Light absorption of organic carbon and its sources at a southeastern U.S. location in summer

Accepted Manuscript Light absorption of organic carbon and its sources at a southeastern U.S. location in summer Mingjie Xie, Xi Chen, Amara L. Holder, Michael D. Hays, Michael Lewandowski, John H. Offenberg, Tadeusz E. Kleindienst, Mohammed Jaoui, Michael P. Hannigan PII:

S0269-7491(18)32814-8

DOI:

10.1016/j.envpol.2018.09.125

Reference:

ENPO 11667

To appear in:

Environmental Pollution

Received Date: 19 June 2018 Revised Date:

24 September 2018

Accepted Date: 25 September 2018

Please cite this article as: Xie, M., Chen, X., Holder, A.L., Hays, M.D., Lewandowski, M., Offenberg, J.H., Kleindienst, T.E., Jaoui, M., Hannigan, M.P., Light absorption of organic carbon and its sources at a southeastern U.S. location in summer, Environmental Pollution (2018), doi: https://doi.org/10.1016/ j.envpol.2018.09.125. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

1 2

Light absorption of organic carbon and its sources at a Southeastern U.S. location in summer

3

Mingjie Xiea,b,c,d,*, Xi Chend, Amara L. Holderd, Michael D. Haysd, Michael Lewandowskie, John H. Offenberge, Tadeusz E. Kleindienste, Mohammed Jaouie, Michael P. Hanniganf

RI PT

4 5 6 7

a

SC

Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, 219 Ningliu Road, Nanjing 210044, China b State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210023, China c Oak Ridge Institute for Science and Education (ORISE), dNational Risk Management Research Laboratory, eNational Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC 27711, USA f Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA

M AN U

8 9 10 11 12 13 14 15 16 17 18 19

TE D

20 21 22

*Correspondence to: Mingjie Xie

24

E-mail: [email protected]; [email protected];

25

Tel: +86-18851903788;

26

Fax: +86-25-58731051;

27

Mailing address: 219 Ningliu Road, Nanjing, Jiangsu, 210044, China

29

AC C

28

EP

23

30 31 32 33 1

ACCEPTED MANUSCRIPT

34

ABSTRACT Light-absorbing organic carbon (OC), also referred to as “brown carbon” (BrC), has been

36

intensively investigated in atmospheres impacted by biomass burning. However, other BrC

37

sources (e.g., secondary formation in the atmosphere) are rarely studied in ambient aerosols. In

38

the current work, forty-five PM2.5 filter samples were collected in Research Triangle Park (RTP),

39

NC, USA from June 1st to July 15th, 2013. The bulk carbonaceous components, including OC,

40

elemental carbon (EC), water soluble OC (WSOC), and an array of organic molecular markers

41

were measured; an ultraviolet/visible spectrometer was used to measure the light absorption of

42

methanol extractable OC and WSOC. The average light absorption per OC and WSOC mass of

43

PM2.5 samples in summer RTP are 0.36 ± 0.16 m2 gC-1 and 0.29 ± 0.13 m2 gC-1, respectively,

44

lower than the ambient aerosol samples impacted by biomass burning and/or fossil fuel

45

combustion (0.7 – 1.6 m2 gC-1) from other places. Less than 1% of the aqueous extracts

46

absorption is attributed to the light-absorbing chromophores (nitroaromatic compounds)

47

identified in this work. To identify the major sources of BrC absorption in RTP in the summer,

48

Positive Matrix Factorization (PMF) was applied to a dataset containing optical properties and

49

chemical compositions of carbonaceous components in PM2.5. The results suggest that the

50

formation of biogenic secondary organic aerosol (SOA) containing organosulfates is an

51

important BrC source, contributing up to half of the BrC absorption in RTP during the

52

summertime.

53

Capsule

SC

M AN U

TE D

EP

AC C

54

RI PT

35

This study identified a linkage between atmospheric BrC and biogenic SOA formation

55

when biomass burning is not significant in Research Triangle Park, NC during the summer.

56

Key words: Brown carbon; Light absorption; Organic molecular marker; Source apportionment;

57

Secondary organic aerosol 2

ACCEPTED MANUSCRIPT

58

1. INTRODUCTION The light extinction of atmospheric particulate matter (PM), including absorption and

60

scattering, plays an important role in the Earth’s radiative balance (IPCC, 2007; Seinfeld, 2008).

61

The organic matter (OM) in PM is commonly treated as purely light scattering in climate models

62

(Chung and Seinfeld, 2002; Myhre et al., 2013). However, many existing studies have observed

63

light-absorbing organic carbon (OC), also termed as “brown carbon” (BrC), from both primary

64

emissions (Saleh et al., 2013, 2014; Washenfelder et al., 2015; Pokhrel et al., 2016; Xie et al.,

65

2017b) and secondary formation in the atmosphere (Iinuma et al., 2010; Nakayama et al., 2010;

66

Lin et al., 2014; Liu et al., 2016; Xie et al., 2017a). Typical BrC can absorb efficiently in the near

67

UV (300 – 400 nm) and visible regions with strong wavelength (λ) dependence (Kirchstetter et

68

al., 2004; Saleh et al., 2014; Laskin et al., 2015). The radiative transfer calculations basing on

69

aircraft measurements of BrC suggested that BrC accounted for ~20% of carbonaceous aerosol

70

(black carbon + brown carbon) warming effect at the tropopause (Liu et al., 2014, 2015; Zhang

71

et al., 2017). Due to the lack of information on the emissions, optical and chemical properties,

72

and atmospheric transformation of BrC associated with different sources, recent modeling

73

studies (Feng et al., 2013; Wang et al., 2014) obtained the optical properties of BrC from

74

previous laboratory biomass burning experiments (Chen and Bond, 2010) or ambient

75

measurements (Liu et al., 2013; Zhang et al., 2013), and very few modeling study considered the

76

BrC absorption from sources (e.g., secondary formation) other than biomass burning (Wang et

77

al., 2014) or the loss of BrC from photo-bleaching. Moreover, the source apportionment of BrC

78

with receptor models were rarely conducted due to the lack of organic tracers related to specific

79

sources (Zhang et al., 2010; Xie et al., 2016). Therefore, the sources and their contributions to

80

atmospheric BrC are still unclear.

AC C

EP

TE D

M AN U

SC

RI PT

59

3

ACCEPTED MANUSCRIPT

Laboratory measurements have demonstrated that biomass burning (BB) can generate

82

substantial BrC with strong light-absorbing chromophores (Chen and Bond, 2010; Saleh et al.,

83

2014). A number of field studies have confirmed that BB is the dominant contributor to BrC

84

absorption in the atmosphere (Washenfelder et al., 2015; Cheng et al., 2016; Zhang et al., 2016).

85

Hecobian et al. (2010) investigated the light-absorption characteristics of water-soluble organic

86

aerosol (WSOC) in the Southeastern United States (US), and attributed 50% of the yearly

87

average light absorption at 365 nm to BB. Washenfelder et al. (2015) found that more than 95%

88

of BrC absorption at a rural site located in the Talladega National Forest in central Alabama

89

(Southeastern US) was attributable to BB organic aerosol (OA) in the summertime. However,

90

light-absorbing WSOC was also observed in urban Los Angeles and Atlanta during the

91

summertime (Zhang et al., 2011), under conditions where the BB influence was not significant,

92

and was linked with secondary organic aerosol (SOA) formation. In the southeastern US,

93

Hecobian et al. (2010) and Zhang et al. (2010) identified a summertime secondary WSOC

94

source/factor with a yearly average contribution of 34% to the WSOC absorption by analyzing

95

PM2.5 with Positive Matrix Factorization (PMF). Therefore, SOA formation is an important

96

source of BrC absorption in the summertime when BB is absent. Despite a number of laboratory

97

studies that have identified potential pathways for secondary BrC formation and degradation

98

(Updyke et al., 2012; Lee et al., 2014; Zhao et al., 2015; Xie et al., 2017a), the precursors,

99

formation mechanisms, compositions, and degradation of secondary BrC in the atmosphere are

100

still unclear. Moreover, the aforementioned ambient studies focused on the light absorption of

101

WSOC, which typically accounts for less than 50% of the methanol extractable OC (MEOC)

102

(Zhang et al., 2013; Cheng et al., 2016).

