Complexation and Adsorption

School of Environmental Science and Engineering, Shandong University, Jinan 250100, China. 5. 2 ... INTRODUCTION. 34. Mercury (Hg) is a persistent tox...
0 downloads 11 Views 2MB Size
Subscriber access provided by UNIV OF DURHAM

Characterization of Natural and Affected Environments

Insights on Chemistry of Mercury Species in Clouds over Northern China: Complexation and Adsorption Tao Li, Yan Wang, Huiting Mao, Shuxiao Wang, Robert W. Talbot, Ying Zhou, Zhe Wang, Xiaoling Nie, and Guanghao Qie Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06669 • Publication Date (Web): 09 Apr 2018 Downloaded from http://pubs.acs.org on April 9, 2018

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

Insights on Chemistry of Mercury Species in Clouds

2

over Northern China: Complexation and Adsorption

3

Tao Li1,5, Yan Wang*,1, Huiting Mao2, Shuxiao Wang3, Robert W. Talbot4, Ying Zhou2, Zhe

4

Wang5, Xiaoling Nie1, Guanghao Qie1 1

5 6

2

School of Environmental Science and Engineering, Shandong University, Jinan 250100, China

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

7

Forestry, Syracuse, NY 13210, USA

8

3

9

Environment, Tsinghua University, & State Environmental Protection Key Laboratory of

10

Sources and Control of Air Pollution Complex, Beijing 100084, China 4

11 12 13 14

State Key Joint Laboratory of Environment Simulation and Pollution Control, School of

Department of Earth and Atmospheric Science, University of Houston, Houston, TX 77204, USA

5

Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China

15 16

ACS Paragon Plus Environment

1

Environmental Science & Technology

Page 2 of 32

17

ABSTRACT: Cloud effects on heterogeneous reactions of atmospheric mercury (Hg) are poorly

18

understood due to limited knowledge of cloudwater Hg chemistry. Here we quantified Hg

19

species in cloudwater at the summit of Mt. Tai in northern China. Total mercury (THg) and

20

methylmercury (MeHg) in cloudwater were on average 70.5 ng L-1 and 0.15 ng L-1, respectively,

21

and particulate Hg (PHg) contributed two-thirds of THg. Chemical equilibrium modeling

22

simulations suggested that Hg complexes by dissolved organic matter (DOM) dominated

23

dissolved Hg (DHg) speciation, which was highly pH dependent. Hg concentrations and

24

speciation were altered by cloud processing, during which significant positive correlations of

25

PHg and MeHg with cloud droplet number concentration (Nd) were observed. Unlike direct

26

contribution to PHg from cloud scavenging of aerosol particles, abiotic DHg methylation was the

27

most likely source of MeHg. Hg adsorption coefficients Kad (5.9 – 362.7 L g-1) exhibited an

28

inverse-power relationship with cloud residues content. Morphology analyses indicated that

29

compared to mineral particles, fly ash particles could enhance Hg adsorption due to more

30

abundant carbon binding sites on the surface. Severe particulate air pollution in northern China

31

may bring substantial Hg into cloud droplets and impact atmospheric Hg geochemical cycling by

32

aerosol-cloud interactions.

33 ACS Paragon Plus Environment

2

Page 3 of 32

34

Environmental Science & Technology

1. INTRODUCTION

35

Mercury (Hg) is a persistent toxic contaminant that ubiquitously exists in the atmosphere.

36

Cloud processing can significantly affect atmospheric Hg transport and fate via scavenging,

37

dissolution, conversion and deposition. Most importantly, clouds, covering ~70% of the earth

38

surface,1 provide sufficient medium for aqueous or heterogeneous reactions2-3 (e.g., gas-liquid

39

partitioning,4 adsorption,5-6 photoredox,7-9 methylation,10-13 etc.), which fundamentally determine

40

atmospheric Hg speciation and transformation.14-15 However, the Hg species, sources and

41

chemical reactions in cloudwater are poorly understood due to the lack of cloudwater Hg

42

measurements.

43

In contrast to extensive work on atmospheric gas- and particulate-phase Hg16-17 (references

44

therein) as well as Hg in precipitations,18-22 only a handful of studies reported measurements23-29

45

and simulations15 of Hg species in cloud/fog water. For example, the concentrations of Hg in

46

cloudwater at Puy De Dôme, France23 and Mt. Mansfield, USA24 were 10 – 50 ng L-1 and 7.5 –

47

71.8 ng L-1, respectively, which were generally higher than precipitation Hg in most North

48

America and Europe regions (< 23 ng L-1)16, 20. A mean concentration of 9.6 ng L-1 was observed

49

in cloud water at Mt. Bamboo, Taiwan, which was attributed largely to coal burning and

50

industrial activities in northern China using trajectory analysis.26 Recently, high methylmercury

51

(MeHg) concentrations were measured in California coastal fogwater (3.4 ± 3.8 ng L-1)27 and

52

marine stratus cloudwater (0.87 ± 0.66 ng L-1)29, which derived from the decomposition of

53

dimethylmercury released by ocean upwelling. MeHg in aquatic environments has two major

54

pathways of formation from reactive Hg species: biotic methylation by anaerobic bacteria30-32

55

and abiotic methylation with methyl donors transfer.13,

56

deposition might directly contribute MeHg to forest food webs, implying the existence of abiotic

33

Tsui et al. found that atmospheric

ACS Paragon Plus Environment

3

Environmental Science & Technology

Page 4 of 32

57

Hg methylation in atmospheric waters (e.g., rainfall, clouds, fogs),34 but the mechanism is

58

unascertained yet.

59

The objective of this study was to fill knowledge gaps of cloudwater Hg species and chemistry.

60

Cloudwater samples were collected at Mt. Tai in polluted northern China to quantify total Hg

61

(THg), dissolved Hg (DHg), particulate Hg (PHg) and MeHg with simultaneous measurements

62

of other chemicophysical parameters. The data were used to address Hg chemical speciation and

63

potential sources of MeHg. Cloud processing effects on Hg behaviors were then investigated.

64

Finally, we elucidated Hg adsorption on different cloud residue particles from micro-view and its

65

implication on atmospheric Hg transfer and transformation in clouds.

66

2. MATERIALS AND METHODS

67

2.1. Field Sampling

68

During 15 June to 11 August 2015, 85 cloudwater samples were collected during 21 non-

69

precipitation cloud events at the summit of Mt. Tai (36°16′N, 117°06′E, 1545 m a.s.l.) in the

70

North China Plain (Figure S1). A single-stage Caltech Active Strand Cloudwater Collector

71

(CASCC) was employed to sample cloudwater. The sampling duration ranged from one to

72

several hours as appropriate to obtain as much as cloudwater volume for analysis. The liquid

73

water content (LWC) and cloud droplet number concentration (Nd) were continuously measured

74

using a fog monitor (FM-120, DMT, USA) employed in previous studies.35-36 Hourly PM2.5 was

75

measured using a real-time particulate monitor (Model 5030 SHARP, Thermo Scientific).

76

In-situ measurements of pH and electrical conductivity were immediately conducted after

77

sampling with a portable pH meter (Model 6350M, JENCO). Acid-cleaned borosilicate glass

78

bottles were used for Hg sample storage. The bottles were soaked in order in HNO3, BrCl and

79

HCl solution for 12 h each, followed by rinsing with Milli-Q water and drying at 500 oC.

ACS Paragon Plus Environment

4

Page 5 of 32

Environmental Science & Technology

80

Cloudwater samples were filtered through 0.45 µm microfilters (ANPEL Laboratory

81

Technologies (Shanghai) Inc.) on site right after collection in priority for analysis of DHg and

82

the unfiltered samples were then preserved for analysis of THg and MeHg. The Hg samples were

83

acidified to 0.5% v/v using high pure HCl. Filtered aliquots (~10 ml each) were also prepared to

84

analyze dissolved organic carbon (DOC), water-soluble ions and carboxylic acids. All liquid

85

samples and filtered particles (i.e., the cloud residues) were stored at 4 oC and refrigerated at –20

86

o

C in the dark.

