Concentrations and Photochemistry of Acetaldehyde, Glyoxal, and

Subscriber access provided by Nottingham Trent University

Environmental Processes

Concentrations and Photochemistry of Acetaldehyde, Glyoxal and Methylglyoxal in the Northwest Atlantic Ocean Yuting Zhu, and David John Kieber Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b01631 • Publication Date (Web): 22 Jul 2019 Downloaded from pubs.acs.org on July 23, 2019

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 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 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.

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

Page 1 of 32

Environmental Science & Technology

1

Concentrations and Photochemistry of Acetaldehyde, Glyoxal and Methylglyoxal in the

2

Northwest Atlantic Ocean

3 4 5 Yuting Zhu1 and David J. Kieber*

6 7 8 9 10 11 12

Department of Chemistry, State University of New York, College of Environmental Science and

13

Forestry, 1 Forestry Drive, Syracuse, New York 13210

14 15 16 17 18 19 20 21 22 23 24

1Present

25

12201, USA

Address: Wadsworth Center, New York State Department of Health, Albany, New York

26 27

*Corresponding

Author: [email protected], Phone: 1-315-470-6951, Fax: 1-315-470-6856

28

1 ACS Paragon Plus Environment


29 30

ABSTRACT The photochemical production and degradation of acetaldehyde, glyoxal and

31

methylglyoxal along with spatiotemporal variations in their concentrations were investigated in

32

the Northwest Atlantic Ocean from September to October 2016. Surface seawater concentrations

33

did not exhibit day-night differences, and ranged from 1.0–7.1, 1.4–4.8, and 0.25–2.8 nmol L-1

34

for acetaldehyde, glyoxal and methylglyoxal, respectively. Higher glyoxal and methylglyoxal

35

concentrations were observed in biologically productive seawater from Georges Bank and

36

coastal Rhode Island compared to the oligotrophic Sargasso Sea, whereas no differences were

37

seen in acetaldehyde concentrations among these stations. Carbonyl photoproduction rates in

38

surface seawater ranged from 0.35–0.79, 0.06–0.2, and 0.02–0.07 nmol L-1 h-1 for acetaldehyde,

39

glyoxal and methylglyoxal, respectively. Methylglyoxal slowly photodegraded in seawater

40

(~0.001–0.03 nmol L-1 h-1), whereas acetaldehyde and glyoxal were photochemically stable.

41

Photochemical sources explained from ~7 to 53% of the estimated total production of

42

acetaldehyde in the surface mixed layer; a similar estimate could not be determined for glyoxal

43

or methylglyoxal, since several processes have not been quantified that potentially affect their

44

concentrations. Our results suggest that acetaldehyde is likely supersaturated in surface seawater

45

relative to its typical atmospheric concentrations, whereas glyoxal and methylglyoxal are

46

significantly undersaturated.

47 48 49

INTRODCUTION Acetaldehyde, glyoxal and methylglyoxal are ubiquitous in the oceans and atmosphere.1,2

50

These species are important components in the marine food web3 and in the photochemical

51

cycling of marine dissolved organic matter.4 In the troposphere, acetaldehyde is an important


Page 2 of 32

Page 3 of 32


52

intermediate in the formation of ozone, peroxyacyl nitrates and hydrogen oxide radicals,5,6 while

53

glyoxal and methylglyoxal are sources of secondary organic aerosol.7,8 There is an important

54

controversy regarding the direction and magnitude of their air-sea exchange, as the contribution

55

of the oceans as a source or removal of these carbonyl compounds in atmospheric budgets is

56

poorly constrained.9–12

57

The ocean is considered a net source of acetaldehyde into the atmosphere.9,10,13 However,

58

uncertainties persist in the ocean’s contribution to the tropospheric acetaldehyde budget (3–57

59

Tg y-1),9,10,13,14 largely due to a lack of data regarding acetaldehyde concentrations in seawater.1

60

Modeling acetaldehyde concentrations in surface seawater is necessary to estimate air-sea fluxes

61

in large-scale models.9 This can be accomplished by either measuring concentrations directly or

62

by measuring production and removal rates. Nearly all rate data have been obtained in coastal

63

waters, not enough to extrapolate photochemical production rates15,17–20 or biological removal

64

rates19–22 to large geographic scales encompassing oligotrophic waters. Photochemical

65

degradation21 and biological production23 may also affect acetaldehyde concentrations, but have

66

not been considered in modelling efforts due to the paucity of data.

67

There is a missing oceanic source of glyoxal and methylglyoxal in current atmospheric

68

models,11,12 as continental sources fail to account for their high mixing ratios in the remote

69

marine atmosphere (7–80 pptv and 10–28 pptv, respectively).11,12,24,25 However, surface seawater

70

concentrations are too low (0.3–5.6 nM and 0.1–3.4 nM, respectively)15,21,24,26 to serve as a

71

source for these compounds in the marine boundary layer (MBL). Therefore, the oceans are

72

likely a sink in the tropospheric budget of these dicarbonyl compounds and not a source as

73

suggested by several investigators.7,11,27



74

The controversy over the direction of the air-sea fluxes for glyoxal and methylglyoxal is

75

largely due to a lack of dicarbonyl concentration measurements in surface seawater, and, as with

76

acetaldehyde, factors affecting dicarbonyl concentrations in seawater are poorly parameterized.

77

Photochemical production is an important dicarbonyl source in the surface oceans, but removal

78

pathways are not known. Published photoproduction rates range between 0.25–1.0 and 0–0.7 nM

79

h-1 for glyoxal and methylglyoxal, respectively.15,17,18 Similar to acetaldehyde, it is premature to

80

extrapolate this limited dataset regionally or globally to predict dicarbonyl seawater

81

concentrations in large-scale models.

