Novel Method for Nitrogen Isotopic Analysis of Soil ... - ACS Publications

Article

A novel method for nitrogen isotopic analysis of soil-emitted nitric oxide (NO) Zhongjie Yu, and Emily M. Elliott Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 8, 2017

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

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

Page 1 of 44

Environmental Science & Technology

1

A novel method for nitrogen isotopic analysis of soil-

2

emitted nitric oxide (NO)

3

Zhongjie Yu* and Emily M. Elliott

4

University of Pittsburgh, Department of Geology and Environmental Science, Pittsburgh,

5

PA 15260, USA

6

* Corresponding author. Phone: (973) 718 0238; Fax: (412) 624 8780; Email: [email protected]

7 8 9 10 11 12 13 14 15 16 17 18 19 20

ACS Paragon Plus Environment


21

ABSTRACT

22

The global inventory of NOx (NOx=NO+NO2) emissions is poorly constrained with a

23

large portion of the uncertainty attributed to soil NO emissions that result from soil

24

abiotic and microbial processes. While natural abundance stable N isotopes (δ15N) in

25

various soil N-containing compounds have proven to be a robust tracer of soil N cycling,

26

soil δ15N-NO is rarely quantified due to the measurement difficulties. Here, we present a

27

new method that collects soil-emitted NO through NO conversion to NO2 in excess ozone

28

(O3) and subsequent NO2 collection in a 20% triethanolamine (TEA) solution as nitrite

29

and nitrate for δ15N analysis using the denitrifier method. The precision and accuracy of

30

the method were quantified through repeated collection of an analytical NO tank and

31

inter-calibration with a modified EPA NOx collection method. The results show that the

32

efficiency of NO conversion to NO2 and subsequent NO2 collection in the TEA solution

33

is >98% under a variety of controlled conditions. The method precision (1σ) and

34

accuracy across the entire analytical procedure are ±1.1‰. We report the first analyses of

35

soil δ15N-NO (-59.8‰ to -23.4‰) from wetting-induced NO pulses at both laboratory

36

and field scales that have important implications for understanding soil NO dynamics.

37 38

TOC Art

39


Page 2 of 44

Page 3 of 44


40

INTRODUCTION

41

Emissions of nitrogen oxides (NOx = NO + NO2) degrade air quality and affect global

42

tropospheric chemistry,1, 2 posing a significant danger to ecosystem and human health.3-6

43

Although fossil fuel combustion is currently the largest source of atmospheric NOx,7, 8

44

NO is also produced in and emitted from natural and fertilized soils.9-11 Due to the spatial

45

segregation of different NOx sources and the short boundary layer lifetime of NOx, there

46

are substantial areas of the world (e.g., tropical and agricultural regions) where the local

47

NOx budget is controlled exclusively by soil NO emissions.3, 7, 12-15 In these regions, soil

48

NO emissions govern the formation and lifetime of tropospheric ozone (O3) and hydroxyl

49

radical, driving reaction chains that produce environmentally important trace gases (e.g.,

50

nitric acid and peroxyacetyl nitrate) and biogenic secondary aerosols.4, 13, 16

51

Various processes, both microbial10, 17-19 and abiotic20-22, are capable of producing

52

NO in soils. Although the strong dependence of soil NO emission on edaphic and

53

climatic factors has long been demonstrated by laboratory and field studies,23-27 a

54

process-based understanding of soil NO dynamics is lacking.14, 28 More importantly, soil

55

NO emission often exhibits an episodic nature (e.g., time scale of minutes), with pulse-

56

like emission events being often triggered by rewetting of dry soils.12, 13, 29-33 In dry

57

agricultural soils, massive NO pulses triggered by coupled fertilization and precipitation

58

during warm seasons can result in daily O3 enhancement up to 16 ppbv.13 Unfortunately,

59

the sources of and processes controlling the pulsed soil NO emission are still

60

mysterious,13, 14 making it difficult to model and up-scale field-observed NO fluxes.

61

While empirical bottom-up models estimate that soil NO emission accounts for about

62

15% of the global NOx inventory,1 inversion of satellite-based NO2 observations have



63

indicated significant underestimates in soil NO emission (e.g., up to a factor of 3) at

64

various spatiotemporal scales.7, 12-16, 29, 34 Indeed, with the substantial reductions in NOx

65

emissions from combustion sources in many countries,2, 35 soils as a source of

66

atmospheric NOx may be more important than we thought, and there is a pressing need to

67

elucidate mechanisms underlying soil NO dynamics.13, 14

68

Stable nitrogen (N) isotope compositions at natural abundances (notated as δ15N)

69

in various soil N-containing compounds are a robust tracer of soil N cycling.36-39

70

Incorporation of δ15N-NO measurements into the soil N isotope systematics is expected

71

to provide a new process-level information of key mechanisms regulating NO production

72

and consumption in soil. Moreover, there is a growing interest in using δ15N of

73

atmospheric N oxides (e.g., NO2 and nitrate (NO3-)) as a tracer to partition NOx emission

74

sources over large spatial and temporal scales.40-43 This interest stems from the

75

observations that NOx emitted from different sources has distinct δ15N values44-49 and that

76

soil-emitted NO is presumably lower in δ15N than NOx from other natural and

77

anthropogenic sources.50-52

78

Despite its promising potential, soil δ15N-NO is rarely measured due to the

79

intermittent nature and low magnitudes of soil NO emission. A summary of published

80

NOx collection methods is provided in Table S1 in the supporting information (SI)),

81

highlighting that none of existing methods have been rigorously verified for their

82

suitability for soil-emitted NO. In pioneering work, Li and Wang50 fertilized a soil

83

monolith in the laboratory and collected NO by first converting NO to NO2 using a

84

chromium trioxide (CrO3)-impregnated solid oxidizer and then trapping the converted

85

NO2 in an annular denuder as nitrite (NO2-) for δ15N analysis. However, it is well


Page 4 of 44

Page 5 of 44


86

documented that NO oxidation efficiency of the CrO3 oxidizer varies dramatically with

87

sample relative humidity (RH) (e.g., 60%).53, 54 Due to this overlooked

88

humidity interference, it is unclear whether N isotopic fractionation can occur during the

89

NO oxidation under varying soil conditions. Recently, Fibiger et al.55 and Wojtal et al.56

90

presented a NOx collection method that utilizes a KMnO4+NaOH solution to actively

91

collect NOx as NO3- for δ15N-NOx determination. Sample δ15N-NOx must be calculated

92

using an isotope mass balance due to a high reagent blank in the solution (5-7 µM NO3-,

93

δ15N=~2‰)49, 55. While the precision of this approach is ±1.5‰, this method is

94

incompatible for δ15N-NO measurement of low and diffuse soil NO emissions, because

95

larger error is propagated from the isotope mass balance calculation if concentration and

96

δ15N value of collected soil NO are significantly lower than the blank.

97

Here, we present a new method for soil δ15N-NO determination (hereafter, “DFC-

98

TEA method”). This method collects NO through NO conversion to NO2 in excess O3

99

and subsequent NO2 collection in a triethanolamine (TEA) solution as NO2- and NO3- for

100

δ15N analysis. The NO collection approach is coupled to a soil dynamic flux chamber

101

(DFC) system for simultaneous NO flux and δ15N-NO measurements. Both laboratory

102

and field method verifications have been conducted to demonstrate suitability of the

103

DFC-TEA method for accurate and precise soil δ15N-NO determination.

104 105

EXPERIMENTAL SECTION

106

DFC system setup

107

The DFC is a technique that has been developed to continuously measure soil-atmosphere

108

fluxes of various compounds including NO.18, 19 A schematic of the developed DFC



109

system is shown in Figure 1. The system consists of five components: air purification unit,

110

gas dilution unit, flux chamber, NO-NOx-NH3 analyzer, and NO collection train. Zero air

111

free of NOx and O3 is produced in the air purification unit for purging the flux chamber

112

and providing air to a O3 generator (Model 146i, Thermo Fisher Scientific) in the NO

113

collection train. NO, NO2, and ammonia (NH3) concentrations in the chamber headspace

114

are measured alternately by a chemiluminescent analyzer (Model 17i, Thermo Fisher

115

Scientific) at 10 s intervals for flux calculations. For method development, reference NO,

116

NO2, and NH3 from three analytical tanks were diluted into the purging flow to simulate

117

soil gas emissions inside the chamber. Two versions of the DFC system were developed

118

for laboratory and field experiments. In the laboratory DFC system, a 1 L Teflon flow-

119

through jar is used as the flux chamber. For the field DFC system, we fabricated a

120

cylindrical flow-through chamber (39 cm I.D. and 30 L inner volume; Figure 1b),

121

following considerations57, 58 for minimizing pressure differentials in chamber headspace.

122

Control tests indicate that NO transmission from the chamber is greater than 98.3%.

