Aqueous Reaction of Dicarbonyls with Ammonia ... - ACS Publications

Subscriber access provided by University of Colorado Boulder

Article

Aqueous Reaction of Dicarbonyls with Ammonia as a Potential Source of Organic Nitrogen in Airborne Nanoparticles Christopher M Stangl, and Murray V Johnston J. Phys. Chem. A, Just Accepted Manuscript • Publication Date (Web): 25 Apr 2017 Downloaded from http://pubs.acs.org on April 27, 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.

The Journal of Physical Chemistry A 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 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

1

Aqueous Reaction of Dicarbonyls with Ammonia

2

as a Potential Source of Organic Nitrogen in

3

Airborne Nanoparticles

4

Christopher M. Stangl1 and Murray V. Johnston1*

5 6 7

1

Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 *Corresponding author. Phone: (302) 831-8014; Fax: (302) 831-6336; Email: [email protected]

8 9

ABSTRACT

10

Nitrogen-containing organic species such as imines and imidazoles can be formed by aqueous

11

reactions of carbonyl-containing compounds in the presence of ammonia. In the work described

12

here, these reactions are studied in airborne aqueous nanodroplets containing ammonium sulfate

13

and glyoxal, methylglyoxal, or glycolaldehyde using a combination of online and offline mass

14

spectrometry. N/C ratios attributed to the organic fraction of the particles (N/Corg) produced from

15

glyoxal and methylglyoxal were quantified across a wide relative humidity range. As RH was

16

lowered, glyoxal was found to increase N/Corg, attributed to “salting-in” with increasing solute

17

concentration, while methylglyoxal led to a decrease in N/Corg, attributed to “salting-out.”

18

Glycolaldehyde was found to evaporate from the droplets rather than react in the aqueous phase,

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

19

and did not form particulate-phase organic matter from aerosol drying under any of the

20

conditions studied. The results are discussed in the context of ambient nanoparticle composition

21

measurements and suggest that aqueous chemistry may significantly impact nanoparticle

22

composition and growth during new particle formation in locations where emissions of water-

23

soluble dicarbonyls are high, such as the eastern United States.

24 25 26

INTRODUCTION Uptake of low-volatility organic vapors by atmospheric particulate matter is known to

27

contribute substantially to the global aerosol mass budget, and can impact climate by dominating

28

nanoparticle growth and leading to the formation of cloud condensation nuclei. A ubiquitous

29

source of such low-volatility organics comes from photochemical oxidation of volatile organic

30

compounds (VOCs) in the gas phase leading to the formation of secondary organic aerosol

31

(SOA).1 An alternative pathway to SOA formation, and one that recently has been receiving

32

significant attention, occurs via aqueous-phase chemical reactions of organic compounds

33

partitioned into aerosol liquid water to form aqueous SOA (aqSOA).2 Numerous laboratory and

34

computational studies have shown that chemical reactions following uptake of water-soluble

35

organic gases into the aqueous phase, i.e. in cloud/fog droplets or deliquesced particles, can lead

36

to the formation of low-volatility organic compounds that will remain in the condensed phase

37

following water evaporation.2–6 A large number of such gaseous precursors shown to undergo

38

aqueous reaction and form aqSOA are photooxidation products of isoprene, including glyoxal,7,8

39

methylglyoxal,9 glycolaldehyde,10 and isoprene epoxydiols (IEPOX),11 due to their high

40

atmospheric gas-phase concentrations and effective Henry’s Law constants.12,13 Glyoxal, for

41

instance, is a well-established aqSOA precursor, and is known to form a variety of lower 2


Page 2 of 27

Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


42

volatility products through numerous reaction pathways once in the condensed phase. These

43

include, but are not limited to, hydrate formation and self-oligomerization,14 hydroxyl radical

44

oxidation to form oxalic acid,15 and irreversible formation of organic nitrogen-containing species

45

(e.g. imidazoles) by reaction with amines or ammonium salts.16–18 The generation of nitrogen-

46

containing organics is of particular interest because this reaction is not photochemically induced

47

and so can occur in the dark, has the potential to form light-absorbing “brown carbon” products

48

that can directly impact radiative forcing,19 and, as is a focus of this work, can potentially explain

49

significant levels of particulate nitrogen observed in ambient measurements of nanoparticle

50

chemical composition.

51

Because aqSOA formation is dependent on the availability of an aqueous phase,20,21 as well

52

as the potential of the gaseous precursor to partition to the aqueous phase (i.e. the Henry’s law

53

constant), which itself is affected by the preexisting aqueous phase composition,2 the extent to

54

which aqSOA contributes to particulate matter is likely to vary by location.22 Consequently, it is

55

suggested that aqSOA formation is most significant in the eastern United States during the

56

summertime, when water-soluble VOC emissions and aerosol water concentrations are highest.23

57

It is thought that aqSOA formation can help explain the discrepancy between regional SOA

58

concentrations measured in ambient studies with those predicted by aerosol models relying

59

mainly on partitioning theory, which are typically much lower.24

60

Recently, nanoparticle chemical composition was measured by our group during new particle

61

formation (NPF) events occurring in both urban25,26 and rural locations27 in the United States.

62

NPF involves the formation and stabilization of molecular clusters that grow quickly, often to

63

climatically relevant sizes.28 In these studies, quantitative elemental composition measurements

64

revealed a substantial amount of nitrogen often present in the growing nanoparticles,

3



65

independent of the measurement location. Periods when the nitrogen mole fraction (N) exceeded

66

twice the sulfur mole fraction (S) were often observed, indicative of particle-phase nitrogen

67

unassociated with sulfate neutralization, herein referred to as “excess N” (N-2S). During a field

68

study, conducted 23 July to 31 August 2012 in Lewes, Delaware,27 concurrent molecular

69

composition measurements aided in characterization of the excess N, and revealed that the most

70

plausible source was organic nitrogen-containing compounds such as imines and imidazoles,

71

which could form via aqueous reaction. In addition, increases in excess N always correlated with

72

a simultaneous decrease in relative humidity, which again suggested that organic nitrogen-

73

containing species, such as those formed through aqueous reaction of glyoxal or methylglyoxal

74

with ammonium sulfate, could be a source of excess N, as such reactions are greatly enhanced by

75

water evaporation.5

76

Herein we report results from a series of laboratory experiments designed to gauge the

77

potential for water-soluble organic compounds (WSOC) relevant to the eastern U.S. to form

78

organic nitrogen through aqueous reaction with ammonium sulfate in nanodroplets.

