations with 2-

216

formylcinnamaldehyde during all haze events (R>0.69, Figure S10), and the ratios of

217

phthalic anhydride and 1,2-PhA to 2-formylcinnamaldehyde increased gradually during

218

the day, indicating that these two products were likely formed from further reactions of

219

2-formylcinnamaldehyde.

220

As shown in Figure 3a, the early generation product (2-formylcinnamaldehyde)

221

presented a peak at noontime, then slightly decayed in the afternoon (1:00–5:00 p.m.)

222

due to its photolysis and OH-oxidation. It is interesting to note that phthaldialdehyde

223

increased first in the morning rather than 2-formylcinnamaldehyde, which could be

224

explained by the fact that phthaldialdehyde is also expected as a primary product in Nap

225

oxidation9 and its much less reactive than 2-formylcinnamaldehyde30,

226

discussion in SI 4). Accordingly, the later generation products (phthalic anhydride and

227

1,2-PhA) were observed to keep increasing in the early afternoon when 2-

228

formylcinnamaldehyde and phthaldialdehyde declined, until they reached peak values

229

at ~5:00 p.m. when the loss rates of dicarbonyl products were at the maximum

230

(Figure 3b). In the evening the opposite happened with the lower loss rates and

231

increasing concentrations of 2-formylcinnamaldehyde and phthaldialdehyde. The

232

evening peaks (at 9:00 p.m.) for dicarbonyls were more pronounced than noontime,

233

probably due to their slower chemical loss rates and lower boundary layer height at

234

night32. The reaction of Nap with NO3 radicals would be a potential pathway for the

235

formation of those products, especially under NOx-rich conditions. But it is found that


31

(detailed


236

the NO3 pathway played only a minor role (0.7, Figure S12) gives evidence

255

that secondary sources accounted for most of phthalic anhydride in Haze1. While, the

256

degree of linear correlation of phthalic anhydride versus OH exposure was clearly lower

257

during Haze2 (R=0.17, Figure S12), especially when relatively high phthalic anhydride


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but low OH exposure occurred during the night of Dec 21. It may be caused by the fact

259

that both primary and secondary pollutants were continuously accumulated during this

260

period. Moreover, a larger uncertainty of OH exposure was attributed to the effects of

261

aged air masses mixing with fresh ones at that time4, 35.

262

Mass fraction of 1,2-PhA in the particle phase

263

As a tracer product, the secondary production of 1,2-PhA(p) in pollution episodes can

264

provide us insights into high-NOx SOA formation from Nap/MN oxidation. The 24h-

265

average concentrations of phthalic anhydride(g), 1,2-PhA(g), and 1,2-PhA(p) from Dec 17

266

to Dec 21 are shown in Figure 4. The concentrations of 1,2-PhA(p) at PKUERS ranged

267

from 0.05 to 0.15 µg/m3 over the haze events, which was comparable to previous

268

observations in Beijing37, but 7-8 times higher than in the PRD region (Table S3)38. It

269

is found that phthalic anhydride(g) and 1,2-PhA(p) displayed a similar trend during the

270

Haze1. And 1,2-PhA(p) presented high values of more than 0.12 µg/m3 in Haze1 when

271

Nap was fully oxidized and OA was largely ascribed to secondary formation. In Haze2,

272

1,2-PhA(p) dropped to 0.07 µg/m3 on Dec 20, mostly due to low photochemical

273

formation of Nap products.

274

The fraction in particle phase (Fp) for 1,2-PhA is defined as Equation (1), based on

275

its measured concentrations from gas- and aerosol-phase samples. The measured Fp of

276

1,2-PhA was 73±13% (average±s.d.) in the haze period, and showed a decreasing trend

277

from Haze1 (80±2%) to Haze2 (62±16%) (Figure 5). The lowest Fp of 1,2-PhA was

278

observed as 51% on Dec 21, with the lowest 1,2-PhA(p) and highest phthalic

279

anhydride(g). The reason for this lower Fp is unclear, but more likely due to the rapid



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280

enhancement of gas-phase phthalic anhydride or 1,2-PhA in this period. Thereby the

281

time to re-establish the gas-to-particle equilibrium with excess gas phase 1,2-PhA was

282

expected to be much longer than early experienced. It might be further explained by the

283

transition of the phase state of OA, which can affect the partitioning equlibrium

284

timescale of SVOC species39,

285

combustion sources are known to be quasi-solid state. SOA dominated by condensable

286

oxygenated products from anthropogenic and biogenic VOCs oxidation is usually

287

assumed to be liquid in classic gas-particle partitioning models, which has a tendency

288

to uptake I/SVOCs into aqueous droplets in aerosol phase. Recent studies showed that

289

many organic matters including carboxylic acids in SOA were most probably

290

transferred to amorphous semi-solid or glassy-state when cooling or drying of aqueous

291

aerosols41, 42. The relative fraction of POA to the total OA increased in Haze2, and

292

ambient RH dropped at noon of Dec 21 (seen in Figure S5b). Consequently, a solid

293

shell might form upon aerosol drying which would prevent 1,2-PhA partitioning to

294

particle phase.

