Two-Dimensional Offline Chromatographic Fractionation for the

Subscriber access provided by University of Newcastle, Australia

Article

Two-dimensional offline chromatographic fractionation for the characterization of humic-like substances in atmospheric aerosol particles Tobias Spranger, Dominik van Pinxteren, and Hartmut Herrmann Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 23 Mar 2017 Downloaded from http://pubs.acs.org on March 24, 2017

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

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

Page 1 of 34

Environmental Science & Technology

1

Two-dimensional offline chromatographic

2

fractionation for the characterization of humic-like

3

substances in atmospheric aerosol particles

4

Tobias Spranger, Dominik van Pinxteren and Hartmut Herrmann*

5

Leibniz-Institut für Troposphärenforschung (TROPOS), Permoserstr. 15, 04318 Leipzig,

6

Germany

7

8

Organic carbon in atmospheric particles comprises a large fraction of chromatographically

9

unresolved compounds, often referred to as humic-like substances (HULIS), which influence

10

particle properties and impacts on climate, human health and ecosystems. To better understand

11

its composition, a two-dimensional (2D) offline method combining size-exclusion (SEC) and

12

reversed-phase liquid chromatography (RP-HPLC) using a new spiked gradient profile is

13

presented. It separates HULIS into 55 fractions of different size and polarity, with estimated

14

ranges of molecular weight and octanol/water partitioning coefficient (log P) from 160–900

15

g/mol and 0.2–3.3, respectively. The distribution of HULIS within the 2D size vs. polarity space

16

is illustrated with heat maps of UV absorption at 254 nm. It is found to strongly differ in a small

17

example set of samples from a background site near Leipzig, Germany. In winter, most intense

18

signals were obtained for largest molecules (>520 g/mol) with low polarity (log P ~ 1.9), while

ACS Paragon Plus Environment

1


Page 2 of 34

19

in summer smaller (225 – 330 g/mol) and more polar (log P ~ 0.55) molecules dominate The

20

method reveals such differences in HULIS composition in a more detailed manner than

21

previously possible and can therefore help to better elucidate the sources of HULIS in different

22

seasons or at different sites. Analyzing Suwannee river fulvic acid as a common HULIS

23

surrogate shows a similar polarity range, but clearly larger sizes than atmospheric HULIS.

24 25

Introduction

26

The atmospheric organic aerosol has been a topic of intense research over the past 15 years,

27

because aerosol particles contain a large fraction of organic carbon (OC) besides from inorganic

28

ions, elemental carbon (EC) and silicates. The organic fraction can contribute up to 70 % of the

29

total particle mass1 and therefore alters microphysical particle properties like hygroscopicity2-4,

30

surface tension5 and the ability of particles to serve as cloud condensation nuclei (CCN

31

activity).4, 6, 7 Thus OC plays an important role for the formation of clouds and the earth radiative

32

budget.8 Moreover, organic particle constituents are expected to be involved in a wide variety of

33

human health issues9, 10 and are critical because of their input into ecosystems.8

34

Despite its importance for humans and environment only a small fraction (5 - 30 %) of OC has

35

been identified on a molecular level11, mainly due to its high complexity with thousands of

36

different substances.12, 13 Typically, OC is dominated by a group of substances often referred to

37

as humic-like substances (HULIS) with a contribution of 20 - 80 % to the water soluble organic

38

carbon (WSOC) in atmospheric aerosol particles.14 HULIS are operationally defined by their

39

extraction method from aerosol particles. Currently, different solid phase extraction (SPE)

40

methods are applied, leading to differences in the chemical composition of extracted HULIS.15-20


2

Page 3 of 34


41

The term HULIS originally derived from a proposed similarity to humic and fulvic substances

42

from terrestrial systems21, but several studies have shown significant differences to those with

43

regard to (i) molecular size22-25, (ii) aromaticity25-27, (iii) elemental composition28 and (iv) CCN

44

activity.2, 6 HULIS can be found in the most different atmospheric environments, such as rural25,

45

29, 30

46

be most important source of HULIS, as the highest concentration can be measured there14, 30, 35,

47

36

48

sources are discussed in the literature.40 While newer analytical techniques like ultra-high-

49

resolution mass spectrometry (UHRMS) help to understand the chemical composition better, the

50

high complexity of HULIS still remains a major problem.13, 41

, urban30-32, marine32, high alpine28, 33 and tropical rainforest.3, 34 Biomass burning seems to

, but also the secondary formation from volatile organic carbon37-39 as well as potential marine

51

Thus, there is a strong need for chromatographic techniques to at least fractionate the complex

52

mixture to get a better understanding of its composition. One-dimensional reversed-phase liquid

53

chromatography (RP-HPLC) with a linear gradient, however, leads to unresolved broad bands

54

with only some individual peaks on top both for HULIS and Suwannee river fulvic acid (SRFA),

55

a fulvic acid mixture commonly used as a HULIS surrogate material.42,

56

distinct features in the chromatographic signals of humic substances, Hutta et al. proposed a

57

stepwise gradient profile demonstrating a separation of terrestrial humic substances into ten

58

fractions,42, 43 This method was also applied to a NaOH-extract of aerosol particles, leading to a

59

lower number of fractions with only low signal intensities, however. A different

60

chromatographic technique commonly applied to complex mixtures of environmental samples is

61

size-exclusion chromatography (SEC). Even though in SEC humic substances often resolve into

62

one or two broad peaks only, fractions with different average molecular weight could still be

63

extracted from these separations.44-47 Three SEC fractions were reported for SRFA, when using

43

To induce more


3


Page 4 of 34

64

an appropriate mobile phase.23, 31, 48 In studies of atmospheric fog or particle extracts, SEC also

65

lead to at least three fractions.31, 48 However, inferring size information of the typically rather

66

small atmospheric organic compounds ( 25 min) was weakened. Very high

164

amounts of MeOH (more than 30 %) deteriorated the separation. 20% MeOH was thus chosen as

165

the optimal mixing ratio, consistent with recommendations by the column manufacturer. The

166

final mobile phase conditions lead to five partially resolved fractions for all tested filters with

167

only small differences in their retention times (RSD 0.7-1.2 %) regardless of the intensity of UV

168

absorption. Even under optimized conditions a baseline separation of individual fraction cannot

169

be expected, because HULIS are known to be a very complex mixture of mainly small molecules

170

(< 1000 g/mol) and thus only a part of the columns dynamic range is effectively used for the

171

separation (roughly 30%).