82

It is not known whether carbonyl compounds photolyze in seawater and affect carbonyl

83

concentrations in the surface oceans. Carbonyl compounds absorb solar radiation in natural

84

waters at wavelengths > 290 nm corresponding to a forbidden n to π* transition,28 and therefore

85

may undergo direct photolysis in seawater. However, this is offset by their hydration, since the

86

hydrated gem diol will not absorb solar radiation reaching the sea surface.29 In cloud water, C1-

87

C3 carbonyl compounds are likely photochemically stable, primarily because they are partially

88

or completely hydrated.30

89

In the present study, spatiotemporal variations in acetaldehyde, glyoxal and

90

methylglyoxal concentrations were determined in the Northwest Atlantic Ocean during a

91

research cruise aboard the R/V Endeavor to investigate the relationship between carbonyl

92

concentrations and environmental parameters. Carbonyl photochemical production rates were

93

also determined during the cruise at two productive and two oligotrophic stations, and photolysis

94

rates were determined using stored 0.2 µm-filtered seawater collected during the cruise. A

95

qualitative assessment of the contribution of photochemistry to acetaldehyde cycling in the ocean


Page 4 of 32

Page 5 of 32


96

surface mixed layer was then made to other biogeochemical processes (i.e., air-sea exchange,

97

biological production) to guide future research on this topic.

98 99 100

MATERIALS AND METHODS Chemicals and Glassware. Acetaldehyde (≥99.5%), glyoxal (40% in water) and

101

methylglyoxal (40% in water) were obtained from Sigma-Aldrich. Acetonitrile (ACN) and

102

methanol were high performance liquid chromatography (HPLC) grade (JT. Baker, Central

103

Valley, PA). High-purity laboratory water (18.2 M cm), hereafter referred to as Milli Q water,

104

was obtained from a Milli Q® gradient A10 ultrapure water system (EMD Millipore, Billerica,

105

MA). The 2,4-dinitrophenylhydrazine, (DNPH, Sigma-Aldrich) was recrystallized twice from

106

heated ACN and stored in the dark at room temperature. The DNPH reagent was prepared by

107

adding ~27 mg recrystallized DNPH to 20 mL solution containing 12 M HCl (reagent grade, J.T.

108

Baker), ACN and Milli Q water (2:5:1, v:v:v).31 Reagent grade carbon tetrachloride (99.9% CCl4,

109

Sigma-Aldrich), was used to purify the DNPH reagent solution.31

110

All glassware was first rinsed with Milli Q water and muffled at 550 C for 8 h.

111

Thermoset screw caps with Teflon-faced silicone inserts were used to tightly seal Qorpak

112

glassware before and after seawater sampling and sample derivatization with DNPH.

113 114

Field Sampling. Seawater samples were collected from the Northwest Atlantic Ocean at

115

four stations, Georges Bank (GB, 41.40 °N, 67.47 °W), Sargasso Sea 1 (SS1, 35.04 °N,

116

69.98 °W), Sargasso Sea 2 (SS2, 36.26 °N, 64.78 °W), and coastal Rhode Island near Block

117

Island (BI, 41.18 °N, 71.16 °W), during the EN589 research cruise aboard the R/V Endeavor

118

from September 16 to October 13, 2016. Hydrographic stations are shown in Figure S1 with



119

hydrographic details given in Table S1. Samples were collected in 12 L Niskin bottles attached

120

to a CTD rosette equipped with Sea-Bird Electronic SBE sensors for conductivity, temperature,

121

and pressure.

122

Seawater samples for photochemistry experiments were gravity filtered from the Niskin

123

bottles with silicone tubing through precleaned32 0.2-µm POLYCAP 75 AS Nylon filters

124

(Whatman) into five 4 L Qorpak glass bottles. The Qorpak bottles were filled with minimum

125

headspace (~3 mL), sealed tightly, and stored in the dark at 4 C until use.

126

Seawater samples used to quantify chromophoric dissolved organic matter (CDOM)

127

absorption spectra, chlorophyll a (Chl a), and carbonyl concentrations were collected at depth

128

with Niskin bottles or at the sea surface using an all-polypropylene bucket. CDOM samples were

129

gravity filtered through a 0.2 µm Whatman Polycap 36AS filter capsule or a precombusted (550

130

C, 8 h) 47 mm diameter GF/F glass fiber filter (Whatman) into 100 mL glass Qorpak bottles

131

leaving very little headspace. Filtered CDOM samples were stored in 100 mL Qorpak bottles in

132

the dark at room temperature prior to analysis in Syracuse, NY. For Chl a, filtration, extraction

133

and analytical details, together with the cruise chlorophyll a dataset, are available from

134

https://www.bco-dmo.org/dataset/710245.

135

Seawater samples collected for carbonyl concentration determinations were gravity

136

filtered through precombusted (550 C, 8 h), 47 mm diameter GF/F glass fiber filters (nominal

137

pore size 0.7 μm) into 5 mL Qorpak vials leaving no headspace, sealed tightly, and derivatized,

138

generally within 30 min but no longer than 1 h of sampling. Prior to derivatization, the DNPH

139

reagent was centrifuged at 1200 rpm for 5 min to separate the aqueous and CCl4 phases.

140

Carbonyl sampling and DNPH additions were done upwind of the ship’s exhaust as the ship

141

headed into the wind to minimize shipboard contamination; for each sample, the vial was rinsed


Page 6 of 32

Page 7 of 32


142

several times with the GF/F-filtered seawater prior to sample collection. A 50 µL aliquot of the

143

DNPH reagent was added to a 5 mL of sample or standard in a Qorpak vial using an Eppendorf

144

model 4780 repeating pipet with a 2.5 mL positive displacement tip. Once reagent was dispensed,

145

the sample vial was quickly screw capped and allowed to react between 12 and 48 h prior to

146

HPLC analysis (see S1 and Zhu and Kieber33) in the main laboratory on board the R/V Endeavor.

147

During the cruise, we compared carbonyl concentrations determined in 0.7 μm gravity-filtered

148

seawater and 0.2 μm gravity filtered (POLYCAP) seawater on several occasions and found no

149

differences. For example, acetaldehyde, glyoxal and methylglyoxal concentrations (± σ) at

150

station SS2 in one CTD cast for the two methods were: 2.74±0.40 vs 2.36±0.49 nM, 1.43±0.04

151

vs 1.38±0.18 nM, and 0.49±0.03 vs 0.56±0.08 nM, respectively.

152

The depth of the surface mixed layer at SS1 and SS2 was determined by the onset of a

153

seawater potential density anomaly of 0.125 kg m-3 relative to near-surface seawater.34 For the

154

shallow-water stations, GB and BI, we did not collect CTD data from seawater deeper than 30 m,

155

and over this depth range the water column was well mixed.