87

Concurrent total gaseous mercury (TGM) was measured using a Tekran model 2537A cold-

88

vapor atomic fluorescence spectrometer (CVAFS) that was used to quantify Hg0 after TGM pre-

89

concentration onto gold traps and thermal desorption, with a 5-minute time resolution, a

90

sampling flow rate of 1.5 L min-1 and a limit of detection of 5–10 fmol/mol (1 ng m-3 = 112

91

fmol/mol). The sampling inlet was ~3 m above the ground and Teflon tube was heated at 50 oC

92

with pre-filtration of aerosols. Measurement details can be found in Mao et al. (2008).37

93

2.2. Laboratory Analyses

94

The US EPA method 1631 was applied for determination of THg and DHg, performed by BrCl

95

oxidation, SnCl2 reduction, purging and gold trapping, and quantification by CVAFS. PHg was

96

calculated as the difference between THg and DHg. Based on the US EPA method 1630, MeHg

97

samples were distilled, ethylated, purged and trapped, desorbed and detected by GC-CVAFS.

98

The method detection limits for Hg and MeHg were 0.2 and 0.01 ng L-1, and the recoveries for

99

matrix spikes were 91 – 97% and 94 – 112%, respectively. The concentrations of Hg and MeHg

100

in blank samples, which were taken by spraying the Teflon strands of the sampler using

101

deionized water, were measured to be 0.9 and 0.03 ng L-1, respectively.

ACS Paragon Plus Environment

5

Environmental Science & Technology

Page 6 of 32

102

Water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO2−, NO3− and SO42−) were

103

measured using ion chromatography (Dionex, ICS-90). Carboxylic acids (formate, acetate,

104

propionate, lactate, butyrate, mesylate and oxalate) were analyzed with ion chromatography

105

(Dionex, ICS-2500). DOC was calculated from the difference between total carbon and inorganic

106

carbon, which were quantified by NDIR detection of CO2 after thermocatalytic oxidation at 650

107

o

108

particles were reweighed after balance at 20 oC for 24 h, to determine cloud residues

109

concentration with the recorded filtration volume.

C with a TOC analyzer (TOC-LCPH/CPN, SHIMADZU, Japan). Preweighed filters retaining

110

The morphology and elemental composition of three typical cloud residues samples were semi-

111

quantitatively analyzed by scanning electron microscopy-energy dispersive X-ray spectrometry

112

(SEM-EDS, GeminiSEM, ZEISS; QUANTAX, Bruker). Elemental mapping was obtained to

113

understand the elemental distributions on individual particles surface.

114

2.3. Chemical Equilibrium Modeling

115

Hg equilibrium speciation was calculated using Visual MINTEQ v3.1.38 Input data include pH

116

values and concentrations of DHg and other components including DOC, water-soluble ions and

117

carboxylic acids (Table S1). A Gaussian DOM model39 was applied to model Hg complexes by

118

DOM. Ionic strength and temperature corrections were made using the Davies equation and van’t

119

Hoff equation, respectively. Redox reactions were not considered. Adsorption of Hg by cloud

120

residues was assumed not to influence the equilibrium speciation of DHg. Details of modeling

121

(Text S1) and stability constants for Hg species (Table S2) are summarized in the Supporting

122

Information.

123

2.4. Adsorption Coefficient

ACS Paragon Plus Environment

6

Page 7 of 32

124 125

Environmental Science & Technology

The adsorption coefficient (Kad) (L g-1) of Hg onto cloud residues can be calculated using the following equation,6 [PHg](ng L-1 )ൗ[Cloud residues](mg L-1 )

126

Kad =

127

Here, solid Hg species that may exist but cannot be distinguished are all regarded as adsorbed

128

[DHg](ng L-1 )

×1000

Hg.

129

2.5. Trajectory and Potential Source Contribution Function (PSCF) Analysis

130

Three-day backward trajectories of air masses arriving at Mt. Tai at a height of 1545 m a.s.l.

131

during cloud events were simulated using the NOAA Hybrid Single-Particle Lagrangian

132

Integrated Trajectory (HYSPLIT) model.40 Potential source regions of cloudwater MeHg were

133

identified by PSCF analysis.41 Details of PSCF can be found in Text S2.

134

3. RESULTS AND DISCUSSION

135

3.1. Chemical Characterization of Cloudwater and Hg

136

Significantly decreased cloudwater acidity was observed at Mt. Tai with volume-weighted

137

mean (VWM) pH value of 5.79 (4.82 – 6.95), compared to the value of 3.86 measured during

138

2007/2008.42 Concentrations of two major anions, sulfate and nitrate, decreased by 42% and

139

30%, respectively, attributed mainly to reduced emissions of SO2 and NOx in recent years

140

(www.stats.gov.cn/english/Statisticaldata/AnnualData/),36 which together with large emissions of

141

ammonia across the North China Plain43 likely caused the increased cloudwater pH values. LWC

142

and Nd varied between 0.01 – 0.90 g m-3 and 67 – 2180 cm-3, respectively. More details are in

143

Table S1 and Figure S2.

144

Concentrations of THg in cloudwater ranged from 10.2 to 773.3 ng L-1 with an average of 70.5

145

ng L-1 (VWM = 47.6 ng L-1), several times higher than those measured in fogs and clouds

146

worldwide (mean of 9.6–24.8 ng L-1, Table S3).23-27 These values were also significantly higher

ACS Paragon Plus Environment

7

Environmental Science & Technology

Page 8 of 32

147

than precipitation concentrations of Hg (3.0 – 32.3 ng L-1) at most remote and urban sites in

148

China, North American, and Europe.16 DHg accounted for 34.3% of THg averaged at 24.1 ng L-1

149

while PHg for two-thirds of THg. The higher PHg proportion in cloudwater was similar to that

150

observed in urban precipitation18 and snow over Arctic land.44 The mean concentration of MeHg

151

was 0.15 ng L-1, 0.3% of THg. It was on average about an order of magnitude lower than that in

152

California coastal fogwater and marine cloudwater,27-29 and slightly lower than that in urban

153

precipitation in Southwest China, but higher than that in precipitation at other mountain sites

154

(0.03 – 0.12 ng L-1).16

155

3.2. Simulated Hg Speciation

156

PHg was the most abundant species (67.8% of THg) (Figure 1a). Without considering DOM

157

complexation, chemical equilibrium modeling simulated major DHg speciation to be Hg(OH)2

158

(10.6%), HgClOH(aq) (7.8%) and HgCl2(aq) (5.9%) (Figure S3), similar to those in Sacramento

159

Valley fogwater.15 However, a statistically significant correlation between DOC and DHg (r =

160

0.592, p < 0.001) suggested the importance of Hg binding to DOM, in agreement with previous

161

water/sediment studies.2,

162

considering Hg complexation with DOM. Hg-DOM complexes became the predominant DHg

163

speciation comprising 21.2% of THg, followed by much less Hg(OH)2 (4.9%), HgClOH(aq)

164

(2.1%) and Hg(NH3)22+ (2.0%). It’s commonly known that bromide has high binding constant

165

with Hg (log K > 20). However, the Hg-bromo speciation made up only 0.4% of THg due likely

166

to the scarcity of bromide ligands in mountaintop cloudwater. In addition, Hg-Oxalate(aq)

167

comprised ~0.2% of THg, while the Hg-acetate complexes, which were studied in laboratory

168

experiments,10 were not found because of much lower acetate concentrations in cloudwater.15

9, 45-46

Figure 1a shows the overall Hg speciation distribution

ACS Paragon Plus Environment

8

Page 9 of 32

Environmental Science & Technology

169

Despite the complexed chemical composition of actual cloudwater, high pH dependence of