AC C

EP

TE D

M AN U

SC

RI PT

81

4

ACCEPTED MANUSCRIPT

To identify the major sources of BrC in summer with no significant BB influences, we

104

analyzed the optical and chemical characteristics of OC in PM with aerodynamic diameter less

105

than 2.5 µm (PM2.5) collected at the US Environmental Protection Agency (EPA), Research

106

Triangle Park (RTP, NC), during the Southern Oxidation and Aerosol Study (SOAS, summer

107

2013). We measured daily average total OC, elemental carbon (EC), WSOC and an array of

108

polar OMMs; UV/Vis absorbance of the MEOC and WSOC was also measured. PMF was

109

applied to optical and selected compositional data to identify and quantify potential sources and

110

atmospheric processes contributing to BrC absorption.

112

2. METHODS

113

2.1 Sampling

M AN U

111

SC

RI PT

103

Ambient PM2.5 samples were collected at the EPA’s Ambient Air Innovative Research Site

115

in RTP, NC (35.889509 °N, 78.874650 °W). This site is located in the Southeastern US with

116

prominent biogenic SOA contribution and influences from anthropogenic pollution (Edney et al.,

117

2003; Kleindienst et al., 2007; Hidy et al., 2014; Nguyen et al., 2014). Two PM2.5 samplers

118

(Tisch Environmental, Village of Cleves, OH) installed with dual cyclone impactors were used

119

for ambient air sampling at a flow rate of 226 L min-1 from June 1 to July 15, 2013. During the

120

entire sampling period, the average ambient temperature was 24.1 ± 1.60 °C (range 21.0 –

121

26.8 °C), and the relative humidity was 78.9 ± 7.12% (62.5 – 92.8%). Daily integrated PM2.5

122

samples were collected onto 90 mm diameter quartz-fiber filters (QF) for 23 h beginning at 7

123

AM (EDT). Two sets of forty-five ambient samples and six field blank filters were obtained for

124

analysis. The two sets of filter samples were collected in parallel during the same time period.

125

Filters were sealed and stored at ≤ -20 °C prior to analysis. One set of filter samples was used for

AC C

EP

TE D

114

5

ACCEPTED MANUSCRIPT

OC-EC, WSOC and gas chromatography-mass spectrometry (GC-MS, ThermoQuest, Austin,

127

TX) analysis; the other set of filter samples was extracted and analyzed using UV/Vis

128

spectrometry (V660, Jasco Incorporated, Easton, MD) and high performance liquid

129

chromatography (HPLC, 1200 Agilent Technologies, Santa Clara, CA) /diode array detector

130

(DAD, G1315C)- quadruple -time of flight mass spectrometry (Q-ToFMS, Agilent 6520).

131

2.2 OC-EC, WSOC and OMMs analysis

RI PT

126

Details of the bulk OC, EC, WSOC and OMM analysis are given in supplemental

133

information. Briefly, the bulk OC and EC were measured using a thermal optical instrument

134

(Sunset Laboratory, Portland, OR) operated with a modified NIOSH method 5040 protocol

135

(NIOSH, 1999). WSOC was extracted from an aliquot of each PM2.5 sample using Milli-Q water

136

and measured on a total organic carbon (TOC) analyzer (TOC-V, CSN, Shimadzu) after

137

filtration. The concentrations of OC-EC and WSOC are given in Table 1. The OMMs in each

138

PM2.5 sample were extracted and analyzed with a GC-MS and a HPLC/DAD-Q-ToFMS. As

139

shown in Table 2, the OMMs analyzed by GC-MS include three isoprene SOA tracers, eight

140

monoterpene SOA tracers and levoglucosan. Four nitro-aromatic compounds (NACs), two

141

isoprene derived organosulfates (iOS) and five monoterpene derived organosulfates (mOS) were

142

measured using HPLC/DAD-Q-ToFMS. The authentic standards and surrogates used for OMMs

143

quantification are provided in supporting information and Table S1. Their recoveries and method

144

detection limits are shown in Table S2. Field blanks were analyzed using identical methods for

145

blank correction, and no contamination was observed for the target compounds.

146

2.3 Light absorption measurement

147

Water extracts. Details of the filter extraction and light absorption measurement are similar to

148

those in Xie et al. (2017b). Briefly, an aliquot of filter (6 cm2) was extracted in 5 mL pure water

AC C

EP

TE D

M AN U

SC

132

6

ACCEPTED MANUSCRIPT

(HPLC grade) ultrasonically for 15 min, and then filtered through a 25 mm diameter

150

polytetrafluoroethylene (PTFE) filter with a 0.2 µm pore size (National Scientific Company).

151

The light absorption of water extracts was measured with a UV-Vis spectrometer over the

152

wavelength (λ) range of 200 nm to 900 nm. To ensure data quality, the wavelength accuracy (±

153

0.3 nm) and repeatability (± 0.05 nm) were monitored periodically. Solvent background was

154

subtracted with a reference cuvette containing pure water.

RI PT

149

SC

The aqueous extract absorption (Aλ,w) measured by UV/Vis spectrometer is converted to light

155 156

absorption coefficient (Absλ,w, Mm-1) by:

157

Abs, = ( , −  , ) ×

158

where A700,w is subtracted from Aλ,w to correct for systematic baseline drift, Vl (m3) is the solvent

159

volume (5 mL) used for extraction, Va (m3) is the air volume sampled by the extracted filter area,

160

L (0.01 m) is the optical path length, and ln (10) converts the absorption coefficient in units of m-

161

1

162

(MAEλ,w, m2 gC-1) is a measure of absorption efficiency (Zhang et al., 2013; Liu et al., 2016),

163

and is calculated by:

ln(10)

(1)

M AN U

 ×

MAE, =

,  !

TE D

from log base-10 to natural log (Hecobian et al., 2010). The bulk mass absorption efficiency

(2)

EP

164



where WSOC is the concentration of WSOC in each sample (µg m-3). The spectral dependence

166

of light absorption, parameterized as the absorption Ångström exponent (Åw), is determined from

167

the slope of linear regression of log10(Absλ,w) vs. log10(λ) over the λ range of 300 to 550 nm.

168

Methanol extracts. The method of sample extraction in methanol and light absorption

169

measurement are the same as those for the water extracts. After extraction, the filter was air dried

170

in the fume hood overnight and analyzed with the Sunset thermal-optical analyzer to measure the

171

residual OC. The extraction efficiency (η, %) of OC by methanol is calculated by:

AC C

165

7

ACCEPTED MANUSCRIPT

!# $ !%

172

"=

173

where OCb is the OC content of each PM2.5 filter before extraction and OCr is the OC content in

174

the residual filter after extraction.

175

The light absorption coefficient for methanol extracts (Absλ,m, Mm-1) is calculated by:

176

Abs,' = ( ,' −  ,' ) ×

177

and the bulk mass absorption efficiency (MAEλ,m, m2 gC-1) for methanol extracts is calculated by:

178

MAE,' =

179

where Coc is the mass concentration of extracted OC (OCb – OCr) for each filter sample (µg m-3).

180

The absorption Ångström exponent for methanol extracts (Åm) is determined from the slope of

181

the linear regression of log10(Absλ,m) vs. log10(λ) over the λ range of 300 to 550 nm. In the

182

current work, Absλ and MAEλ were focused at 365 nm, since BrC can have significant absorption

183

at this wavelength, and λ = 365 nm is long enough to avoid the influence from other species (e.g.,

184

nitrate) (Hecobian et al., 2010). This wavelength is also used in most of the previous studies on

185

ambient BrC absorption in solution (Zhang et al., 2011, 2013; Cheng et al., 2016). The

186

measurement uncertainty was evaluated by replicate analysis in our previous work (Xie et al.,

187

2017b), which suggested an uncertainty lower than 5% for light absorption measurement.

188

2.4 PMF analysis and data selection

× 100%

ln(10)

(4)

,(

(5)

EP

TE D

M AN U

)*+

SC

  ×

RI PT

(3)

AC C

189

!#

A PMF2 model (Paatero, 1998a, b) coupled with a bootstrap technique (Hemann et al., 2009)

190

was applied to attribute BrC absorption (Abs365) to specific sources or atmospheric processes.