172 173

Characterization of the SEC fractions.

174

To characterize the five SEC-fractions, UV-Vis and ESI-Time-of-flight (ToF)-MS

175

measurements were performed. The UV-Vis spectra were measured during the 1st-dimension

176

separation with the use of the DAD in a range of 190 nm-500 nm. The absorption maxima

177

(Figure 2) are between 204-210 nm with a steady decay of the signal into the visible light range,

178

similar to previous literature results.15, 17, 20, 26 Atmospheric organic particulate material with an


8

Page 9 of 34


179

absorption in the near-UV (300-400 nm) and visible light range (>400 nm) is also associated

180

with the term “brown carbon” (BrC) and can have an impact on the radiative forcing of the

181

atmosphere61. The obtained HULIS spectra thus highlight a linkage between HULIS and BrC.

182

The coefficient E2 / E3 (absorption at 250 nm/ absorption at 365 nm) is a parameter indicating

183

relative molecular sizes for aromatic moieties containing molecules in humic/ fulvic acids, and

184

dissolved organic matter in river and lakewater.62-65 As larger aromatic molecules have on

185

average a stronger absorption at 365 nm than smaller ones due to larger π-systems and stronger

186

π-π*-excitation, the E2/E3-value is smaller for larger molecules. HULIS are expected to contain

187

aromatic structures as well, which is why we applied this to study trends in average molecular

188

size between the SEC fractions. The averaged E2/E3-values from all filter measurements are

189

presented in Table 1 and show a clear (nearly) linear increase for the fractions 1 to 5,

190

corroborating a decreasing average molecular size with increasing retention time as expected. In

191

the ESI-ToF-MS spectra (Figure S2), a huge variety of signals was observed in all five fractions.

192

Their average mass can be calculated with different methods66, here we use the number averaged

193

molar mass MWn and the mass averaged molar mass MWw as defined in eqs. (1) and (2).

194

(1)

=

∑( )

∑( )

195

(2)

=

∑( )

∑( )

196

Mn is an individual m/z value and I the intensity of the corresponding signal. These parameters

197

(MWn and MWw) likely do not accurately reflect the true average molar masses due to different

198

ionization and transmission efficiencies of individual substances in ESI-MS, . The observed mass

199

ranges and distributions are also heavily influenced by the instrument settings for ionization and

200

transmission. Therefore, the average masses and also the mass spectra shown in Figure S2 only


9


Page 10 of 34

201

serve as relative comparisons between the SEC fractions and should not be used as a comparison

202

with other measurements in the literature. Both values show a clear decrease in the average

203

molar mass for later eluting fractions in both ionization modes (Table 1). Even though SEC

204

retention is determined by hydrodynamic radii and these are not necessarily strictly correlated

205

with molecular masses for chemically complex mixtures like HULIS, this result still indicates

206

broadly decreasing molecular sizes in the 5 SEC fractions. To characterize the SEC fractions

207

further and to investigate the correlation between molar mass and retention time for a complex

208

mixture we performed a calibration with a variety of standard substances, which are listed in

209

Table S3 and are expected to have at least some similarity to HULIS constituents in terms of

210

molecular size and chemical functionalities. This approach is considered superior to the usually

211

performed SEC calibration using polymeric standard substances (like PSS, PEG, PMA) since it

212

better represents the complexity of atmospheric organic aerosol constituents and also allows for

213

more data points in the relevant mass range between 100-1000 g/mol. The calibration curve

214

(Figure S3) shows a linear correlation between the logarithmic molar mass and the retention time

215

(with R2 = 0.926). Overall, the different characterization approaches clearly show, that molecular

216

size is the main separation mechanism for the proposed SEC method, despite the large chemical

217

inhomogeneity of HULIS.

218 219

RP-HPLC development.

220

Due to its complex nature, resolving all individual constituents of the HULIS mixture with RP-

221

HPLC is not possible. Using a typical linear gradient leads to a broad unresolved band with only

222

some superimposed individual peaks, as shown in Figure 3 A. For humic substances and a NaOH

223

extract of aerosol particles it was shown that using a stepwise gradient (with increasing content


10

Page 11 of 34


224

of DMF in the organic phase) leads to a somewhat improved fractionation.42 Using a similar

225

gradient with ACN or MeOH as organic solvent (due to the higher polarity of atmospheric

226

samples compared to soil samples) a comparable fractionation for atmospheric HULIS and

227

SRFA was observed as shown in Figure 3 B. Both solvents gave similar results, but ACN was

228

preferred due to the weaker background signal and the reduced backpressure in the gradient

229

steps. While the stepwise gradient is an improvement over the standard linear gradient with

230

respect to inducing distinct features in the UV signal, the purity of the fractions was just around

231

70-80 % for a 5-step gradient and even worse for a 10-step gradient. The purity was determined

232

by extracting the selected fraction, reinjecting it into the HPLC and measuring its distribution

233

over all fractions. A purity of 100 % would result if UV absorption was measured only in the

234

selected fraction in the second run with no overlap to neighboring fractions. To improve the

235

purity of the fractions, several variants of a new and unique gradient profile were tested. The

236

profile consists of repetitively increasing, decreasing, and constant organic eluent fractions,

237

which were varied in terms of their slopes and lengths. The final gradient profile is shown in

238

Figure 3 C and lead to a highly reproducible separation into 11 fractions with RSDs of start/stop

239

retention times of individual fractions < 0.1 % and RSDs of the peak areas < 0.9 % and a fraction

240

purity between 95 – 99 %, tested for a selection of samples and fractions. This new gradient

241

profile on its own, as a 1D-experiment, yields chromatographic features indicating even small

242

differences in the distribution of hydrophobicity within a HULIS sample, which could be easily

243

overlooked with the stepwise or linear gradient profiles. In addition, it is very well suited for

244

fraction collection in multidimensional approaches due to the well-defined fraction peaks. To get

245

a better understanding of the range of substances expected in the different fractions, a variety of

246

substances with different polarities (Table S3) were tested for the fraction they would end up in.


