Atmospheric Mercury Emissions from Residential Coal Combustion in

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Atmospheric Mercury Emissions from Residential Coal Combustion in Guizhou Province, Southwest China Zikang Cui, Zhonggen Li, Yanzhe Zhang, Xuefeng Wang, Qili Li, Leiming Zhang, Xinbin Feng, Xinyu Li, Lihai Shang, and Zuxiu Yao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03997 • Publication Date (Web): 12 Feb 2019 Downloaded from http://pubs.acs.org on February 14, 2019

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Atmospheric Mercury Emissions from Residential Coal Combustion in Guizhou Province, Southwest China Zikang Cui,†,‡ Zhonggen Li,*,† Yanzhe Zhang,§ Xuefeng Wang,§ Qili Li,§ Leiming Zhang,|| Xinbin Feng,*,† Xinyu Li,†,‡ Lihai Shang,† and Zuxiu Yao⊥ †State

Key Laboratory of Environmental Geochemistry, Institute of Geochemistry,

Chinese Academy of Sciences, Guiyang 550081, China ‡University

§School

||Air

of Chinese Academy of Sciences, Beijing 100049, China

of Earth Sciences, China University of Geosciences, Wuhan 430074, China

Quality Research Division, Science and Technology Branch, Environment and

Climate Change Canada, Toronto, Canada ⊥College

of Earth Sciences, Chengdu University of Technology, Chengdu, 610059,

China

Corresponding Author *Correspondence: [email protected] (Z. Li), [email protected] (X. Feng); Phone: +86-136-0851-7028; Fax: +86-851-8589-1334

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HIGHLIGHTS (1) On-site measurements of residential coal combustion (RCC) showed mercury emission ratios of 96.2-100.0% (2) Total mercury in flue gas was mainly affected by mercury in fueled coal (3) Speciation of emitted mercury (Hg0:Hg2+:Hg(p)) were in the ratio of 91%:8%:1% (4) RCC emitted more than twice of Hg than those from coal-fired power plants in Guizhou in recent years


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GRAPHIC ABSTRACT


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ABSTRACT Coal combustion represented a very important atmospheric mercury (Hg) source in the past five decades, especially in eastern Asia. Compared with coal-fired power plants (CFPPs) and industrial boilers, Hg emissions from the residential sector have not drawn much attention. In this study, two field campaigns were carried out to quantify Hg emission ratios and Hg speciation discharged into the ambient atmosphere from residential coal combustion (RCC) in Guizhou province, southwest China. The average Hg emission ratio, based on the mass balance calculation from coal samples collected in 27 families, was estimated to be 99.6%, higher than those found in the majority of the previous studies (52.0-99.8%). Total Hg in the exhausted flue gas from five families in different areas in Guizhou ranged from 5.4 to 18.5 µg/m3 and mainly affected by the Hg contents in the fuel (lump coal or briquette coal). Hg species in flue gas from RCC were measured on-site for the first time in the world, indicating Hg in the exhausted flue gas was all dominated by Hg0 (91.2±3.8%) rather than Hg2+ (7.6±3.5%) or Hg(p) (1.2±1.7%), despite different coal types with different associated Hg contents being used in different families. Such a finding is very different from a previous assumption with Hg(p) as the dominant emitted species. Total Hg emissions from RCC in Guizhou were estimated to be 48.9 Mg (106 grams) between 1990 and 2016, with annual emission amount of 1.2-2.3 Mg Hg/yr. Annual Hg emission amounts from RCC were likely more than double of those emitted from CFPPs in this province in the more recent years, indicating the necessity of better quantifying this source sector and setting stricter emission control measures. KEYWORDS: Atmospheric emission; Mercury speciation; Residential coal combustion 4 ACS Paragon Plus Environment

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1. INTRODUCTION Mercury (Hg) is a global pollutant that can transport long distance in the atmosphere.1,2 Since industrial revolution, 1.54 Tg (1012 grams) of Hg in total has been released into various environmental compartments from anthropogenic activities,3 resulting in higher Hg levels and negative impacts on ecosystem health.4-6 Emissions of Hg from coal combustion into the atmosphere were estimated to be 26.4 Gg (109 grams) in total from 1850 to 2010,3 making coal combustion as the most important global atmosphere Hg source since 1950s.7 Among these, China is the largest emitter contributing about 530-696 Mg Hg/yr.8-11 Since 1989, coal production and consumption in China have been ranked the first in the world,12 and coal consumption continued increasing from 2000 to 2013.13 As a result, coal combustion contributed about 38-50% of total Hg emissions in China in recent years.8,10,11,14 For example, the total anthropogenic Hg emissions in China increased from 356 Mg/yr to 538 Mg/yr from 2000 to 2010 with an annual increase rate of 4.2%, in which 175-254 Mg Hg was emitted from coal combustion every year.11 It is, however, noted that Hg emissions from coal-fired power plants (CFPPs) started declining in more recent years due to strict emission control measures.9 On the other hand, the importance of residential coal combustion seemed to be increasing.9 While pollution control devices have been installed in industrial boilers and CFPPs, no such practices have been enforced in residential coal combustion (RCC), resulting in flue gas discharged near the surface and causing direct impact on ambient environment 5 ACS Paragon Plus Environment