123

Details about the flux measurement, the chamber tests and the specifications for each

124

DFC component are provided in the SI.

125

NO collection train

126

To collect NO for δ15N-NO analysis, a Teflon-coated diaphragm pump is used to sample

127

chamber air passing through the NO collection train (Figure 1). The sample flow rate (1.6

128

standard liter per minute (slpm)) is controlled by a mass flow controller. For the NO

129

conversion in excess O3, a length of Teflon tubing (9.5 mm I.D., ca. 240 cm length)

130

serves as the reaction tube. A O3 flow of 0.4 slpm, produced from photolysis of O2 in

131

zero air at 185 nm by the O3 generator, is mixed with the sample flow at the starting point


Page 6 of 44

Page 7 of 44


132

of the reaction tube (Figure 1). To prevent generation of HOx radicals during the

133

photolysis, water vapor is removed from the zero air using two drying columns and a

134

Teflon filter is attached before the O3 addition point to decompose remaining HOx

135

radicals.59 Long-term (5 months) average O3 concentration after the mixing of the sample

136

and O3 flows was 2911±32 ppbv as measured by an O3 monitor (Model 202, 2B

137

Technologies). The flow leaving the reaction tube is forced to pass through a 500 mL gas

138

washing bottle with a fritted cylinder containing a solution of TEA (Fisher Scientific,

139

Certified Grade) in water (20% (v/v), 70 mL). The stopper of the gas washing bottle was

140

lengthened so that 70 mL of the solution just covered the frit.

141

Determination of reaction time

142

Reaction of NO with excess O3 forms NO2 (R1 in Table S3 in the SI). In a dark

143

environment, the efficiency of NO to NO2 conversion is limited by the formation of

144

higher nitrogen oxide species (i.e. nitrate radical (NO3) and dinitrogen pentoxide (N2O5);

145

R2-R5 in Table S3 in the SI).59-63 In order to model the NO conversion in the reaction

146

tube, the reaction time is needed. Following Fuchs et al.,61 the reaction time in the

147

reaction tube was experimentally determined by sampling zero air that contained a

148

constant NO concentration (27 ppbv) using the NO collection train and varying the

149

excess O3 concentrations (266-2890 ppbv). The ending point of the reaction tube was

150

attached to the sampling inlet of the chemiluminescent analyzer for NO concentration

151

determination. The NO concentration decay was then fitted to a single exponential

152

function assuming pseudo-first order loss of NO in excess O3 (details are described in the

153

SI). Due to the inner tubing of the chemiluminescent analyzer, the estimated reaction

154

time essentially includes the reaction tube plus the analyzer inner tubing. To correct this



155

overestimate, the reaction time of the inner tubing was estimated by repeating the

156

experiment with the mixing point of the sample and O3 flow directly attached to the

157

analyzer inlet for NO concentration determination.

158

Preparation of TEA solution

159

Triethanolamine is a tertiary amine and has long been used to scrub acidic gases in fuel

160

gas treating processes and to coat passive filters for ambient NO2 monitoring.52, 64-66 We

161

used a 20% TEA solution for NO2 collection. Its reagent N blank was determined to be

162

0.12±0.04 µM (details are given in the SI).

163

It is reported that aging of the TEA solution can cause significant efficiency

164

decrease in collecting NO2.55 This aging problem may occur to a greater degree with

165

more diluted TEA solutions.55 Therefore, to minimize alteration of TEA from its original

166

state, we sub-sampled new TEA (i.e., freshly opened bottle) into 15 mL glass vials in a

167

glovebox with a 95% N2 + 5% H2 atmosphere to avoid contact with ambient air. Vials

168

were then capped, tightly wrapped with Parafilm, sealed in Ziploc bags, and stored under

169

dark at 4 °C until further use. One glass vial was opened to make a fresh 20% TEA

170

solution immediately prior to each sample collection. The storage time of TEA used in

171

this study was up to approximately 4 months since sub-sampling.

172

Measurement of NO2- and NO3- in TEA solution

173

Both NO2- and NO3- can be produced from the reaction between NO2 and TEA.64-66 NO2-

174

+NO3- concentration in the TEA collection samples was measured using a modified

175

spongy cadmium method.67 Detailed measurement protocol is given in the SI. Control

176

tests using 10 µM NO2- or NO3- in 20% TEA solution indicate that the precision (1 σ,

177

n=8) of the method is ±0.09 µM and ±0.36 µM for NO2- and NO3- measurements,


Page 8 of 44

Page 9 of 44


178

respectively. Due to the multiple reduction and neutralization steps during the

179

measurements and the N blank inherent to the 20% TEA solution (~0.12 µM), standards

180

were always prepared in 20% TEA solution for concentration calibration.

181

Isotopic analysis

182

The isotopic composition of collected NO2- and NO3- in the TEA solution was measured

183

using the bacterial denitrifier method.68-69 In brief, denitrifying bacteria lacking the N2O

184

reductase enzyme (Pseudomonas aureofaciens) are used to convert 5-20 nmol of NO2-

185

and NO3- into gaseous N2O. Using He as a carrier gas, the N2O is then purified in a series

186

of chemical traps, cryo-focused, and finally analyzed on a GV Instruments Isoprime

187

Continuous Flow Isotope Ratio Mass Spectrometer at m/z 44, 45, and 46 at the University

188

of Pittsburgh Regional Stable Isotope Lab for Earth and Environmental Science

189

Research.

190

Special considerations were taken during the isotopic analysis to ensure precise

191

and accurate measurement of the δ15N of the TEA collection samples. First, the TEA

192

collection samples were neutralized using 12 N HCl to pH ~8 before sample injection to

193

avoid overwhelming the buffering capacity of the bacterial medium.70 Second, in light of

194

the expected low δ15N of soil-emitted NO50-52 and the presence of NO2- as the dominant

195

collection product (see below), a NO2- isotopic standard with low δ15N value (KNO2,

196

RSIL20, USGS Reston; δ15N = -79.6‰, δ18O = 4.5‰)70 is used together with other

197

international NO3- reference standards (IAEA-N3, USGS34, and USGS35) to calibrate

198

δ15N and δ18O measurements. Third, following the IT principle (i.e., identical treatment

199

of sample and reference material), a blank-matching strategy is used to make the isotopic

200

standards in the same matrix (i.e., 20% TEA) as collection samples and to match both the



201

molar N amount and injection volume (±5%) between the collection samples and the

202

standards (Figure 2). This ensures that the isotopic interference of any blank N associated

203

with the bacterial medium68, 71 and the TEA solution is minimized. The percentage

204

difference (Pdiff) in the major N2O (m/z 44) peak area between each collection sample and

205

RSIL20 measured within the same batch is calculated to quantify how precisely the

206

blank-matching strategy is implemented (Figure 2). Finally, the ∆17O (∆17O=δ17O -

207

0.52×δ18O)72 of the analyte N2O is independently measured for collected samples with

208

sufficient concentration for 50 nmol injection using the N2O thermal decomposition

209

method.73 The resolved ∆17O is then used to correct the isobaric interference on the δ15N

210

analysis resulting from the NO oxidation by O3 according to Kaiser et al.73

211

Quantification of method precision and accuracy

212

The precision of the DFC-TEA method was quantified through repeated NO collection

213

using the reference NO tank (50.4 ppmv). The collection was conducted under a variety

214

of conditions, including differing NO concentrations (12-749 ppbv), chamber

215

temperatures (11.5-30.8 °C), RH (27.1-92.0%), purging flow rates in the field chamber

216

(5-20 slpm), and coexistence of NH3 in high concentrations (500 ppbv). In light of the

217

high temporal variability of soil NO emission, we limited the collection time for each

218

sample to be less than 2 h. Given that soils can produce and emit nitrous acid (HONO)74,

219

75

220

the δ15N-NO analysis by soil HONO emission was minimized by forcing the sample flow

221

to pass through a HONO scrubber (250 mL fritted gas washing bottle containing 50 mL

222

of 1 mM phosphate buffer solution at pH 7.0)76 before entering the NO collection train.

and that HONO positively interferes NO2 collection in TEA solution,65 interference of


Page 10 of 44

Page 11 of 44

223


While there is no certified isotopic standard for gaseous NO, the accuracy of the

224

DFC-TEA method was evaluated through inter-calibration with a modified EPA NOx

225

collection method. A detailed description of the modified EPA method has been provided

226

by Felix et al.44 and Walters et al.47 In brief, gas samples from the NO and NO2 tanks

227

were collected directly into evacuated 1 L borosilicate gas sampling bulb containing 10

228

mL of a NO2 absorbing solution (H2SO4+H2O2) on a vacuum line. The absorbing solution

229

oxidizes NO2 into NO3-. For the NO collection, the collection was terminated with a

230

small vacuum remaining in the bottle. The bottle was then quickly vented to the

231

laboratory atmosphere to allow introduction of O2 into the bottle for the conversion of

232

NO to NO2.77 After the collection, the bottles were allowed to stand for 1 week with

233

occasional shaking to facilitate the conversion of NOx to NO3-. The residual NOx

234

headspace concentration was measured after a 1 week period and indicates that the

235

collection was 100%. The absorbing solution was then collected and neutralized for δ15N

236

analysis using the denitrifier method. The results show that the NO and NO2 tanks had

237

δ15N values of -71.4±0.5‰ (n=4) and -39.8±0.2‰ (n=3), respectively.