170

DHg speciation profile was apparently observed (Figure 1b). In general, Hg-DOM complexes

171

dominated DHg at acidic pH < 6.0, but its proportion declined significantly from ~90% at

172

pH=6.0 to 10 – 20% at pH near 7.0. In contrast, Hg(OH)2 became one of the major speciation

173

(increasing from < 5% at pH = 6.0 to > 50% of DHg at pH near 7.0) with increasing alkalinity,

174

owing to OH– surpassing other ligands at higher pH. This variation pattern was similar to what

175

was previously found for ferric speciation in cloudwater in southern China: decreased Fe(III)-

176

oxalate but increased Fe(III)-hydroxyl speciation with rising pH values.38 Figure 1b also

177

demonstrates the significance of chloride ligand in DHg speciation, as notable amounts of Hg-

178

chloride complexes were calculated in samples with elevated chloride concentrations (> ~3 mg

179

L-1). The binding of Hg by chloride mainly formed HgCl2(aq) at pH < 6.0 and HgClOH(aq) at

180

pH > 6.0. Furthermore, Hg(NH3)22+ was found to mainly exist at pH > 6.0 and more abundant

181

ammonium (over 25 mg L-1) increased Hg(NH3)22+ complexes more often as pH values

182

approached 7.0 (Figure S4).

183 184

Figure 1. (a) Hg speciation distribution, and (b) simulated DHg speciation by chemical

185

equilibrium modeling versus pH values for each cloudwater sample. Only species exceeding

ACS Paragon Plus Environment

9

Environmental Science & Technology

Page 10 of 32

186

0.1% (mole ratio) of THg are displayed. The x-axis ticks in (b) represent pH values of each

187

sample and the pH increment gradient is not evenly spaced.

188

3.3. Correlations of Measured Hg Species with Cloud Parameters

189

Since cloudwater parameters can control dissolved trace elements,38,

47

the relationships of

190

measured Hg species with pH, LWC, conductivity and Nd were analyzed. Inorganic Hg species

191

and MeHg were correlated differently with pH and LWC (Figure S5). Specifically, increased

192

cloudwater acidity with pH from neutral (~7.0) to weakly acidic (4.8) did not significantly

193

promote DHg and PHg, but did MeHg due probably to lowered pH stimulating Hg methylation.48

194

LWC had dilution effects on DHg and PHg concentrations with logarithmic inverse

195

relationships, while the effects were negligible on MeHg.

196

ACS Paragon Plus Environment

10

Page 11 of 32

Environmental Science & Technology

197

Figure 2. Cloud droplet number concentrations (Nd) versus (a) inorganic Hg species and (b)

198

MeHg, and conductivity versus (c) inorganic Hg species and (d) MeHg. Concentrations in (a)

199

and (b) were normalized to be their air equivalent concentrations by multiplying LWC.

200

Nd was not correlated with cloudwater concentrations of inorganic PHg and DHg as well as

201

MeHg, despite its good relationship with LWC during most non-precipitation cloud events

202

(Figure S6). Note that DHg air equivalent concentrations remained nearly constant over a two

203

orders of magnitude varying range of Nd (Figure 2a). However, PHg (r = 0.61, p < 0.001) and

204

MeHg (r = 0.73, p < 0.001) were found to be significantly correlated with Nd (Figure 2a,b). This

205

indicates that more cloud droplets dissolved larger absolute amounts of PHg and MeHg, but not

206

DHg. It is most likely a result of high atmospheric particulate-bound mercury (PBM)

207

concentrations (83 pg m-3 on average we measured at Mt. Tai, unpublished data) and fractions

208

(~3.7% of total atmospheric Hg) produced via gas-to-particle partitioning due to the combined

209

effect of severe particulate air pollution and intense Hg emissions.16 Moreover, high

210

concentrations (508.5 pg m-3) and content (6.6 µg g-1) of PBM in PM2.5 were measured in the

211

adjacent Jinan city,49 ~50 kilometers north of Mt. Tai. Thus, cloud scavenging of PBM should be

212

an important source of PHg in cloudwater leading to the positive correlation between Nd and

213

PHg. Figure 2c displays a strong correlation between PHg and conductivity, further indicating

214

substantial, direct contributions of air pollution to PHg in cloudwater.

215

The sources and transformation of DHg are very complex and many uncertain factors (e.g.,

216

gas-liquid partitioning, Hg complexation and photoredox)2-3, 50 can control DHg in cloudwater.

217

The correlations of DHg with PHg (r = 0.68, p < 0.001) and conductivity (r = 0.55, p < 0.001,

218

Figure 2c) suggested common factors controlling DHg and PHg, and PBM is one of those. The

219

poor correlation between DHg and Nd (Figure 2a) suggested that atmospheric particles unlikely

ACS Paragon Plus Environment

11

Environmental Science & Technology

Page 12 of 32

220

contributed to DHg directly, but PHg photolysis could be one pathway for DHg formation.51

221

Adsorbing gaseous elemental and/or oxidized Hg into cloud droplets was probably another

222

source of DHg, as implied by higher correlation coefficients of DHg than PHg (Table S4) with

223

secondary ions (e.g., sulfate, nitrate) and DOC, which were mainly formed from their gas

224

precursors.

225

For MeHg, its good correlation with Nd (Figure 2b) could not sufficiently demonstrate its

226

origin from aerosol particles, because MeHg was poorly correlated with conductivity (Figure

227

2d), PHg and DHg as well as other chemical components in cloudwater (Table S4), which

228

indicates different sources of MeHg rather than direct air pollution contribution. Abiotic Hg

229

methylation was speculated to be the most possible source of MeHg in cloudwater as discussed

230

in the next section.

231

3.4. Potential Sources of MeHg

232

The presence of MeHg in cloudwater suggested that there definitely existed MeHg sources

233

compensating for its (photo)degradation52-54. Identifying specific MeHg source is difficult at

234

present. As discussed above, MeHg in cloudwater did not seem to be contributed directly from

235

dissolution of atmospheric gaseous and particulate pollutants. Then MeHg could come from

236

marine environments, biotic or abiotic methylation of inorganic Hg.

237

The PSCF analysis indicates that the middle and southwest China were the regions

238

contributing the most and the Yellow Sea the least to cloudwater MeHg at Mt. Tai (Figure S7).

239

Considering the distance of Mt. Tai over 200 km inland, it was highly unlikely that cloudwater

240

MeHg at Mt. Tai had marine influence, which was also indicated by the poor correlations of

241

MeHg with Cl-, Na+ and mesylate (Table S4).

ACS Paragon Plus Environment

12

Page 13 of 32

Environmental Science & Technology

242

MeHg in aquatic ecosystems is predominantly produced by anaerobic Hg methylating bacteria

243

such as sulfate-reducing bacteria, iron-reducing bacteria and methanogens.30-31, 55 These bacteria

244

commonly inhabit in anaerobic environments and possess two essential methylation gens, hgcA

245

and hgcB.32, 56 In cloudwater at Mt. Tai, diverse pathogens and functional bacteria had been

246

identified.36, 57 However, they were almost all aerobic bacteria rather than anaerobe because the

247

distinctively high oxic envrionment of cloud droplets was unsuitable for anaerobic bacteria to

248

survive. So the biotic methylation of inorgnic Hg to MeHg in cloudwater was likely to be

249

insignificant.

250 251

Figure 3. Mass ratios of MeHg to DHg in cloudwater versus ionic strength with corresponding

252

Nd. Elevated MeHg formation generally occurred at lower ionic strength with higher Nd. The

253

colors indicate MeHg concentrations and the circle sizes represent cloud droplet numbers.