295

40.

Particles in primary OA (POA) emitted from

𝐶particle

(Eq 1)

𝐹𝑝 = 𝐶particle + 𝐶gas

296

The contribution to 1,2-PhA(p) through partitioning to OA mass was also calculated

297

by the absorptive partitioning model (SI 7.2), on the assumptions of equilibrium

298

partitioning, homogeneous mixing, and liquid-like OA. During Haze1 and Haze2, the

299

OA mass concentration was as high as 70±14 µg/m3 and the average temperature was

300

275±2 K. The modelled Fp of 1,2-PhA (black dots in Figure 5) for this haze periods was

301

predicted to be ~100%, when theroretical saturated concentration (C*) of 1,2-PhA


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302

ranged between 0.02 to 4.18 µg/m3 using estimated vapor pressure (Pv) from the

303

multiphase system online property prediction tool developed by University of

304

Manchester (UManSysProp). Given the uncertaities of sampling, measurements, and

305

Pv estimation, it implies that the partitioning of 1,2-PhA could be generally explained

306

by the model for the period of Haze1. But a larger overestimation (38%) by the model

307

was found in Haze2 when more fresh emissions encountered, leading to a long

308

timescale for gas-particle equilibrium of 1,2-PhA. However, some field studies in

309

autumn and summer in U.S. reported the substantial underestimation of Fp for 1,2-PhA

310

by the model, where much lower OA levels (2.3–3.7 µg/m3) were observed43,

311

Therefore, the Fp estimation by absorptive partitioning mdoel seems to be of larger

312

uncertatinties in both clean and heavily polluted regions.

44.

313

Besides absorptive gas-particle partitioning on organic aerosols, heterogeneous

314

processes in aqueouse phase might also play a role in 1,2-PhA(p) production during haze

315

periods, such as the dissolution of gas-phase 1,2-PhA in aerosol water44 and the

316

hydrolysis reactions of phthalic anhydride with alkaline aerosol components45. The

317

dissolution of 1,2-PhA in aerosol water was estimated based on Henry’s law (SI 8) by

318

assuming that particles were neutralized. The predicted fractions of 1,2-PhA in aerosol

319

water (Faq) were one order of magnitude smaller than the observed Fp, and gradually

320

increased with aerosol water content (AWC) (Figure S14). It indicates that the

321

dissolution to the aquesou phase contributed to nearly 10% of 1,2-PhA(p) under higher

322

AWC conditions in Haze2. That’s to say, after considering the 1,2-PhA dissolution to



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323

aqueous phase, the absorptive partitioning model would overestimate the partitioning

324

of 1,2-PhA to OA mass to a larger extent.

325

Hydrolysis reaction of phthalic anhydride with alkaline aerosol components is

326

another possible pathway for 1,2-PhA(p) formation44. Previous kinetic study showed that

327

pH could enhance the hydrolysis rate of phthalic anhydride by 1-2 orders of magnitude

328

when pH>845. Using the ISORROPIA-II model and measurements of aerosol

329

composition, the average pH in aerosol water was estimated to be 4.0±0.2 and 4.3±0.3

330

during Haze1 and Haze2, respectively (SI 9 and Figure S15). It showed that ambient

331

aerosols during haze episodes were acidic, implying that reactions of phthalic anhydride

332

with alkaline components were restrained.

333

It is reported that the formation of particle-phase I/SVOC are complicated and

334

affected by mutiple parameters, including ambient temperature46, RH47, phase state of

335

aerosol41, and homogeneous/heterogeneous reactions48,

336

tentative investigation on SOA formation through the partitioning of a tracer compound.

337

In the future, high time-resolution measurements of various oxidation products in both

338

gas- and particle-phase are needed to further address the associated interactions among

339

above parameters in urban SOA formation.

340

Estimation of SOA from Nap and MN

49.

This study presents a

341

The gas-particle partitioning of 1,2-PhA in pollution episodes provides guidance for

342

SOA formation of 2-ring PAHs. The amount of SOA due to Nap and MN in haze

343

periods can be calculated using a tracer-based approach in which the laboratory mass

344

fractions (fSOA) of 1,2-PhA(p) in Nap/MN-SOA are applied to 1,2-PhA(p) in ambient


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50-52.