238

Laboratory soil δ15N-NO measurements

239

To test the DFC-TEA method using real soil samples, approximately 4 kg of soil was

240

collected from the upper 10 cm of an urban forest soil in Pittsburgh, PA. Before use, soil

241

samples were sieved by passing through a 2-mm sieve and air-dried for 14 days. To

242

trigger NO pulses, 35 g of air-dried soil samples was added to the Teflon jar, mixed

243

thoroughly, and wetted by deionized water to achieve 100% water holding capacity. With

244

the continuous purging of the jar headspace, the soil samples were subject to drying-out

245

over the next 48 h, and NO was collected periodically for the δ15N-NO analysis.



246

Field soil δ15N-NO measurements

247

To verify the DFC-TEA method under varying field conditions, the field DFC system

248

was deployed using the University of Pittsburgh Mobile Air Quality Laboratory to

249

measure δ15N-NO in a field soil rewetting experiment (see Figure S10 in the SI for the

250

field setup). A waterproof tarp (300 cm×240 cm) was erected over a fallow, urban plot in

251

Pittsburgh, PA for 2 weeks (8/15/2016 - 8/29/2016) to exclude precipitation inputs. After

252

the drying period, four soil plots were respectively wetted on four consecutive days using

253

500 mL of MilliQ water, 20 mM KNO3 (δ15N=46.5±0.3‰), 10 mM NaNO2

254

(δ15N=1.0±0.4‰), and 20 mM NH4Cl (δ15N=1.7±0.1‰) solutions. These N amendment

255

solutions were chosen because they are common precursors of NO in major NO-

256

producing processes.31, 36 Previous studies have reported that common δ15N values of N

257

fertilizers are not very different from 0‰ (e.g., -4.4‰ to 0.3‰),78 while δ15N values of

258

atmospherically deposited NO2, NO3- and NH4+ could vary over a wider range (e.g., -

259

10‰ to 15‰), depending on source contributions.42, 79 Hence, the δ15N values of the

260

amended NO2- and NH4+ are within the environmentally relevant range, whereas the δ15N

261

of the added NO3- is significant higher. The NO, NO2, and NH3 fluxes were continuously

262

measured before and after the soil rewetting, and NO was collected periodically for the

263

δ15N-NO analysis.

264 265

RESULTS AND DISCUSSION

266

We evaluate each step in the NO collection and report isotopic results that document the

267

overall precision and accuracy of the δ15N-NO analysis. We then present δ15N-NO


Page 12 of 44

Page 13 of 44


268

measurements from laboratory and field soil rewetting experiments that demonstrate

269

utility of the DFC-TEA method for resolving soil NO dynamics.

270

NO conversion in excess O3

271

The reaction time of the inner tubing of the chemiluminescent analyzer and the reaction

272

tube plus the inner tubing were estimated to be 1.4 s and 6.4 s, respectively, resulting in a

273

reaction time of the reaction tube of 5 s at the measured flow temperature (22 °C) (Figure

274

S7 in the SI). This estimated reaction time is consistent with the residence time calculated

275

from the assumption of plug flow in the reaction tube. Based on this reaction time and the

276

average O3 concentration of 2911 ppbv, numerical model calculations including reactions

277

R1-R580 and NO3 loss on the interior tubing wall (R6 in Table S2 in the SI)81 indicate that

278

NO is quantitatively converted in the reaction tube and that the specific conversion of NO

279

to NO2 is between 98.7% and 99.0% over a wide range of NO concentrations (0-1000

280

ppbv) at 22 °C (Figure S8a in the SI). Notably, the remaining NO from the conversion

281

exists primarily as N2O5 (Figure S8b in the SI).

282

Deviations from controlled laboratory condition in the field may result in

283

variations in the modeled NO conversion efficiency.61 We therefore modeled the effects

284

of temperature variation and soil emission of biogenic volatile organic carbon (BVOC)82

285

on the NO conversion (reactions R7 and R8 in Table S2 in the SI)83. The results indicate

286

that the conversion of NO to NO2 is not likely to fall below 98% over a temperature

287

range of 0-40°C in conjunction with high BVOC emissions (e.g., 100 ppbv isoprene in

288

the chamber) (details on the extended modeling are given in the SI). In addition, slight

289

variations in the reaction time may result from changes in temperature and pressure of the

290

sample flow (e.g., pressure increase induced by the attachment of the gas washing bottle).



291

While the effect of these variations on the NO conversion is difficult to empirically

292

quantify, any uncertainty in converting NO under the tested conditions is reflected in the

293

over method precision and accuracy for the δ15N-NO measurement.

294

NO2 collection in TEA solution

295

The 20% TEA solution was 100% efficient at collecting NO2. This was confirmed

296

by collecting a flow of reference NO2 at 1 ppmv using the laboratory DFC system (Table

297

1). Importantly, because the 20% TEA solution foams rigorously upon sparging, the

298

applied total flow rate (1.6 slpm of the sample flow plus 0.4 slpm of the O3 flow) was

299

chosen to avoid solution spill. We have also tested TEA solution from another brand

300

(BioUltra) that foams much less rigorously (coarse bubbles). However, consistent low

301

collection efficiency (0.05). The deviations from 100% NO recovery likely reflect inefficiencies in the NO

309

conversion (see above), the high uncertainty in the NO3- concentration determination

310

(e.g., for the 12 ppbv and 25 ppbv NO collection samples), and/or NO loss within the

311

system (e.g., NO loss in the HONO scrubbing solution and on the interior wall of the

312

field chamber). Importantly, the high and consistent NO recovery is a direct evidence that


Page 14 of 44

Page 15 of 44


313

the sub-sampling was effective to minimize the TEA aging problem, if any, for a storage

314

time of at least 4 months.

315

For all the tank collection samples (n=52), about 90% of the collected NO or NO2

316

was in the form of NO2-, and the remainder as NO3- (Table 1). A 90% NO2-+10% NO3-

317

stoichiometry has been previously reported for active NO2 sampling using TEA-coated

318

cartridges.65 While a satisfactory explanation for the NO3- production cannot be given at

319

this time,65 the observed stoichiometry is best approximated by the redox reaction

320

between NO2 and TEA in the presence of water that gives a theoretical 1:1 conversion of

321

NO2 to NO2-.64, 65, 84 Although it is well known that N2O5 hydrolyzes in water as HNO3,85

322

which is preserved as NO3- in an alkaline TEA solution, whether N2O5 produced in the

323

NO conversion can be collected in the TEA solution as NO3- is not possible to quantify in

324

this case due to the high uncertainty in the NO3- concentration determination (i.e., ±0.36

325

µM) but will be the subject of future research.

326

It is worth noting that collection efficiency of the 20% TEA solution may be

327

subject to decrease over longer collection periods due to presence of O2, O3, and CO2 in

328

the sample flow that can compete with NO2 for TEA oxidation and decrease solution pH.

329

Given that the DFC-TEA method described here is developed to characterize transient

330

variations of soil NO emissions, use of 20% TEA solution for prolonged collection (i.e.,

331

>2 h) should be further investigated to ensure high and consistent collection efficiency.

332

Analytical uncertainty of the denitrifier method and the total N blank

333

The pooled standard deviation for each of the isotopic standards made in 20% TEA

334

solution and measured along with individual sample sets was: 0.3‰, 0.3‰, and 0.8‰ for

335

δ15N of IAEA-N3, USGS34, and RSIL20, respectively; 0.7‰ and 0.7‰ for δ18O of



336

IAEA-N3 and USGS34, respectively; and 1.2‰ for ∆17O of USGS35. The lower

337

precision of the δ15N analysis of RSIL20 (0.8‰ relative to 0.3‰ for other standards) is

338

due to the larger uncertainty in measuring diluted RSIL20 solutions that require large

339

injection volumes (Figure 3a). To further understand this volume dependence, we

340

estimated the total N blank associated with the δ15N analysis of the TEA samples (i.e.,

341

TEA N blank + blank N associated with the denitrifier medium68, 71) by quantifying

342

shrinkage of the N isotope-ratio scale between USGS34 and RSIL20 measured in each

343

run of the TEA collection samples86 (more details are described in the SI). The results

344

show that the fractional blank size (fB) ranged between 0.04 and 0.18 across different runs

345

and was significantly, positively correlated with the sample volume and the measured

346

δ15N of RSIL20 (δ15NRSIL20-m) (Figure 3a). Fitting a linear equation to the molar amount

347

of the total N blank and the sample volume indicates that the N blank likely consisted of

348

a constant component of 0.46±0.12 nmol and a sample volume-dependent component of

349

0.23±0.06 nmol·mL-1 (Figure S5 in the SI; Figure 2); this is consistent with the blank size

350

estimated by injecting blank 20% TEA solution (details are provided in the SI). From the

351

linear relationship between fB and δ15NRSIL20-m, the δ15N of the blank N appears to be

352

~10‰ across different runs (Figure 3a). These consistent and predictable behaviors of the

353

total N blank indicate with a high degree of confidence that its isotope effect is implicitly

354

corrected during the δ15N analysis using the blank-matching strategy.