254

Although MeHg was independent of inorganic Hg concentrations, the increased mass ratios of

255

MeHg to DHg along with decreased ionic strength (Figure 3) could be an indicator for abiotic

ACS Paragon Plus Environment

13

Environmental Science & Technology

Page 14 of 32

256

formation of MeHg from DHg in cloudwater. Despite the not very high overall ionic strength, it

257

seemed that both MeHg/DHg mass ratios and absolute MeHg concentrations were elevated when

258

ionic strength lowered, indicating inhibited Hg methylation by stronger ionic strength. Since Hg

259

complexation with organic compounds (methyl donors, e.g., acetate,10 methylcobalamin,58 low-

260

molecular-weight organics11,

261

methylation, the decreased DHg activity and growing competition of inorganic ligands with

262

organics for DHg, which were likely caused by increased ionic strength, might have reduced the

263

availability of DHg complexation with methyl donors, thus leading to the decrease in MeHg

264

formation. In this study, MeHg exhibited no correlations with DOC and acetate. Instead, it was

265

correlated significantly to propionate (Table S4), indicating formation of MeHg via Hg

266

alkylation by propionic acid as proposed by Yin et al.33 Some volatile organic compounds

267

(VOCs) that potentially provide the methyl groups were detected concurrently in in-cloud air

268

(e.g., carbonyls, aromatics, chloromethane and bromomethane)59 and in cloudwater (e.g.,

269

iodomethane) at Mt. Tai. The wide existence of potential methyl donors considerably supported

270

the feasibility of abiotic Hg methylation to MeHg in cloudwater, even though the specific methyl

271

donor has not been ascertained at present. Elevated MeHg concentrations were also found to be

272

accompanied by higher Nd (Figure 3). We hypothesized that more cloud droplets could enhance

273

the uptake of gaseous VOCs potentially providing more methyl donors, and furthermore, the

274

presence of cloud residue particles may acting as catalyst for Hg reactions6 favored MeHg

275

formation as indicated by their linear correlation (r = 0.46, p = 0.004). Future work is needed to

276

identify the methyl donors and methylation mechanisms.

277

33

and methyl iodine13) plays an essential role in abiotic Hg

3.5. Hg Species Variation by Cloud Processing

ACS Paragon Plus Environment

14

Page 15 of 32

Environmental Science & Technology

278

Trace elements properties such as solubility, speciation, reactivity and micromorphology can

279

be modified by cloud processing. 38, 41, 47 Figure 4 presents the temporal variations of Hg species

280

and Nd during a continuous cloud event (1-3 August 2015). Clearly, concentrations of PHg and

281

MeHg varied in phase with Nd. MeHg even rose to peak values as Nd reached up to near or more

282

than 2000 cm-3, while DHg appeared to be independent of Nd. Slightly higher averaged daytime

283

DHg and PHg corresponded to higher daytime Nd. These indicate more contributions of PBM to

284

inorganic Hg than Hg2+ photoreduction to Hg0 followed by outgassing from cloud droplets.2, 8

285

Note that averaged daytime MeHg concentration (0.071 pg m-3) was somewhat lower than

286

nighttime one (0.097 pg m-3) despite higher Nd due maybe to MeHg photodegradation, which

287

was found to be facilitated mainly by complexation with DOM depending on ligands types.2, 52-54

288

In view of the abundant DOM in cloudwater, MeHg photodegradation in cloud droplets might

289

have happened during daytime leading to lower daytime MeHg.

290 291

Figure 4. Temporal variation of air equivalent concentrations of Hg species during the cloud

292

event on 1-3 August 2015. The daytime and nighttime concentrations of Nd and Hg species

293

(mean ± sd) are listed. The 30 min averaged Nd and hourly PM2.5 are displayed. Pies charts show

ACS Paragon Plus Environment

15

Environmental Science & Technology

Page 16 of 32

294

Hg speciation distributions for selected cloudwater samples. The Nd could be a rough indicator

295

of aerosol particles incorporated into clouds.

296

During cloud event (Figure 4), most (~70%) of PM2.5 was scavenged within the first few hours

297

followed by a constant lower concentration. DHg showed higher concentrations than PHg at the

298

initial stage of cloud event, whereas PHg rapidly surpassed DHg as cloud processes went on.

299

Much dissolution of PBM in cloudwater should be responsible for the more DHg in the first two

300

cloudwater samples. Moreover, Hg speciation was markedly changed by cloud processing in

301

different cloud periods: 52.3% of THg were the dissolved Hg-DOM(aq) complexes in the early

302

stage; PHg overtook Hg-DOM(aq) and became the dominant species (more than 80% of THg) in

303

the middle stage; in the dissipating stage, PHg still dominated Hg speciation, followed by

304

increased Hg-DOM(aq). The changed Hg speciation, determined mainly by pH with more Hg-

305

DOM(aq) complexes formed in more acid cloudwater, should play a critical role in Hg

306

dissolution during cloud processing.

307

Simple theoretical calculations were conducted to assess the relative importance of

308

contributions from possible sources to Hg in cloudwater. Assuming that gas-liquid partitioning

309

of Hg0 reached an equilibrium, 1.48 pg m-3 of cloudwater Hg (corresponding to 6.45 ng L-1 at

310

mean LWC of 0.23 g m-3) was obtained using Henry’s law constant for Hg0 (1.3×10-3 mol m-3

311

Pa-1)60 and the averaged TGM concentration that we measured at Mt. Tai (2.18 ng m-3, Hg0 can

312

approximately equal to TGM as Hg0 accounts for > 99% of TGM at remote sites in China16). It

313

was evidently far less than the mean concentration of THg (13.9 pg m-3) and even DHg (4.7 pg

314

m-3) in cloudwater. This clearly suggests more important sources for Hg in cloudwater other than

315

gaseous Hg0. If the measured 83 pg m-3 of PBM during the campaign had the same cloud

316

scavenging efficiency as PM2.5, i.e. ~70%, ~58.1 pg m-3 of PBM should have entered cloudwater.

ACS Paragon Plus Environment

16

Page 17 of 32

Environmental Science & Technology

317

The amount was over 4 times more than THg in cloudwater. Even if cloud scavenging efficiency

318

for PBM was lowered to 20% (the scavenging ratio for Fe),38 PBM could still have contributed

319

16.6 pg m-3 of THg. These results again allude to the potential importance of PBM contributions

320

to cloudwater Hg.

321

3.6. Hg Adsorption on Cloud Residues

322

Reversible adsorption of DHg on soot in cloudwater significantly influences Hg species

323

transformation, which has been incorporated into atmospheric mercury modeling.2, 6, 14 Cloud

324

residues content was measured to be 0.7 – 290 mg L-1 (mean 55 mg L-1) and moderately

325

correlated to Nd (r = 0.51, p < 0.01). Adsorption coefficients Kad (5.9 – 362.7 L g-1) were highly

326

dependent on cloud residues content, rather than Nd, with an inversely power-law relationship

327

(Figure 5a). Solids effect,61-62 which results from the competition of solute binding to organic

328

matter between aqueous and solid phase, could explain the negative effects of cloud residues

329

content on Kad. More cloud residues in cloudwater could likely increase particulate aggregation

330

and decrease available binding sites for organic matter to complex Hg. THg concentrations,

331

which were slightly correlated to cloud residues, seemed to have very limited influence on Hg

332

adsorption, indicating that Hg adsorption should be adsorbent rather than adsorbate controlled. In

333

addition, Kad was elevated as cloudwater pH increased from 5.01 to 6.95, attributed partially to

334

the reduced Hg-DOM complexation in aqueous phase caused by the higher pH.

335

During field sampling, we found three types of filtered cloud residues that differed greatly in

336

color as represented by sample I, II and III (Figure 5a). The dark sample I, grey sample II and

337

light brown sample III had a high (67.0 mg L-1), moderate (42.5 mg L-1) and low (29.7 mg L-1)

338

concentration of cloud residues, respectively. More importantly, notably higher Kad was

339

calculated in sample III (165.4 L g-1) than in the other two samples (14.8 and 8.1 L g-1). To

ACS Paragon Plus Environment

17

Environmental Science & Technology

Page 18 of 32

340

understand what may have caused different Kad values in the three cloudwater samples other than

341

solids effect, their physicochemical characterization was investigated.