156

Carbonyl Photoproduction and Photolysis Experiments. Shipboard irradiation

157

experiments were conducted with 0.2 µm gravity-filtered seawater samples at GB, BI, SS1 and

158

SS2. For each station, 0.2-µm filtered seawater was transferred from a 4 L Qorpak bottle to

159

Teflon-sealed quartz tubes35 (2 cm ID, ~90 mL) within 24 h after sampling and 1 h before

160

sunlight exposure on the aft deck of the R/V Endeavor. For each experiment, four irradiated

161

seawater samples and four dark controls (wrapped in several layers of aluminum foil) were

162

placed in a 3-cm deep circulating seawater bath along with actinometry vials to measure the

163

photon exposure (see section S1 for details). The water-bath temperature ranged from 18.0 to

164

29.5 C, depending on the sampling location (e.g., 21 and 29 C for GB and SS1, respectively);



165

the water-bath temperature varied by < 2 C during an experiment. Samples were exposed to

166

solar radiation from ~0900 to ~1700 local time. The solar irradiance was determined with a

167

NIST-traceable calibrated OL-754 Spectroradiometer (Optronics) that was located ~10 m above

168

sea level. The OL-754 recorded the solar irradiance from 290–600 nm every 15 min at 1 nm

169

intervals.

170

Acetaldehyde, glyoxal and methylglyoxal concentrations were determined in the seawater

171

used for the photochemical experiment and in each quartz tube at the end of the experiment (for

172

details see section S2 and Zhu and Kieber33). To quantify carbonyl concentrations, seawater

173

samples were transferred directly from the quartz tubes into Milli Q water rinsed and pre-baked

174

(550 C, 8 h) 5 mL Qorpak vials leaving no headspace. Once a vial was flushed with a water

175

sample and overfilled, it was quickly sealed with a green thermoset screw cap leaving no

176

headspace. After sampling, each vial was briefly re-opened (facing the wind) to add the reagent

177

and then quickly reclosed. Separate samples were taken from the quartz tubes for all sunlight-

178

exposed samples and dark controls to determine seawater absorption spectra according to the

179

procedure outlined in the S3.

180

The photochemical degradation of acetaldehyde was determined using 14C-labeled

181

acetaldehyde freshly synthesized from uniformly labeled 14C ethanol according to the procedure

182

outlined in S4. Glyoxal and methylglyoxal photolysis rates were not determined with 14C-labeled

183

compounds, since they could not be synthesized easily prior to photochemical experiments.

184

Details for the experimental set up and carbonyl analyses for the photolysis experiments are

185

presented in section S5.


Page 8 of 32

Page 9 of 32

186


Statistical Analyses. Statistics were done using Sigmaplot 11.0 and SigmaStat. t-tests

187

were performed if data were normally distributed, and a Mann-Whitney Rank Sum test was used

188

when normality or equal variance tests failed. An α level of 0.05 was used for all statistics.

189 190 191

RESULTS AND DISCUSSION Spatiotemporal Variations in Carbonyl Concentrations in Near-Surface Seawater.

192

The spatial distribution of carbonyl concentrations observed in surface seawater (0–5 m) at all

193

sampling stations and along transects between stations in the Northwest Atlantic Ocean are

194

shown in Figure 1. Concentrations of acetaldehyde, glyoxal and methylglyoxal ranged from 1.0–

195

7.1, 1.4–4.8, and 0.25–2.8 nM, with average concentrations (± σ) of 3.02 (±1.1), 2.51 (±0.9), and

196

0.82 (±0.6) nM, respectively. The biologically productive stations (i.e., Georges Bank and

197

coastal Rhode Island) were characterized by relatively high levels of CDOM (a320nm > 0.63 m-1),

198

Chl a (1.4–3.5 µg/L), and cooler temperatures (17.1–18.7 C) compared to surface seawater in

199

the two Sargasso Sea stations, which were warmer (24.3–28.2 C) and had lower levels of

200

CDOM (0.08 < a320nm < 0.13 m-1) and Chl a (0.03–0.05 µg/L) (Figure 1). A similar trend was

201

observed for glyoxal and methylglyoxal; concentrations (average ± σ) were significantly higher

202

(3.28 ± 0.69 and 1.24 ± 1.24 nM, respectively) in CDOM-rich, productive and cooler seawater at

203

GB and BI compared to concentrations observed in the oligotrophic and warmer Sargasso Sea

204

stations (1.65 ± 0.19 and 0.43 ± 0.17 nM, respectively) (p < 0.001, Mann-Whitney Rank Sum

205

Test). This finding is consistent with prior results showing elevated dicarbonyl concentrations in

206

the gas phase36,37 and aerosols in the MBL overlying biological productive ocean waters,38,39

207

suggesting a possible link between dicarbonyl production in the MBL and biological activity

208

(e.g., isoprene production) in the underlying seawater. In contrast, acetaldehyde concentrations



209

showed no significant differences between biologically productive and oligotrophic waters, with

210

average ± σ concentrations of 3.28 ± 1.46 and 2.71 ± 0.64 nM, respectively (p > 0.05, Mann-

211

Whitney Rank Sum Test).

212

A positive correlation (r =0.81) was obtained between glyoxal and methylglyoxal surface

213

concentrations (Figure S2), suggesting that the cycling of these two dicarbonyl compounds may

214

be controlled by similar pathways in surface waters. A gale occurred in the vicinity of the BI

215

station on October 9th (Figure 1, panel B), with carbonyl sampling commencing on October 10th;

216

the unusually high dicarbonyl concentrations (Figure 1, panels E–F) were likely the result of

217

strong winds mixing bottom sediments into the water column at this shallow-water station (ca.

218

42 m). Therefore, surface dicarbonyl concentrations from BI were not included in the correlation

219

shown in Figure S2.