11


Page 12 of 34

247

Compound polarities were characterized by the octanol-water partitioning coefficient P or log P.

248

The log P values were calculated using ALGOPS 2.167 and taken as the average from the

249

different models in ALGOPS with its corresponding standard deviation. For carboxylic acids, log

250

P values were calculated from the non-dissociated form as it should be the dominating form in

251

the acidified eluent. The measurements show a linear correlation of log P with the fraction

252

number (R2 = 0.784; Figure S4), very similar to the linear correlation of log P with retention time

253

obtained from one tested linear gradient (R2 = 0.794, not shown). The retention times from linear

254

gradient run also correlate strongly with the retention times from a spiked gradient run

255

(R2 = 0.957). Both results indicate that the spiked gradient has the same separation mechanism as

256

a traditional linear gradient. The calibration was therefore used to determine the log P ranges of

257

the individual fractions, as shown below.

258 259

2D-Approach.

260

To increase the number of fractions HULIS and other samples can be separated into, the

261

optimized SEC fractionation was combined with the spiked gradient RP-HPLC in a 2D-offline

262

method. Therefore, the five SEC fractions of multiple sample injections were collected,

263

concentrated as described in the experimental section, and injected into the RP-HPLC, leading to

264

a total of 55 final fractions.

265

As a first application, SRFA was analyzed with the new 2D-method. Even though SRFA did not

266

show clear peaks in the SEC we separated into 5 fractions within the 1st dimension, splitting the

267

main peak at different retention times as shown in Figure 4 A. The results of the fractionation are

268

visualized in a heat map constructed from the SEC and RP-HPLC separations on x- and y-axis,

269

respectively, and the fraction of total UV absorption at 254 nm on a color scale, indicating the


12

Page 13 of 34


270

signal distribution across the 55 individual fractions. To estimate physical properties from the

271

retention times in the two dimensions, we used the above-described calibrations with standard

272

compounds. This way the height of each rectangle in the heat map represents a constant log P

273

range of 0.31, while the width represents different ranges of molecular weight (MW). It has to be

274

noted that the scale direction of the SEC axis has been reversed to give increasing MW along the

275

axis. In Figure 4 A, the first fraction thus includes molecules between approx. 320 – 450 g/mol,

276

while the molecular ranges for the following fractions are approx. 450 – 550, 550 – 650, 650 –

277

750, and 750 – 1000 g/mol. The 2D heat map shows the global maximum of the UV-absorption

278

(6.2 % of the total absorption) for molecules between 550 – 650 g/mol with a log P of ~ 1.44.

279

Molecules within the same size range but with slightly lower polarity have a similar fractional

280

absorption of 6.0 %. The 3rd most intense peak derives from larger molecules (650 – 750 g/mol)

281

with lower polarity (log P ~ 2.06) with a fractional absorption of 5.8 %. In general, there is a

282

clear trend of increasing polarity with decreasing molecular size for SRFA.

283

The obtained results for the size range of SRFA constituents are comparable to data from the

284

literature. Stenson et al.68 measured most signals between 350 – 1200 m/z with an ESI-Fourier

285

transform ion cyclotron resonance MS (FTICR-MS) and the highest intensity around 500 m/z.

286

This maximum is lower than the one in our measurement, which might be related to a stronger

287

UV-absorption of larger molecules. In addition, ESI-MS intensities of individual signals are

288

prone to severe interferences from the multitude of analytes and the obtained mass spectra likely

289

do not fully represent the true composition.69 For a better comparison with atmospheric HULIS

290

samples, the 2D analysis of SRFA was repeated with SEC fraction limits identical to those

291

typically applied to atmospheric samples, while the HPLC fractions remained unchanged (Figure

292

4 B). For these fraction limits, the majority of the absorption derives from only the first SEC


13


Page 14 of 34

293

fraction for the largest molecules, which is in contrast to the HULIS samples discussed in the

294

following, where absorption is distributed across all five fractions.

295 296 297

Application to atmospheric samples.

298

To demonstrate the potential of the developed 2D approach for ambient HULIS samples, we

299

analyzed four filter samples from the Melpitz field site near Leipzig, Germany and compared the

300

results among each other and with SRFA. Melpitz is a mid-European rural background station

301

with strong influences from continental polluted air masses for eastern wind directions

302

(especially in winter) and mixed maritime-continental air masses for western wind directions.70

303

To study the variability of HULIS composition under different conditions, filters from summer

304

and winter with eastern and western air mass inflow were analyzed (Table S1). For the

305

atmospheric implication of these analyses it would helpful to have information about the

306

concentrations in each of the 55 fractions, additionally to the fractional absorption. For an

307

estimation of concentration from absorption, the UV-absorption of the aqueous filter extracts,

308

defined as total peak area from the SEC measurements, was correlated with the WSOC

309

concentrations measured separately by TOC analysis as described above. The data show a strong

310

linear correlation (R2 = 0.901, Figure S5) for the four filter samples, indicating a good agreement

311

between UV-absorption at 254 nm and the WSOC concentration. With the assumption that the

312

correlation is identical for every fraction, the fractional UV-absorption could be regarded as a

313

measure for the distribution of WSOC within a sample. For a larger number of samples,

314

however, it is likely that the observed correlation will be different due to different chemical

315

compositions, depending on the sources of the sampled particles. Additionally, it is also likely


14

Page 15 of 34


316

that the UV-detector response differs within one sample for the different fractions, especially for

317

the SEC. Larger, more aromatic substances should have a stronger absorption than smaller ones

318

and therefore, the observed correlation of total absorption with WSOC should be taken with

319

caution and the fractional absorption can just be a rough estimate of the distribution of organic

320

mass in the two-dimensional size versus polarity space.

321

The 2D heat maps of four analyzed ambient samples are shown in Figure 5. A comparison of

322

HULIS (Figure 5) and SRFA (Figure 4) 2D heat maps shows a very similar distribution of the

323

polarity for both sample types, but large differences in the size distribution. For SRFA 80 % of

324

the fractional absorption derives from molecules larger than 520 g/mol. Even for the most similar

325

ambient case WW, this value is only 37 %. Molecules smaller than 450 g/mol are responsible for

326

9 % of the UV-absorption only for SRFA, but 44 – 78 % for the studied HULIS samples, making

327

SRFA only very roughly suited as surrogate standard for ambient HULIS.