342

343 344

Figure 5. (a) Dependence of Hg adsorption coefficient Kad on cloud residues content. Photos of

345

typical cloud residues filters of three cloudwater samples I, II and III are displayed. (b) Water-

346

soluble ions composition, and (c) SEM images and corresponding EDS spectra of cloud residues

347

for the three cloudwater samples. Only elements over 0.1% of total mass can be determined by

348

EDS.

349

ACS Paragon Plus Environment

18

Page 19 of 32

Environmental Science & Technology

350

Water-soluble ions composition in the three cloudwater samples was compared in Figure 5b.

351

Sample I had much more secondary ions than samples II and III. Moreover, the ions composition

352

in sample III differed from the other two with NH4+ and Ca2+ accounting for 47% and 18% of

353

total ions, respectively, indicating soil dust being a significant component of the cloudwater

354

sample III. However, there were comparable amounts of anthropogenic trace elements such as

355

Zn, Pb and Se in samples III and I (Figure S8, unpublished data). The samples composition

356

suggested that the cloudwater had contributions from soil dust and industrial sources alike.

357

Surface morphology and elemental composition of particles in cloud residues were

358

characterized using SEM-EDS (Figure 5c). Overall, cloud residues in the three samples were

359

comprised of highly mixed particles whose sizes ranged from nanometers to about ten

360

micrometers. These particles were primarily identified as irregularly shaped and lamellate

361

mineral materials, spherical and ellipsoidal fly ash, aggregates of nanoparticles (chain-like soot

362

particles), porous substances, etc. Cloud residues in samples I and III were similar and consisted

363

of more small fly ash and aggregates of finer particles, while particles in sample II were coarser

364

and more diverse. The predominant elements in cloud residues determined by EDS were C, O,

365

Si, Al, Fe and Ca with less Mg, K, Na and Mn, indicating mixtures of abundant carbonaceous

366

and crustal materials. Carbon content in our results was the highest (36.2 – 48.0%), fairly

367

consistent with Li et al.’s study in which elemental carbon (EC) particles accounted for 49.3% of

368

cloud residues,63 indicative of large contributions from abundant EC in northern China.64 The

369

abundant refractory Si, Al and Fe in our cloud residues could come from dust materials (e.g.,

370

silicate, hematite) and fly ash (e.g., SiO2, Al2O3). Figure 5c shows more spherical particles and

371

about 2–3 times higher Si and Al content in sample III than I and II, indicating more fly ash

372

particles in sample III. Fly ash can substantially capture Hg in flue gas65-66 and in aqueous

ACS Paragon Plus Environment

19

Environmental Science & Technology

Page 20 of 32

373

solutions,67 due to its stronger physisorption resulting from porous structure, smaller diameter

374

and higher specific surface area. Hence, a much higher Kad value was obtained for Hg in sample

375

III. Indeed, backward trajectories analyses (Figure S9) corroborated that air masses of sample III

376

could be greatly impacted by the industrial flue gases/dusts containing abundant fly ash particles

377

emitted from two huge iron and steel plants (Laiwu and Rizhao).

378

Elemental maps of single particles in cloud residues (Figure 6) illustrate the spatial

379

distributions of major elements (C and O, Si, Al, K) on the surface of individual crystal mineral

380

and fly ash particles. The crustal mineral particle surface exhibited high intensity (abundance) of

381

Si, Al, O and K while low intensity of C (Figure 6a). In contrast, the fly ash particle surface

382

(Figure 6b) showed higher intensity of C than the other elements. It should be noted that some

383

small minerals attached to the fly ash surface displaying stronger intensity of Si, Al and O than

384

that of C (Figure 6b). Unburnt carbon in fly ash plays significant roles in Hg oxidation and

385

surface adsorption,65 probably via the formation of C-M bond to facilitate the catalytic oxidation

386

of elemental Hg68 and via Hg chemisorption by surface carbon-oxygen functional groups.66

387

Therefore, the disparities of carbon distribution between fly ash and mineral particles shown in

388

Figure 6 indicate that carbonaceous matters (e.g., humic acid) are very prone to be associated

389

with fly ash particles rather than mineral particles, and thus provide more carbon adsorption

390

points on fly ash to enhance greatly the Hg chemisorption.

391

ACS Paragon Plus Environment

20

Page 21 of 32

Environmental Science & Technology

392

Figure 6. Elemental mapping images of individual (a) crystal minerals and (b) ellipsoidal fly ash

393

particles in cloud residues. Ch0 represents the analyzed microdomain. The density of colored

394

dots in each image indicates the intensity (abundance) of analyzed element. The C distributions

395

on two particles are distinctly inconsistent. The sizes of both particles are about 1 µm.

396

These results highlighted the significant importance of fly ash particles for facilitating Hg

397

adsorption on cloud residues in cloudwater. The adsorption coefficient Kad was not only affected

398

by the quantity of cloud residues, but also depended on the nature of residue particles (e.g.,

399

surface properties, elemental composition). Given the complexity of cloud residues, other factors

400

such as halogen content, unburnt carbon type and association of natural organic matter (NOM)

401

with iron oxyhydroxides may also affect Hg adsorption,65-66, 69-70 which warrant further study.

402

3.7. Summary and Environmental Perspective

403

The results provide valuable information on cloudwater Hg chemistry in severely air polluted

404

northern China, including Hg concentration, chemical speciation and potential sources, etc. We

405

find highly polluted Hg species in cloudwater, dominated by PHg and Hg-DOM complexes. PHg

406

should be mainly contributed from ambient aerosols while MeHg may be formed via abiotic Hg

407

methylation. Cloud processing likely plays an important role in Hg transport and transformation

408

by changing Hg concentration and speciation.

409

Our findings of Hg adsorption on cloud residues are critical to improving the understanding of

410

atmospheric Hg behaviors in clouds. High concentrations of aerosols in northern China could

411

generate more, smaller cloud droplets35,

412

adsorption on cloud residues, especially the fly ash particles with more binding sites. The

413

measured Kad for cloud residues (5.9 – 362.7 L g-1, mean of 69.8 L g-1) is significantly higher

414

than that obtained with NIST atmospheric particulate matter (3 – 91 L g-1)6 and the value used in

71

and contribute greatly to PHg in cloudwater via

ACS Paragon Plus Environment

21

Environmental Science & Technology

Page 22 of 32

415

transport model (45 L g-1).72 The stronger Hg adsorption on realistic cloud residues could inhibit

416

aqueous reduction of Hg(II) and subsequent volatilization of Hg0, leading to enhanced Hg wet

417

deposition2 and higher ecological risks than estimation. Since photodissolution of PHg has been

418

observed in rainwater,51 the abundant PHg in cloudwater could contribute largely to DHg

419

accompanied by DOM complexation. Once PHg dissolves in cloudwater to be reactive Hg,

420

heterogeneous reactions (e.g., photoredox, methylation-demethylation) would take place. In the

421

context of climate change induced by aerosol-cloud interactions,71,

422

microstructure and lifetime induced by particulate air pollution are expected to greatly impact

423

atmospheric Hg cycling and fate.

424

ASSOCIATED CONTENT

425

Supporting Information

426

Supporting Information Available: Text S1–2, Figure S1–9, Table S1–4 and 14 References

427

(PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

428

AUTHOR INFORMATION

429

Corresponding Author

430

*Phone: +086-531-88361157; e-mail: [email protected]

431

Notes

432

The authors declare no competing financial interest.