355

Isobaric interference from mass-independent oxygen isotopic composition

356

The δ18O of RSIL20 calibrated against IAEA-N3 and USGS34 ranged from -

357

25.8±0.9‰ to -22.7±1.5‰ across different runs, with an average of -23.7±1.1‰. This

358

results in an isotopic offset of about 28‰ between the measured apparent δ18O and the


Page 16 of 44

Page 17 of 44


359

“true” δ18O (4.5‰) of RSIL20, in line with the branching fractionation between NO3- and

360

NO2- during denitrification (25-30‰).70 This implies that the oxygen isotopic exchange

361

between NO2- and water is limited in the alkaline TEA solution. Not surprisingly,

362

positive ∆17O values were observed in the N2O generated from collected samples. To

363

understand the transfer of the ∆17O anomaly from O3 during the NO conversion, a

364

theoretical ∆17O of the NO2 produced from the NO+O3 reaction (R1 in Table S2 in the

365

SI) was calculated to be 22.5±1.8‰ (details are provided in the SI). This theoretical ∆17O

366

value is not very different from the measured ∆17O values, which had an average of

367

19.7±0.8‰ across different runs (Table 1), indicating that the NO+O3 reaction essentially

368

dominated during the NO conversion. The measured ∆17O values led to a 1.0-1.2‰

369

correction of the measured δ15N values. For samples without sufficient concentrations for

370

∆17O measurement, the average ∆17O value (19.7‰) was used for the correction. This is

371

not a complete correction, in that the expression of the isobaric interference depends on fB

372

relative to each sample. Nevertheless, the resultant overcorrection on the δ15N of the low

373

concentration samples is 0.05; Figure S6b in the SI). The DFC-TEA method and the EPA NOx

383

collection method generally agree within 0.3‰, although discrepancies within individual

384

sets of collected samples ranged from -1.3‰ to 1.6‰. The largest discrepancies between

385

the two methods occurred with the lowest sample concentrations (i.e., 12 ppbv NO

386

collection samples) (Figure 3b). For these low concentration samples, isotopic analyses

387

were conducted on 5 nmol of NO2-+NO3- (achieved with a 3.8 mL injection of the

388

collection samples) and of a fB of 0.18. Therefore, although Pdiff did not correlate with the

389

sample concentration (Figure S6a in the SI), the collection samples with lower

390

concentrations were more prone to random error in matching blank between the standards

391

and samples due to their higher fB. Consequently, for accurate δ15N-NO analyses, soil NO

392

should be collected to achieve >3 µM NO2-+NO3- in the solution within 2 h (equivalent to

393

collecting a flow of >26 ppbv NO over a 2 hour period). Blank 20% TEA solution should

394

then be used to dilute both soil NO collection samples and isotopic standards within a

395

batch to a common concentration for injection of 10 nmol of N using the denitrifier

396

method. Control tests using a soil NO sample collected from the laboratory rewetting

397

experiment (δ15N = -37.1‰, [NO2-]+[NO3-] = 9.2 µM) indicate that dilution-induced

398

uncertainty in the δ15N was 3 µM

399

NO2-+NO3- in the solution (data not shown). This uncertainty is within the analytical

400

uncertainty (i.e., ±0.8‰ for RSIL20). Therefore, we always group samples with similar

401

concentrations such that the dilution factor does not exceed 3.

402

Overall, our inter-calibration effort demonstrates that although the NO recovery

403

was slightly less than 100%, fractionation during chamber mixing and NO conversion

404

and collection is effectively minimized under the tested conditions. The derived standard


Page 18 of 44

Page 19 of 44


405

deviation of ±1.1‰ based on all the collection samples with an average Pdiff of ±7% (i.e.,

406

sample peak area is within 100±7% of that of RSIL20) represents the overall accuracy

407

and precision across the entire method, accounting for propagated errors from the total N

408

blank and its mismatch between the standards and samples. While the method precision is

409

lower than that of the modified EPA method (Table S1 in the SI), our integrated method

410

featuring simultaneous NO flux measurement and collection is the first to show its

411

suitability for unbiased soil δ15N-NO determination under realistic, varying soil

412

conditions. Furthermore, the method is more convenient than previous methods and does

413

not require time-consuming pretreatments for δ15N analysis (Table S1 in the SI). Given

414

the good result from the inter-calibration, the tank NO can be utilized as a secondary

415

standard for correcting the isobaric interference. For instance, the tank NO can be

416

collected before and after soil NO collection; ∆17O of the tank collection samples can

417

then be estimated using an empirical relationship scaling a 1‰ increase from accepted

418

δ15N value (-71.4‰ in this case) to every 18.8‰ increase in ∆17O to correct the soil

419

collection samples.86

420

Application to pulsed soil NO emissions

421

Pulsed NO emission was triggered by soil rewetting under both the laboratory and field

422

conditions (Figure 4). In the laboratory, the pulsed NO emission had evident temporal

423

variations with a rapid initial NO pulse being triggered upon the rewetting (Figure 4a).

424

While the initial NO pulse was absent under the field conditions, possibly due to the

425

relatively high pre-wetting soil water content (0.17 cm3·cm-3), the rewetting and N

426

amendments caused significantly increased NO emission as compared to the pre-wetting



427

emission (47±16 nmol·m-2·min-1). Particularly, a dramatic increase in NO emission was

428

triggered by the NO2- addition (Figure 4b).

429

Twenty and 15 samples were collected for the δ15N-NO analysis from the

430

laboratory and field experiments, respectively (Table S5 and S6 in the SI). The average

431

NO recovery was 102.2±5.6% and 108.6±11.0% for the laboratory and field collection

432

samples, respectively. The >100% recovery was detected mostly in samples collected

433

under the NO2- addition (NO recovery = 117.5±11.6%; Table S6 in the SI). We suspect

434

that the >100% NO recovery might result from our underestimation of the soil NO

435

emission due to the slow response time of the chemiluminescent analyzer (>30 s),

436

especially given that transient fluctuations in the NO flux were likely triggered by the

437

NO2- addition (Figure 4b). Alternatively, the >100% recovery could result from soil

438

emission of NOy (NOy = NO2 + HONO + HNO3 + other non-NO reactive N oxides),87

439

that can potentially be collected in the TEA solution as NO2- and/or NO3-.65 If soil NOy

440

emission was significant during measurement, it would be detected as NO2 by our

441

chemiluminescent analyzer with a molybdenum convertor.88 Because the NO2 flux never

442

exceed 2% of the simultaneous NO flux (Figure S11 and Figure S12 in the SI),

443

contributions of NOy emission to the NO recovery and the measured δ15N-NO are

444

considered negligible. Future application of the DFC-TEA method can be coupled to a

445

faster NO measurement system and existing denuder and wet chemistry methods76, 89 that

446

quantitatively scrub NOy without significant loss of NO.

447

The measured soil δ15N-NO exhibited intriguing patterns that are indicative of

448

mechanisms underlying the soil NO emissions (Figure 4). In the laboratory rewetting of

449

the air-dried soil samples, the initial NO pulse had higher δ15N values (-36.7~-39.9‰)


Page 20 of 44

Page 21 of 44


450

than NO emission after 12 h post-wetting (-52.0~-53.6‰; Figure 4a). Recent work by

451

Homyak et al.33 provided evidence that in arid soils, abiotic reactions govern the rapid

452

initial NO pulse, whereas microbial processes control later emissions as microbes recover

453

from drought stress. Therefore, the higher δ15N-NO values associated with the initial NO

454

pulse may suggest that abiotic reactions likely bear a smaller isotopic fractionation on

455

NO production than microbial processes. However, the temporal variation of δ15N-NO

456

could also result from changing rates of microbial NO production90 or sequential

457

resuscitation of different microbial groups91 during the rewetting. Further constraints on

458

the relevant isotope effects are needed to tease apart the relative importance of abiotic

459

and microbial pathways sustaining pulsed NO emissions in soils. In the field rewetting

460

experiment where an initial NO pulse was lacking, the measured soil δ15N-NO responded

461

differently to the added N precursors (Figure 4b). First, the δ15N-NO values that evolved

462

from the NH4+ (-59.8‰ to -56.0‰) and NO2- (-34.4‰ to -23.4‰) amendments were

463

significantly lower and higher relative to the control (MilliQ water addition; -44.3‰ to -

464

41.3‰), respectively, in spite of the almost equal δ15N of the added NH4+ and NO2-.