328

The analyzed ambient samples also reveal clear differences between the HULIS extracts. For

329

the winter samples at least two maxima can be identified, the global one for the largest molecules

330

(>520 g/mol) with medium polarity (log P of 1.6-2.2; two fractions with 5.1% of total UV-

331

absorption each) and one local maximum (4 % fractional absorption) at medium sizes (320-

332

450 g/mol) and slightly higher polarity (log P ~ 1.75). In the winter west sample (WW), the first

333

and second maximum are slightly shifted to higher polarity compared to the winter east samples

334

(WE), with a fractional absorption for the global maximum of 6.1 % and 3.5 % for the 2nd

335

maximum. Additionally, there is a third weak maximum at medium size and high polarity (log

336

P ~ 0.5) with a fractional absorption of 3.5 %. For the summer samples, more absorption arises

337

in the smaller and more polar fractions. This trend is most distinct for the summer west sample

338

(SW), where the absorption of the fraction with the largest molecules is very small. Only 6 % of


15


Page 16 of 34

339

the total absorption arises from this SEC fraction, while the absorption from the largest

340

molecules of the summer east sample (SE) is 24 % and the average of both winter samples is

341

32 %. SW has a very sharp and intense global maximum (6.1 %) for molecules between 229 –

342

337 g/mol and a log P ~ 0.5. This fraction is also present in SE, but not as a maximum and only

343

with a fractional UV-absorption of 2.7 %. SE has its global maximum (4.6 %) for medium sized

344

molecules and a log P around 1.1 and the 2nd maximum (4.1 %) in the same fraction as the global

345

maximum of WW. These four samples already show clear differences in the composition of

346

HULIS depending on the season and the air mass inflow. The winter HULIS seems to consist of

347

larger and less polar molecules than the summer HULIS, which might be related to emissions

348

from biomass burning or other combustion processes. The smaller and more polar molecules are

349

most likely linked to secondary formation from volatile organic precursor compounds.

350

Comparing SW to WE, around 70 % of the total UV-absorption is relocated within the 2D size

351

vs. polarity space, highlighting the large differences in the composition of HULIS that can occur

352

even at one same sampling site in different air mass regimes. Moreover, the developed 2D

353

method is also able to identify and illustrate more subtle differences within the four regimes

354

themselves (compare Figure 5 with Figure S6). The most distinct differences can be seen for SW

355

and SW-2, where the SEC fraction with largest molecules (>520 g/mol) is responsible for 6%

356

and 25% of total signal intensity, respectively. This demonstrates the potential of the method to

357

resolve chemical differences between different HULIS compositions. More detailed studies on a

358

larger set of ambient samples will be done and can be expected to yield further interesting

359

insights into the chemical composition of HULIS from different atmospheric regimes. It is also

360

highly likely that the different compositions lead to different aerosol particle properties like

361

hygroscopicity, CCN activation, interaction with radiation, particle toxicity, and ecosystem


16

Page 17 of 34


362

impacts. The developed 2D-LC fractionation will also enable detailed downstream analytical

363

studies of the individual fractions and with regard to the different absorption properties, new

364

possibilities for future studies of light absorbing BrC in atmospheric particles.

365 366 367

FIGURES

368 Figure 1. SEC chromatograms of the winter east HULIS sample with different concentrations of

370

ammonium hydrogen carbonate.

normalized absorbance

369

371 372

Figure 2. UV-spectra of all five fractions of the winter east HULIS sample, normalized to

373

maximum of each fraction.


17


Page 18 of 34

A

B

C

374 375

Figure 3. RP-HPLC chromatograms of the winter east HULIS sample with a linear (A), stepwise

376

(B) and the new spiked gradient (C).


18

Page 19 of 34


SRFA

A OH O

3

OH

O H

2.49 H

H

Fractional UV−absorption

log P

O

2

O

0.06

OH

0.04 O

1.24

CH3

0.02

OH

1

O

OH

O

0.69 OH OH O

0 200

300

400

500 600 700800 1000

MW / g/mol

25.5 29.5

26.6

22.9 24.5

21.9 20.9 19.9

22.9 22.0

18.5

Time SEC / min

B

log P

3


2

0.10 0.05 1

0 200

377

300

400

500 600 700800 1000

MW / g/mol

378

Figure 4. 2D heat maps of molecular size, polarity and fractional UV absorption for SRFA with

379

two different fraction limits (in minutes) for the SEC and the corresponding SEC chromatogram

380

in the middle: A optimized fraction limits for SRFA; B fraction limits set as for an average

381

atmospheric sample.


19


WW

Page 20 of 34

WE [WSOC] = 4.25 µg/m3

[WSOC] = 6.87 µg/m3 3

Fractional UV−absorption 0.06

2

0.04

log P

log P

3

Fractional UV−absorption 0.05 0.04 0.03 0.02 0.01

2

0.02 1

1

0

0 200

300

400

500 600 700 800

200

300

MW / g/mol

400

500 600 700 800

MW / g/mol

SW

SE [WSOC] = 3.11 µg/m3

[WSOC] = 3.00 µg/m3 3

Fractional UV−absorption 0.06

2

0.04

log P

log P

3


2

0.04 0.03 0.02

0.02 1

0

0 200

382

0.01 1

300

400

500 600 700 800

200

MW / g/mol

300

400

500 600 700 800

MW / g/mol

383

Figure 5. 2D heat maps of WW, WE, SW and SE. The color scale is set to the corresponding

384

maximum value of each 2D chromatogram.

385


20

Page 21 of 34


386

TABLES

387

Table 1. Characterization of the SEC fractions of the winter east HULIS sample: Average time

388

window, absorption coefficient (E2/E3: 254 nm/365 nm) and the average molecular weights,

389

calculated with different approaches from number (MWn) and mass averaged (MWw) negative

390

ESI mass spectra as well as from a calibration with standard compounds. See text for details. Fraction

Average time E2/E3 window

MWn (negative mode)

MWw (negative mode)

MWcalibration at taverage

1

19.6 – 22.5

3.80 ± 0.34

775.0

806.7

681.6

2

22.5 – 23.4

4.58 ± 0.48

713.2

749.2

491.2

3

23.4 – 25.3

5.93 ± 0.47

675.0

726.0

388.3

4

25.3 – 27.4

6.70 ± 0.73

655.7

703.0

276.4

5

27.4 – 29.5

7.28 ± 0.80

620.1

671.2

192.4

391 392 393

ASSOCIATED CONTENT

394

Supporting Information

395

The Supporting Information is available free of charge on the ACS Publications website.