191

Details of this method have been introduced in several previous studies (Xie et al., 2012, 2013a,

192

b). Briefly, PMF resolves factor profiles and contributions from an array of compositional data of

193

ambient particles by minimizing the sum of squared, scaled residues (Q). One thousand replicate

194

data sets were generated from the original data set with the stationary black bootstrap technique 8

ACCEPTED MANUSCRIPT

and analyzed with PMF. The factor profiles of bootstrap solutions are compared to that of the

196

base case solution for matching rate calculation. A high factor matching rate reflects the

197

uniqueness of base case factors and robustness of the solution to input data (Xie et al., 2012).

198

The measurement days resampled in each bootstrapped data set were recorded to evaluate the

199

bias and variability due to random resampling error in the PMF solution. In the current work, the

200

factor number was determined by the interpretability of different PMF solutions (3 – 5 factors)

201

and factor matching rate (at least > 50%). Details of the simulation statistics for 3- to 5-factor

202

solutions are provided in Table S3 of the supporting information.

SC

RI PT

195

Due to the limited sample size (N = 45), OMMs with identical sources and significant

204

correlations (p < 0.05) were added together as one input for PMF analysis. The final input

205

species include Abs365,m, Abs365,w, OC, EC, WSOC, isoprene SOA tracers (sum of the three

206

tracers in Table 2), iOS (sum of the two iOS tracers in Table 2), mOS (sum of the five mOS

207

tracers in Table 2) and levoglucosan. The NACs and monoterpene SOA tracers were not

208

included for PMF analysis due to the uninterpretable PMF solution. One possible explanation is

209

that the NACs identified in this work can be generated from both biomass burning (Lin et al.,

210

2016, 2017) and photo-oxidation of aromatic VOCs (Iinuma et al., 2010; Xie et al., 2017a);

211

besides biogenic emissions, biomass burning also emits monoterpenes as precursors for SOA

212

formation (Greenberg et al., 2006), so the contribution of monoterpene SOA cannot be separated

213

from biomass burning during PMF analysis. GC-MS analysis was unavailable for two samples

214

collected on July 2nd and 14th 2013, and these two samples were excluded from the PMF analysis.

215

The estimation of uncertainties for input species concentrations and treatment of missing values

216

are provided in Xie et al. (2016). All measurements used in PMF analysis were above the limit of

217

detection.

AC C

EP

TE D

M AN U

203

9

ACCEPTED MANUSCRIPT

218

3. RESULTS

219

3.1 Bulk components and BrC absorption The statistics of bulk OC, EC and WSOC concentrations and the light absorption of WSOC

221

and MEOC are provided in Table 1. The average concentration of OC was 1.77 ± 0.74 µg m-3,

222

ranging from 0.72 to 3.61 µg m-3. Concentrations of EC were more than 10 times lower than OC

223

with an average concentration of 0.092 ± 0.051 µg m-3. WSOC accounted for 17.9 – 80.2%

224

(average 48.9 ± 15.1%) of OC, much lower than the fraction of OC extractable by methanol

225

(84.9 ± 7.57%).

SC

RI PT

220

The Abs365,w ranged from 0.067 to 0.46 Mm-1, with an average value of 0.21 ± 0.097 Mm-1;

227

the corresponding average MAE365,w and Åw are 0.29 ± 0.13 m2 gC-1 and 9.33 ± 1.13,

228

respectively. The MEOC had a significantly (p < 0.05) higher average light absorption

229

coefficient (Abs365,m, 0.52 ± 0.23 Mm-1) and mass absorption efficiency (MAE365,m, 0.36 ± 0.16

230

m2 gC-1) compared to that of WSOC. The ranges of Abs365,m and MAE365,m are 0.17 – 0.99 Mm-1

231

and 0.18 – 1.44 m2 gC-1. While the average Åm (5.49 ± 0.88) is significantly (p < 0.05) lower

232

than Åw.

233

3.2 Speciated OMMs in PM2.5

EP

TE D

M AN U

226

The statistics of the polar OMMs concentrations are listed in Table 2. Among the four

235

identified NACs, 4-nitrocatechol has the highest concentrations (0.057 ± 0.042 ng m-3), followed

236

by 4-nitrophenol (0.018 ± 0.027 ng m-3). Two sulfate esters from isoprene oxidation (Surratt et

237

al., 2006, 2007) and five from monoterpene oxidation (Surratt et al., 2007, 2008; Stone et al.,

238

2012) were detected in all PM2.5 samples, with average concentrations ranging from 0.66 ± 0.50

239

– 3.23 ± 2.38 ng m-3 (Table 2). The three identified isoprene SOA tracers, 2-methylglyceric acid,

240

2-methylthreitol and 2-methylerythritol, had average concentrations of 8.71 ± 8.22, 40.3 ± 39.7

AC C

234

10

ACCEPTED MANUSCRIPT

and 96.8 ± 97.1 ng m-3, respectively. The 3-methyl-1,2,3-butanetricarboxylic acid (30.9 ± 20.3

242

ng m-3) is the most abundant species among the eight monoterpene SOA tracers, followed by 3-

243

hydroxyglutaric acid (19.5 ± 14.7 ng m-3) and 3-acetyl pentanedioic acid (14.8 ± 12.5 ng m-3).

244

Levoglucosan, a widely used organic tracer for BB (Simoneit et al., 1999; Zhang et al., 2009a), is

245

detected in our samples at concentrations ranging from 1.47 to 23.3 ng m-3.

246

3.3 PMF results

RI PT

241

A four-factor solution (anthropogenic emission, organosulfate formation, biomass burning

248

and isoprene SOA formation) was chosen due to the most interpretable factors and high factor

249

matching rate (70.2%) between the bootstrapped and base case solutions. The 3-factor solution

250

combined the anthropogenic emission and biomass burning factors into one factor (Fig. S1); the

251

5-factor solution had a factor matching rate lower than 50% (Table S3), and the majority of bulk

252

solution absorption could not be related to any specific source (Fig. S2). Figs. 1 and 2 exhibit the

253

factor profiles and factor contributions to Abs365,m based on the 4-factor PMF solution. The

254

average relative factor contributions to Abs365,m, Abs365,w, OC, EC and WSOC are given in Fig.

255

S3. The factor profiles presented in Fig. 1 are normalized by

256

∗ ,-. = ∑4

257

where F*kj is the relative weight of species j in factor k to the other factors. The simulated sum of

258

factor contributions to Abs365,m agreed with the measured Abs365,m (PMF factor

259

contributions/observation = 0.91 ± 0.19, r = 0.88, t test p <0.01).

(6)

AC C

0 156 12

EP

012

TE D

M AN U

SC

247

260

In Fig. 1, the anthropogenic emission factor is characterized by the highest percentages of

261

EC and OC. The organosulfate formation factor contains the highest percentages of WSOC, iOS

262

and mOS. Levoglucosan is almost uniquely loaded in the BB factor with low percentages of

263

Abs365,m and Abs365,w. Very low percentages of bulk components and BrC absorption are 11

ACCEPTED MANUSCRIPT

attributed to the isoprene SOA formation factor. As shown in Fig. S3, the organosulfate

265

formation factor has the highest average contributions to Abs365,m (47%), Abs365,w (46%) and

266

WSOC (46%) among the four factors, followed by the anthropogenic emission factor (Abs365,m

267

35%, Abs365,w 40% and WSOC 30%).

268

4. DISCUSSION

270

4.1 Comparison of light-absorbing properties to other studies

SC

269

RI PT

264

In the current study, MAE365,m (0.36 ± 0.16 m2 gC-1) and MAE365,w (0.29 ± 0.13 m2 gC-1)

272

for ambient PM2.5 samples were much lower than those obtained for winter in Beijing (MAE365,m

273

1.45 ± 0.26 m2 gC-1, MAE365,w 1.22 ± 0.11 m2 gC-1) (Cheng et al., 2016) and summer in Los

274

Angeles (MAE365,m ~1.6 m2 gC-1, MAE365,w 0.71 m2 gC-1) (Zhang et al., 2013), where BB and

275

anthropogenic emissions contributed substantially to BrC absorption. MAE365,m and MAE365,w

276

values similar to this study were obtained in sampling sites located in Southeastern US during

277

summer periods (between ~0.2 and ~0.5 m2 gC-1) (Hecobian et al., 2010; Zhang et al., 2011; Liu

278

et al., 2013). This might be due to the fact that biogenic SOA makes up a substantial portion of

279

the organic aerosol in Southeastern US and has weak or no absorption (Zhang et al., 2011). The

280

Åm and Åw can be used to reflect the spectral dependence of BrC absorption in methanol and

281

water extracts, respectively. In the current work, the average Åm (5.49 ± 0.88) is much lower

282

than Åw (9.33 ± 1.13), and similar results were also obtained in winter Beijing (Åm 6.99 ± 0.27,

283

Åw 7.28 ± 0.24) (Cheng et al., 2016) and summer Los Angeles (Åm 4.82 ± 0.49, Åw 7.58 ± 0.49)

284

(Zhang et al., 2013), suggesting that the absorption of strong BrC chromophores might be less

285

dependent on wavelength than weak BrC chromophores in the same aerosol sample.