79

Furthermore, we suggest that these reactions are plausible sources of the excess N observed

80

during ambient measurements of NPF in Lewes, Delaware.

81 82

EXPERIMENTAL SECTION

83

Generation and Collection of Dried Nanodroplets. Aqueous solutions containing either

84

glyoxal (GLY, 40% in H2O, Acros Organics), methylglyoxal (MGLY, ~40% in H2O, Sigma-

85

Aldrich), or glycolaldehyde (GCA, solid dimer, Sigma-Aldrich) and ammonium sulfate (AS,

86

99.9999%, Acros Organics) were prepared to be 5 mM organic/5 mM (NH4)2SO4 using ultrapure

4


Page 4 of 27

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


87

water (18.2 MΩ·cm). All solutions had a pH in the range of 4-5, measured with a pH probe

88

(accuTupH, Fisher Scientific), as expected for an aqueous ammonium sulfate solution. No

89

attempt was made to investigate lower pH values since ambient nanoparticle composition

90

measurements relevant to this study suggest a 2:1 mole ratio of ammonia to sulfuric acid.

91

Assuming a Henry’s law constant for glyoxal of 2.4x107 M/atm, reported by Ip et al. for an

92

aqueous solution containing a sulfate:glyoxal molar ratio of 1:1,29 this would give an

93

approximate gas phase mixing ratio of 0.2 ppb for glyoxal above solution in our experiments,

94

which is within the range of ambient glyoxal concentrations of 0.01-5 ppb.7,13,21,30,31

95

Polydisperse aerosol was generated from each solution via nebulization (ATM 226, Topas

96

GmbH, Dresden, Germany) to produce internally-mixed nanodroplets with an expected

97

theoretical size range of 0.1-0.5 µm. The droplets were subsequently passed through one or more

98

home-built diffusion dryer tubes containing silica gel beads surrounding the aerosol flow path to

99

lower the relative humidity and promote the reaction. Residence time of particles in each dryer

100

tube was 1-2 seconds, resulting in a short reaction time for each aerosol system studied. In most

101

experiments, two dryers were used to maintain a relative humidity of about 60% as measured

102

with a hygrometer (Fisher Scientific). Depending on the number of dryers used (0 to 3) and the

103

system studied, the relative humidity at the exit of the assembly could be maintained in four

104

separate regimes: 90-95%, 70-75%, 55-60%, and 25-40%. During any individual experiment,

105

the relative humidity varied less than +/- 2%. The size distribution of aerosol exiting the dryer

106

tube assembly was measured with a scanning mobility particle sizer (model 3081 DMA, model

107

3788 N-WCPC, TSI, Inc.), and found to have a mode diameter of 50-60 nm for all systems

108

studied.

5



109

Upon exiting the dryer tube(s), particles were collected onto a quartz microfiber filter

110

(Whatman GF/D, GE Life Sciences) continuously for 1 hour, allowing ~500 µg of mass to be

111

collected, determined by weighing the filter before and after collection (Accu-124D, Fisher

112

Scientific). Extraction of the captured material was performed immediately following collection

113

by sonicating each filter in 2 mL of 1:1 acetonitrile/water (Optima grade, Fisher Scientific) for a

114

final concentration of ~0.2 mg/mL. All samples were stored at -20˚C immediately following

115

extraction and analyzed within 24 hours of particle collection. In addition, 200 µL bulk aliquots

116

of each solution were dried under vacuum overnight, and the brown residue redissolved in 1:1

117

ACN/H2O to ~0.2 mg/mL.

118

Off-line Molecular Analysis by ESI-HRMS. Molecular composition analysis of the particle

119

extracts was performed by positive-ion mode direct infusion electrospray ionization high-

120

resolution mass spectrometry (ESI-HRMS) using a Thermo Q Exactive Orbitrap mass

121

spectrometer. Scans were performed in the mass range of m/z 50-750, with a mass resolving

122

power of m/∆m = 100,000 at m/z 100. Background subtraction was carried out using a filter

123

blank (sonication of a clean filter in 1:1 ACN/H2O). Molecular formulas were assigned to the

124

peaks in each spectrum within a 5 ppm mass accuracy window using Thermo Xcalibur software

125

(version 3.0) with parameters of C1-30, H2-60, O0-15, N0-10, Na0-1. Removal of background ions was

126

performed by omitting peaks with a signal-to-noise less than 5 and a relative intensity less than

127

0.1%. For the remaining peaks with assigned formulas, N/C ratios and mass-weighted intensity

128

fractions (MIF) were calculated. MIF accounts for the fact that peaks with larger masses and

129

intensities likely represent a larger fraction of the overall sample mass, and is determined by

130

=

131

respectively.32 Mass-intensity weighted N/C ratios for each sample were then determined by

( )

( )

, where (m/z)i and Ii represent the mass-to-charge ratio and intensity of peak i,

6


Page 6 of 27

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


132

= ∑ / × . It should be noted that the weighted N/C ratio using MIF /

133

gives an accurate representation of the true N/C ratio of the sample only under the assumption

134

that all species in each positive ion spectrum have the same response factors.32

135

On-line elemental composition analysis by NAMS-II. A modified configuration of the

136

nano aerosol mass spectrometer (NAMS), herein referred to as NAMS-II, was used to quantify

137

the elemental composition of the dried particles produced from each nanodroplet system. The

138

working principle of NAMS has been described in detail previously.33 For this study, dried

139

nanodroplets, generated in the same manner as described above, were introduced into NAMS-II

140

through a flow-limiting orifice and focused into a collimated beam via an aerodynamic lens. The

141

lens system is designed such that particles of a particular size range will be axially focused

142

toward the ionization source region, which for this study was approximately 30-100 nm

143

aerodynamic diameter. The focused particle beam was aligned to pass through the focal point of

144

a free-firing Nd:YAG laser (Quantel USA) with 532 nm wavelength and ~230 mJ pulse energy.