220

Acetaldehyde concentrations remained relatively constant regardless of changes in the

221

wind speed, seawater optical properties or shortwave solar irradiance from 295 to 2800 nm

222

(Figure 1). Likewise, no correlation was observed between acetaldehyde concentrations and

223

either glyoxal or methylglyoxal, perhaps because acetaldehyde had much higher photochemical

224

production rates and potentially faster biological turnover times (≤ 1 d) compared to the

225

dicarbonyl compounds.21 Turnover times ≤ 1 d were previously observed for acetaldehyde in

226

oligotrophic waters and in an eutrophic upwelling region in the North Atlantic Ocean.19

227

There was good agreement between carbonyl concentrations measured in this study and

228

literature values. Surface mixed layer acetaldehyde concentrations measured in this study are

229

within the range of previously reported concentrations measured in the Atlantic Ocean and the

230

North Pacific Ocean (1–9 nM).13–15,24,40 Likewise, concentrations of glyoxal and methylglyoxal

231

determined here in the NW Atlantic agree with those reported in the Sargasso Sea, the Caribbean


Page 10 of 32

Page 11 of 32


232

Sea, and in coastal samples from Capetown to Bremerhaven (0.3–5.6 nM and 0.1–3.4 nM for

233

glyoxal and methylglyoxal, respectively).15,24,26

234

Carbonyl concentrations were previously shown to exhibit day-night variations in surface

235

seawater, with the highest concentrations observed in the early afternoon and the lowest

236

concentrations detected before dawn.15,16 In the present study, concentrations from all stations,

237

including the underway stations, collected during the day were compared to those collected

238

during the night/early morning (19:00–8:00). Average acetaldehyde, glyoxal and methylglyoxal

239

concentrations ± σ were 3.33 ± 1.2, 2.45 ± 0.93, 0.89 ± 0.71 nM during the day and 2.47 ± 0.81,

240

2.58 ± 0.87, 0.70 ± 0.41 nM during the night/early morning, respectively. When day and night

241

concentrations were compared, no significant differences were seen for glyoxal or methylglyoxal

242

(p > 0.05, Mann-Whitney Rank Sum test), whereas for acetaldehyde daytime concentrations

243

were significantly higher, but only slightly (ca. 1 nM) compared to the night/early morning (p
0.05, t-

415

test) were observed between acetaldehyde losses in light-exposed samples and dark controls for

416

Milli Q water and seawater from SS1. For seawater from station GB, 14C acetaldehyde decreased

417

slightly faster in dark controls compared to light incubations (p < 0.05, t-test). The observed

418

acetaldehyde losses were not due to microbial consumption, since seawater samples were 0.2-µm

419

filtered twice, once during sample collection during the EN589 cruise and a second time just

420

prior to the photolysis experiment; losses were likely not due to chemical reactions (e.g., aldol

421

condensation) either, since concentrations were low. Observed losses were also not due to the

422

photolysis of acetaldehyde, since no differences were seen between light-exposed samples and

423

dark controls in Milli Q water or SS1 seawater, and losses were less in light-exposed samples

424

compared to dark controls at station GB.

425

Observed losses of 14C-labelled acetaldehyde in seawater were less than 0.73 nM over the

426

9 h incubation, which translated to a loss rate less than ~0.08 nM h-1. This loss rate is slower

427

than our measured acetaldehyde photoproduction rates by ~1 order of magnitude. One possible

428

explanation for observed losses in the light and dark samples was that acetaldehyde interacted

429

with the inner surface of the quartz tubes and/or Teflon stoppers. Although losses to the glass

430

surface are possible, it is much more likely that acetaldehyde losses occurred entirely or partly

431

through diffusion through the Teflon stoppers, since acetaldehyde diffuses through Teflon.52

432

Irrespective of the mechanism for the observed loss, overall the loss of 14C-acetaldehyde

433

was negligible in seawater (16 and 24% over 9 h for SS1 and GB, respectively) and much slower

434

than observed rates of photoproduction. Although 14C-acetaldehyde losses were observed, total

435

acetaldehyde concentrations (sum of radioactive and nonradioactive acetaldehyde) remained



436

constant at ~6 and 7 nM throughout the dark incubations for up to 9 h in GB and SS1 seawater,

437

respectively (p > 0.05). Ambient acetaldehyde concentrations did not change in the dark controls

438

because they were likely close to equilibrium with 12C-acetaldehyde in the Teflon stoppers

439

yielding no net diffusion through the Teflon, since most of the total acetaldehyde was 12C-

440

acetaldehyde (ca. 70%).

441

Implications for Carbonyl Cycling. The role of photochemistry in regulating carbonyl

442

concentrations in the surface mixed layer was evaluated for acetaldehyde using a simple box

443

model, assuming that vertical and horizontal mixing were, to a first order approximation,

444

negligible. We only considered acetaldehyde, since no biological uptake or production data are

445

available to constrain the model for glyoxal or methylglyoxal.

446

Since observed temporal and surface mixed layer depth variations in carbonyl

447

concentrations at each hydrographic station were small, it was reasonable to assume that

448

carbonyl concentrations were approximately in steady state. Therefore, production rates should

449

be approximately equal to loss rates in the surface mixed layer. For acetaldehyde, we assumed to

450

a first order approximation that microbial consumption was responsible for 100% of its loss,

451

since rates of other potential loss terms have not been reported in the literature and photolysis is

452

negligible. We used a published lifetime for biological consumption of 1 d (the upper limit of

453

acetaldehyde’s literature value for biological turnover obtained from light and dark

454

incubations)20–22 and treated the surface mixed layer as a simple box to calculate the total source

455

needed to balance its loss. The estimated total surface mixed layer source needed to balance the

456

biological loss of acetaldehyde was 30–212 and 46–140 µmol m-2 d-1 for coastal and oligotrophic

457

waters, respectively. By dividing the depth-integrated photochemical production rate (Table S2)

458

by the total source, it was determined that photochemical production was responsible for 7–23


Page 20 of 32

Page 21 of 32


459

and 26–53% of the gross production of acetaldehyde in the coastal and oligotrophic ocean

460

surface mixed layer, respectively. When coastal and oligotrophic results are taken together,

461

photoproduction was responsible for an average of ~21% of the gross mixed layer production of

462

acetaldehyde in the study area. This generally agrees with Dixon et al.19 who observed that 17–

463

68% of the gross production of acetaldehyde in the Mauritanian upwelling region in the North

464

Atlantic Gyre was due to its photochemical production.