286

AC C

EP

TE D

M AN U

271

The light-absorbing properties obtained in this work are derived from the measurements of

12

ACCEPTED MANUSCRIPT

aqueous extracts using a UV-Vis spectrometer, and cannot reflect the BrC absorption in airborne

288

particles directly. The atmospheric aerosol absorption not only depends on the BrC mass

289

concentration and the structures of BrC chromophores, but also the size distribution, shapes, and

290

mixing state of airborne particles (Bond et al., 2006; Lack and Cappa, 2010; Cappa et al., 2012;

291

Saleh et al., 2014; Laskin et al., 2015). However, the solution-based measurements of BrC

292

absorption are not subject to black carbon (BC) or other absorbers, since the BrC components are

293

isolated, thereby permitting a direct measurement of BrC chromophores absorption (Liu et al.,

294

2013). The particle-based measurements with optical instruments typically quantify the

295

absorption of all components, including BC, BrC, and dust, and differentiating BrC absorption

296

from the total can be difficult due to large contribution from BC. Moreover, the assumptions

297

associated with Mie calculations for optical properties of airborne particles may lead to

298

substantial uncertainty, such as the mixing state of particles (external, internal, or a mixture). Liu

299

et al. (2013) found high correlations (r2 > 0.7) between the bulk solution absorption and Mie-

300

predicted BrC absorption, and inferred that the actual atmospheric absorption is approximately 2

301

times as the bulk solution absorption. Therefore, the light-absorbing properties obtained in this

302

work can represent the absorbing characteristics of BrC chromophores isolated from ambient

303

aerosols.

304

4.2 Contributions of NACs to Abs365

AC C

EP

TE D

M AN U

SC

RI PT

287

305

NACs are a group of light absorbing chromophores that have been observed in BB

306

emissions (Claeys et al., 2012; Mohr et al., 2013; Lin et al., 2016, 2017) and SOA from the

307

oxidation of certain aromatic volatile organic compounds (VOCs) under high NOX conditions

308

(Iinuma, et al., 2010; Lin et al., 2015; Xie et al., 2017a). NACs are also detected in a variety of

309

atmospheric environments with a variety of contributing sources (Desyaterik et al., 2013; Kahnt

13

ACCEPTED MANUSCRIPT

et al., 2013; Zhang et al., 2013; Teich et al., 2017). The contribution of total NACs to the light

311

absorption of aqueous extracts of ambient particles can be more than 3% (Zhang et al., 2013;

312

Teich et al., 2017). In the current work, the light absorption of individual NACs in sample

313

extracts was estimated as the product of the concentrations of NACs and the MAE365 of the

314

individual compounds in methanol and water. The MAE365,m and MAE365,w for individual NACs

315

were obtained from Xie et al. (2017a) and Zhang et al. (2013), respectivley. The MAE365,w for

316

C6H6NO3 is not available in Zhang et al. (2013), and thus the MAE365,m for C6H6NO3 reported in

317

Xie et al., (2017a) is used as a surrogate. The average contributions to Abs365,m and Abs365,w from

318

the four NACs detected in this work are 0.079 ± 0.083% and 0.21± 0.16%, respectively. The

319

estimated average contribution of total NACs to Abs365,w is comparable to those obtained under

320

acidic conditions during the summer in Germany (Waldstein and Melpitz, 0.13 ± 0.05 – 0.15 ±

321

0.10) and in China (Xianghe and Wangdu, 0.46 ± 0.24 – 0.56 ± 0.31) (Teich et al., 2017), but

322

lower than that observed in the Los Angeles summer (~3%) (Zhang et al., 2013). Among the four

323

NACs in this work, C6H5NO4 (4-nitrocatechol) has the highest contribution to bulk extracts

324

absorption, accounting for 67.2 ± 11.8% and 68.7 ± 12.0% of total NACs contributions to

325

Abs365,m and Abs365,w, respectively. However, the NACs only account for a very small fraction of

326

BrC absorption in ambient PM, and are subject to atmospheric processes (e.g., aging and photo-

327

bleaching) (Lee et al., 2014; Zhao et al, 2015). Therefore, further studies are needed to determine

328

which additional light absorbing chromophores, such as highly conjugated compounds (e.g.,

329

polycyclic aromatic compounds and high molecular weight humic like substances), are

330

responsible for BrC absorption in the atmosphere.

331

4.3 Correlation matrix analysis

332

AC C

EP

TE D

M AN U

SC

RI PT

310

Because the NACs identified in this work had minor contributions (< 1%) to Abs365,m and

14

ACCEPTED MANUSCRIPT

Abs365,w, and the other OMMs were less likely to contribute to BrC absorption due to their non-

334

conjugated, chain-like structures, a correlation matrix plot (Fig. 3) was used to examine the

335

relationships of all measurements conducted in this work, especially for BrC absorption versus

336

organic composition. As shown in Fig. 3, the NACs weakly correlate (r < 0.4) with most other

337

OMMs, including levoglucosan. Possible reasons are as follows: the observed NACs are not

338

from BB; NACs and levoglucosan undergo different formation processes during BB, or have

339

different atmospheric lifetimes or atmospheric processing mechanisms. One potential source of

340

ambient NACs in these samples is the oxidation of gaseous aromatics with NOX (Xie et al.,

341

2017a). However, high time resolution concentration data of NACs, volatile aromatics and other

342

gaseous pollutants (e.g, NOX, O3) are needed for validation. The iOS and mOS, representing the

343

formation of organosulfates from photo-oxidation of biogenic VOCs, correlated significantly (r =

344

0.53 – 0.94, p < 0.01). Guo et al. (2015) estimated a pH range of 0.5 to 2 for particle water in the

345

Southeastern US during the summer, and such acidic conditions favor the formation of

346

organosulfates (Surratt et al., 2008). The three isoprene SOA tracers listed in Table 1 correlated

347

strongly (r = 0.77 – 0.97, p < 0.01); however, only four of the eight monoterpene SOA tracers (3-

348

acetyl pentanedioic acid, 3-acetyl hexanedioic acid, 3-methyl-1,2,3-butanetricarboxylic acid and

349

3-hydroxyglutaric acid) showed strong correlation (r > 0.7). Except 2-hydroxy-4-isopropyladipic

350

acid and 3-hydroxy-4,4-dimethylglutaric acid, the other monoterpene SOA tracers correlate with

351

levoglucosan significantly (r = 0.50 – 0.60, p < 0.01). This is because biomass burning can also

352

generate monoterpenes serving as precursors for SOA formation (Greenberg et al., 2006), and

353

the monoterpene SOA tracers are linked to both biogenic SOA and biomass burning. The

354

average concentration of levoglucosan (9.25 ± 5.40 ng m-3) in this study is much lower than

355

other locations in Southeastern US (summer 18.7 ± 44.7 ng m-3; winter 170 ± 180 ng m-3)

AC C

EP

TE D

M AN U

SC

RI PT

333

15

ACCEPTED MANUSCRIPT

356

(Zhang et al., 2010), and no significant (p > 0.05) correlation was observed between

357

levoglucosan and Abs365, suggesting that BB is not the dominant BrC source in this work.

358

4.4 Sources of BrC absorption As shown in Figs. 1, 2 and S1, the organosulfate formation factor accounts for major BrC

360

absorption and contributes 47% of Abs365,m and 46% of Abs365,w on average. The organosulfate

361

factor is characterized by the highest loadings of WSOC, iOS and mOS, indicating that a

362

substantial fraction of BrC absorption is from biogenic SOA. However, the organosulfate

363

molecules identified in this work might not be chromophores themselves (Nguyen et al. 2012).