145

Particles present in or near the focal point of the laser pulse undergo laser-induced plasma

146

ionization (LIPI), which forms positively, multiply-charged atomic ions that are electrostatically

147

extracted from the ionization region, mass analyzed by time-of-flight, and detected by a

148

microchannel plate.

149

Given the high energy ionization mechanism employed, strictly elemental ions are observed

150

in each particle mass spectrum. Averaging a sufficient number of particle spectra and calculating

151

the mole fractions of the elements present allows for determination of the elemental composition,

152

which is typically accurate to ±10% of the expected value based on analyses of known particle

153

standards.34 A bootstrapping method was applied to the dataset such that 20 individual particles

154

were randomly sampled with replacement and averaged together, and this process repeated 100

7



155

times to create a 100-sample “averaged” dataset from which the mean elemental mole fractions

156

and their standard deviations were determined. At least 150 particle spectra were obtained for

157

each experiment.

158

For this study, mole fractions of C, O, N, and S were determined for each system investigated

159

(although H was observed, it is not quantitative by NAMS-II analysis and so was omitted from

160

the elemental mole fraction apportionment). Excess N, if present, was calculated as N-2S, and

161

the N/C ratio of the organic fraction of the particles was calculated as Excess N / C.

162 163 164

RESULTS AND DISCUSSION Offline molecular composition analysis by ESI-HRMS. Figure 1 shows an ESI mass

165

spectrum of the GLY/AS droplets collected onto a filter following drying to ~60% RH.

166

Nitrogen-containing species (red peaks) were found to comprise the majority of products.

167

Molecular formulas assigned to reaction products via accurate mass measurements matched

168

those previously reported for bulk aqueous solutions of glyoxal/(NH4)2SO4.35 Molecular

169

formulas for the major peaks are given in Figure S2. Table 1 shows the mass-intensity weighted

170

N/C ratios determined for each bulk solution and dried nanodroplet system by ESI-HRMS. In the

171

case of the GLY/AS system, no statistically significant difference is observed between N/Cweighted

172

of the dried bulk solutions and dried nanodroplets, and in fact the two spectra appear nearly

173

identical, suggesting that organo-nitrogen formation by aqueous reaction occurs to a similar

174

extent in both cases. Given the short time period between nanodroplet drying and collection

175

(100% for dried microdroplets containing a 1:1 molar ratio

247

of glyoxal and ammonium sulfate, and suggested this to be due to retained water, which is

248

kinetically limited in its evaporation from the drying droplets.38 Hawkins et al. noted increased

249

viscosity of dried droplets containing glyoxal and amines, thought to be caused by oligomeric

250

reaction products.40 In addition, Smith et al. studied the hygroscopic phase transitions of particles

251

containing ammonium sulfate and isoprene photo-oxidation products, and found that the

252

efflorescence relative humidity decreased with increasing organic volume fraction (ε), with

253

efflorescence being eliminated when ε ≥ 0.6.41 NAMS-II analysis of dried (RH ≈ 60%) pure

254

glyoxal droplets in the absence of ammonium sulfate (Figure S7), however, yielded an O/C ratio

255

consistent with previously identified glyoxal oligomerization products, suggesting that aqueous

256

reactions caused by the presence of ammonium sulfate inhibit the loss of water in the dried

257

particles.39 Interestingly, O/Corg of the dried MGLY/AS droplets was 0.3, which is consistent

258

with aldol condensation products of methylglyoxal, proposed to account for the vast majority of

259

aerosol-phase material produced by methylglyoxal and enhanced by particle phase ammonia in

260

evaporated droplets.42 This observation suggests that glyoxal increases droplet viscosity to a

261

greater extent than methylglyoxal via reaction with ammonium sulfate.

262

To investigate the dependence of relative humidity on organic nitrogen formation, additional

263

experiments were performed in which the number of diffusion dryer tubes that the GLY/AS and

264

MGLY/AS droplets passed through prior to analysis was varied from 0-3. Figure 3a shows the

265

change in N/Corg as a function of the relative humidity to which the droplets are dried before

266

entering NAMS-II. A clear trend is observed in which N/Corg of the GLY/AS droplets increases

267

as the extent of drying increases. This can be explained by an increase in solute concentrations as

268

more solvent is evaporated from the droplets, which promotes formation of organo-nitrogen

12


Page 12 of 27

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


269

compounds by increasing molecular interactions between GLY and ammonia as the solutes

270

become supersaturated.5 In addition, evaporative loss of glyoxal to the gas phase is slow due to

271

its high effective Henry’s law constant, which has been shown to increase exponentially with

272

ammonium sulfate concentration and sulfate ionic strength, i.e. “salting-in.”8,29,43,44 For

273

MGLY/AS droplets, the opposite trend was observed where N/Corg decreased as the extent of

274

droplet drying increased. This observation suggests that, unlike glyoxal, methylglyoxal

275

evaporates from the drying droplets faster than it reacts to produce organo-nitrogen species, with

276

less remaining in the condensed phase as the relative humidity is lowered. In addition, a

277

continuous decrease in both the C mole fraction and the excess N mole fraction was found as