465

Our budget for acetaldehyde in the surface mixed layer is based on biological uptake data

466

that are highly variable spatiotemporally, since multiple physical, chemical and biological factors

467

may affect these rates. As such, the acetaldehyde budget presented here is meant to be a

468

qualitative assessment that biological processes are an important in acetaldehyde cycling in

469

seawater. Recent discoveries suggest that air-sea exchange13,53 and biological production23 can also

470 471

serve as sources of acetaldehyde in the surface mixed layer. For air-sea exchange, we have

472

discussed previously that air-sea fluxes for acetaldehyde vary in the literature by ± 5 µmol m-2 d-

473

1,

474

layer. Our preliminary estimate for the biological production rate based on the biological

475

production of acetaldehyde from axenic cultures of the diatom species T. pseudonana that was

476

shown by Halsey et al.23 (see section S9 for calculation details) is ~36–55 µmol m-2 d-1 in the

477

surface mixed layer in biologically productive waters at stations GB and BI and ~0.0006–0.0021

478

µmol m-2 d-1 in oligotrophic waters at stations SS1 and SS2. Based on this very preliminary

479

estimate (see section S9 for calculation uncertainties), the biological production of acetaldehyde

480

may be an important source for this compound in coastal waters (ca. ~27–85%), but only a minor

481

source in the Sargasso Sea (ca. < 003%) during our cruise.

which is small (ca. 4–17%) relative to our estimated total production flux in the surface mixed



482

It is unclear whether glyoxal and methylglyoxal cycling in the surface mixed layer is

483

regulated by their photochemical production since microbial consumption rates of these

484

compounds have not been determined in seawater. In the only study to date, there was no

485

biological consumption observed for glyoxal in unfiltered Hiroshima Bay seawater that was

486

incubated up to 48 h.21 This lack of biological turnover may explain why glyoxal maintains

487

steady-state concentrations only slightly lower than acetaldehyde even though its photochemical

488

production rates are ~4–6 times lower (Table 1). It is highly unlikely that air-sea exchange is a

489

major contributor for dicarbonyl cycling in surface seawater, since photochemical fluxes of

490

glyoxal and methylglyoxal are ~1–2 orders of magnitudes higher than calculated air-sea fluxes.

491

For both dicarbonyl compounds, uncertainties in estimating their sources and fates in the surface

492

mixed layer are associated with a lack of knowledge of potential biological sources, and

493

insufficient data for microbial consumption rates and air-sea fluxes.

494

Concentration and photochemical results presented here for acetaldehyde, glyoxal and

495

methylglyoxal in the NW Atlantic Ocean provide valuable insights into the biogeochemical

496

controls on carbonyl concentrations in seawater. However, these data cannot be used alone to

497

model carbonyl cycling in the surface mixed layer until corresponding biological production and

498

removal rates are studied in detail along with a better understanding of the factors that may affect

499

these rates. Especially problematic is the lack of knowledge regarding the biological release of

500

carbonyl compounds from the particulate phase into the dissolved phase or uptake into the

501

particulate phase from the dissolved phase, and the possible deleterious effects of UV radiation

502

on these processes, as has been shown to occur for a variety of other biologically-mediated

503

processes in natural waters.54 It will not be possible to use biogeochemical models to predict

504

carbonyl concentrations or air-sea fluxes with any confidence in seawater without further


Page 22 of 32

Page 23 of 32


505

elucidation of the biological controls on carbonyl cycling. For these biological controls,

506

molecular data are needed regarding specific microbial communities and metabolic pathways

507

that may be involved in carbonyl transformations (e.g., acetaldehyde metabolism in cells with the

508

SAR11 genome23).

509 510

NOTES

511

The authors declare no competing financial interest.

512 513

ACKNOWLEDGMENTS

514

We thank and the captain and crew of the R/V Endeavor for logistical support during the EN 589

515

marine aerosol cruise, and our colleagues Drs. William Keene, Amanda Frossard, Steven

516

Beaupre, Joanna Kinsey and Michael Long. This study was supported by NSF Chemical

517

Oceanography award OCE-1536605 to DJK. We thank Mr. Lei Xue for the spectrophotometer

518

flow cell pathlength determination and Mr. John Bisgrove for Optronics OL754 measurements.

519 520

SUPPORTING INFORMATION

521

The SI contains details for 14C acetaldehyde synthesis, quantification of carbonyl concentrations,

522

and seawater absorption measurements; and text with associated calculations for air-sea fluxes,

523

photon exposure, carbonyl photolysis, climatological spectral scalar irradiance, depth-dependent

524

photoproduction rates, and diatom production rates of acetaldehyde. Five supporting figures

525

depict sampling station locations; methylglyoxal vs glyoxal concentrations; salinity, temperature,

526

and a320nm depth profiles at SS1 and SS2; modeled acetaldehyde, glyoxal and methylglyoxal

527

depth-dependent photoproduction rates and depth profiles at GB, BI, SS1 and SS2; and



528

concentration of 14C acetaldehyde dark and sunlight-exposed Milli Q water or 0.2-µm filtered

529

SSI and GB seawater. Two supporting tables list hydrographic details of the main sampling

530

stations and summarize depth-integrated photochemical fluxes of carbonyl compounds in the

531

surface mixed layer at GB, BI, SS1 and SS2.

532 533

REFERENCES

534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567

(1) (2) (3) (4) (5) (6) (7) (8) (9)

(10)

(11) (12)