364

Song et al. (2013) and Nguyen et al. (2012) investigated the absorption of laboratory generated

365

biogenic SOA inferring that the light-absorbing compounds were aldol condensation oligomers

366

with nitroxy organosulfate groups formed in acidic aerosols. Presently, two iOS and five mOS

367

species were identified, and three of the five mOS species are nitroxy organosulfates (Table 1).

368

The PMF results of this work support the theory that the organosulfate formation process is

369

closely related to BrC absorption in Southeastern US. The organosulfates measured in this work

370

are formed through the reactions of biogenic VOCs and sulfuric acid (or SO2) (Surratt et al.,

371

2006, 2007, 2008), and an association has been observed between anthropogenic emission and

372

SOA formation from isoprene and monoterpenes (Budisulistiorini et al., 2015; Xu et al., 2015).

373

These might explain the presence of EC in the organosulfate formation as well as isoprene SOA

374

factors.

AC C

EP

TE D

M AN U

SC

RI PT

359

375

The anthropogenic emission factor has the second highest average contribution to WSOC

376

(30%), Abs365,m (35%) and Abs365,w (40%). Weber et al. (2007) suggested that WSOC from

377

PM2.5 in the Southeastern US is mainly SOA. So it may be that the anthropogenic emission

378

factor has a contribution from anthropogenic SOA. However, due to the lack of anthropogenic

16

ACCEPTED MANUSCRIPT

SOA tracers, the anthropogenic SOA contribution was unresolved here and likely lumped into

380

the anthropogenic emission factor. Previous studies have demonstrated that both primary motor

381

vehicle emissions and SOA formation with aromatic VOCs emitted from anthropogenic sources

382

contain BrC chromophores (Xie et al., 2017a, b). In the absence of BB emissions, we tentatively

383

suggest that biogenic SOA containing organosulfates formed under acidic conditions is an

384

important source of BrC absorption in RTP during the summer. However, the BrC absorption

385

attributable to primary and secondary anthropogenic emissions, respectively, needs further study.

SC

RI PT

379

In the current work, the small sample size might result in large uncertainties in PMF results.

387

Zhang et al. (2009b) found that OMM-based PMF analysis could derive stable factors with high

388

OC contributions from data set with a small sample size (50 – 60), but their factor contributions

389

were subject to considerable uncertainties. As such, the two PMF factors with high contributions

390

to OC (organosulfate formation and anthropogenic emission) resolved in this work are valid, but

391

their contributions to bulk solution absorption should be treated with caution. Moreover, the

392

grouping of OMMs with identical sources for PMF analysis neglected the variability between

393

species. To understand the impact of species grouping on PMF results, individual OMMs were

394

used instead of grouped OMMs (e.g., iOS) for an additional PMF simulation, and a 4-factor

395

solution was chosen due to the most interpretable factors with a factor matching rate of 18.8%.

396

Similar as the PMF analysis using grouped OMMs, the factor profiles and contributions

397

presented in Figs. S4 and S5 suggest a substantial contribution of Abs365,m (49%) form

398

organosulfate formation factors. These results validated the grouping of OMMs for PMF analysis

399

in this work, which enhanced the robustness of PMF solution by increasing the factor matching

400

rate between the bootstrapped and base case solutions.

AC C

EP

TE D

M AN U

386

401

17

ACCEPTED MANUSCRIPT

402

5.0 CONCLUSION To understand the sources of BrC absorption during the summer in RTP, NC, when the

404

influence of BB was less significant, the light absorption of MEOC and WSOC in PM2.5 and the

405

chemical compositions of OC were measured and analyzed with a PMF receptor model. The

406

average MAE365,m and MAE365,w observed in the current study are 0.36 ± 0.16 m2 gC-1 and 0.29

407

± 0.13 m2 gC-1, respectively, comparable to the places where organic aerosols are dominated by

408

biogenic SOA in summer (e.g., Southeastern US), but weaker than the locations with

409

considerable influences from BB or anthropogenic emissions (e.g., Beijing, Los Angeles). The

410

four NACs identified in PM2.5 samples account for less than 1% of the aqueous extracts

411

absorption, and further studies are warranted to explore the unexplained BrC chromophores. The

412

weak correlation between Abs365 and levoglucosan (p > 0.05) suggests that BB is not an

413

important BrC source in RTP during the summer. A 4-factor PMF solution was resolved from

414

the data set with grouped OMMs, and the orgnaosulfate formation factor had average

415

contributions of 47% and 46% to Abs365,m and Abs365,w, respectively. These results were

416

validated by PMF analysis using individual OMMs, and suggested that BrC chromophores could

417

be generated during the formation process of biogenic SOA containing organosulfate under

418

acidic conditions. However, the BrC absorption attributable to primary and secondary

419

anthropogenic emissions requires further work.

421

SC

M AN U

TE D

EP

AC C

420

RI PT

403

ACKNOWLEDGEMENTS/DISCLAIMER

422

This research was supported by the State Key Laboratory of Pollution Control and

423

Resource Reuse Foundation (No. PCRRF17040), the National Natural Science Foundation of

424

China (NSFC, 41701551), the Startup Foundation for Introducing Talent of NUIST (No.

18

ACCEPTED MANUSCRIPT

2243141801001). The U.S. Environmental Protection Agency, through its Office of Research

426

and Development, also funded and collaborated in the research described here under Contract

427

EP-C-15-008 to Jacobs Technology, Inc. This research was supported in part by an appointment

428

to the Postdoctoral Research Program at the National Risk Management Research Laboratory

429

administered by the Oak Ridge institute for Science and Education through Interagency

430

Agreement No. 92433001 between the U.S. Department of Energy and the U.S. Environmental

431

Protection Agency. Data used in the writing of this manuscript is available at the U.S.

432

Environmental Protection Agency’s Environmental Dataset Gateway (https://edg.epa.gov). The

433

views expressed in this article are those of the authors and do not necessarily represent the views

434

or policies of the U.S. Environmental Protection Agency.

M AN U

SC

RI PT

425

435

REFERENCES

437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463

Bond, T.C., Habib, G., Bergstrom, R.W., 2006. Limitations in the enhancement of visible light absorption due to mixing state. Journal of Geophysical Research: Atmospheres 111, D20211. doi:10.1029/2006JD007315. Budisulistiorini, S.H., Li, X., Bairai, S.T., Renfro, J., Liu, Y., Liu, Y.J., McKinney, K.A., Martin, S.T., McNeill, V.F., Pye, H.O.T., Nenes, A., Neff, M.E., Stone, E.A., Mueller, S., Knote, C., Shaw, S.L., Zhang, Z., Gold, A., Surratt, J.D., 2015. Examining the effects of anthropogenic emissions on isoprene-derived secondary organic aerosol formation during the 2013 Southern Oxidant and Aerosol Study (SOAS) at the Look Rock, Tennessee ground site. Atmospheric Chemistry and Physics 15, 8871-8888. Cappa, C.D., Onasch, T.B., Massoli, P., Worsnop, D.R., Bates, T.S., Cross, E.S., Davidovits, P., Hakala, J., Hayden, K.L., Jobson, B.T., 2012. Radiative absorption enhancements due to the mixing state of atmospheric black carbon. Science 337, 1078-1081. Chen, Y., Bond, T.C., 2010. Light absorption by organic carbon from wood combustion. Atmospheric Chemistry and Physics 10, 1773-1787. Cheng, Y., He, K.-b., Du, Z.-y., Engling, G., Liu, J.-m., Ma, Y.-l., Zheng, M., Weber, R.J., 2016. The characteristics of brown carbon aerosol during winter in Beijing. Atmospheric Environment 127, 355-364. Chung, S.H., Seinfeld, J.H., 2002. Global distribution and climate forcing of carbonaceous aerosols. Journal of Geophysical Research: Atmospheres 107, AAC 14-11-AAC 14-33. Claeys, M., Vermeylen, R., Yasmeen, F., Gómez-González, Y., Chi, X., Maenhaut, W., Mészáros, T., Salma, I., 2012. Chemical characterisation of humic-like substances from urban, rural and tropical biomass burning environments using liquid chromatography with UV/vis photodiode array detection and electrospray ionisation mass spectrometry. Environmental Chemistry 9, 273-284. Desyaterik, Y., Sun, Y., Shen, X., Lee, T., Wang, X., Wang, T., Collett, J.L., 2013. Speciation of “brown” carbon in cloud water impacted by agricultural biomass burning in eastern China. Journal of Geophysical Research: Atmospheres, 118, 7389-7399. Edney. E.O., Kleindienst, T.E., Conver, T.S., McIver, C.D., Weathers, W.S., 2003. Polar organic oxygenates in PM2.5 at a southeastern site in the United States. Atmospheric Environment 37, 3947-3965. Feng, Y., Ramanathan, V., Kotamarthi, V.R., 2013. Brown carbon: a significant atmospheric absorber of solar radiation? Atmos. Chem. Phys. 13, 8607-8621.