278

drying increased, again suggesting that less organic remained in the droplets to promote NH3

279

uptake and form particle-phase organic nitrogen. In a trial carried out where the droplets were

280

dried to ~27% RH, the C mole fraction was nearly zero, and excess N was completely absent in

281

our measurements. Methylglyoxal has a lower effective Henry’s law constant than glyoxal in

282

pure water, and has been shown to decrease substantially with increasing sulfate ionic strength,

283

i.e. “salting-out.”45 In agreement with the results of Galloway et al., the authors suggest that

284

methylglyoxal heavily evaporates out early in the drying process as the droplets are still dilute,

285

leaving little to react with ammonium sulfate.38

286

Additionally, we investigated the effect of RH on the C/S ratios of the GLY/AS and

287

MGLY/AS dried nanodroplets measured by NAMS-II. C/S gives an idea of the amount of

288

semivolatile organic remaining in the particle phase available for reaction relative to nonvolatile

289

sulfate. As shown in Figure 3b, C/S was found to decrease with decreasing RH for both the

290

GLY/AS and MGLY/AS nanodroplets. This was expected, as decreasing the RH decreases the

291

volume of aerosol liquid water, and hence the amount of dissolved organic, while the moles of

13



292

sulfate remains constant. We reinforce that although the mole ratio of organics to AS decreases

293

in our experiments during drying, the molal concentrations of both organics and AS in the

294

droplets increase. In addition, C/S is much larger in both systems at the highest RH studied, since

295

in those trials the aerosol did not pass through a diffusion dryer that aids in removing volatile

296

species, hence equilibrium gas phase mixing ratios of organics were likely much higher than in

297

trials utilizing one or more dryer tubes. C/S was consistently lower for the MGLY/AS system,

298

likely due to enhanced loss of methylglyoxal to the gas phase with increased drying (salting-out).

299

Although glyoxal also evaporates with increased drying, the increase in particle viscosity at

300

lower RH, as well as the salting-in effect, offset the loss of glyoxal to the gas phase, and

301

contribute to a consistently larger C/S ratio observed in our measurements. Based on the results

302

of Waxman et al., for a bulk aqueous solution of ammonium sulfate and GLY, an increase in

303

[SO42-] by a factor of 2 would lead to an estimated increase in the effective Henry’s law constant

304

of glyoxal by a factor of ~2.7.45 However, our observations suggest that such aqueous carbonyl

305

chemistry occurring in the aerosol phase is complicated by a number of additional factors

306

including dynamic changes in liquid water content, reactant concentrations, Henry’s law

307

constants, particle viscosity, and irreversible product formation, and so the exact effects of such

308

chemistry on ambient organic aerosol formation and growth warrants further research.

309

Implications for Ambient New Particle Formation. The ambient nanoparticle composition

310

measurements behind the motivation of this work took place from 23 July to 31 August 2012 in

311

Lewes, Delaware, a coastal location in the eastern U.S.27 Considering three representative NPF

312

events during which excess N was observed (12, 13, and 21 August), the excess N mole fractions

313

ranged from ~0.05-0.06 at their maxima, leading to N/Corg = 0.1-0.2. A recurring observation

314

during these events was that the increase in excess N mole fraction occurred just following a

14


Page 14 of 27

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


315

sharp decrease in relative humidity. On 12 August, for instance, RH dropped from about 95% at

316

6:00 EST to 60% by 12:00 EST, while over the same time period the sulfur (sulfate) fraction

317

increased by a factor of 5 and excess N increased by a factor of 3 (Figure S8), leading to N/Corg ≈

318

0.2 and C/S ≈ 8. This observation suggests that if imines and imidazoles are the cause of excess

319

N, a decrease in liquid water content of the particles coupled with an increase of sulfate mass

320

fraction was enhancing their formation, in agreement with our laboratory results. Other studies

321

have also shown that the formation rate of nitrogen-containing species in aqueous GLY/AS and

322

MGLY/AS aerosols is greatly increased as the solute environment is concentrated when water is

323

actively removed from the particles.5,6 In our experiments where the nanodroplets were dried to a

324

comparable relative humidity of 55-60%, both glyoxal and methylglyoxal produced large enough

325

N/Corg ratios (~0.4 and ~0.2, respectively) to be considered plausible contributors to the

326

formation of organic nitrogen observed in Lewes.

327

Based on these results, if we consider methylglyoxal to be the major contributor to the N/Corg

328

in Lewes, almost all of the carbonaceous matter in those particles would have had to arise from

329

methylglyoxal chemistry, which seems unlikely. In addition, the C/S ratio measured in our

330

experiments for MGLY/AS at a comparable RH was far lower than the C/S ratio observed in

331

Lewes. Alternatively, if we consider glyoxal to be the major contributor, approximately half of

332

the carbonaceous matter in Lewes could be explained by glyoxal chemistry, with the remainder

333

likely due to condensation of other oxygenated organics from e.g. monoterpenes. In this case,

334

approximately half of the observed C/S ratio of ~8 during NPF could be explained by glyoxal

335

chemistry, which is comparable to the C/S measured in our laboratory experiments for GLY/AS

336

at a comparable RH.

15



337

Recently, Boone et al. reported an average N/C ratio of 0.24 for CHON compounds

338

identified in positive mode ESI-MS spectra of cloudwater samples collected over Alabama in the

339

summer of 2013, and stated that a large fraction of the observed compounds corresponded to

340

isoprene oxidation products.46 Altieri et al. analyzed cloudwater samples collected in New Jersey

341

by ultrahigh-resolution mass spectrometry, and reported an average N/C ratio of 0.16 for the

342

>200 CHON+ compounds that were identified, suggesting that many of those compounds were

343

likely formed by secondary atmospheric processes involving reduced nitrogen species.47 We note

344

that these N/C ratios are in good agreement with those observed for the growing nanoparticles

345

measured in our ambient studies in Lewes.