396

Studied filter samples with sampling date, wind direction, OC and WSOC measurements (Table

397

S1); SEC chromatograms with different mixing ratios of the mobile phase (Figure S1); Table of

398

spiked gradient profile (Table S2); List of all substances used for the calibration of both

399

separation dimensions with the corresponding measured data (Table S3); LC-ESI-ToF-MS

400

spectra of the five SEC fractions from the winter east HULIS sample (Figure S2); Calibration


21


Page 22 of 34

401

curve for the SEC (Figure S3); Calibration curve for the RP-HPLC (Figure S4); Correlation plot

402

of the measured UV-absorption and TOC measurements (Figure S5) (PDF).

403 404

AUTHOR INFORMATION

405

Corresponding Author

406

* Phone: 49 341 2717 7024. Fax: 49 341 2717 99 7024. E-mail: [email protected].

407

Author Contributions

408

The manuscript was written through contributions of all authors and all authors have given

409

approval to the final version of the manuscript

410

Notes

411

The authors declare no competing financial interest.

412

ACKNOWLEDGMENT

413

This work was funded by the German Research Foundation (DFG) in the project HuCar as PI

414

1102/4-1 and HE 3086/28-1. The authors would also like to thank Gerald Spindler, Anett Dietze,

415

and Anke Rödger for providing the filter samples and additional data.

416

REFERENCES

417

1.

Kanakidou, M.; Seinfeld, J. H.; Pandis, S. N.; Barnes, I.; Dentener, F. J.; Facchini, M. C.;

418

Van Dingenen, R.; Ervens, B.; Nenes, A.; Nielsen, C. J.; Swietlicki, E.; Putaud, J. P.; Balkanski,

419

Y.; Fuzzi, S.; Horth, J.; Moortgat, G. K.; Winterhalter, R.; Myhre, C. E. L.; Tsigaridis, K.;

420

Vignati, E.; Stephanou, E. G.; Wilson, J., Organic aerosol and global climate modelling: a

421

review. Atmos Chem Phys 2005, 5, 1053-1123.


22

Page 23 of 34

422


2.

Dinar, E.; Taraniuk, I.; Graber, E. R.; Anttila, T.; Mentel, T. F.; Rudich, Y., Hygroscopic

423

growth of atmospheric and model humic-like substances. J Geophys Res-Atmos 2007, 112,

424

(D05211).

425

3.

Fors, E. O.; Rissler, J.; Massling, A.; Svenningsson, B.; Andreae, M. O.; Dusek, U.;

426

Frank, G. P.; Hoffer, A.; Bilde, M.; Kiss, G.; Janitsek, S.; Henning, S.; Facchini, M. C.;

427

Decesari, S.; Swietlicki, E., Hygroscopic properties of Amazonian biomass burning and

428

European background HULIS and investigation of their effects on surface tension with two

429

models linking H-TDMA to CCNC data. Atmos Chem Phys 2010, 10, (12), 5625-5639.

430

4.

Kristensen, T. B.; Wex, H.; Nekat, B.; Nojgaard, J. K.; van Pinxteren, D.; Lowenthal, D.

431

H.; Mazzoleni, L. R.; Dieckmann, K.; Koch, C. B.; Mentel, T. F.; Herrmann, H.; Hallar, A. G.;

432

Stratmann, F.; Bilde, M., Hygroscopic growth and CCN activity of HULIS from different

433

environments. J Geophys Res-Atmos 2012, 117, (D22203).

434

5.

Salma, I.; Ocskay, R.; Varga, I.; Maenhaut, W., Surface tension of atmospheric humic-

435

like substances in connection with relaxation, dilution, and solution pH. J Geophys Res-Atmos

436

2006, 111, (D23205).

437

6.

Dinar, E.; Taraniuk, I.; Graber, E. R.; Katsman, S.; Moise, T.; Anttila, T.; Mentel, T. F.;

438

Rudich, Y., Cloud Condensation Nuclei properties of model and atmospheric HULIS. Atmos

439

Chem Phys 2006, 6, 2465-2481.

440

7.

Padro, L. T.; Tkacik, D.; Lathem, T.; Hennigan, C. J.; Sullivan, A. P.; Weber, R. J.;

441

Huey, L. G.; Nenes, A., Investigation of cloud condensation nuclei properties and droplet growth

442

kinetics of the water-soluble aerosol fraction in Mexico City. J Geophys Res-Atmos 2010, 115,

443

(D09204).


23


444

8.

Page 24 of 34

IPCC, Summary for Policymakers. In Climate Change 2013: The Physical Science Basis.

445

Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel

446

on Climate Change, Stocker, T. F.; Qin, D.; Plattner, G.-K.; Tignor, M.; Allen, S. K.; Boschung,

447

J.; Nauels, A.; Xia, Y.; Bex, V.; Midgley, P. M., Eds. Cambridge University Press: Cambridge,

448

United Kingdom and New York, NY, USA, 2013; pp 1–30.

449 450

9.

Mauderly, J. L.; Chow, J. C., Health effects of organic aerosols. Inhal Toxicol 2008, 20,

(3), 257-288.

451

10. Baltensperger, U.; Dommen, J.; Alfarra, R.; Duplissy, J.; Gaeggeler, K.; Metzger, A.;

452

Facchini, M. C.; Decesari, S.; Finessi, E.; Reinnig, C.; Schott, M.; Warnke, J.; Hoffmann, T.;

453

Klatzer, B.; Puxbaum, H.; Geiser, M.; Savi, M.; Lang, D.; Kalberer, M.; Geiser, T., Combined

454

determination of the chemical composition and of health effects of secondary organic aerosols:

455

The POLYSOA project. J Aerosol Med Pulm D 2008, 21, (1), 145-154.