AC C

EP

TE D

436

19

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

Greenberg, J., Friedli, H., Guenther, A., Hanson, D., Harley, P., Karl, T., 2006. Volatile organic emissions from the distillation and pyrolysis of vegetation. Atmospheric Chemistry and Physics 6, 81-91. Guo, H., Xu, L., Bougiatioti, A., Cerully, K.M., Capps, S.L., Hite Jr, J.R., Carlton, A.G., Lee, S.H., Bergin, M.H., Ng, N.L., Nenes, A., Weber, R.J., 2015. Fine-particle water and pH in the Southeastern United States. Atmospheric Chemistry and Physics 15, 5211-5228. Hecobian, A., Zhang, X., Zheng, M., Frank, N., Edgerton, E.S., Weber, R.J., 2010. Water-soluble organic aerosol material and the light-absorption characteristics of aqueous extracts measured over the Southeastern United States. Atmospheric Chemistry and Physics 10, 5965-5977. Hemann, J.G., Brinkman, G.L., Dutton, S.J., Hannigan, M.P., Milford, J.B., Miller, S.L., 2009. Assessing positive matrix factorization model fit: a new method to estimate uncertainty and bias in factor contributions at the measurement time scale. Atmospheric Chemistry and Physics 9, 497-513. Hidy, G.M., Blanchard, C.L., Baumann, K., Edgerton, E., Tanenbaum, S., Shaw, S., Knipping, E., Tombach, I., Jansen, J., Walters, J., 2014. Chemical climatology of the Southeastern United States, 1999-2013. Atmospheric Chemistry and Physics 14, 11893-11914. Iinuma, Y., Böge, O., Gräfe, R., Herrmann, H., 2010. Methyl-nitrocatechols: Atmospheric tracer compounds for biomass burning secondary organic aerosols. Environmental Science & Technology 44, 8453-8459. IPCC. Assessment Record: Climate Change 2007; Cambridge University Press: New York, 2007. Kahnt, A., Behrouzi, S., Vermeylen, R., Safi Shalamzari, M., Vercauteren, J., Roekens, E., Claeys, M., Maenhaut, W., 2013. One-year study of nitro-organic compounds and their relation to wood burning in PM10 aerosol from a rural site in Belgium. Atmospheric Environment 81, 561-568. Kirchstetter, T.W., Novakov, T., Hobbs, P.V., 2004. Evidence that the spectral dependence of light absorption by aerosols is affected by organic carbon. Journal of Geophysical Research-Atmospheres 109, D21208. doi:10.1029/2004JD004999. Kleindienst, T.E., Jaoui, M., Lewandowski, M., Offenberg, J.H., Lewis, C.W., Bhave, B.V., Edney E.O., 2007. Estimates of the contributions of biogenic and anthropogenic hydrocarbon precursors to secondary organic aerosol at a southeastern U.S. location. Atmospheric Environment 41, 8288-8300. Lack, D., Cappa, C., 2010. Impact of brown and clear carbon on light absorption enhancement, single scatter albedo and absorption wavelength dependence of black carbon. Atmospheric Chemistry and Physics 10, 4207-4220. Laskin, A., Laskin, J., Nizkorodov, S.A., 2015. Chemistry of Atmospheric Brown Carbon. Chemical Reviews 115, 4335-4382. Lee, H.J., Aiona, P.K., Laskin, A., Laskin, J., Nizkorodov, S.A., 2014. Effect of solar radiation on the optical properties and molecular composition of laboratory proxies of atmospheric brown carbon. Environmental Science & Technology 48, 10217-10226. Lin, P., Aiona, P.K., Li, Y., Shiraiwa, M., Laskin, J., Nizkorodov, S.A., Laskin, A., 2016. Molecular characterization of brown carbon in biomass burning aerosol particles. Environmental Science & Technology 50, 11815-11824. Lin, P., Bluvshtein, N., Rudich, Y., Nizkorodov, S.A., Laskin, J., Laskin, A., 2017. Molecular chemistry of atmospheric brown carbon inferred from a nationwide biomass burning event. Environmental Science & Technology 51, 11561-11570. Lin, P., Liu, J.M., Shilling, J.E., Kathmann, S.M., Laskin, J., Laskin, A., 2015. Molecular characterization of brown carbon (BrC) chromophores in secondary organic aerosol generated from photo-oxidation of toluene. Physical Chemistry Chemical Physics 17, 23312-23325. Lin, Y.-H., Budisulistiorini, S.H., Chu, K., Siejack, R.A., Zhang, H., Riva, M., Zhang, Z., Gold, A., Kautzman, K.E., Surratt, J.D., 2014. Light-absorbing oligomer formation in secondary organic aerosol from reactive uptake of isoprene epoxydiols. Environmental Science & Technology 48, 12012-12021. Liu, J., Bergin, M., Guo, H., King, L., Kotra, N., Edgerton, E., Weber, R.J., 2013. Size-resolved measurements of brown carbon in water and methanol extracts and estimates of their contribution to ambient fine-particle light absorption. Atmospheric Chemistry and Physics 13, 12389-12404. Liu, J., Lin, P., Laskin, A., Laskin, J., Kathmann, S.M., Wise, M., Caylor, R., Imholt, F., Selimovic, V., Shilling, J.E., 2016. Optical properties and aging of light-absorbing secondary organic aerosol. Atmospheric Chemistry and Physics 16, 12815-12827. Liu, J., Scheuer, E., Dibb, J., Diskin, G.S., Ziemba, L.D., Thornhill, K.L., Anderson, B.E., Wisthaler, A., Mikoviny, T., Devi, J.J., Bergin, M., Perring, A.E., Markovic, M.Z., Schwarz, J.P., Campuzano-Jost, P., Day, D.A., Jimenez, J.L., Weber, R.J., 2015. Brown carbon aerosol in the North American continental troposphere: sources, abundance, and radiative forcing. Atmospheric Chemistry and Physics 15, 7841-7858.