Carpenter, L. J.; Nightingale, P. D. Chemistry and release of gases from the surface ocean. Chem. Rev. 2015, 115 (10), 4015–4034. Lary, D. J.; Shallcross, D. E. Central role of carbonyl compounds in atmospheric chemistry. J. Geophys. Res. D 2000, 105 (D15), 19771–19778. Kieber, D. J.; McDaniel, J.; Mopper, K. Photochemical source of biological substrates in sea water: implications for carbon cycling. Nature 1989, 341 (6243), 637–639. Moran, M. A.; Zepp, R. G. Role of photoreactions in the formation of biologically labile compounds from dissolved organic matter. Limnol. Oceanogr. 1997, 42 (6), 1307–1316. Roberts, J. M. The atmospheric chemistry of organic nitrates. Atmos. Environ. 1990, 24 (2), 243–287. Singh, H. B.; Kanakidou, M.; Crutzen, P. J.; Jacob, D. J. High concentrations and photochemical fate of oxygenated hydrocarbons in the global troposphere. Nature 1995, 378 (6552), 50–54. 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. D 2008, 113 (15), D15303. Carlton, A. G.; Turpin, B. J.; Altieri, K. E.; Seitzinger, S.; Reff, A.; Lim, H.-J.; Ervens, B. Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments. Atmos. Environ. 2007, 41 (35), 7588–7602. Millet, D. B.; Guenther, A.; Siegel, D. A.; Nelson, N. B.; Singh, H. B.; de Gouw, J. A.; Warneke, C.; Williams, J.; Eerdekens, G.; Sinha, V.; Karl, T.; Flocke, F.; Apel, E.; Riemer, D.D.; Palmer, P.; Barkley, M. Global atmospheric budget of acetaldehyde: 3-D model analysis and constraints from in-situ and satellite observations. Atmos. Chem. Phys. 2010, 10 (7), 3405–3425. Singh, H. B.; Salas, L. J.; Chatfield, R. B.; Czech, E.; Fried, A.; Walega, J.; Evans, M. J.; Field, B. D.; Jacob, D. J.; Blake, D.; Heikes, B. Analysis of the atmospheric distribution, sources, and sinks of oxygenated volatile organic chemicals based on measurements over the Pacific during TRACE-P. J. Geophys. Res. D 2004, 109 (15), D15S07. Sinreich, R.; Coburn, S.; Dix, B.; Volkamer, R. Ship-based detection of glyoxal over the remote tropical Pacific Ocean. Atmos. Chem. Phys. 2010, 10 (23), 11359–11371. Lawson, S. J.; Selleck, P. W.; Galbally, I. E.; Keywood, M. D.; Harvey, M. J.; Lerot, C.; Helmig, D.; Ristovski, Z. Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere. Atmos. Chem. Phys. 2015, 15 (1), 223– 240. 24 ACS Paragon Plus Environment

Page 24 of 32

Page 25 of 32

568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613


(13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25)

(26) (27)

(28) (29)

Beale, R.; Dixon, J. L.; Arnold, S. R.; Liss, P. S.; Nightingale, P. D. Methanol, acetaldehyde, and acetone in the surface waters of the Atlantic Ocean. J. Geophys. Res. C 2013, 118 (10), 5412–5425. Yang, M.; Beale, R.; Liss, P.; Johnson, M.; Blomquist, B.; Nightingale, P. Air–sea fluxes of oxygenated volatile organic compounds across the Atlantic Ocean. Atmos. Chem. Phys. 2014, 14 (14), 7499–7517. Zhou, X.; Mopper, K. Photochemical production of low-molecular-weight carbonyl compounds in seawater and surface microlayer and their air-sea exchange. Mar. Chem. 1997, 56 (3–4), 201–213. Mopper, K.; Stahovec, W. L. Sources and sinks of low molecular weight organic carbonyl compounds in seawater. Mar. Chem. 1986, 19 (4), 305–321. Kieber, R. J.; Zhou, X.; Mopper, K. Formation of carbonyl compounds from UV-induced photodegradation of humic substances in natural waters: Fate of riverine carbon in the sea. Limnol. Oceanogr. 1990, 35 (7), 1503–1515. Mopper, K.; Zhou, X.; Kieber, R. J.; Kieber, D. J.; Sikorski, R. J.; Jones, R. D. Photochemical degradation of dissolved organic carbon and its impact on the oceanic carbon cycle. Nature 1991, 353 (6339), 60–62. Dixon, J. L.; Beale, R.; Nightingale, P. D. Production of methanol, acetaldehyde, and acetone in the Atlantic Ocean. Geophys. Res. Lett. 2013, 40 (17), 4700–4705. Beale, R.; Dixon, J. L.; Smyth, T. J.; Nightingale, P. D. Annual study of oxygenated volatile organic compounds in UK shelf waters. Mar. Chem. 2015, 171, 96–106. Takeda, K.; Katoh, S.; Mitsui, Y.; Nakano, S.; Nakatani, N.; Sakugawa, H. Spatial distributions of and diurnal variations in low molecular weight carbonyl compounds in coastal seawater, and the controlling factors. Sci. Total Environ. 2014, 493, 454–462. de Bruyn, W. J.; Clark, C. D.; Senstad, M.; Barashy, O.; Hok, S. The biological degradation of acetaldehyde in coastal seawater. Mar. Chem. 2017, 192, 13–21. Halsey, K. H.; Giovannoni, S. J.; Graus, M.; Zhao, Y.; Landry, Z.; Thrash, J. C.; Vergin, K. L.; de Gouw, J. Biological cycling of volatile organic carbon by phytoplankton and bacterioplankton. Limnol. Oceanogr. 2017, 62 (6), 2650–2661. Zhou, X.; Mopper, K. Apparent partition coefficients of 15 carbonyl compounds between air and seawater and between air and freshwater; implications for air-sea exchange. Environ. Sci. Technol. 1990, 24 (12), 1864–1869. Mahajan, A. S.; Prados-Roman, C.; Hay, T. D.; Lampel, J.; Pöhler, D.; Groβmann, K.; Tschritter, J.; Frieß, U.; Platt, U.; Johnston, P.; Kreher, K.; Wittrock, F.; Burrows, J. P.; Plane, J. M.C.; Saiz-Lopez, A. Glyoxal observations in the global marine boundary layer. J. Geophys. Res. D 2014, 119 (10), 6160–6169. van Pinxteren, M.; Herrmann, H. Glyoxal and methylglyoxal in Atlantic seawater and marine aerosol particles: method development and first application during the Polarstern cruise ANT XXVII/4. Atmos. Chem. Phys. 2013, 13 (23), 11791–11802. Coburn, S.; Ortega, I.; Thalman, R.; Blomquist, B.; Fairall, C. W.; Volkamer, R. Measurements of diurnal variations and eddy covariance (EC) fluxes of glyoxal in the tropical marine boundary layer: Description of the Fast LED-CE-DOAS instrument. Atmos. Meas. Tech. 2014, 7 (10), 3579–3595. Leighton, P. A.; Blacet, F. E. The photolysis of the aliphatic aldehydes. II. acetaldehyde. J. Am. Chem. Soc. 1933, 55 (5), 1766–1774. Bell, R. P.; Clunie, J. C. The hydration of acetaldehyde in aqueous solution. Trans. 25 ACS Paragon Plus Environment