346

Nguyen et al. investigated the formation of nitrogen-containing organic compounds by

347

photooxidation of isoprene in a Teflon chamber under both low and high-NOx conditions, and

348

found the average N/C ratio of the SOA produced in the high-NOx system to only be 0.019,48

349

which is insufficient to explain excess N in Lewes. In addition, the organic nitrogen was found

350

to be in the form of organic nitrates, which was ruled out as a possible source of the excess N in

351

Lewes due to the low abundance of particle-phase nitrates.27 Liu et al. studied the reactive uptake

352

of gas-phase ammonia by SOA derived from a-pinene ozonolysis and OH oxidation of m-xylene,

353

and found the mean N/C ratios of the reacted aerosols to be 0.016 ± 0.004 and 0.065 ± 0.011,

354

respectively.49 These values are also too small for these sources to be significant contributors to

355

excess N in Lewes, and provide further support for the hypothesis that aqueous reaction of water-

356

soluble dicarbonyls such as glyoxal by reaction with reduced nitrogen compounds is the more

357

likely source in ambient aerosol.

358

CONCLUSION

16


Page 16 of 27

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


359

In our laboratory studies reported here, glyoxal contributed to the largest mole fraction of

360

organic nitrogen formed by aqueous reaction with ammonium sulfate in drying nanodroplets,

361

suggesting that if such a process was responsible for the excess N observed in Lewes, glyoxal

362

was likely a large contributor. It is possible that methylglyoxal could explain a portion of the

363

organic nitrogen observed in Lewes as well, although its contribution is likely smaller, as N/Corg

364

was observed to decrease along with relative humidity in our laboratory experiments, opposite of

365

the trend observed in our ambient measurements. Glycolaldehyde likely did not contribute to

366

organic nitrogen formation in Lewes, as it was found to completely evaporate in our dried

367

droplet studies before reacting with ammonium sulfate, in agreement with other previously

368

published studies.38 It should be noted that nanoparticle size, as well as the rate of

369

droplet/particle drying, differed between our laboratory and ambient studies, and so only a

370

qualitative comparison between the two can be made at this time. Overall, our results suggest

371

that aqueous dicarbonyl chemistry may in fact play a significant role in altering the chemical

372

composition of growing ambient nanoparticles in locations such as the eastern U.S., and for the

373

specific case of Lewes, Delaware in summertime this chemistry could explain half of the organic

374

matter in growing nanoparticles during NPF. Future work should be directed towards

375

investigating the contributions of such reactions on the growth rate and composition in particle

376

formation experiments.

377 378 379

SUPPORTING INFORMATION Figures S1-S8 as specified in the text.

380

17



381 382

ACKNOWLEDGEMENTS This research was supported by the National Science Foundation under grant number CHE-

383

1408455. The Orbitrap mass spectrometer used in this study was purchased under grant number

384

S10 OD016267-01 and supported by grant number 1 P30 GM110758-01, both from the National

385

Institutes of Health.

386 387

18


Page 18 of 27

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


388

REFERENCES CITED

389 390 391

(1)

Kroll, J. H.; Seinfeld, J. H. Chemistry of Secondary Organic Aerosol: Formation and Evolution of Low-Volatility Organics in the Atmosphere. Atmos. Environ. 2008, 42 (16), 3593–3624.

392 393

(2)

McNeill, V. F. Aqueous Organic Chemistry in the Atmosphere: Sources and Chemical Processing of Organic Aerosols. Environ. Sci. Technol. 2015, 49 (3), 1237–1244.

394 395 396

(3)

Lim, Y. B.; Tan, Y.; Perri, M. J.; Seitzinger, S. P.; Turpin, B. J. Aqueous Chemistry and Its Role in Secondary Organic Aerosol (SOA) Formation. Atmos. Chem. Phys. 2010, 10 (21), 10521–10539.

397 398 399

(4)

Kua, J.; Krizner, H. E.; De Haan, D. O. Thermodynamics and Kinetics of Imidazole Formation from Glyoxal, Methylamine, and Formaldehyde: A Computational Study. J. Phys. Chem. A 2011, 115 (9), 1667–1675.

400 401 402

(5)

Lee, A. K. Y.; Zhao, R.; Li, R.; Liggio, J.; Li, S. M.; Abbatt, J. P. D. Formation of Light Absorbing Organo-Nitrogen Species from Evaporation of Droplets Containing Glyoxal and Ammonium Sulfate. Environ. Sci. Technol. 2013, 47 (22), 12819–12826.

403 404 405 406

(6)

De Haan, D. O.; Hawkins, L. N.; Kononenko, J. A.; Turley, J. J.; Corrigan, A. L.; Tolbert, M. A.; Jimenez, J. L. Formation of Nitrogen-Containing Oligomers by Methylglyoxal and Amines in Simulated Evaporating Cloud Droplets. Environ. Sci. Technol. 2011, 45 (3), 984–991.

407 408 409

(7)

Volkamer, R.; San Martini, F.; Molina, L. T.; Salcedo, D.; Jimenez, J. L.; Molina, M. J. A Missing Sink for Gas-Phase Glyoxal in Mexico City: Formation of Secondary Organic Aerosol. Geophys. Res. Lett. 2007, 34 (19), 1–5.

410 411 412

(8)

Ervens, B.; Volkamer, R. Glyoxal Processing by Aerosol Multiphase Chemistry: Towards a Kinetic Modeling Framework of Secondary Organic Aerosol Formation in Aqueous Particles. Atmos. Chem. Phys. 2010, 10 (17), 8219–8244.