345

PM2.5 (defined as “tracer product-based method”, Eq 2)

346

PKUERS also had a primary source, which would cause a positive error in SOA

347

calculation. The estimation of primary 1,2-PhA(p) was determined from the reported

348

PMF-resolved sources (PMF, positive matrix factorization) of PM2.5 in Beijing winter

349

and emission factors of 1,2-PhA(p) for specific sources (method details in SI 10.1, Eq

350

S15). Excluding primary 1,2-PhA(p), Nap/MN-SOA was then estimated from secondary

351

1,2-PhA(p) dividing the weighted-average fSOA of 1,2-PhA(p) for Nap and MN under

352

high-NOx conditions (i.e., 1.9%). Note that the laboratory-derived fSOA may differ with

353

haze conditions in the field and should be treated with caution (SI 10.1). The

354

uncertainties of Nap-SOA estimated by tracer method are mainly from quantification

355

of 1,2-PhA(p) (e.g., filter absorption of 1,2-PhA(g) or phthalic anhydride(g), recoveries of

356

1,2-PhA(p) in filters, and GC-MS analysis). Overall, the total uncertainty of estimated

357

SOA was about 81% through error propagation (Eq S16). 𝑃ℎ𝐴𝑚𝑒𝑎 ― 𝑃ℎ𝐴𝑝𝑟𝑖

Measured 1,2-PhA(p) at

(Eq 2)

358

SOA𝑁𝑎𝑝 + 𝑀𝑁 =

359

The calculated SOA from Nap and MN was in the range of 4.6–6.8 μg/m3 and

360

accounted for 15.2–32.3% of the total SOA produced in Haze1, which highlights the

361

importance of Nap/MN oxidation during the secondary pollution dominated episodes.

362

However, the Nap/MN-SOA in Haze2 was calculated to significantly drop by a factor

363

of 4–45 (0.1–1.6 μg/m3), only explaining 0.3–4.6% of SOA formation, likely due to the

364

influence of increased fresh emissions (Table S8). The average contribution of Nap and

365

MN to SOA using tracer approach was 14.9±13% for the whole haze periods (Table 2).

366

These results can be considered as upper limits of SOA for 2-ring PAHs, due to the

𝑓𝑆𝑂𝐴



367

possible overestimation of 1,2-PhA(p) from filter uptake of gas-phase phthalic anhydride

368

or 1,2-PhA. In addition, the fSOA of 1,2-PhA(p) used in Eq2 might be under-predicted,

369

largely because of the fact that laboratory experiments may not fully simulate

370

atmospheric processing under heavy haze conditions.

371

To compare the contributions of major SOA precursors, the SOA formation relative

372

to CO from monocylic-aromatics (benzene, toluene, C8- and C9-aromatics) and PAHs

373

(Nap and MN) were also estimated by the consumed precursors upon OH exposure and

374

their SOA yields under high-NOx conditions4, 53, defined as “precursor consumption-

375

based method” (described in SI 10.2 and Eq S17-18). During 2016 AIRLESS campaign,

376

monocylic- and polycylic- aromatics together were calculated to produce up to 1.7 μg

377

m-3 ppm-1 CO of SOA in the afternoon (12:00 p.m. to 4:00 p.m.) during haze periods

378

(Figure S16), comparable to those results (2.0 μg m-3 ppm-1 CO) in spring of Shandong

379

Province in eastern China under high-NOx conditions. The oxidation of measured

380

precursors could roughly explain 23–30% of SOA formation by extrapolating SOA

381

yields at high OA loading (70 μg/m3) and low temperature (275 K) conditions using a

382

two-product model, when the SOA fraction in measured OA was assumed to be 40%

383

(SI 10.3)3, 54. The total error for this method was about 47% with consideration of

384

uncertainties in precursors consumption and SOA yields (SI 10.2). The single-ring

385

aromatics explained 16.5±2.4% of SOA formation (Table 2), which has been reported

386

as the major SOA precurors in urban environments53, 55. In this study, Nap and MN,

387

only less than 7% of the emission of aromatics (derived from their emission ratios in


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388

Table S9), contributed 10.2±1.3% of SOA, which is matchable to C8 aromatics

389

(9.8±1.4%).