433

ACKNOWLEDGEMENTS

73

alterations of cloud

434

We appreciate Dr. Jeffrey L. Collett Jr. and Tao Wang for providing the cloudwater sampling

435

method. We also thank Dr. Jianmin Chen for supplying important data and Chen Wu, Yaxin Li,

ACS Paragon Plus Environment

22

Page 23 of 32

Environmental Science & Technology

436

Chao Zhu, Xianmang Xu, Jiarong Li and Fengchun Yang for helping the field experiments. This

437

work was financially supported by the National Natural Science Foundation of China

438

(41475115), Ministry of Science and Technology of China (2016YFE0112200) and H2020

439

Marie Skłodowska-Curie Actions (690958-MARSU-RISE-2015).

440

REFERENCES

441

(1)

442

Girolamo, L.; Getzewich, B.; Guignard, A.; Heidinger, A.; Maddux, B. C.; Menzel, W. P.;

443

Minnis, P.; Pearl, C.; Platnick, S.; Poulsen, C.; Riedi, J.; Sun-Mack, S.; Walther, A.; Winker, D.;

444

Zeng, S.; Zhao, G., Assessment of Global Cloud Datasets from Satellites: Project and Database

445

Initiated by the GEWEX Radiation Panel. B. Am. Meteorol. Soc. 2013, 94 (7), 1031-1049.

446

(2)

447

Ryjkov, A.; Semeniuk, K.; Subir, M.; Toyota, K., Mercury physicochemical and biogeochemical

448

transformation in the atmosphere and at atmospheric interfaces: a review and future directions.

449

Chem. Rev. 2015, 115 (10), 3760-802.

450

(3)

451

atmospheric mercury modeling II. Mercury surface and heterogeneous chemistry – A missing

452

link. Atmos. Environ. 2012, 46, 1-10.

453

(4)

454

dissolved gaseous mercury in the surface waters of the Arctic Ocean. Mar. Chem. 2008, 110 (3-

455

4), 190-194.

456

(5)

457

Waters: Occurrence and Determination of Particulate Hg(0). Environ. Sci. Technol. 2015, 49

458

(16), 9742-9.

Stubenrauch, C. J.; Rossow, W. B.; Kinne, S.; Ackerman, S.; Cesana, G.; Chepfer, H.; Di

Ariya, P. A.; Amyot, M.; Dastoor, A.; Deeds, D.; Feinberg, A.; Kos, G.; Poulain, A.;

Subir, M.; Ariya, P. A.; Dastoor, A. P., A review of the sources of uncertainties in

Andersson, M. E.; Sommar, J.; Gårdfeldt, K.; Lindqvist, O., Enhanced concentrations of

Wang, Y.; Li, Y.; Liu, G.; Wang, D.; Jiang, G.; Cai, Y., Elemental Mercury in Natural

ACS Paragon Plus Environment

23

Environmental Science & Technology

Page 24 of 32

459

(6)

Seigneur, C.; Abeck, H.; Chia, G.; Reinhard, M.; Bloom, N. S.; Prestbo, E.; Saxena, P.,

460

Mercury adsorption to elemental carbon (soot) particles and atmospheric particulate matter.

461

Atmos. Environ. 1998, 32 (14-15), 2649-2657.

462

(7)

463

homogeneous and surface-catalyzed mercury(II) reduction by iron(II). Environ. Sci. Technol.

464

2013, 47 (13), 7204-13.

465

(8)

466

Isotopes by Photoreduction in Aquatic Systems. Science 2007, 318 (5849), 417-420.

467

(9)

468

complexation by natural organic matter in anoxic environments. Proc. Natl. Acad. Sci. U.S.A.

469

2011, 108 (4), 1479-1483.

470

(10)

471

methylation of divalent mercury in the aqueous phase. Sci. Total. Environ. 2003, 304 (1-3), 127-

472

136.

473

(11)

474

Abiotic Production of Methylmercury by Solar Radiation. Environ. Sci. Technol. 2005, 39 (4),

475

1071.

476

(12)

477

as a potential source of methylmercury in wet deposition. Atmos. Environ. 2007, 41 (8), 1663-

478

1668.

479

(13)

480

inorganic mercury species in natural waters. Nat. Commun. 2014, 5, 4633.

Amirbahman, A.; Kent, D. B.; Curtis, G. P.; Marvin-Dipasquale, M. C., Kinetics of

Bergquist, B. A.; Blum, J. D., Mass-Dependent and -Independent Fractionation of Hg

Gu, B.; Bian, Y.; Miller, C. L.; Dong, W.; Jiang, X.; Liang, L., Mercury reduction and

Gårdfeldt, K.; Munthe, J.; Strömberg, D.; Lindqvist, O., A kinetic study on the abiotic

Siciliano, S. D.; O'Driscoll, N. J.; Tordon, R.; Hill, J.; Beauchamp, S.; Lean, D. R. S.,

Hammerschmidt, C. R.; Lamborg, C. H.; Fitzgerald, W. F., Aqueous phase methylation

Yin, Y.; Li, Y.; Tai, C.; Cai, Y.; Jiang, G., Fumigant methyl iodide can methylate

ACS Paragon Plus Environment

24

Page 25 of 32

Environmental Science & Technology

481

(14)

Pleuel, K.; Munthe, J., Modelling the atmospheric mercury cycle-chemistry in fog

482

droplets. Atmos. Environ. 1995, 29 (12), 1441-1457.

483

(15)

484

Armstrong, D.; Collett, J.; Herckes, P., Speciation of Mercury(II) and Methylmercury in Cloud

485

and Fog Water. Aerosol Air Qual. Res. 2011, 11 (2), 161-169.

486

(16)

487

atmospheric mercury in China: a critical review. Atmos. Chem. Phys. 2015, 15 (16), 9455-9476.

488

(17)

489

spatiotemporal variations of atmospheric speciated mercury: a review. Atmos. Chem. Phys. 2016,

490

16 (20), 12897-12924.

491

(18)

492

temporal distributions of total and methyl mercury in precipitation in core urban areas,

493

Chongqing, China. Atmos. Chem. Phys. 2012, 12 (20), 9417-9426.

494

(19)

495

Tripathee, L., Characterizations of wet mercury deposition on a remote high-elevation site in the

496

southeastern Tibetan Plateau. Environ. Pollut. 2015, 206, 518-26.

497

(20)

498

Barres, J. A.; Dvonch, J. T., Spatial patterns and temporal trends in mercury concentrations,

499

precipitation depths, and mercury wet deposition in the North American Great Lakes region,

500

2002-2008. Environ. Pollut. 2012, 161, 261-71.

501

(21)

502

(Pengjiayu) in the subtropical Northwest Pacific Ocean. Atmos. Environ. 2013, 77, 474-481.

Bittrich, D.; Chadwick, S.; Babiarz, C.; Manolopoulos, H.; Rutter, A.; Schauer, J.;

Fu, X. W.; Zhang, H.; Yu, B.; Wang, X.; Lin, C. J.; Feng, X. B., Observations of

Mao, H.; Cheng, I.; Zhang, L., Current understanding of the driving mechanisms for

Wang, Y. M.; Wang, D. Y.; Meng, B.; Peng, Y. L.; Zhao, L.; Zhu, J. S., Spatial and

Huang, J.; Kang, S.; Zhang, Q.; Guo, J.; Sillanpaa, M.; Wang, Y.; Sun, S.; Sun, X.;

Risch, M. R.; Gay, D. A.; Fowler, K. K.; Keeler, G. J.; Backus, S. M.; Blanchard, P.;

Sheu, G.-R.; Lin, N.-H., Characterizations of wet mercury deposition to a remote islet

ACS Paragon Plus Environment

25

Environmental Science & Technology

Page 26 of 32

503

(22)

Weiss-Penzias, P. S.; Gay, D. A.; Brigham, M. E.; Parsons, M. T.; Gustin, M. S.; Ter

504

Schure, A., Trends in mercury wet deposition and mercury air concentrations across the U.S. and

505

Canada. Sci. Total. Environ. 2016, 568, 546-56.