456

11. Chow, J. C.; Doraiswamy, P.; Watson, J. G.; Antony-Chen, L. W.; Ho, S. S. H.;

457

Sodeman, D. A., Advances in integrated and continuous measurements for particle mass and

458

chemical, composition. J Air Waste Manage 2008, 58, (2), 141-163.

459

12. Lin, P.; Rincon, A. G.; Kalberer, M.; Yu, J. Z., Elemental Composition of HULIS in the

460

Pearl River Delta Region, China: Results Inferred from Positive and Negative Electrospray High

461

Resolution Mass Spectrometric Data. Environ Sci Technol 2012, 46, (14), 7454-7462.

462

13. Dzepina, K.; Mazzoleni, C.; Fialho, P.; China, S.; Zhang, B.; Owen, R. C.; Helmig, D.;

463

Hueber, J.; Kumar, S.; Perlinger, J. A.; Kramer, L. J.; Dziobak, M. P.; Ampadu, M. T.; Olsen, S.;

464

Wuebbles, D. J.; Mazzoleni, L. R., Molecular characterization of free tropospheric aerosol


24

Page 25 of 34


465

collected at the Pico Mountain Observatory: a case study with a long-range transported biomass

466

burning plume. Atmos Chem Phys 2015, 15, (9), 5047-5068.

467 468 469 470

14. Zheng, G. J.; He, K. B.; Duan, F. K.; Cheng, Y.; Ma, Y. L., Measurement of humic-like substances in aerosols: A review. Environ Pollut 2013, 181, 301-314. 15. Varga, B.; Kiss, G.; Ganszky, I.; Gelencser, A.; Krivacsy, Z., Isolation of water-soluble organic matter from atmospheric aerosol. Talanta 2001, 55, (3), 561-572.

471

16. Decesari, S.; Facchini, M. C.; Fuzzi, S.; Tagliavini, E., Characterization of water-soluble

472

organic compounds in atmospheric aerosol: A new approach. J Geophys Res-Atmos 2000, 105,

473

(D1), 1481-1489.

474

17. Baduel, C.; Voisin, D.; Jaffrezo, J. L., Comparison of analytical methods for Humic Like

475

Substances (HULIS) measurements in atmospheric particles. Atmos Chem Phys 2009, 9, (16),

476

5949-5962.

477

18. Duarte, R. M. B. O.; Duarte, A. C., Application of non-ionic solid sorbents (XAD resins)

478

for the isolation and fractionation of water-soluble organic compounds from atmospheric

479

aerosols. J Atmos Chem 2005, 51, (1), 79-93.

480

19. Fan, X. J.; Song, J. Z.; Peng, P. A., Comparative study for separation of atmospheric

481

humic-like substance (HULIS) by ENVI-18, HLB, XAD-8 and DEAE sorbents: Elemental

482

composition, FT-IR, H-1 NMR and off-line thermochemolysis with tetramethylammonium

483

hydroxide (TMAH). Chemosphere 2013, 93, (9), 1710-1719.


25


Page 26 of 34

484

20. Fan, X. J.; Song, J. Z.; Peng, P. A., Comparison of isolation and quantification methods

485

to measure humic-like substances (HULIS) in atmospheric particles. Atmos Environ 2012, 60,

486

366-374.

487 488

21. Havers, N.; Burba, P.; Lambert, J.; Klockow, D., Spectroscopic characterization of humic-like substances in airborne particulate matter. J Atmos Chem 1998, 29, (1), 45-54.

489

22. Kiss, G.; Tombacz, E.; Varga, B.; Alsberg, T.; Persson, L., Estimation of the average

490

molecular weight of humic-like substances isolated from fine atmospheric aerosol. Atmos

491

Environ 2003, 37, (27), 3783-3794.

492

23. Reemtsma, T.; These, A., On-line coupling of size exclusion chromatography with

493

electrospray ionization-tandem mass spectrometry for the analysis of aquatic fulvic and humic

494

acids. Anal Chem 2003, 75, (6), 1500-1507.

495

24. These, A.; Reemtsma, T., Limitations of electrospray ionization of fulvic and humic acids

496

as visible from size exclusion chromatography with organic carbon and mass spectrometric

497

detection. Anal Chem 2003, 75, (22), 6275-6281.

498

25. Pavlovic, J.; Hopke, P. K., Chemical nature and molecular weight distribution of the

499

water-soluble fine and ultrafine PM fractions collected in a rural environment. Atmos Environ

500

2012, 59, 264-271.

501

26. Duarte, R. M. B. O.; Pio, C. A.; Duarte, A. C., Spectroscopic study of the water-soluble

502

organic matter isolated from atmospheric aerosols collected under different atmospheric

503

conditions. Anal Chim Acta 2005, 530, (1), 7-14.


26

Page 27 of 34


504

27. Duarte, R. M. B. O.; Silva, A. M. S.; Duarte, A. C., Two-Dimensional NMR Studies of

505

Water-Soluble Organic Matter in Atmospheric Aerosols. Environ Sci Technol 2008, 42, (22),

506

8224-8230.

507

28. Krivacsy, Z.; Gelencser, A.; Kiss, G.; Meszaros, E.; Molnar, A.; Hoffer, A.; Meszaros,

508

T.; Sarvari, Z.; Temesi, D.; Varga, B.; Baltensperger, U.; Nyeki, S.; Weingartner, E., Study on

509

the chemical character of water soluble organic compounds in fine atmospheric aerosol at the

510

Jungfraujoch. J Atmos Chem 2001, 39, (3), 235-259.

511

29. Feczko, T.; Puxbaum, H.; Kasper-Giebl, A.; Handler, M.; Limbeck, A.; Gelencser, A.;

512

Pio, C.; Preunkert, S.; Legrand, M., Determination of water and alkaline extractable atmospheric

513

humic-like substances with the TU Vienna HULIS analyzer in samples from six background

514

sites in Europe. J Geophys Res-Atmos 2007, 112, (D23s10).

515

30. Baduel, C.; Voisin, D.; Jaffrezo, J. L., Seasonal variations of concentrations and optical

516

properties of water soluble HULIS collected in urban environments. Atmos Chem Phys 2010, 10,

517

(9), 4085-4095.

518 519

31. Samburova, V.; Zenobi, R.; Kalberer, M., Characterization of high molecular weight compounds in urban atmospheric particles. Atmos Chem Phys 2005, 5, 2163-2170.