413 414 415 416

(9)

Altieri, K. E.; Seitzinger, S. P.; Carlton, A. G.; Turpin, B. J.; Klein, G. C.; Marshall, A. G. Oligomers Formed through in-Cloud Methylglyoxal Reactions: Chemical Composition, Properties, and Mechanisms Investigated by Ultra-High Resolution FT-ICR Mass Spectrometry. Atmos. Environ. 2008, 42 (7), 1476–1490.

417 418 419

(10)

Perri, M. J.; Seitzinger, S.; Turpin, B. J. Secondary Organic Aerosol Production from Aqueous Photooxidation of Glycolaldehyde: Laboratory Experiments. Atmos. Environ. 2009, 43 (8), 1487–1497.

420 421 422 423 424

(11)

Marais, E. A.; Jacob, D. J.; Jimenez, J. L.; Campuzano-Jost, P.; Day, D. A.; Hu, W.; Krechmer, J.; Zhu, L.; Kim, P. S.; Miller, C. C.; et al. Aqueous-Phase Mechanism for Secondary Organic Aerosol Formation from Isoprene: Application to the Southeast United States and Co-Benefit of SO2 Emission Controls. Atmos. Chem. Phys. Discuss. 2015, 15 (21), 32005–32047.

425 426

(12)

Lim, H.-J.; Carlton, A. G.; Turpin, B. J. Isoprene Forms Secondary Organic Aerosol through Cloud Processing: Model Simulations. Environ. Sci. Technol. 2005, 39 (12), 19



427

4441–4446.

428 429 430

(13)

Fu, T. M.; Jacob, D. J.; Wittrock, F.; Burrows, J. P.; Vrekoussis, M.; Henze, D. K. Global Budgets of Atmospheric Glyoxal and Methylglyoxal, and Implications for Formation of Secondary Organic Aerosols. J. Geophys. Res. Atmos. 2008, 113 (15).

431 432 433

(14)

Loeffler, K. W.; Koehler, C. A.; Paul, N. M.; De Haan, D. O. Oligomer Formation in Evaporating Aqueous Glyoxal and Methyl Glyoxal Solutions. Environ. Sci. Technol. 2006, 40 (20), 6318–6323.

434 435 436

(15)

Tan, Y.; Perri, M. J.; Seitzinger, S. P.; Turpin, B. J. Effects of Precursor Concentration and Acidic Sulfate in Aqueous Glyoxal - OH Radical Oxidation and Implications for Secondary Organic Aerosol. Environ. Sci. Technol. 2009, 43 (21), 8105–8112.

437 438

(16)

De Haan, D. O.; Tolbert, M. A.; Jimenez, J. L. Atmospheric Condensed-Phase Reactions of Glyoxal with Methylamine. Geophys. Res. Lett. 2009, 36 (11), 1–5.

439 440 441 442

(17)

Ortiz-Montalvo, D. L.; Hakkinen, S. A. K.; Schwier, A. N.; Lim, Y. B.; McNeill, V. F.; Turpin, B. J. Ammonium Addition (and Aerosol pH) Has a Dramatic Impact on the Volatility and Yield of Glyoxal Secondary Organic Aerosol. Environ. Sci. Technol. 2014, 48 (1), 255–262.

443 444 445

(18)

Powelson, M. H.; Espelien, B. M.; Hawkins, L. N.; Galloway, M. M.; De Haan, D. O. Brown Carbon Formation by Aqueous-Phase Carbonyl Compound Reactions with Amines and Ammonium Sulfate. Environ. Sci. Technol. 2013, 48 (2), 985–993.

446 447 448

(19)

Shapiro, E. L.; Szprengiel, J.; Sareen, N.; Jen, C. N.; Giordano, M. R.; McNeill, V. F. Light-Absorbing Secondary Organic Material Formed by Glyoxal in Aqueous Aerosol Mimics. Atmos. Chem. Phys. Discuss. 2009, 9 (1), 59–80.

449 450 451

(20)

Faust, J. A.; Wong, J. P. S.; Lee, A. K. Y.; Abbatt, J. P. D. Role of Aerosol Liquid Water in Secondary Organic Aerosol Formation from Volatile Organic Compounds. Environ. Sci. Technol. 2017, 51 (3), 1405–1413.

452 453 454

(21)

Trainic, M.; Abo Riziq, A.; Lavi, A.; Flores, J. M.; Rudich, Y. The Optical, Physical and Chemical Properties of the Products of Glyoxal Uptake on Ammonium Sulfate Seed Aerosols. Atmos. Chem. Phys. 2011, 11 (18), 9697–9707.

455 456 457

(22)

Sareen, N.; Waxman, E. M.; Turpin, B. J.; Volkamer, R.; Carlton, A. G. Potential of Aerosol Liquid Water to Facilitate Organic Aerosol Formation: Assessing Knowledge Gaps about Precursors and Partitioning. Environ. Sci. Technol. 2017, 51 (6), 3327-3335.

458 459 460

(23)

Carlton, A. G.; Turpin, B. J. Particle Partitioning Potential of Organic Compounds Is Highest in the Eastern US and Driven by Anthropogenic Water. Atmos. Chem. Phys. 2013, 13 (20), 10203–10214.

461 462 463 464

(24)

Carlton, A. G.; Turpin, B. J.; Altieri, K. E.; Seitzinger, S. P.; Mathur, R.; Roselle, S. J.; Weber, R. J. CMAQ Model Performance Enhanced When in-Cloud Secondary Organic Aerosol Is Included: Comparisons of Organic Carbon Predictions with Measurements. Environ. Sci. Technol. 2008, 42 (23), 8798–8802.

465

(25)

Pennington, M. R.; Klems, J. P.; Bzdek, B. R.; Johnston, M. V. Nanoparticle Chemical

20


Page 20 of 27

Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


466 467

Composition and Diurnal Dependence at the CalNex Los Angeles Ground Site. J. Geophys. Res. Atmos. 2012, 117 (D21), D00V10.