390

The estimated contributions of Nap and MN to SOA from above two approaches are

391

consistent within uncertainties, suggesting that 2-ring PAH is an important contributor

392

to anthropogenic SOA in urban haze formation, and the emission intensities of various

393

PAH sources need to be further quantified. Given the observations of speciated tracer

394

products in gas- and particle-phase, the SOA estimated by parameterized approaches

395

(both tracer- and precursor-based method) may be improved if ambient yields of tracer

396

products and SOA could be elucidated and validated.

397

ASSOCIATED CONTENT

398

Supporting Information

399

The supporting information is available free of charge on the ACS Publications

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website.

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AUTHOR INFORMATION

402

Corresponding Author

403

Tel.: +86-10-62757973;

e-mail: [email protected]

404

Tel.: +86-10-62754789;

e-mial: [email protected]

405

ORCID

406

Ying Liu: 0000-0001-5139-0211

407

Tong Zhu: 0000-0002-2752-7924

408

Notes

409

The authors declare no competing financial interests.



410

ACKNOWLEDGEMENT

411

We sincerely thank the entire team of AIRLESS project for their excellent

412

collaboration. We thank Handix Corporation for providing the ACSM ,and the technical

413

support from Dr. Hongliang Zhang and Dr. Ping Chen. We appreciate for the advice by

414

Dr. Hongli Wang in the wall loss tests. This study was funded by the National Natural

415

Science Foundation of China (81571130100, 41875153), National Key R&D Program

416

of China (2016YFC0202206, 2015CB553401), Key Program of National Natural

417

Science Foundation of China (91644215, 41330635, 91544107).

418

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627 628



Page 32 of 37

629

Table 1. Information of Nap and its gas-phase oxidation products observed by PTR-

630

QiTOF Compound

Formula

[M+H]+

Naphthalene

C10H8

129.0699

Phase PTR Sensitivity, Distribution ncps/ppb g

3122

Detection Limit, ppt

Proposed Structure

17 O

2- formylcinnamaldehyde C10H8O2

161.0597

g,

pa

4572b

O

6 O

Phthaldialdehyde

C8H6O2

135.0441

g

3997b

3 O O

Phthalic anhydride

C8H4O3

149.0233

g

4313b

12

O O

O

1,2-Phthalic acid

C8H6O4

167.0339

g, p

3288b

OH

3

OH O

631

a Normally

632

b

very low concentration in the particle phase.

Sensitivity was estimated from compounds with similar structure or molecular weight.

633


Page 33 of 37


634

Table 2. Comparision of SOA formation calculated by the tracer product-based method

635

and the precursor consumption-based method. Precursors Benzene

Explained percentage of SOA, % Tracer product-based Precursor consumptionmethod based method 1.98±0.37

Toluene

-

1.91±0.32

C8 aromatics

-

9.81±1.35

C9 aromatics

-

2.77±0.36

Naphthalene Methylnaphthalene

14.9±13.0

636 637


7.64±0.99 2.56±0.36


638 639

Figure 1. High-resolution peak fitting for Nap oxidation products from a one-day

640

average mass spectrum in PTR-QiTOF (mass resolution about 6000 m/Δm), (a) 2-

641

formylcinnamaldehyde (C10H9O2+ at m/Q 161), (b) phthaldialdehyde (C8H7O2+ at m/Q

642

135), (c) phthalic anhydride (C8H5O3+ at m/Q 149) and (d) 1,2-phthalic acid (C8H7O4+

643

at m/Q 167).

644


Page 34 of 37

Page 35 of 37


645 646

Figure 2. Measured time series of Nap, MN, and their oxidation products at PKUERS

647

during the haze episodes from Dec 17 to Dec 21. (a) PM2.5, O3+NO2 and organic aerosol

648

(OA); (b) Nap (C10H8) and MN (C11H10); (c) Oxidation products from Nap (C10H8O2,

649

C8H6O2, and C8H4O3); (d) Oxidation products from MN (C11H10O2, C9H8O2, and

650

C9H6O3). Unit in ppt.

651



652 653

Figure 3. Diurnal patterns of Nap and its oxidation products during all the haze periods.

654


Page 36 of 37

Page 37 of 37


655 656

Figure 4. The 24h-average concentrations of gas-phase phthalic anhydride, 1,2-phthalic

657

acid , and particle-phase 1,2-phthalic acid from Dec 17 to Dec 21.

658



659 660

Figure 5. (a) Measured OA concentration from Dec 17 to Dec 21; (b) The measured

661

and modelled Fp for 1,2-PhA in Beijing, compared with previous field studies and

662

model prediction. Black solid dots represent the Fp predicted by the partitioning model.

663 664 665


Page 38 of 37

Potentially Important Contribution of Gas-Phase Oxidation of

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