AC C

464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518

20

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

Liu, J., Scheuer, E., Dibb, J., Ziemba, L.D., Thornhill, K.L., Anderson, B.E., Wisthaler, A., Mikoviny, T., Devi, J.J., Bergin, M., 2014. Brown carbon in the continental troposphere. Geophysical Research Letters 41, 21912195. Mohr, C., Lopez-Hilfiker, F.D., Zotter, P., Prévôt, A.S.H., Xu, L., Ng, N.L., Herndon, S.C., Williams, L.R., Franklin, J.P., Zahniser, M.S., Worsnop, D.R., Knighton, W.B., Aiken, A.C., Gorkowski, K.J., Dubey, M.K., Allan, J.D., Thornton, J.A., 2013. Contribution of nitrated phenols to wood burning brown carbon light absorption in Detling, United Kingdom during winter time. Environmental Science & Technology 47, 6316-6324. Myhre, G., Samset, B.H., Schulz, M., Balkanski, Y., Bauer, S., Berntsen, T.K., Bian, H., Bellouin, N., Chin, M., Diehl, T., Easter, R.C., Feichter, J., Ghan, S.J., Hauglustaine, D., Iversen, T., Kinne, S., Kirkevåg, A., Lamarque, J.F., Lin, G., Liu, X., Lund, M.T., Luo, G., Ma, X., van Noije, T., Penner, J.E., Rasch, P.J., Ruiz, A., Seland, Ø., Skeie, R.B., Stier, P., Takemura, T., Tsigaridis, K., Wang, P., Wang, Z., Xu, L., Yu, H., Yu, F., Yoon, J.H., Zhang, K., Zhang, H., Zhou, C., 2013. Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations. Atmospheric Chemistry and Physics 13, 1853-1877. Nakayama, T., Matsumi, Y., Sato, K., Imamura, T., Yamazaki, A., Uchiyama, A., 2010. Laboratory studies on optical properties of secondary organic aerosols generated during the photooxidation of toluene and the ozonolysis of α-pinene. Journal of Geophysical Research: Atmospheres 115, D24204. doi:10.1029/2010JD014387. Nguyen, T.B., Lee, P.B., Updyke, K.M., Bones, D.L., Laskin, J., Laskin, A., Nizkorodov, S.A., 2012. Formation of nitrogen- and sulfur-containing light-absorbing compounds accelerated by evaporation of water from secondary organic aerosols. Journal of Geophysical Research: Atmospheres 117, D01207. doi:10.1029/2011JD016944. Nguyen, T.K.V., Petters, M.D., Suda, S.R., Guo, H., Weber, R.J., Carlton, A.G., 2014. Trends in particle-phase liquid water during the Southern Oxidant and Aerosol Study. Atmospheric Chemistry and Physics 14, 1091110930. NIOSH, 1999. National Institute of Occupational Safety and Health. Elemental carbon (diesel particulate): Method 5040, Rep. https://www.cdc.gov/niosh/docs/2003-154/pdfs/5040f3.pdf (1999), last accessed December, 2016. Paatero, P., 1998a. User’s Guide for Positive Matrix Factorization Program PMF2 and PMF3, Part 1: Tutorial. University of Helsinki, Helsinki, Finland. Paatero, P., 1998b. User’s Guide for Positive Matrix Factorization Program PMF2 and PMF3, Part 2: Reference. University of Helsinki, Helsinki, Finland. Pokhrel, R.P., Wagner, N.L., Langridge, J.M., Lack, D.A., Jayarathne, T., Stone, E.A., Stockwell, C.E., Yokelson, R.J., Murphy, S.M., 2016. Parameterization of single-scattering albedo (SSA) and absorption Ångström exponent (AAE) with EC / OC for aerosol emissions from biomass burning. Atmospheric Chemistry and Physics 16, 9549-9561. Saleh, R., Hennigan, C.J., McMeeking, G.R., Chuang, W.K., Robinson, E.S., Coe, H., Donahue, N.M., Robinson, A.L., 2013. Absorptivity of brown carbon in fresh and photo-chemically aged biomass-burning emissions. Atmospheric Chemistry and Physics 13, 7683-7693. Saleh, R., Robinson, E.S., Tkacik, D.S., Ahern, A.T., Liu, S., Aiken, A.C., Sullivan, R.C., Presto, A.A., Dubey, M.K., Yokelson, R.J., Donahue, N.M., Robinson, A.L., 2014. Brownness of organics in aerosols from biomass burning linked to their black carbon content. Nature Geoscience 7, 647-650. Seinfeld, J., 2008. Atmospheric science: Black carbon and brown clouds. Nature Geoscience 1, 15-16. Simoneit, B.R.T., Schauer, J.J., Nolte, C.G., Oros, D.R., Elias, V.O., Fraser, M.P., Rogge, W.F., Cass, G.R., 1999. Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles. Atmospheric Environment 33, 173-182. Song, C., Gyawali, M., Zaveri, R.A., Shilling, J.E., Arnott, W.P., 2013. Light absorption by secondary organic aerosol from α-pinene: Effects of oxidants, seed aerosol acidity, and relative humidity. Journal of Geophysical Research: Atmospheres 118, 11,741-711,749. Stone, E.A., Yang, L., Yu, L.E., Rupakheti, M., 2012. Characterization of organosulfates in atmospheric aerosols at Four Asian locations. Atmospheric Environment 47, 323-329. Surratt, J.D., Gómez-González, Y., Chan, A.W.H., Vermeylen, R., Shahgholi, M., Kleindienst, T.E., Edney, E.O., Offenberg, J.H., Lewandowski, M., Jaoui, M., Maenhaut, W., Claeys, M., Flagan, R.C., Seinfeld, J.H., 2008. Organosulfate formation in biogenic secondary organic aerosol. The Journal of Physical Chemistry A 112, 8345-8378. Surratt, J.D., Kroll, J.H., Kleindienst, T.E., Edney, E.O., Claeys, M., Sorooshian, A., Ng, N.L., Offenberg, J.H., Lewandowski, M., Jaoui, M., Flagan, R.C., Seinfeld, J.H., 2007. Evidence for organosulfates in secondary organic aerosol. Environmental Science & Technology 41, 517-527.

AC C

519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573

21

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

Surratt, J.D., Murphy, S.M., Kroll, J.H., Ng, N.L., Hildebrandt, L., Sorooshian, A., Szmigielski, R., Vermeylen, R., Maenhaut, W., Claeys, M., Flagan, R.C., Seinfeld, J.H., 2006. Chemical composition of secondary organic aerosol formed from the photooxidation of isoprene. The Journal of Physical Chemistry A 110, 9665-9690. Teich, M., van Pinxteren, D., Wang, M., Kecorius, S., Wang, Z., Müller, T., Močnik, G., Herrmann, H., 2017. Contributions of nitrated aromatic compounds to the light absorption of water-soluble and particulate brown carbon in different atmospheric environments in Germany and China. Atmospheric Chemistry and Physics 17, 1653-1672. Updyke, K.M., Nguyen, T.B., Nizkorodov, S.A., 2012. Formation of brown carbon via reactions of ammonia with secondary organic aerosols from biogenic and anthropogenic precursors. Atmospheric Environment 63, 22-31. Wang, X., Heald, C.L., Ridley, D.A., Schwarz, J.P., Spackman, J.R., Perring, A.E., Coe, H., Liu, D., Clarke, A.D., 2014. Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon. Atmospheric Chemistry and Physics 14, 1098911010. Washenfelder, R.A., Attwood, A.R., Brock, C.A., Guo, H., Xu, L., Weber, R.J., Ng, N.L., Allen, H.M., Ayres, B.R., Baumann, K., Cohen, R.C., Draper, D.C., Duffey, K.C., Edgerton, E., Fry, J.L., Hu, W.W., Jimenez, J.L., Palm, B.B., Romer, P., Stone, E.A., Wooldridge, P.J., Brown, S.S., 2015. Biomass burning dominates brown carbon absorption in the rural Southeastern United States. Geophysical Research Letters 42, 653-664. Weber, R.J., Sullivan, A.P., Peltier, R.E., Russell, A., Yan, B., Zheng, M., de Gouw, J., Warneke, C., Brock, C., Holloway, J.S., Atlas, E.L., Edgerton, E., 2007. A study of secondary organic aerosol formation in the anthropogenic-influenced Southeastern United States. Journal of Geophysical Research: Atmospheres 112, D13302. Xie, M., Barsanti, K.C., Hannigan, M.P., Dutton, S.J., Vedal, S., 2013a. Positive matrix factorization of PM2.5 eliminating the effects of gas/particle partitioning of semivolatile organic compounds. Atmospheric Chemistry and Physics 13, 7381-7393. Xie, M., Chen, X., Hays, M.D., Lewandowski, M., Offenberg, J., Kleindienst, T.E., Holder, A.L., 2017a. Light absorption of secondary organic aerosol: Composition and contribution of nitroaromatic compounds. Environmental Science & Technology 51, 11607-11616. Xie, M., Hannigan, M.P., Dutton, S.J., Milford, J.B., Hemann, J.G., Miller, S.L., Schauer, J.J., Peel, J.L., Vedal, S., 2012. Positive matrix factorization of PM2.5: Comparison and implications of using different speciation data sets. Environmental Science & Technology 46, 11962-11970. Xie, M., Hays, M.D., Holder, A.L., 2017b. Light-absorbing organic carbon from prescribed and laboratory biomass burning and gasoline vehicle emissions. Scientific Reports 7, 7318. Xie, M., Mladenov, N., Williams, M.W., Neff, J.C., Wasswa, J., Hannigan, M.P., 2016. Water soluble organic aerosols in the Colorado Rocky Mountains, USA: composition, sources and optical properties. Scientific Reports 6, 39339. Xie, M., Piedrahita, R., Dutton, S.J., Milford, J.B., Hemann, J.G., Peel, J.L., Miller, S.L., Kim, S.-Y., Vedal, S., Sheppard, L., Hannigan, M.P., 2013b. Positive matrix factorization of a 32-month series of daily PM2.5 speciation data with incorporation of temperature stratification. Atmospheric Environment 65, 11-20. Xu, L., Guo, H., Boyd, C.M., Klein, M., Bougiatioti, A., Cerully, K.M., Hite, J.R., Isaacman-VanWertz, G., Kreisberg, N.M., Knote, C., Olson, K., Koss, A., Goldstein, A.H., Hering, S.V., de Gouw, J., Baumann, K., Lee, S.-H., Nenes, A., Weber, R.J., Ng, N.L., 2015. Effects of anthropogenic emissions on aerosol formation from isoprene and monoterpenes in the southeastern United States. Proceedings of the National Academy of Sciences 112, 37-42. Zhang, Y., Forrister, H., Liu, J., Dibb, J., Anderson, B., Schwarz, J.P., Perring, A.E., Jimenez, J.L., Campuzano-Jost, P., Wang, Y., 2017. Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere. Nature Geoscience 10, 486. Zhang, X., Hecobian, A., Zheng, M., Frank, N.H., Weber, R.J., 2010. Biomass burning impact on PM2.5 over the Southeastern US during 2007: Integrating chemically speciated FRM filter measurements, MODIS fire counts and PMF analysis. Atmospheric Chemistry and Physics 10, 6839-6853. Zhang, X., Kim, H., Parworth, C.L., Young, D.E., Zhang, Q., Metcalf, A.R., Cappa, C.D., 2016. Optical properties of wintertime aerosols from residential wood burning in Fresno, CA: Results from DISCOVER-AQ 2013. Environmental Science & Technology 50, 1681-1690. Zhang, X., Lin, Y.-H., Surratt, J.D., Weber, R.J., 2013. Sources, composition and absorption Ångström exponent of light-absorbing organic components in aerosol extracts from the Los Angeles Basin. Environmental Science & Technology 47, 3685-3693. Zhang, X., Lin, Y.-H., Surratt, J.D., Zotter, P., Prévôt, A.S.H., Weber, R.J., 2011. Light-absorbing soluble organic