506

(23)

507

into tropospheric clouds, Journal de Physique IV (Proceedings), EDP sciences: 2003; pp 525-

508

528.

509

(24)

510

elements in cloud water and precipitation collected on Mt. Mansfield, Vermont. J. Envion.

511

Monitor. 2003, 5 (4), 584.

512

(25)

513

Atmos. Environ. 2006, 40 (33), 6321-6328.

514

(26)

515

Taiwan during the northeast monsoon season. Atmos. Environ. 2011, 45 (26), 4454-4462.

516

(27)

517

Collett, J. L.; Flegal, A. R., Total and monomethyl mercury in fog water from the central

518

California coast. Geophys. Res. Lett. 2012, 39 (3), L03804.

519

(28)

520

D.; Farlin, J.; Moranville, R.; Olson, A., Total- and monomethyl-mercury and major ions in

521

coastal California fog water: Results from two years of sampling on land and at sea. Elem. Sci.

522

Anth. 2016, 4, 000101.

523

(29)

524

MacDonald, A. B.; Wang, Z.; Jonsson, H., Aircraft Measurements of Total Mercury and

Gauchard, P.-A.; Dommergue, A.; Ferrari, C.; Laj, P.; Boutron, C. In Mercury speciation

Malcolm, E. G.; Keeler, G. J.; Lawson, S. T.; Sherbatskoy, T. D., Mercury and trace

Ritchie, C. D.; Richards, W.; Arp, P. A., Mercury in fog on the Bay of Fundy (Canada).

Sheu, G.-R.; Lin, N.-H., Mercury in cloud water collected on Mt. Bamboo in northern

Weiss-Penzias, P. S.; Ortiz, C.; Acosta, R. P.; Heim, W.; Ryan, J. P.; Fernandez, D.;

Weiss-Penzias, P.; Coale, K.; Heim, W.; Fernandez, D.; Oliphant, A.; Dodge, C.; Hoskins,

Weiss-Penzias, P.; Sorooshian, A.; Coale, K.; Heim, W.; Crosbie, E.; Dadashazar, H.;

ACS Paragon Plus Environment

26

Page 27 of 32

Environmental Science & Technology

525

Monomethyl Mercury in Summertime Marine Stratus Cloudwater from Coastal California, USA.

526

Environ. Sci. Technol. 2018.

527

(30)

528

Gu, B., Oxidation and methylation of dissolved elemental mercury by anaerobic bacteria. Nat.

529

Geosci. 2013, 6 (9), 751-754.

530

(31)

531

production below the mixed layer in the North Pacific Ocean. Nat. Geosci. 2013, 6 (10), 879-884.

532

(32)

533

Qian, Y.; Brown, S. D.; Brandt, C. C., The genetic basis for bacterial mercury methylation.

534

Science 2013, 339 (6125), 1332-1335.

535

(33)

536

inorganic Hg(II) by photochemical processes in the environment. Chemosphere 2012, 88 (1), 8-

537

16.

538

(34)

539

and transfers of methylmercury in adjacent river and forest food webs. Environ. Sci. Technol.

540

2012, 46 (20), 10957-64.

541

(35)

542

Wang, W.; Ding, A.; Herrmann, H., Chemical composition and droplet size distribution of cloud

543

at the summit of Mount Tai, China. Atmos. Chem. Phys. 2017, 17 (16), 9885-9896.

544

(36)

545

Chemical Composition and Bacterial Community in Size-Resolved Cloud Water at the Summit

546

of Mt. Tai, China. Aerosol and Air Quality Research 2018, 18 (1), 1-14.

Hu, H.; Lin, H.; Zheng, W.; Tomanicek, S. J.; Johs, A.; Feng, X.; Elias, D. A.; Liang, L.;

Blum, J. D.; Popp, B. N.; Drazen, J. C.; Anela Choy, C.; Johnson, M. W., Methylmercury

Parks, J. M.; Johs, A.; Podar, M.; Bridou, R.; Jr, H. R.; Smith, S. D.; Tomanicek, S. J.;

Yin, Y.; Chen, B.; Mao, Y.; Wang, T.; Liu, J.; Cai, Y.; Jiang, G., Possible alkylation of

Tsui, M. T.; Blum, J. D.; Kwon, S. Y.; Finlay, J. C.; Balogh, S. J.; Nollet, Y. H., Sources

Li, J.; Wang, X.; Chen, J.; Zhu, C.; Li, W.; Li, C.; Liu, L.; Xu, C.; Wen, L.; Xue, L.;

Zhu, C.; Chen, J.; Wang, X.; Li, J.; Wei, M.; Xu, C.; Xu, X.; Ding, A.; Collett, J. L.,

ACS Paragon Plus Environment

27

Environmental Science & Technology

Page 28 of 32

547

(37)

Mao, H.; Talbot, R. W.; Sigler, J. M.; Sive, B. C., Seasonal and diurnal variations of Hg°

548

over New England. Atmos. Chem. Phys. 2008, 8 (5), 1403-1421.

549

(38)

550

Evolution of trace elements in the planetary boundary layer in southern China: Effects of dust

551

storms and aerosol-cloud interactions. J. Geophys. Res.: Atmos. 2017, (122), 3492-3506.

552

(39)

553

geochemical assessment model for environmental systems. Environmental Research Laboratory

554

Office of Research & Development Usepa 1991, 37 (106), 371-383.

555

(40)

556

NOAA’s HYSPLIT Atmospheric Transport and Dispersion Modeling System. B. Am. Meteorol.

557

Soc. 2015, 96 (12), 2059-2077.

558

(41)

559

solubility of trace elements in fine particles at a mountain site, southern China: regional sources

560

and cloud processing. Atmos. Chem. Phys. 2015, 15 (15), 8987-9002.

561

(42)

562

Wang, W.; Wang, T., Characterization of cloud water chemistry at Mount Tai, China: Seasonal

563

variation, anthropogenic impact, and cloud processing. Atmos. Environ. 2012, 60, 467-476.

564

(43)

565

Whitburn, S.; Coheur, P. F.; Gu, B., Ammonia Emissions May Be Substantially Underestimated

566

in China. Environ. Sci. Technol. 2017, 51 (21), 12089-12096.

567

(44)

568

distribution, partitioning and speciation in coastal vs. inland High Arctic snow. Geochim.

569

Cosmochim. Ac. 2007, 71 (14), 3419-3431.

Li, T.; Wang, Y.; Zhou, J.; Wang, T.; Ding, A.; Nie, W.; Xue, L.; Wang, X.; Wang, W.,

Allison, J. D.; Brown, D. S.; NovoGradac, K. J., MINTEQA2/PRODEFA2, a

Stein, A. F.; Draxler, R. R.; Rolph, G. D.; Stunder, B. J. B.; Cohen, M. D.; Ngan, F.,

Li, T.; Wang, Y.; Li, W. J.; Chen, J. M.; Wang, T.; Wang, W. X., Concentrations and

Guo, J.; Wang, Y.; Shen, X.; Wang, Z.; Lee, T.; Wang, X.; Li, P.; Sun, M.; Collett, J. L.;

Zhang, X.; Wu, Y.; Liu, X.; Reis, S.; Jin, J.; Dragosits, U.; Van Damme, M.; Clarisse, L.;

Poulain, A. J.; Garcia, E.; Amyot, M.; Campbell, P. G. C.; Ariya, P. A., Mercury

ACS Paragon Plus Environment

28

Page 29 of 32

Environmental Science & Technology

570

(45)

Haitzer, M.; Aiken, G. R.; Ryan, J. N., Binding of mercury(II) to dissolved organic

571

matter: the role of the mercury-to-DOM concentration ratio. Environ. Sci. Technol. 2002, 36 (16),

572

3564.

573

(46)

574

Chemosphere 2004, 55 (3), 319-31.

575

(47)

576

Transition metals in atmospheric liquid phases: Sources, reactivity, and sensitive parameters.