465

Secondly, despite the high δ15N of the added NO3- (i.e., 46.5‰), the δ15N-NO values

466

measured from the NO3- amendment (-40.7‰ to -39.4‰) were not significantly different

467

from those in the control. The measured soil δ15N-NO and its differential responses to the

468

amended N sources indicate that various soil NO-producing processes (e.g., nitrification,

469

denitrification, and chemodenitrification), stimulated by different N amendments, likely

470

bear distinguishable isotopic imprints on NO production, similar to what has been

471

observed in soil nitrous oxide (N2O) studies.37-39 For example, N2O production in soil

472

was found to be associated with a larger isotope effect for nitrification of NH4+ (e.g., -



473

45‰ to -67‰) than denitrification of NO2- (e.g., -35‰ to -22‰).37-39 Thus, soil δ15N-NO

474

measurement could potentially provide important implications for understanding

475

couplings between soil NO and N2O emissions, in that NO is the precursor of N2O in

476

most abiotic and microbial processes.10, 17-20 Finally, the measured soil δ15N-NO values

477

are significantly lower than other measured NOx emissions sources,44, 45, 47-49 confirming

478

use of soil δ15N-NO as a robust tracer of regional N deposition.41, 42 Quantification of

479

isotope effects associated with NO dynamics in soils therefore represents an important

480

avenue for future research on the soil-atmosphere cycling of reactive N.

481 482

ACKNOWLEDGEMENT

483

This material is based upon work supported by a National Science Foundation CAREER

484

award (Grant No. 1253000) to EME. We thank Kathrine Redling, Vivian Feng, Madeline

485

Ellgass, and Madeline Gray for assistance with isotopic measurements.

486 487

SUPPORTING INFORMATION AVAILABLE

488

Supporting information includes a description of: (1) comparison between the DFC-TEA

489

method and previously published NOx collection methods; (2) the dynamic flux chamber

490

system; (3) the protocol for NO2- and NO3- concentration measurement using the

491

modified spongy cadmium reduction method; (4) the total N blank and the blank-

492

matching strategy; (5) extended modeling of the NO conversion in excess O3; (6)

493

calculation of the theoretical ∆17O value of the NO2 produced from the NO+O3 reaction;

494

(7) experimental setup of the field rewetting experiment; (8) soil NOy emissions in the


Page 22 of 44

Page 23 of 44


495

laboratory and field soil rewetting experiments; and (9) complete datasets of the

496

laboratory and field collection samples.

497 498

REFERENCES CITED

499

(1) Climate change 2013: the physical science basis. Contribution of working group I to

500

the fifth assessment report of the Intergovernmental Panel on Climate Change. 2013.

501 502

(2) Richter, A.; Burrows, J. P.; Nüß, H.; Granier, C.; Niemeier, U. Increase in

503

tropospheric nitrogen dioxide over China observed from space. Nature 2007, 437(7055),

504

129-132.

505 506

(3) Jacob, D. J.; Heikes, E. G.; Fan, S. M.; Logan, J. A.; Mauzerall, D. L.; Bradshaw, J.

507

D.; Singh, H. B.; Gregory, G. L.; Talbot, R. W.; Blake, D. R.; Sachse, G. W. Origin of

508

ozone and NOx in the tropical troposphere: A photochemical analysis of aircraft

509

observations over the South Atlantic basin. J. Geophys. Res. Atmos. 1996, 101(D19),

510

24235-24250.

511 512

(4) Jang, M.; Czoschke, N. M.; Lee, S.; Kamens, R. M. Heterogeneous atmospheric

513

aerosol production by acid-catalyzed particle-phase reactions. Science 2002, 298(5594),

514

814-817.

515 516

(5) Likens, G. E.; Driscoll, C. T.; Buso, D. C. Long-term effects of acid rain: response

517

and recovery of a forest ecosystem. Science 1996, 272(5259), 244.

518



519

(6) Akimoto, H. Global air quality and pollution. Science, 2003, 302(5651), 1716-1719.

520 521

(7) Jaeglé, L.; Steinberger, L.; Martin, R. V.; Chance, K. Global partitioning of NOx

522

sources using satellite observations: Relative roles of fossil fuel combustion, biomass

523

burning and soil emissions. Faraday discuss. 2005, 130, 407-423.

524 525

(8) Zhang, R.; Tie, X.; Bond, D.W. Impacts of anthropogenic and natural NOx sources

526

over the US on tropospheric chemistry. PNAS 2003, 100(4), 1505-1509.

527 528

(9) Galbally, I. E.; Roy, C. R. Loss of fixed nitrogen from soils by nitric oxide exhalation.

529

Nature 1978, 275, 734-735.

530 531

(10) Skiba, U.; Smith, K. A. Nitrification and denitrification as sources of nitric oxide

532

and nitrous oxide in a sandy loam soil. Soil Biol. Biochem. 1993, 25(11), 1527-1536.

533 534

(11) Yienger, J. J.; Levy, H. Empirical model of global soil‐biogenic NOx emissions. J.

535

Geophys. Res. Atoms. 1995, 100(D6), 11447-11464.

536 537

(12) Bertram, T. H.; Heckel, A.; Richter, A.; Burrows, J. P.; Cohen, R. C. Satellite

538

measurements of daily variations in soil NOx emissions. Geophys. Res. Lett. 2005, 32(24),

539

L24812.

540


Page 24 of 44

Page 25 of 44


541

(13) Hudman, R. C.; Russell, A. R.; Valin, L. C.; Cohen, R. C. Interannual variability in

542

soil nitric oxide emissions over the United States as viewed from space. Atmos. Chem.

543

Phys. 2010, 10(20), 9943-9952.

544 545

(14) Steinkamp, J.; Lawrence, M. G. Improvement and evaluation of simulated global

546

biogenic soil NO emissions in an AC-GCM. Atmos. Chem. Phys. 2011, 11(12), pp.6063-

547

6082.

548 549

(15) Vinken, G. C. M.; Boersma, K. F.; Maasakkers, J. D.; Adon, M.; Martin, R. V.

550

Worldwide biogenic soil NOx emissions inferred from OMI NO2 observations. Atmos.

551

Chem. Phys. 2014, 14(18), 10363-10381.

552 553

(16) Steinkamp, J.; Ganzeveld, L. N.; Wilcke, W.; Lawrence, M. G. Influence of

554

modelled soil biogenic NO emissions on related trace gases and the atmospheric

555

oxidizing efficiency. Atmos. Chem. Phys. 2009, 9(8), 2663-2677.

556 557

(17) Zumft, W. G. Cell biology and molecular basis of denitrification. Microbiol. Mol.

558

Bio. Rev. 1997, 61(4), 533-616.

559 560

(18) Kester, R. A.; De Boer, W.; Laanbroek, H. J. Production of NO and N2O by Pure

561

Cultures of Nitrifying and Denitrifying Bacteria during Changes in Aeration. Appl.

562

Environ. Microbiol. 1997, 63(10), 3872-3877.

563



564

(19) Firestone, M. K.; Davidson, E. A. Microbiological basis of NO and N2O production

565

and consumption in soil. In Exchange of trace gases between terrestrial ecosystems and

566

the atmosphere; Andreae, M. O.; Schimel, D. S.; Robertson, G. P. Eds.; John Wiley &

567

Sons Ltd: Berlin 1989; pp 7-21.

568 569

(20) Venterea, R. T.; Rolston, D. E. Nitric and nitrous oxide emissions following

570

fertilizer application to agricultural soil: Biotic and abiotic mechanisms and kinetics. J.

571

Geophys. Res. Atoms. 2000, 105(D12), 15117-15129.

572 573

(21) McCalley, C. K.; Sparks, J. P. Abiotic gas formation drives nitrogen loss from a

574

desert ecosystem. Science 2009, 326(5954), 837-840.

575 576

(22) Homyak, P. M.; Kamiyama, M.; Sickman, J. O.; Schimel, J. P. Acidity and organic

577

matter promote abiotic nitric oxide production in drying soils. Global Change Biol. 2016,

578

23(4), 1735-1747.

579 580

(23) Yang, W. X.; Meixner, F. X. Laboratory studies on the release of nitric oxide from

581

sub-tropical grassland soils: The effect of soil temperature and moisture. In Gaseous

582

Nitrogen emissions from grasslands; Jarvis, S. C.; Pain, B. F. Eds.; Cab International:

583

1997; pp 67-71.