520

32. Krivacsy, Z.; Kiss, G.; Ceburnis, D.; Jennings, G.; Maenhaut, W.; Salma, I.; Shooter, D.,

521

Study of water-soluble atmospheric humic matter in urban and marine environments. Atmos Res

522

2008, 87, (1), 1-12.

523

33. Kristensen, T. B.; Du, L.; Nguyen, Q. T.; Nojgaard, J. K.; Koch, C. B.; Nielsen, O. F.;

524

Hallar, A. G.; Lowenthal, D. H.; Nekat, B.; van Pinxteren, D.; Herrmann, H.; Glasius, M.;


27


Page 28 of 34

525

Kjaergaard, H. G.; Bilde, M., Chemical properties of HULIS from three different environments.

526

J Atmos Chem 2015, 72, (1), 65-80.

527

34. Claeys, M.; Vermeylen, R.; Yasmeen, F.; Gomez-Gonzalez, Y.; Chi, X. G.; Maenhaut,

528

W.; Meszaros, T.; Salma, I., Chemical characterisation of humic-like substances from urban,

529

rural and tropical biomass burning environments using liquid chromatography with UV/vis

530

photodiode array detection and electrospray ionisation mass spectrometry. Environ Chem 2012,

531

9, (3), 273-284.

532

35. Lin, P.; Engling, G.; Yu, J. Z., Humic-like substances in fresh emissions of rice straw

533

burning and in ambient aerosols in the Pearl River Delta Region, China. Atmos Chem Phys 2010,

534

10, (14), 6487-6500.

535

36. Krivacsy, Z.; Hoffer, A.; Sarvari, Z.; Temesi, D.; Baltensperger, U.; Nyeki, S.;

536

Weingartner, E.; Kleefeld, S.; Jennings, S. G., Role of organic and black carbon in the chemical

537

composition of atmospheric aerosol at European background sites. Atmos Environ 2001, 35, (36),

538

6231-6244.

539

37. Vione, D.; Maurino, V.; Minero, C., Photosensitised humic-like substances (HULIS)

540

formation processes of atmospheric significance: a review. Environ Sci Pollut R 2014, 21, (20),

541

11614-11622.

542

38. Robinson, A. L.; Donahue, N. M.; Shrivastava, M. K.; Weitkamp, E. A.; Sage, A. M.;

543

Grieshop, A. P.; Lane, T. E.; Pierce, J. R.; Pandis, S. N., Rethinking organic aerosols:

544

Semivolatile emissions and photochemical aging. Science 2007, 315, (5816), 1259-1262.


28

Page 29 of 34


545

39. El Haddad, I.; Marchand, N.; Temime-Roussel, B.; Wortham, H.; Piot, C.; Besombes, J.

546

L.; Baduel, C.; Voisin, D.; Armengaud, A.; Jaffrezo, J. L., Insights into the secondary fraction of

547

the organic aerosol in a Mediterranean urban area: Marseille. Atmos Chem Phys 2011, 11, (5),

548

2059-2079.

549

40. Cavalli, F.; Facchini, M. C.; Decesari, S.; Mircea, M.; Emblico, L.; Fuzzi, S.; Ceburnis,

550

D.; Yoon, Y. J.; O'Dowd, C. D.; Putaud, J. P.; Dell'Acqua, A., Advances in characterization of

551

size-resolved organic matter in marine aerosol over the North Atlantic. J Geophys Res-Atmos

552

2004, 109, (D24215).

553

41. Nizkorodov, S. A.; Laskin, J.; Laskin, A., Molecular chemistry of organic aerosols

554

through the application of high resolution mass spectrometry. Phys Chem Chem Phys 2011, 13,

555

(9), 3612-3629.

556

42. Hutta, M.; Gora, R., Novel stepwise gradient reversed-phase liquid chromatography

557

separations of humic substances, air particulate humic-like substances and lignins. J Chromatogr

558

A 2003, 1012, (1), 67-79.

559

43. Gora, R.; Hutta, M., Reversed-phase liquid chromatographic characterization and

560

analysis of air particulates humic (-like) substances in presence of pollens. J Chromatogr A 2005,

561

1084, (1-2), 39-45.

562

44. Janos, P.; Zatrepalkova, I., High-performance size-exclusion chromatography of humic

563

substances on the hydroxyethyl methacrylate column. J Chromatogr A 2007, 1160, (1-2), 160-

564

165.


29


Page 30 of 34

565

45. Morgan, T. J.; Herod, A. A.; Brain, S. A.; Chambers, F. M.; Kandiyoti, R., Examination

566

of soil contaminated by coal-liquids by size exclusion chromatography in 1-methyl-2-

567

pyrrolidinone solution to evaluate interference from humic and fulvic acids and extracts from

568

peat. J Chromatogr A 2005, 1095, (1-2), 81-88.

569

46. Asakawa, D.; Iimura, Y.; Kiyota, T.; Yanagi, Y.; Fujitake, N., Molecular size

570

fractionation of soil humic acids using preparative high performance size-exclusion

571

chromatography. J Chromatogr A 2011, 1218, (37), 6448-6453.

572

47. Gora, R.; Hutta, M.; Roharik, P., Characterization and analysis of soil humic acids by off-

573

line combination of wide-pore octadecylsilica column reverse phase high performance liquid

574

chromatography with narrow bore column size-exclusion chromatography and fluorescence

575

detection. J Chromatogr A 2012, 1220, 44-49.

576

48. Wang, Y. L.; Chiu, C. A.; Westerhoff, P.; Valsaraj, K. T.; Herckes, P., Characterization

577

of atmospheric organic matter using size-exclusion chromatography with inline organic carbon

578

detection. Atmos Environ 2013, 68, 326-332.

579

49. Andracchio, A.; Cavicchi, C.; Tonelli, D.; Zappoli, S., A new approach for the

580

fractionation of water-soluble organic carbon in atmospheric aerosols and cloud drops. Atmos

581

Environ 2002, 36, (32), 5097-5107.

582

50. Samburova, V.; Szidat, S.; Hueglin, C.; Fisseha, R.; Baltensperger, U.; Zenobi, R.;

583

Kalberer, M., Seasonal variation of high-molecular-weight compounds in the water-soluble

584

fraction of organic urban aerosols. J Geophys Res-Atmos 2005, 110, (D23210).