468 469 470

(26)

Bzdek, B. R.; Zordan, C. A.; Pennington, M. R.; Luther III, G. W.; Johnston, M. V. Quantitative Assessment of the Sulfuric Acid Contribution to New Particle Growth. Environ. Sci. Technol. 2012, 46 (8), 4365–4373.

471 472 473

(27)

Bzdek, B. R.; Lawler, M. J.; Horan, A. J.; Pennington, M. R.; DePalma, J. W.; Zhao, J.; Smith, J. N.; Johnston, M. V. Molecular Constraints on Particle Growth during New Particle Formation. Geophys. Res. Lett. 2014, 41, 6045–6054.

474 475

(28)

Bzdek, B. R.; Johnston, M. V. New Particle Formation and Growth in the Troposphere. Anal. Chem. 2010, 82 (19), 7871–7878.

476 477

(29)

Ip, H. S. S.; Huang, X. H. H.; Yu, J. Z. Effective Henry’s Law Constants of Glyoxal, Glyoxylic Acid, and Glycolic Acid. Geophys. Res. Lett. 2009, 36 (1), L01802.

478 479

(30)

Liggio, J.; Li, S.-M.; McLaren, R. Reactive Uptake of Glyoxal by Particulate Matter. J. Geophys. Res. Atmos. 2005, 110 (D10), D10304.

480 481 482

(31)

Wittrock, F.; Richter, A.; Oetjen, H.; Burrows, J. P.; Kanakidou, M.; Myriokefalitakis, S.; Volkamer, R.; Beirle, S.; Platt, U.; Wagner, T. Simultaneous Global Observations of Glyoxal and Formaldehyde from Space. Geophys. Res. Lett. 2006, 33 (16), L16804.

483 484 485

(32)

Heaton, K. J.; Sleighter, R. L.; Hatcher, P. G.; Hall IV, W. A.; Johnston, M. V. Composition Domains in Monoterpene Secondary Organic Aerosol. Environ. Sci. Technol. 2009, 43 (20), 7797–7802.

486 487

(33)

Pennington, M. R.; Johnston, M. V. Trapping Charged Nanoparticles in the Nano Aerosol Mass Spectrometer (NAMS). Int. J. Mass Spectrom. 2012, 311, 64–71.

488 489 490

(34)

Zordan, C. A.; Pennington, M. R.; Johnston, M. V. Elemental Composition of Nanoparticles with the Nano Aerosol Mass Spectrometer. Anal. Chem. 2010, 82 (19), 8034–8038.

491 492 493

(35)

Kampf, C. J.; Jakob, R.; Hoffmann, T. Identification and Characterization of Aging Products in the Glyoxal/Ammonium Sulfate System - Implications for Light-Absorbing Material in Atmospheric Aerosols. Atmos. Chem. Phys. 2012, 12 (14), 6323–6333.

494 495 496 497

(36)

Galloway, M. M.; Chhabra, P. S.; Chan, A. W. H.; Surratt, J. D.; Flagan, R. C.; Seinfeld, J. H.; Keutsch, F. N. Glyoxal Uptake on Ammonium Sulphate Seed Aerosol: Reaction Products and Reversibility of Uptake under Dark and Irradiated Conditions. Atmos. Chem. Phys. 2009, 9 (10), 3331–3345.

498 499 500

(37)

Wong, J. P. S.; Lee, A. K. Y.; Abbatt, J. P. D. Impacts of Sulfate Seed Acidity and Water Content on Isoprene Secondary Organic Aerosol Formation. Environ. Sci. Technol. 2015, 49 (22), 13215–13221.

501 502 503 504

(38)

Galloway, M. M.; Powelson, M. H.; Sedehi, N.; Wood, S. E.; Millage, K. D.; Kononenko, J. A.; Rynaski, A. D.; De Haan, D. O. Secondary Organic Aerosol Formation during Evaporation of Droplets Containing Atmospheric Aldehydes, Amines, and Ammonium Sulfate. Environ. Sci. Technol. 2014, 48 (24), 14417–14425.

21



505 506 507

(39)

Nozière, B.; Dziedzic, P.; Córdova, A. Products and Kinetics of the Liquid-Phase Reaction of Glyoxal Catalyzed by Ammonium Ions (NH4+). J. Phys. Chem. A 2009, 113 (1), 231–237.

508 509 510

(40)

Hawkins, L. N.; Baril, M. J.; Sedehi, N.; Galloway, M. M.; De Haan, D. O.; Schill, G. P.; Tolbert, M. A. Formation of Semisolid, Oligomerized Aqueous SOA: Lab Simulations of Cloud Processing. Environ. Sci. Technol. 2014, 48 (4), 2273–2280.

511 512 513

(41)

Smith, M. L.; Bertram, A. K.; Martin, S. T. Deliquescence, Efflorescence, and Phase Miscibility of Mixed Particles of Ammonium Sulfate and Isoprene-Derived Secondary Organic Material. Atmos. Chem. Phys. 2012, 12 (20), 9613–9628.

514 515 516

(42)

De Haan, D. O.; Corrigan, A. L.; Tolbert, M. A.; Jimenez, J. L.; Wood, S. E.; Turley, J. J. Secondary Organic Aerosol Formation by Self-Reactions of Methylglyoxal and Glyoxal in Evaporating Droplets. Environ. Sci. Technol. 2009, 43 (21), 8184–8190.

517 518 519 520

(43)

Kampf, C. J.; Waxman, E. M.; Slowik, J. G.; Dommen, J.; Pfaffenberger, L.; Praplan, A. P.; Prévôt, A. S. H.; Baltensperger, U.; Hoffmann, T.; Volkamer, R. Effective Henry’s Law Partitioning and the Salting Constant of Glyoxal in Aerosols Containing Sulfate. Environ. Sci. Technol. 2013, 47 (9), 4236–4244.