577

Chemical reviews 2005, 105 (9), 3388-3431.

578

(48)

579

methylmercury in low pH lakes. Environ. Toxicol. Chem. 1990, 9 (7), 853-869.

580

(49)

581

Wang, G.; Zhou, J.; Qie, G., Characteristics and potential sources of atmospheric particulate

582

mercury in Jinan, China. Sci. Total. Environ. 2017, 574, 1424-1431.

583

(50)

584

Scientific uncertainties in atmospheric mercury models I: Model science evaluation. Atmos.

585

Environ. 2006, 40 (16), 2911-2928.

586

(51)

587

of Mercury in Rainwater. J. Atmos. Chem. 2008, 60 (2), 153-168.

588

(52)

589

in surface water of the Florida Everglades: importance of dissolved organic matter-

590

methylmercury complexation. Environ. Sci. Technol. 2014, 48 (13), 7333-40.

591

(53)

592

to natural organic ligands. Nat. Geosci. 2010, 3 (7), 473-476.

Ravichandran, M., Interactions between mercury and dissolved organic matter--a review.

Deguillaume, L.; Leriche, M.; Desboeufs, K.; Mailhot, G.; George, C.; Chaumerliac†, N.,

Winfrey, M. R.; Rudd, J. W. M., Environmental factors affecting the formation of

Li, Y.; Wang, Y.; Li, Y.; Li, T.; Mao, H.; Talbot, R.; Nie, X.; Wu, C.; Zhao, Y.; Hou, C.;

Lin, C.-J.; Pongprueksa, P.; Lindberg, S. E.; Pehkonen, S. O.; Byun, D.; Jang, C.,

Kieber, R. J.; Parler, N. E.; Skrabal, S. A.; Willey, J. D., Speciation and Photochemistry

Tai, C.; Li, Y.; Yin, Y.; Scinto, L. J.; Jiang, G.; Cai, Y., Methylmercury photodegradation

Zhang, T.; Hsu-Kim, H., Photolytic degradation of methylmercury enhanced by binding

ACS Paragon Plus Environment

29

Environmental Science & Technology

Page 30 of 32

593

(54)

Qian, Y.; Yin, X.; Lin, H.; Rao, B.; Brooks, S. C.; Liang, L.; Gu, B., Why Dissolved

594

Organic Matter Enhances Photodegradation of Methylmercury. Environ. Sci. Tech. Let. 2014, 1

595

(10), 426-431.

596

(55)

597

Molecular composition of organic matter controls methylmercury formation in boreal lakes. Nat.

598

Commun. 2017, 8, 14255.

599

(56)

600

Palumbo, A. V.; Somenahally, A. C.; Elias, D. A., Global prevalence and distribution of genes

601

and microorganisms involved in mercury methylation. Sci. Adv. 2015, 1 (9), e1500675.

602

(57)

603

in cloud water at Mt Tai: similarity and disparity under polluted and non-polluted cloud episodes.

604

Atmos. Chem. Phys. 2017, 17 (8), 5253-5270.

605

(58)

606

kinetic isotope fractionation of mercury during abiotic methylation of Hg(II) by

607

methylcobalamin in aqueous chloride media. Chem. Geol. 2013, 336, 26-36.

608

(59)

609

Cloud/Fog on Atmospheric VOCs in the Free Troposphere: A Case Study at Mount Tai in

610

Eastern China. Aerosol Air Qual. Res. 2017, 17 (10), 2401-2412.

611

(60)

612

Atmos. Chem. Phys. 2015, 15 (8), 4399-4981.

613

(61)

614

Environ. Sci. Technol. 1985, 19 (9), 789-96.

Bravo, A. G.; Bouchet, S.; Tolu, J.; Bjorn, E.; Mateos-Rivera, A.; Bertilsson, S.,

Podar, M.; Gilmour, C. C.; Brandt, C. C.; Soren, A.; Brown, S. D.; Crable, B. R.;

Wei, M.; Xu, C.; Chen, J.; Zhu, C.; Li, J.; Lv, G., Characteristics of bacterial community

Jiménez-Moreno, M.; Perrot, V.; Epov, V. N.; Monperrus, M.; Amouroux, D., Chemical

Yang, F.; Wang, Y.; Li, H.; Yang, M.; Li, T.; Cao, F.; Chen, J.; Wang, Z., Influence of

Sander, R., Compilation of Henry's law constants (version 4.0) for water as solvent.

Voice, T. C.; Weber, W. J., Sorbent concentration effects in liquid/solid partitioning.

ACS Paragon Plus Environment

30

Page 31 of 32

Environmental Science & Technology

615

(62)

Lu, Y.; Allen, H. E., A predictive model for copper partitioning to suspended particulate

616

matter in river waters. Environ. Pollut. 2006, 143 (1), 60-72.

617

(63)

618

amp; apos; an; Sheng, G.; Zhou, Z., In situ chemical composition measurement of individual

619

cloud residue particles at a mountain site, southern China. Atmos. Chem. Phys. 2017, 17 (13),

620

8473-8488.

621

(64)

622

Torres, O.; Ahn, C.; Lu, Z.; Cao, J.; Mao, Y., Constraining black carbon aerosol over Asia using

623

OMI aerosol absorption optical depth and the adjoint of GEOS-Chem. Atmos. Chem. Phys. 2015,

624

15 (18), 10281-10308.

625

(65)

626

ash compositions on the adsorption and oxidation of mercury in flue gas from coal combustion.

627

Fuel 2016, 163, 232-239.

628

(66)

629

chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention. J.

630

Hazard. Mater. 2016, 301, 400-6.

631

(67)

632

885-888.

633

(68)

634

flue gas by modified fly ash. J. Environ. Sci. 2013, 25 (2), 393-398.

635

(69)

636

Tarazona, M. R., The influence of carbon particle type in fly ashes on mercury adsorption. Fuel

637

2009, 88 (7), 1194-1200.

Lin, Q.; Zhang, G.; Peng, L.; Bi, X.; Wang, X.; Brechtel, F. J.; Li, M.; Chen, D.; Peng, P.;

Zhang, L.; Henze, D. K.; Grell, G. A.; Carmichael, G. R.; Bousserez, N.; Zhang, Q.;

Wang, F.; Wang, S.; Meng, Y.; Zhang, L.; Wu, Q.; Hao, J., Mechanisms and roles of fly

Deng, S.; Shu, Y.; Li, S.; Tian, G.; Huang, J.; Zhang, F., Chemical forms of the fluorine,

Sen, A. K.; De, A. K., Adsorption of mercury(II) by coal fly ash. Water Res. 1987, 21 (8),

Xu, W.; Wang, H.; Zhu, T.; Kuang, J.; Jing, P., Mercury removal from coal combustion

López-Antón, M. A.; Abad-Valle, P.; Díaz-Somoano, M.; Suárez-Ruiz, I.; Martínez-

ACS Paragon Plus Environment

31

Environmental Science & Technology

Page 32 of 32

638

(70)

Gu, B.; Mishra, B.; Miller, C.; Wang, W.; Lai, B.; Brooks, S. C.; Kemner, K. M.; Liang,

639

L., X-ray fluorescence mapping of mercury on suspended mineral particles and diatoms in a

640

contaminated freshwater system. Biogeosciences 2014, 11 (18), 5259-5267.

641

(71)

642

buffered system. Nature 2009, 461 (7264), 607-13.

643

(72)

644

formulation description and analysis of wet deposition results. Atmos. Environ. 2002, 36 (13),

645

2135-2146.

646

(73)

647

(6153), 1457-8.

Stevens, B.; Feingold, G., Untangling aerosol effects on clouds and precipitation in a

Jr, O. R. B.; Brehme, K. A., Atmospheric mercury simulation using the CMAQ model:

Krabbenhoft, D. P.; Sunderland, E. M., Global change and mercury. Science 2013, 341

648

ACS Paragon Plus Environment

32