614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659

(30) (31) (32) (33) (34) (35) (36) (37) (38)

(39)

(40)

(41) (42) (43)

(44)

Faraday Soc. 1952, 48, 439. Epstein, S. A.; Tapavicza, E.; Furche, F.; Nizkorodov, S. A. Direct photolysis of carbonyl compounds dissolved in cloud and fog droplets. Atmos. Chem. Phys. 2013, 13 (18), 9461– 9477. Kieber, R. J.; Mopper, K. Determination of picomolar concentrations of carbonyl compounds in natural waters, including seawater, by liquid chromatography. Environ. Sci. Technol. 1990, 24 (10), 1477–1481. Toole, D. A.; Kieber, D. J.; Kiene, R. P.; Siegel, D. A.; Nelson, N. B. Photolysis and the dimethylsulfide (DMS) summer paradox in the Sargasso Sea. Limnol. Oceanogr. 2003, 48 (3), 1088–1100. Zhu, Y.; Kieber, D. J. Wavelength and temperature-dependent apparent auantum yields for photochemical production of carbonyl compounds in the North Pacific Ocean. Environ. Sci. Technol. 2018, 52 (4), 1929–1939. Monterey, G.; Levitus, S. Seasonal Variability of Mixed Layer Depth for the World Ocean; National Oceanic and Atmosphric Administration: Silver Spring, Maryland, 1997. Kieber, D. J.; Yocis, B. H.; Mopper, K. Free-floating drifter for photochemical studies in the water column. Limnol. Oceanogr. 1997, 42 (8), 1829–1833. Lerot, C.; Stavrakou, T.; De Smedt, I.; Müller, J.-F.; Van Roozendael, M. Glyoxal vertical columns from GOME-2 backscattered light measurements and comparisons with a global model. Atmos. Chem. Phys. 2010, 10 (24), 12059–12072. Chan Miller, C.; Gonzalez Abad, G.; Wang, H.; Liu, X.; Kurosu, T.; Jacob, D. J.; Chance, K. Glyoxal retrieval from the Ozone Monitoring Instrument. Atmos. Meas. Tech. 2014, 7 (11), 3891–3907. Bikkina, S.; Kawamura, K.; Miyazaki, Y.; Fu, P. High abundances of oxalic, azelaic, and glyoxylic acids and methylglyoxal in the open ocean with high biological activity: Implication for secondary OA formation from isoprene. Geophys. Res. Lett. 2014, 41 (10), 3649–3657. Kawamura, K.; Hoque, M. M. M.; Bates, T. S.; Quinn, P. K. Molecular distributions and isotopic compositions of organic aerosols over the western North Atlantic: Dicarboxylic acids, related compounds, sugars, and secondary organic aerosol tracers. Org. Geochem. 2017, 113, 229–238. Kameyama, S.; Tanimoto, H.; Inomata, S.; Tsunogai, U.; Ooki, A.; Takeda, S.; Obata, H.; Tsuda, A.; Uematsu, M. High-resolution measurement of multiple volatile organic compounds dissolved in seawater using equilibrator inlet–proton transfer reaction-mass spectrometry (EI–PTR-MS). Mar. Chem. 2010, 122 (1–4), 59–73. Betterton, E. A.; Hoffmann, M. R. Henry’s Law constants of some environmentally important aldehydes. Environ. Sci. Technol. 1988, 22 (12), 1415–1418. Lp, H. S. S.; Huang, X. H.; Yu, J. Effective Henry’s law constants of glyoxal, glyoxylic acid, and glycolic acid. Geophys. Res. Lett. 2009, 36 (1), L01802. Zhou, S.; Gonzalez, L.; Leithead, A.; Finewax, Z.; Thalman, R.; Vlasenko, A.; Vagle, S.; Miller, L. A.; Li, S.-M.; Bureekul, S.; Furutani, H.; Uematsu, M.; Volkamer, R.; Abbatt, J. Formation of gas-phase carbonyls from heterogeneous oxidation of polyunsaturated fatty acids at the air–water interface and of the sea surface microlayer. Atmos. Chem. Phys. 2014, 14 (3), 1371–1384. Chiu, R.; Tinel, L.; Gonzalez, L.; Ciuraru, R.; Bernard, F.; George, C.; Volkamer, R. UV photochemistry of carboxylic acids at the air-sea boundary: A relevant source of glyoxal 26 ACS Paragon Plus Environment

Page 26 of 32

Page 27 of 32

660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690


(45)

(46) (47) (48) (49) (50) (51) (52) (53)

(54)

and other oxygenated VOC in the marine atmosphere. Geophys. Res. Lett. 2017, 44 (2), 1079–1087. Kieber, D. J.; Keene, W. C.; Frossard, A. A.; Long, M. S.; Maben, J. R.; Russell, L. M.; Kinsey, J. D.; Tyssebotn, I. M. B.; Quinn, P. K.; Bates, T. S. Coupled ocean-atmosphere loss of marine refractory dissolved organic carbon. Geophys. Res. Lett. 2016, 43 (6), 2765–2772. Denman, K. L.; Gargett, A. E. Time and space scales of vertical mixing and advection of phytoplankton in the upper ocean. Limnol. Oceanogr. 1983, 28 (5), 801–815. Lee, C.; Wakeham, S.; Arnosti, C. Particulate organic matter in the sea: The composition conundrum. AMBIO A J. Hum. Environ. 2004, 33 (8), 565–575. Kaiser, K.; Benner, R. Organic matter transformations in the upper mesopelagic zone of the North Pacific: Chemical composition and linkages to microbial community structure. J. Geophys. Res. C 2012, 117 (1), C01023. Reisch, C. R.; Stoudemayer, M. J.; Varaljay, V. A.; Amster, I. J.; Moran, M. A.; Whitman, W. B. Novel pathway for assimilation of dimethylsulphoniopropionate widespread in marine bacteria. Nature 2011, 473 (7346), 208–211. Radianingtyas, H.; Wright, P. C. Alcohol dehydrogenases from thermophilic and hyperthermophilic archaea and bacteria. FEMS Microbiol. Rev. 2003, 27 (5), 593–616. Zhu, Y. Photochemical Production, Photolysis, and Concentrations of Carbonyl Compounds in Seawater (Doctoral Dissertation), 2018. Tumbiolo, S.; Vincent, L.; Gal, J. F.; Maria, P. C. Thermogravimetric calibration of permeation tubes used for the preparation of gas standards for air pollution analysis. Analyst 2005, 130 (10), 1369–1374. Schlundt, C.; Tegtmeier, S.; Lennartz, S. T.; Bracher, A.; Cheah, W.; Krüger, K.; Quack, B.; Marandino, C. A. Oxygenated volatile organic carbon in the western Pacific convective center: ocean cycling, air–sea gas exchange and atmospheric transport. Atmos. Chem. Phys. 2017, 17 (17), 10837–10854. Aas, P.; Lyons, M. M.; Pledger, R.; Mitchell, D. L.; Jeffrey, W. H. Inhibition of bacterial activities by solar radiation in nearshore waters and the Gulf of Mexico. Aquat. Microb. Ecol. 1996, 11, 229–238.