584


Page 26 of 44

Page 27 of 44


585

(24) Van Dijk, S. M.; Gut, A.; Kirkman, G. A.; Gomes, B. M.; Meixner, F. X.; Andreae,

586

M. O. Biogenic NO emissions from forest and pasture soils: Relating laboratory studies

587

to field measurements. J. Geophys. Res. Atmos. 2002, 107(D20).

588 589

(25) Hall, S. J.; Matson, P. A. Nitrogen oxide emissions after nitrogen additions in

590

tropical forests. Nature 1999, 400(6740), 152-155.

591 592

(26) Davidson, E. A.; Keller, M.; Erickson, H. E.; Verchot, L. V.; Veldkamp, E. Testing a

593

Conceptual Model of Soil Emissions of Nitrous and Nitric Oxides. Bioscience 2000,

594

50(8), 667-680.

595 596

(27) Davidson, E. A.; Verchot, L. V. Testing the Hole‐in‐the‐Pipe Model of nitric and

597

nitrous oxide emissions from soils using the TRAGNET database. Global Biogeochem.

598

Cycles 2000, 14(4), 1035-1043.

599 600

(28) Hudman, R. C.; Moore, N. E.; Mebust, A. K.; Martin, R. V.; Russell, A. R.; Valin, L.

601

C.; Cohen, R. C. Steps towards a mechanistic model of global soil nitric oxide emissions:

602

implementation and space based-constraints. Atmos. Chem. Phys. 2012, 12(16), 7779-

603

7795.

604 605

(29) Jaeglé, L.; Martin, R. V.; Chance, K.; Steinberger, L.; Kurosu, T. P.; Jacob, D. J.;

606

Modi, A. I.; Yoboué, V.; Sigha‐Nkamdjou, L.; Galy‐Lacaux, C. Satellite mapping of



607

rain‐induced nitric oxide emissions from soils. J. Geophys. Res. Atmos. 2004, 109(D21),

608

D21310.

609 610

(30) Oikawa, P. Y.; Ge, C.; Wang, J.; Eberwein, J. R.; Liang, L. L.; Allsman, L. A.;

611

Grantz, D. A.; Jenerette, G. D. Unusually high soil nitrogen oxide emissions influence air

612

quality in a high-temperature agricultural region. Nat. Commun. 2015, 6, 8753.

613 614

(31) Davidson, E. A. Sources of nitric oxide and nitrous oxide following wetting of dry

615

soil. Soil Sci. Soc. Am. J. 1992, 56(1), 95-102.

616 617

(32) Davidson, E. A. Pulses of nitric oxide and nitrous oxide flux following wetting of

618

dry soil: An assessment of probable sources and importance relative to annual

619

fluxes. Ecol. Bull. 1992, 149-155.

620 621

(33) Homyak, P. M.; Blankinship, J. C.; Marchus, K.; Lucero, D. M.; Sickman, J. O.;

622

Schimel, J. P. Aridity and plant uptake interact to make dryland soils hotspots for nitric

623

oxide (NO) emissions. PNAS 2016, 113(19), E2608-E2616.

624 625

(34) Wang, Y.; McElroy, M. B.; Martin, R. V.; Streets, D. G.; Zhang, Q.; Fu, T. M.

626

Seasonal variability of NOx emissions over east China constrained by satellite

627

observations: Implications for combustion and microbial sources. J. Geophys. Res.

628

Atmos. 2007, 112(D6).

629


Page 28 of 44

Page 29 of 44


630

(35) Hudman, R. C.; Jacob, D. J.; Turquety, S.; Leibensperger, E. M.; Murray, L. T.; Wu,

631

S.; Gilliland, A. B.; Avery, M.; Bertram, T. H.; Brune, W.; Cohen, R. C. Surface and

632

lightning sources of nitrogen oxides over the United States: Magnitudes, chemical

633

evolution, and outflow. J. Geophys. Res. Atmos. 2007, 112(D12).

634 635

(36) Denk, T. R.; Mohn, J.; Decock, C.; Lewicka-Szczebak, D.; Harris, E.; Butterbach-

636

Bahl, K.; Kiese, R.; Wolf, B. The nitrogen cycle: A review of isotope effects and isotope

637

modeling approaches. Soil Biol. Biochem. 2017, 105, 121-137.

638 639

(37) Mariotti, A.; Germon, J. C.; Hubert, P.; Kaiser, P.; Letolle, R.; Tardieux, A.;

640

Tardieux, P. Experimental determination of nitrogen kinetic isotope fractionation: some

641

principles; illustration for the denitrification and nitrification processes. Plant Soil 1981,

642

62(3), 413-430.

643 644

(38) Sutka, R. L.; Ostrom, N. E.; Ostrom, P. H.; Breznak, J. A.; Gandhi, H.; Pitt, A. J.; Li,

645

F. Distinguishing nitrous oxide production from nitrification and denitrification on the

646

basis of isotopomer abundances. Appl. Environ. Microbio. 2006, 72(1), 638-644.

647 648

(39) Park, S.; Pérez, T.; Boering, K. A.; Trumbore, S. E.; Gil, J.; Marquina, S.; Tyler, S.

649

C. Can N2O stable isotopes and isotopomers be useful tools to characterize sources and

650

microbial pathways of N2O production and consumption in tropical soils?. Global

651

Biogeochem. Cycles 2011, 25(1), GB1001.

652



653

(40) Hastings, M. G.; Casciotti, K. L.; Elliott, E. M. Stable isotopes as tracers of

654

anthropogenic nitrogen sources, deposition, and impacts. Elements 2013, 9(5), 339-344.

655 656

(41) Elliott, E. M.; Kendall, C.; Wankel, S. D.; Burns, D. A.; Boyer, E. W.; Harlin, K.;

657

Bain, D. J.; Butler, T. J. Nitrogen isotopes as indicators of NOx source contributions to

658

atmospheric nitrate deposition across the midwestern and northeastern United

659

States. Environ. Sci. Technol. 2007, 41(22), 7661-7667.

660 661

(42) Elliott, E. M.; Kendall, C.; Boyer, E. W.; Burns, D. A.; Lear, G. G.; Golden, H. E.;

662

Harlin, K.; Bytnerowicz, A.; Butler, T. J.; Glatz, R. Dual nitrate isotopes in dry

663

deposition: Utility for partitioning NOx source contributions to landscape nitrogen

664

deposition. J. Geophys. Res. Biogeosci. 2009, 114(G4), G04020.

665 666

(43) Hastings, M. G.; Jarvis, J. C.; Steig, E. J. Anthropogenic impacts on nitrogen

667

isotopes of ice-core nitrate. Science 2009, 324(5932), 1288-1288.

668 669

(44) Felix, J. D.; Elliott, E. M.; Shaw, S. L. Nitrogen isotopic composition of coal-fired

670

power plant NOx: influence of emission controls and implications for global emission

671

inventories. Environ. Sci. Technol. 2012, 46(6), 3528-3535.

672 673

(45) Redling, K.; Elliott, E.; Bain, D.; Sherwell, J. Highway contributions to reactive

674

nitrogen deposition: tracing the fate of vehicular NOx using stable isotopes and plant

675

biomonitors. Biogeochemistry 2013, 116(1-3), 261-274.


Page 30 of 44

Page 31 of 44


676 677

(46) Hoering, T. The isotopic composition of the ammonia and the nitrate ion in

678

rain. Geochim. Cosmochim. Acta 1957, 12(1), 97-102.

679 680

(47) Walters, W. W.; Goodwin, S. R.; Michalski, G. Nitrogen stable isotope composition

681

(δ15N) of vehicle-emitted NOx. Environ. Sci. Technol. 2015, 49(4), 2278-2285.

682 683

(48) Walters, W. W.; Tharp, B. D.; Fang, H.; Kozak, B. J.; Michalski, G. Nitrogen

684

isotope composition of thermally produced NOx from various fossil-fuel combustion

685

sources. Environ. Sci. Technol. 2015, 49(19), 11363-11371.

686 687

(49) Fibiger, D. L.; Hastings, M. G. First measurements of the nitrogen isotopic

688

composition of NOx from biomass burning. Environ. Sci. Technol. 2016, 50(21), 11569-

689

11574.

690 691

(50) Li, D.; Wang, X. Nitrogen isotopic signature of soil-released nitric oxide (NO) after

692

fertilizer application. Atmos. Environ. 2008, 42(19), 4747-4754.

693 694

(51) Felix, J. D.; Elliott, E. M. The agricultural history of human‐nitrogen interactions as

695

recorded in ice core δ15N‐NO3-. Geophys. Res. Lett. 2013, 40(8), 1642-1646.

696



697

(52) Felix, J. D.; Elliott, E.M. Isotopic composition of passively collected nitrogen

698

dioxide emissions: Vehicle, soil and livestock source signatures. Atmos. Environ. 2014,

699

92, 359-366.