521 522 523

(44)

Kurtén, T.; Elm, J.; Prisle, N. L.; Mikkelsen, K. V; Kampf, C. J.; Waxman, E. M.; Volkamer, R. Computational Study of the Effect of Glyoxal–Sulfate Clustering on the Henry’s Law Coefficient of Glyoxal. J. Phys. Chem. A 2015, 119 (19), 4509–4514.

524 525 526 527

(45)

Waxman, E. M.; Elm, J.; Kurtén, T.; Mikkelsen, K. V; Ziemann, P. J.; Volkamer, R. Glyoxal and Methylglyoxal Setschenow Salting Constants in Sulfate, Nitrate, and Chloride Solutions: Measurements and Gibbs Energies. Environ. Sci. Technol. 2015, 49 (19), 11500–11508.

528 529 530

(46)

Boone, E. J.; Laskin, A.; Laskin, J.; Wirth, C.; Shepson, P. B.; Stirm, B. H.; Pratt, K. A. Aqueous Processing of Atmospheric Organic Particles in Cloud Water Collected via Aircraft Sampling. Environ. Sci. Technol. 2015, 49 (14), 8523–8530.

531 532 533

(47)

Altieri, K. E.; Turpin, B. J.; Seitzinger, S. P. Composition of Dissolved Organic Nitrogen in Continental Precipitation Investigated by Ultra-High Resolution FT-ICR Mass Spectrometry. Environ. Sci. Technol. 2009, 43 (18), 6950–6955.

534 535 536

(48)

Nguyen, T. B.; Laskin, J.; Laskin, A.; Nizkorodov, S. A. Nitrogen-Containing Organic Compounds and Oligomers in Secondary Organic Aerosol Formed by Photooxidation of Isoprene. Environ. Sci. Technol. 2011, 45 (16), 6908–6918.

537 538 539

(49)

Liu, Y.; Liggio, J.; Staebler, R. Reactive Uptake of Ammonia to Secondary Organic Aerosols: Kinetics of Organonitrogen Formation. Atmos. Chem. Phys. 2015, 15 (23), 13569–13584.

540 541 542

22


Page 22 of 27

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

543


TABLES

544 545 546 547

Table 1. Mass-intensity-weighted N/C ratios of aqSOA products produced by drying nanodroplets and bulk solutions of each system investigated, as determined by positive mode ESI-HRMS.

548 549

Reaction system Avg. N/Cweighted Bulk 5 mM glyoxal/5mM (NH4)2SO4 0.60 5 mM methylglyoxal/5mM (NH4)2SO4 0.29 5 mM glycolaldehyde/5mM (NH4)2SO4 0.27 Aerosol 5 mM glyoxal/5mM (NH4)2SO4 0.59±0.05 5 mM methylglyoxal/5mM (NH4)2SO4 0.24±0.06 5 mM glycolaldehyde/5mM (NH4)2SO4 Not Detected For samples with errors reported, values are averages of three replicate samples, and errors represent one standard deviation.

550 551 552 553 554 555

Table 2. Mean elemental mole fractions, excess N mole fraction, and organic N/C ratio measured by NAMS-II for each of the dried nanodroplet systems studied at various RH. Reported errors of the N/C ratio represent one standard deviation of the mean. Reaction system 5 mM glyoxal/ 5mM (NH4)2SO4

5 mM methylglyoxal/ 5mM (NH4)2SO4

RH

C

O

N

S

Excess N

N/Corganic

91±1.5% 72±1.5% 60±1.5% 38±1.5%

0.27 0.17 0.16 0.11

0.54 0.62 0.63 0.68

0.16 0.16 0.16 0.16

0.03 0.05 0.05 0.05

0.09 0.06 0.06 0.06

0.33±0.04 0.35±0.07 0.38±0.06 0.55±0.08

95±1.5% 70±1.5% 55±1.5% 28±1.5%

0.21 0.15 0.11 0.03

0.49 0.50 0.51 0.56

0.23 0.25 0.26 0.27

0.07 0.11 0.12 0.14

0.09 0.04 0.02 0

0.41±0.07 0.27±0.09 0.18±0.13 0

556

23



557

FIGURES

558 559 560

561 562 563 564 565 566 567

Figure 1. High-resolution ESI mass spectrum of the glyoxal/ammonium sulfate nanodroplets collected onto a filter after drying to 60% RH. Peaks shown in black correspond to compounds assigned elemental formulas containing only carbon, oxygen, and hydrogen, whereas peaks shown in red correspond to compounds containing organic nitrogen. Major peaks are labeled with nominal m/z values. Accurate measurements and molecular assignments are given in Figure S2.

568 569

24


Page 24 of 27

Page 25 of 27

O+3 100

% Relative Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C+3/O+4 80 O+2/S+4 60 40

O+6 +5 N +4 C +5 O

N+3

C+2 N+2

N+4

20

S+3

S+5 2

570 571 572

3

4

5

6

7

8

9

10

11

m/z (+) Figure 2. NAMS-II averaged mass spectrum of ~200 individual particle spectra collected from the glyoxal/ammonium sulfate nanodroplets after drying to 60% RH.

573 574

25



575 576 577 578 579 580

Figure 3. Relative humidity dependence of the organic N/C ratio (a) and C/S ratio (b) measured by NAMS-II for the GLY/AS and MGLY/AS dried droplets. Y-error bars represent one standard deviation of the means, and x-error bars represent the uncertainty of the hygrometer probe (±1.5%). Excess N was not observed in the lowest RH trial of the MGLY/AS system, shown as an open diamond in (a).

581 582

26


Page 26 of 27

Page 27 of 27

583

TOC Graphic

584

0.4

0.2

0.0

G LY M G Le LY w es ,D E

585

0.6

Organic N/C ratio

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


27


Aqueous Reaction of Dicarbonyls with Ammonia ... - ACS Publications

Recommend Documents