691

FIGURES AND TABLES

692 693

Figure 1 (A) a320nm and chlorophyll a, (B) wind speed (black line) and seawater temperature

694

(blue line), (C) shortwave solar irradiance in air from 295 to 2800 nm (Eshortwave, W m-2)

695

measured by the Eppley Precision Spectral Pyranometer installed on the R/V Endeavor, (D)

696

acetaldehyde seawater concentrations and % saturation (red line) assuming 0.2 ppbv mixing ratio

697

above the seawater surface, (E) glyoxal and (F) methylglyoxal seawater concentrations all

698

plotted as a function of sampling day based on the local time. Note that no % saturation line is

699

presented for the dicarbonyl compounds in panels E and F because these compounds were

700

extremely undersaturated in seawater (< 1% saturation). Grey areas in the background of panels

701

C–F depict nighttime sampling periods (19:00–8:00). Sampling locations are shown in Figure S1.

702

Sampling periods for the main hydrographic stations are noted from left to right above panel A. 28 ACS Paragon Plus Environment

Page 28 of 32

Page 29 of 32


703 704

Figure 2 Depth profiles of reagent blank-corrected carbonyl compound concentrations and the

705

sigma theta density anomaly (σθ) at stations SS1 and SS2. The LOD is shown with a grey

706

vertical line for panels showing carbonyl concentrations. The dataset for each station was

707

averaged from three and two CTD casts for SS1 and SS2, respectively. Error bars denote

708

standard deviation. See Figure S3 for depth profiles of temperature, salinity and a320nm from the

709

same casts.

710



Page 30 of 32

711 712

Table 1 Concentrations of acetaldehyde (C2), glyoxal (G) and methylglyoxal (MG), a320nm,

713

water-bath temperature (T), and the photon exposure from 290 to 400 nm (𝐸𝑖𝑛𝑐𝑢𝑏) determined for

714

the shipboard solar irradiation experiments at the four main hydrographic stations. Dark (nM)a

715 716 717 718 719 720 721 722

GB SS1 SS2 BI

Light (nM)a

C2

G

MG

C2

G

MG

T (C)

2.3 (0.3) 3.2 (0.5) 2.4 (0.5) 3.3 (0.2)

3.1 (0.09) 1.5 (0.09) 1.4 (0.20) 3.3 (0.10)

0.96 (0.02) 0.42 (0.06) 0.56 (0.08) 1.2 (0.10)

8.5 (0.3) 6.4 (1.0) 5.0 (0.4) 9.5 (0.4)

4.2 (0.2) 2.2 (0.3) 1.8 (0.1) 4.9 (0.2)

1.5 (0.09) 0.7 (0.09) 0.7 (0.04) 1.7 (0.10)

21.0 29.4 28.8 19.7

aAverage

a320nm (m-1) 0.649 0.079 0.101 0.746

𝐸𝑖𝑛𝑐𝑢𝑏b (mol quanta m-2) 2.82 3.31 2.28 1.83

carbonyl concentration in the four quartz tubes incubated in the dark and exposed to sunlight (light). Values in parentheses represent the standard deviation. n = 12 for stations GB, SS1 and SS2, n = 8 for station BI including replication within a quartz tube. bThe photon exposure from 290 to 400 nm (𝐸 𝑖𝑛𝑐𝑢𝑏) was calculated from the photon exposure quantified by the nitrate and nitrite actinometers and the spectral shape of the noontime solar irradiance recorded by the OL-754 spectroradiometer; see section S1 for details regarding calculation of 𝐸𝑖𝑛𝑐𝑢𝑏.

723


Page 31 of 32


724

Table 2 Observed and climatological pseudo-first order photolysis rate constants (𝑘𝑃 ― 𝑜𝑏𝑠 and 𝑘𝑃,

725

respectively) for the photolysis of methylglyoxal in seawater when exposed to sunlight. The

726

water-bath temperature and a320nm are given for each photolysis experiment.

727 728 729 730

𝑘𝑃 ― 𝑜𝑏𝑠 𝑘𝑃 𝜏1/2 ― 𝑝ℎ𝑜𝑡𝑜 𝐸𝑖𝑛𝑐𝑢𝑏a T a320nm (m-1) (mol quanta m-2)-1 (d-1) (d) (mol quanta m-2) (C) GB 23.6 2.95 0.668 0.0479 0.135 5.1 SS1 24.1 3.25 0.110 0.0157 0.046 15 BI 23.0 2.98 0.740 0.0509 0.107 6.6 aPhoton exposure integrated from 290 to 400 nm (𝐸 𝑖𝑛𝑐𝑢𝑏). 𝐸𝑖𝑛𝑐𝑢𝑏 was calculated from the photon exposure quantified by the nitrate and nitrite actinometers and the spectral shape of the noontime solar irradiance recorded by the OL-754 spectroradiometer; see section S1 for details regarding calculation of 𝐸𝑖𝑛𝑐𝑢𝑏.



731 732

For Table of Contents only (Graphic Abstract):

733

734


Page 32 of 32

Concentrations and Photochemistry of Acetaldehyde, Glyoxal, and

Recommend Documents