30

Page 31 of 34


585

51. Sullivan, A. P.; Weber, R. J., Chemical characterization of the ambient organic aerosol

586

soluble in water: 2. Isolation of acid, neutral, and basic fractions by modified size-exclusion

587

chromatography. J Geophys Res-Atmos 2006, 111, (D05315).

588 589

52. Jandera, P., Column selectivity for two-dimensional liquid chromatography. J Sep Sci 2006, 29, (12), 1763-1783.

590

53. Cavalli, F.; Viana, M.; Yttri, K. E.; Genberg, J.; Putaud, J. P., Toward a standardised

591

thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR

592

protocol. Atmos Meas Tech 2010, 3, (1), 79-89.

593

54. van Pinxteren, D.; Brueggemann, E.; Gnauk, T.; Iinuma, Y.; Mueller, K.; Nowak, A.;

594

Achtert, P.; Wiedensohler, A.; Herrmann, H., Size- and time-resolved chemical particle

595

characterization during CAREBeijing-2006: Different pollution regimes and diurnal profiles. J

596

Geophys Res-Atmos 2009, 114, (D00g09).

597

55. Lee, A. K. Y.; Zhao, R.; Li, R.; Liggio, J.; Li, S. M.; Abbatt, J. P. D., Formation of Light

598

Absorbing Organo-Nitrogen Species from Evaporation of Droplets Containing Glyoxal and

599

Ammonium Sulfate. Environ Sci Technol 2013, 47, (22), 12819-12826.

600 601

56. Nguyen, T. B.; Laskin, A.; Laskin, J.; Nizkorodov, S. A., Brown carbon formation from ketoaldehydes of biogenic monoterpenes. Faraday Discuss 2013, 165, 473-494.

602

57. Noziere, B.; Dziedzic, P.; Cordova, A., Products and Kinetics of the Liquid-Phase

603

Reaction of Glyoxal Catalyzed by Ammonium Ions (NH4+). J Phys Chem A 2009, 113, (1), 231-

604

237.


31


Page 32 of 34

605

58. Teich, M.; van Pinxteren, D.; Kecorius, S.; Wang, Z. B.; Herrmann, H., First

606

Quantification of Imidazoles in Ambient Aerosol Particles: Potential Photosensitizers, Brown

607

Carbon Constituents, and Hazardous Components. Environ Sci Technol 2016, 50, (3), 1166-

608

1173.

609

59. Hong, P.; Koza, S.; Bouvier, E. S. P., A Review Size-Exclusion Chromatography for the

610

Analysis of Protein Biotherapeutics and Their Aggregates. J Liq Chromatogr R T 2012, 35, (20),

611

2923-2950.

612 613 614 615

60. Pujar, N. S.; Zydney, A. L., Electrostatic effects on protein partitioning in size-exclusion chromatography and membrane ultrafiltration. J Chromatogr A 1998, 796, (2), 229-238. 61. Laskin, A.; Laskin, J.; Nizkorodov, S. A., Chemistry of Atmospheric Brown Carbon. Chem Rev 2015, 115, (10), 4335-4382.

616

62. Dehaan, H.; Deboer, T., Applicability of Light Absorbency and Fluorescence as

617

Measures of Concentration and Molecular-Size of Dissolved Organic-Carbon in Humic Lake

618

Tjeukemeer. Water Res 1987, 21, (6), 731-734.

619

63. Morris, D. P.; Hargreaves, B. R., The role of photochemical degradation of dissolved

620

organic carbon in regulating the UV transparency of three lakes on the Pocono Plateau. Limnol

621

Oceanogr 1997, 42, (2), 239-249.

622 623 624 625

64. Peuravuori, J.; Pihlaja, K., Molecular size distribution and spectroscopic properties of aquatic humic substances. Anal Chim Acta 1997, 337, (2), 133-149. 65. Minor, E.; Stephens, B., Dissolved organic matter characteristics within the Lake Superior watershed. Org Geochem 2008, 39, (11), 1489-1501.


32

Page 33 of 34

626 627


66. Cooper, A. R., Recent Advances in Molecular-Weight Determination. Polym Eng Sci 1989, 29, (1), 2-12.

628

67. Tetko, I. V.; Gasteiger, J.; Todeschini, R.; Mauri, A.; Livingstone, D.; Ertl, P.; Palyulin,

629

V.; Radchenko, E.; Zefirov, N. S.; Makarenko, A. S.; Tanchuk, V. Y.; Prokopenko, V. V.,

630

Virtual computational chemistry laboratory - design and description. J Comput Aid Mol Des

631

2005, 19, (6), 453-463.

632

68. Stenson, A. C.; Marshall, A. G.; Cooper, W. T., Exact masses and chemical formulas of

633

individual Suwannee River fulvic acids from ultrahigh resolution electrospray ionization Fourier

634

transform ion cyclotron resonance mass spectra. Anal Chem 2003, 75, (6), 1275-1284.

635

69. Noziere, B.; Kaberer, M.; Claeys, M.; Allan, J.; D'Anna, B.; Decesari, S.; Finessi, E.;

636

Glasius, M.; Grgic, I.; Hamilton, J. F.; Hoffmann, T.; Iinuma, Y.; Jaoui, M.; Kahno, A.; Kampf,

637

C. J.; Kourtchev, I.; Maenhaut, W.; Marsden, N.; Saarikoski, S.; Schnelle-Kreis, J.; Surratt, J. D.;

638

Szidat, S.; Szmigielski, R.; Wisthaler, A., The Molecular Identification of Organic Compounds

639

in the Atmosphere: State of the Art and Challenges. Chem Rev 2015, 115, (10), 3919-3983.

640

70. Spindler, G.; Brueggemann, E.; Gnauk, T.; Gruner, A.; Mueller, K.; Herrmann, H., A

641

four-year size-segregated characterization study of particles PM10, PM2.5 and PM1 depending

642

on air mass origin at Melpitz. Atmos Environ 2010, 44, (2), 164-173.

643 644


33


645

Page 34 of 34

Table of Contents graphic

646


34

Two-Dimensional Offline Chromatographic Fractionation for the

Recommend Documents