700 701

(53) Hutchinson, G. L.; Yang, W. X.; Andre, C. E. Overcoming humidity dependence of

702

the chromium trioxide converter used in luminol-based nitric oxide detection. Atmos.

703

Environ. 1998, 33(1), 141-145.

704 705

(54) Robinson, J. K.; Bollinger, M. J.; Birks, J. W. Luminol/H2O2 chemiluminescence

706

detector for the analysis of nitric oxide in exhaled breath. Anal. Chem. 1999, 71(22),

707

5131-5136.

708 709

(55) Fibiger, D. L.; Hastings, M. G.; Lew, A. F.; Peltier, R. E. Collection of NO and NO2

710

for isotopic analysis of NOx emissions. Anal. Chem. 2014, 86(24), 12115-12121.

711 712

(56) Wojtal, P. K.; Miller, D. J.; O'Conner, M.; Clark, S. C.; Hastings, M. G. Automated,

713

high-resolution mobile collection system for the nitrogen isotopic analysis of NOx. J. Vis.

714

Exp. 2016, 118, e54962.

715 716

(57) Pape, L.; Ammann, C.; Nyfeler-Brunner, A.; Spirig, C.; Hens, K.; Meixner, F. X. An

717

automated dynamic chamber system for surface exchange measurement of non-reactive

718

and reactive trace gases of grassland ecosystems. Biogeosciences, 2009, 6(3), 405-429.

719


Page 32 of 44

Page 33 of 44


720

(58) Yu, Z.; Slater, L. D.; Schäfer, K. V.; Reeve, A. S.; Varner, R. K. Dynamics of

721

methane ebullition from a peat monolith revealed from a dynamic flux chamber system. J.

722

Geophys. Res. Biogeosci. 2014, 119(9), 1789-1806.

723 724

(59) Miyazaki, K.; Matsumoto, J.; Kato, S.; Kajii, Y. Development of atmospheric NO

725

analyzer by using a laser-induced fluorescence NO2 detector. Atmos. Environ. 2008,

726

42(33), 7812-7820.

727 728

(60) Hargrove, J.; Zhang, J. Measurements of NOx, acyl peroxynitrates, and NOy with

729

automatic interference corrections using a NO2 analyzer and gas phase titration. Rev. Sci.

730

Instrum. 2008, 79(4), pp.046109-046109.

731 732

(61) Fuchs, H.; Dubé, W. P.; Lerner, B. M.; Wagner, N. L.; Williams, E. J.; Brown, S. S.

733

A sensitive and versatile detector for atmospheric NO2 and NOx based on blue diode laser

734

cavity ring-down spectroscopy. Environ. Sci. Technol. 2009, 43(20), 7831-7836.

735 736

(62) Wild, R. J.; Edwards, P. M.; Dubé, W. P.; Baumann, K.; Edgerton, E. S.; Quinn, P.

737

K.; Roberts, J. M.; Rollins, A. W.; Veres, P. R.; Warneke, C.; Williams, E. J. A

738

Measurement of Total Reactive Nitrogen, NOy, together with NO2, NO, and O3 via

739

Cavity Ring-down Spectroscopy. Environ. Sci. Technol. 2014, 48(16), 9609-9615.

740



741

(63) Wagner, N. L.; Dubé, W. P.; Washenfelder, R. A.; Young, C. J.; Pollack, I. B.;

742

Ryerson, T. B.; Brown, S. S. Diode laser-based cavity ring-down instrument for NO3,

743

N2O5, NO, NO2 and O3 from aircraft. Atmos. Meas. Tech. 2011, 4(6), 1227-1240.

744 745

(64) Glasius, M.; Carlsen, M. F.; Hansen, T. S.; Lohse, C. Measurements of nitrogen

746

dioxide on Funen using diffusion tubes. Atmos. Environ. 1999, 33(8), 1177-1185.

747 748

(65) Cape, J. N. The use of passive diffusion tubes for measuring concentrations of

749

nitrogen dioxide in air. Crit. Rev. Anal. Chem. 2009, 39(4), 289-310.

750 751

(66) Wei, Y.; Oshima, M.; Simon, J.; Motomizu, S. The application of the

752

chromatomembrane cell for the absorptive sampling of nitrogen dioxide followed by

753

continuous determination of nitrite using a micro-flow injection system. Talanta, 2002,

754

57(2), 355-364.

755 756

(67) Jones, M. N. Nitrate reduction by shaking with cadmium: alternative to cadmium

757

columns. Water Res. 1984, 18(5), 643-646.

758 759

(68) Sigman, D. M.; Casciotti, K. L.; Andreani, M.; Barford, C.; Galanter, M. B. J. K.;

760

Böhlke, J. K. A bacterial method for the nitrogen isotopic analysis of nitrate in seawater

761

and freshwater. Anal. Chem. 2001, 73(17), 4145-4153.

762


Page 34 of 44

Page 35 of 44


763

(69) Casciotti, K. L.; Sigman, D. M.; Hastings, M. G.; Böhlke, J. K.; Hilkert, A.

764

Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater

765

using the denitrifier method. Anal. Chem. 2002, 74(19), 4905-4912.

766 767

(70) Casciotti, K. L.; Böhlke, J. K.; McIlvin, M. R.; Mroczkowski, S. J.; Hannon, J. E.

768

Oxygen isotopes in nitrite: analysis, calibration, and equilibration. Anal. Chem. 2007,

769

79(6), 2427-2436.

770 771

(71) McIlvin, M. R.; Casciotti, K. L. Technical updates to the bacterial method for nitrate

772

isotopic analyses. Anal. Chem. 2011, 83(5), 1850-1856.

773 774

(72) Michalski, G.; Savarino, J.; Böhlke, J. K.; Thiemens, M. Determination of the total

775

oxygen isotopic composition of nitrate and the calibration of a ∆17Ο nitrate reference

776

material. Anal. Chem. 2002, 74(19), 4989-4993.

777 778

(73) Kaiser, J.; Hastings, M. G.; Houlton, B. Z.; Röckmann, T.; Sigman, D. M. Triple

779

oxygen isotope analysis of nitrate using the denitrifier method and thermal decomposition

780

of N2O. Anal. Chem. 2007, 79(2), 599-607.

781 782

(74) Su, H.; Cheng, Y.; Oswald, R.; Behrendt, T.; Trebs, I.; Meixner, F. X.; Andreae, M.

783

O.; Cheng, P.; Zhang, Y.; Pöschl, U. Soil nitrite as a source of atmospheric HONO and

784

OH radicals. Science 2011, 333(6049), 1616-1618.

785



786

(75) Oswald, R.; Behrendt, T.; Ermel, M.; Wu, D.; Su, H.; Cheng, Y.; Breuninger, C.;

787

Moravek, A.; Mougin, E.; Delon, C.; Loubet, B. HONO emissions from soil bacteria as a

788

major source of atmospheric reactive nitrogen. Science 2013, 341(6151), 1233-1235.

789 790

(76) Zhou, X.; Qiao, H.; Deng, G.; Civerolo, K. A method for the measurement of

791

atmospheric HONO based on DNPH derivatization and HPLC analysis. Environ. Sci.

792

Technol. 1999, 33(20), 3672-3679.

793 794

(77) Method 7 – Determination of nitrogen oxide emissions from stationary sources; US

795

Environmental Protection Agency; www3.epa.gov/ttn/emc/promgate/m-07.pdf.

796 797

(78) Michalski, G.; Kolanowski, M.; Riha, K.M. Oxygen and nitrogen isotopic

798

composition of nitrate in commercial fertilizers, nitric acid, and reagent salts. Isotopes

799

Environ. Health Stud. 2015, 51(3), 382-391.

800 801

(79) Altieri, K.E.; Hastings, M.G.; Peters, A.J.; Oleynik, S.; Sigman, D.M. Isotopic

802

evidence for a marine ammonium source in rainwater at Bermuda. Glob. Biogeochem.

803

Cycles 2014, 28(10), 1066-1080.

804 805

(80) Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies

806

Evaluation Number 15; Jet Propulsion Laboratory, National Aeronautics and Space

807

Administration: Pasadena, CA, 2006; https://trs.jpl.nasa.gov/handle/2014/41648.

808


Page 36 of 44

Page 37 of 44


809

(81) Dubé, W. P.; Brown, S. S.; Osthoff, H. D.; Nunley, M. R.; Ciciora, S. J.; Paris, M.

810

W.; McLaughlin, R. J.; Ravishankara, A. R. Aircraft instrument for simultaneous, in situ

811

measurement of NO3 and N2O5 via pulsed cavity ring-down spectroscopy. Rev. Sci.

812

Instrum. 2006, 77(3), 034101.

813 814

(82) Atkinson, R.; Arey, J. Gas-phase tropospheric chemistry of biogenic volatile organic

815

compounds: a review. Atmos. Environ. 2003, 37, 197-219.

816 817

(83) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R.