AC C

574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629

22

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

aerosol in Los Angeles and Atlanta: A contrast in secondary organic aerosol. Geophysical Research Letters 38, L21810. doi:10.1029/2011GL049385. Zhang, Y., Sheesley, R.J., Bae, M.-S., Schauer, J.J., 2009. Sensitivity of a molecular marker based positive matrix factorization model to the number of receptor observations. Atmospheric Environment 43, 4951-4958. Zhang, Y., Sheesley, R.J., Schauer, J.J., Lewandowski, M., Jaoui, M., Offenberg, J.H., Kleindienst, T.E., Edney, E.O., 2009. Source apportionment of primary and secondary organic aerosol using Positive Matrix Factorization (PMF) of molecular markers. Atmospheric Environment 43, 5567-5574. Zhao, R., Lee, A.K.Y., Huang, L., Li, X., Yang, F., Abbatt, J.P.D., 2015. Photochemical processing of aqueous atmospheric brown carbon. Atmospheric Chemistry and Physics 15, 6087-6100.

AC C

630 631 632 633 634 635 636 637 638

23

ACCEPTED MANUSCRIPT

Table 1. Concentrations of bulk carbonaceous components and light-absorbing properties.

1.62 0.087 0.82 49.8 86.9

0.21 0.29 9.33 0.52 0.36 5.49 0.42 0.84

b

Min

Max

% of Missing values

0.74 0.051 0.45 15.1 7.57

0.72 0.0091 0.20 17.9 58.2

3.61 0.29 2.24 80.2 97.4

0.00 2.22 26.7 26.7 0.00

0.21 0.26 9.37

0.097 0.13 1.13

0.067 0.12 5.79

0.46 0.67 11.9

0.00 26.7 0.00

0.49 0.34 5.25 0.097 0.77

0.23 0.16 0.88 0.43 0.37

RI PT

1.77 0.092 0.84 48.9 84.9

a

SC

Std

0.17 0.18 4.29 0.26 0.35

0.99 1.14 9.10 0.70 1.98

0.00 0.00 0.00 0.00 26.7

EP

TE D

standard deviation; calculated as missing No. of observations/total sample number (N = 45) × 100%.

AC C

a

Median

M AN U

Bulk components -3 OC (µg m ) -3 EC (µg m ) -3 WSOC (µg m ) WSOC/OC (%) MEOC/OC (%) WSOC absorption -1 Abs365,w (Mm ) 2 -1 MAE365,w (m gC ) Åw MEOC absorption -1 Abs365,m (Mm ) 2 -1 MAE365,m (m gC ) Åm Abs365,w/Abs365,m MAE365,w/MAE365,m

Mean

1

b

ACCEPTED MANUSCRIPT

Table 2. Speciated organic compounds (ng m-3) in PM2.5. Std

Min

Max

% of Missing values

0.018 0.0068 0.057 0.0082

0.0073 0.0048 0.059 0.0056

0.027 0.0092 0.042 0.0090

0.0007 0.0004 0.0060 0.0010

0.12 0.060 0.16 0.046

11.1 2.22 22.2 4.44

1.59 3.23

1.54 2.45

0.96 2.38

0.12 0.069

3.90 8.56

0.00 0.00

1.17 1.69 2.66 0.66 2.20

0.98 1.55 2.25 0.60 1.96

1.20 1.25 2.09 0.50 1.67

0.027 0.074 0.086 0.027 0.029

7.68 4.13 8.80 1.85 6.39

0.00 0.00 0.00 0.00 0.00

14.8 4.11 30.9 19.5 4.06 4.30 3.80 3.79 9.25

SC

M AN U

8.71 40.3 96.8

RI PT

Median

5.51 31.2 70.1

8.22 39.7 97.1

0.40 2.53 7.80

45.3 177 438

4.44 4.44 4.44

10.7 2.88 29.7 15.4 3.08 3.88 3.18 3.07 9.09

12.5 3.10 20.3 14.7 5.03 3.18 2.62 2.41 5.40

1.97 0.62 3.11 1.31 0.23 0.38 0.38 0.34 1.47

46.7 10.6 73.1 48.9 31.9 11.3 10.1 8.85 23.3

6.67 8.89 4.44 4.44 4.44 26.7 6.67 20.0 6.67

EP

Quantified using authentic standards; b quantified as 2-methyl-4-nitrophenol; c quantified as 2-methyl-4-nitroresorcinol; d quantified as camphor sulfonic acid; e quantified as cis-ketopinic acid.

AC C

a

Mean

TE D

Nitroaromatic compounds (NACs) a C6H5NO3 (4-Nitrophenol) b C7H7NO3 a C6H5NO4 (4-Nitrocatechol) c C7H7NO4 d Isoprene sulfate ester (iOS) C2H4O6S C5H12O7S d Monoterpene sulfate esters (mOS) C10H18O5S C10H16O7S C10H17NO7S C10H17NO8S C10H17NO10S e Isoprene SOA tracers 2-Methylglyceric acid 2-Methylthreitol 2-Methylerythritol e Monoterpene SOA tracers 3-Acetyl pentanedioic acid 3-Acetyl hexanedioic acid 3-Methyl-1,2,3-butanetricarboxylic acid 3-Hydroxyglutaric acid 2-Hydroxy-4-isopropyladipic acid 3-Hydroxy-4,4-dimethylglutaric acid Pinic acid Pinonic acid a Levoglucosan

2

ACCEPTED MANUSCRIPT

Figure Captions Fig. 1. Median factor profiles for the 4-factor solution. The whiskers represent the variability in the factor profile derived from the bootstrapped PMF solutions (one standard deviation).

RI PT

Fig. 2. Temporal variations in factor contributions to Abs365,m derived from the 4-factor PMF solution.

AC C

EP

TE D

M AN U

SC

Fig. 3. Correlation contour plot of the Pearson’s correlation coefficient (r) between the optical and chemical measurements of organic aerosol. Compounds are grouped by class.

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Figure 1

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Figure 2

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Figure 3

ACCEPTED MANUSCRIPT

Highlights

> BrC absorption in summer at RTP, NC is similar to other Southeastern US locations. > Less than 1% of BrC absorption is attributed to identified nitroaromatic compounds.

RI PT

> Biomass burning is not the dominant source for BrC absorption in summer at RTP, NC.

AC C

EP

TE D

M AN U

SC

> Biogenic secondary organic aerosol formation is a major BrC source in this work.