818

G.; Jenkin, M. E.; Rossi, M. J.; Troe, J.; Subcommittee, I. U. P. A. C. Evaluated kinetic

819

and photochemical data for atmospheric chemistry: Volume II–gas phase reactions of

820

organic species. Atmos. Chem. Phys. 2006, 6(11), 3625-4055.

821 822

(84) Dahal, B.; Hastings, M. G. Technical considerations for the use of passive samplers

823

to quantify the isotopic composition of NOx and NO2 using the denitrifier method. Atmos.

824

Environ. 2016, 143, 60-66.

825 826

(85) Riemer, N.; Vogel, H.; Vogel, B.; Anttila, T.; Kiendler‐Scharr, A.; Mentel, T. F.

827

Relative importance of organic coatings for the heterogeneous hydrolysis of N2O5 during

828

summer in Europe. J. Geophys. Res. Atmos. 2009, 114(D17), D17307.

829



830

(86) Coplen, T. B.; Böhlke, J. K.; Casciotti, K. L. Using dual‐bacterial denitrification to

831

improve δ15N determinations of nitrates containing mass‐independent 17O. Rapid

832

Commun. Mass Spectrom. 2004, 18(3), 245-250.

833 834

(87) Soper, F. M.; Boutton, T. W.; Groffman, P. M.; Sparks, J. P. Nitrogen trace gas

835

fluxes from a semiarid subtropical savanna under woody legume encroachment. Global

836

Biogeochem. Cycles 2016, 30(5), 614-628.

837 838

(88) Dunlea, E. J.; Herndon, S. C.; Nelson, D. D.; Volkamer, R. M.; San Martini, F.;

839

Sheehy, P. M.; Zahniser, M. S.; Shorter, J. H.; Wormhoudt, J. C.; Lamb, B. K.; Allwine,

840

E. J. Evaluation of nitrogen dioxide chemiluminescence monitors in a polluted urban

841

environment. Atmos. Chem. Phys. 2007, 7(10), 2691-2704.

842 843

(89) De Santis, F.; Allegrini, I.; Di Filippo, P.; Pasella, D. Simultaneous determination of

844

nitrogen dioxide and peroxyacetyl nitrate in ambient atmosphere by carbon-coated

845

annular diffusion denuder. Atmos. Environ. 1996, 30(14), 2637-2645.

846 847 848

(90) Mariotti, A.; Leclerc, A.; Germon, J. C. Nitrogen isotope fractionation associated

849

with the NO2-→N2O step of denitrification in soils. Can. J. Soil Sci. 1982, 62(2), 227-241.

850


Page 38 of 44

Page 39 of 44


851

(91) Placella, S. A.; Brodie, E. L.; Firestone, M. K. Rainfall-induced carbon dioxide

852

pulses result from sequential resuscitation of phylogenetically clustered microbial

853

groups. PNAS 2012, 109(27), 10931-10936.

854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872



873 874 875

Page 40 of 44

Table 1. Summary of the reference NO and NO2 tank collection using the DFC-TEA method under varying environmental conditions. The complete dataset is given in Table S4 in the SI.a RH (%)

NO2-+NO3(µM)

Recoveryb (%)

NO2- percent (%)

Pdiff (%)

δ15Nc (‰)

25.3

132.5 4.7

101.4 3.6

87.4 0.3

3.3 5.1

-40.1 0.8

44.6 27.1 34.2

1.4 4.1 11.9

95.0 100.7 98.2

97.0 93.1 94.0

-0.7 -1.2 0.7

-73.0 (-71.7) -70.3 (-69.2) -71.0 (-69.9)

18.8

749 ppbv NO (n=4) 120 22.8 47.5 14.2 NO collection – laboratory DFC system – temperature effect 34 ppbv NO (n=4) 120 11.5 92.0 4.0 101 ppbv NO (n=4) 120 30.8 28.8 11.8 NO collection – laboratory DFC system – interference 34 ppbv NO 120 23.0 33.1 4.0 + 500 ppbv NH3 (n=3) 101 ppbv NO 120 23.1 46.5 11.7 + 500 ppbv NH3 (n=4) 101 ppbv NO 120 22.3 89.7d 11.6 + HONO (n=4) NO collection – field DFC systeme 25 ppbv NO (n=4) 120 21.4 40.8 3.1 34 ppbv NO (n=4) 120 21.9 50.4 3.9 56 ppbv NO (n=3) 120 21.2 44.8 6.2 101 ppbv NO (n=4) 120 21.7 36.6 11.7

99.3

90.7

3.5

-70.6 (-69.4)

20.6

99.8 98.7

89.3 89.5

2.4 3.6

-71.1 (-70.0) -70.8 (-69.7)

20.0

99.5

88.2

-3.8

-70.1 (-69.0)

97.5

91.5

2.6

-71.2 (-70.2)

19.5

96.7

89.8

2.8

-71.0 (-69.9)

19.6

103.9 97.6 96.0 97.1

94.3 92.8 92.9 89.5

4.3 -1.8 -2.0 1.0

-72.9 (-71.7) -70.7 (-69.6) -71.5 (-70.4) -71.0 (-69.9)

19.5

Mean Standard error (1 σ)

98.5 3.5

91.7 3.4

1.1 5.1

-71.1 (-70.0) 1.1 (1.1)

19.7 0.8

Time T (min) (°C) NO2 collection – laboratory DFC system 1002 ppbv NO2 (n=4) 135 23.7 Standard error (1 σ) Sample

NO collection – laboratory DFC system 12 ppbv NO (n=3) 120 23.0 34 ppbv NO (n=4) 120 24.8 101 ppbv NO (n=4) 120 23.1

876 877 878 879 880 881 882 883 884 885 886 887 888

a: Out of 56 NO and NO2 tank collection samples, 52 samples yielded consistent results

wherein 4 samples were detected as outliers on the basis of erroneous concentrations. These outliers were not included in this table. b: NO (NO2) recovery was calculated by dividing measured NO2-+NO3- concentration by the theoretical concentration calculated using the collection time, sample flow rate (1.6 slpm), NO (NO2) concentration, and the TEA solution volume. The TEA solution volume was corrected for evaporative loss by weighing the gas washing bottle containing the solution before and after each sample collection. c: Relative to N2 in the air. δ15N values before the isobaric correction are shown in the brackets. d: RH was measured after the HONO scrubber instead of in the Teflon chamber. e: The chamber purging flow rates were 20 slpm, 15 slpm, 9 slpm, and 5 slpm for the 25 ppbv NO, 34 ppbv NO, 56 ppbv NO, and 101 ppbv NO collection, respectively.


∆17O (‰)

Page 41 of 44


889 890

Figure 1. (a) Schematic of the DFC system (not to scale) consisting of the following: (1)

891

diaphragm pump, (2) air purification columns, (3) drying columns, (4) humidifier, (5)-(7)

892

NO, NO2, and NH3 reference tanks, (8) mass flow controller, (9) flux chamber, (10)

893

temperature and relative humidity sensor, (11) in-line PTFE particulate filter assembly,

894

(12) HONO scrubber, (13) moisture exchanger, (14) reaction tube, (15) gas washing

895

bottle containing TEA solution, (16) O3 generator, (17) NO-NOx-NH3 analyzer; (b)

896

picture showing the field chamber. Specifications of each component of the DFC system

897

are given in the Table S2 in the SI.



898 899

Figure 2. Illustration of the blank-matching strategy for correcting N blanks associated with the

900

TEA solution and denitrifier method.


Page 42 of 44

Page 43 of 44


901 902

Figure 3. (a) The measured δ15N of RSIL20 (δ15NRSIL20-m) as a function of the fraction of

903

analyte N2O-N derived from the total N blank (fB). Sample injection volume, standard

904

deviation of δ15NRSIL20-m, and number of replicates for the individual runs are given in the

905

brackets. The dot in red (56 ppbv collection sample) was not included in the linear

906

regression. (b) The measured δ15N of the NO collection sample as a function of the

907

sample NO2-+NO3- concentration. The dash line and the shaded area represent the mean ±

908

(1 σ) of the δ15N of the NO tank measured using the modified EPA NOx collection

909

method.

910 911 912 913 914 915



916 917

Figure 4. NO emission (lines) and δ15N-NO (dots) results from the laboratory (a) and

918

field (b) rewetting experiments. The error bar on the x-axis denotes the time span of each

919

collection sample. In the field rewetting experiment, four soil plots were respectively

920

wetted on four consecutive days using 500 mL of MilliQ water (black), 20 mM KNO3

921

(red; δ15N=46.5±0.3‰), 10 mM NaNO2 (dark blue; δ15N=1.0±0.4‰), and 20 mM NH4Cl

922

(light blue; δ15N=1.7±0.1‰) solutions.


Page 44 of 44

Novel Method for Nitrogen Isotopic Analysis of Soil ... - ACS Publications

Recommend Documents