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and human health. Several studies have investigated Hg emissions from this source. For example, Streets et al. provided a Hg emission ratio of 83% from RCC in China,8 and showed the emission speciation profile of 88%:9%:3% for particulate mercury (Hg(p)), gaseous elemental mercury (Hg0) and oxidized gaseous mercury (Hg2+), but it is not clear how their data were obtained. Their estimates of 19.7 Mg Hg emission from RCC in 1999 accounted for 3.68% of the total national Hg emission in China. Other studies in China focused on individual provinces.12,15,16 To date, no direct measurements have been made on Hg total concentration and speciation in the flue gas and associated influencing factors in residential coal-burning sector. Guizhou province of south China has large reserves of coal.17 Due to the unique climate of karst mountain areas and the location on Yunnan-Guizhou plateau, coal is a crucial energy source for heating and livelihood in rural Guizhou (Figure 1).18 57.4% of rural residents relied on this kind of energy, more than twice of the national average.19 In some coal producing areas in western Guizhou, such as Bijie city, this proportion goes up to 90%. Annual amount of coal consumption for residential use in Guizhou province from 1990 to 2016 reached to 9.05 Tg on average (Figure S1 of Supporting Information). Over the past two decades, emissions of acid gas and other pollutants (such as particulate matter and Hg) from CFPPs have been gradually reduced benefiting from the installation of air pollution control devices, such as electrostatic precipitators, flue gas desulfurization and selective catalytic reduction.20,21 However, the consumption of domestic coal remains stable in rural areas and with no pollution control equipments.22 6 ACS Paragon Plus Environment

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Hg emissions from this source sector have not been properly included in the national emission database. In the present study, Hg emissions from RCC in Guizhou of southwest China were measured on site with the aim to (1) determine the Hg emission ratios and estimate the total amount of Hg emissions from this source, and (2) identify Hg speciation profile from the discharged flue gas, a knowledge that is needed to understand the potential environment and human health impacts caused by Hg.

2. MATERIALS AND METHODS 2.1. Sampling Sites and Sample Collections Residential coal combustion is very popular in Guizhou, not only in rural areas but also in urban areas, due to the coal resource in this province is relative rich, especially in the central to western province.18 In the present study, two research campaigns were conducted for quantifying Hg emissions from RCC. During the first campaign in winter 2011, paired feed coal and slag were collected from 27 families in Yunyan district and Nanming district of core Guiyang city area to evaluate the Hg emission ratio from RCC (Figure 2b). In each family, 0.5-1 kg feed coal and similar amount of its corresponding slag were collected. At the same time, a survey was conducted to identify the coal type and usage information (lump coal vs honeycomb briquette, bituminous vs anthracite, place of coal production, installation of the chimneys). During the second campaign in winter 2012, additional flue gas, along with the feed coal and slag, were gathered in 5 families in different areas, namely Shuicheng county in Liupanshui city (family A), 7 ACS Paragon Plus Environment

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Jinsha county in Bijie city (family B), Xingren county in Qianxi’nan autonomous prefecture (family C), suburb of Guiyang city (family D), and Dejiang county in Tongren city (family E) in Guizhou province as indicated in Figure 2a. The flue gas sampling was started immediately after ca. 2 kg of lump coal or a piece of honeycomb briquette was added into the stove, and lasted until the feed coal was almost burned out, for a period of about 2.5-3 h. Hg concentration obtained in the flue gas represents the mean value of the flue gas from this batch of coal, then a new batch of feed coal was added for another round of sampling. A portion of the feed coal and slag was collected from each sampling run before and after the sampling, respectively. At least three samplings were collected in each family. Field flue gas measurement and the household stove are displayed in Figure 3a-c. All the investigated stoves were similar to each other as shown in Figure 3b. During the flue gas sampling, the lids of the stoves were closed to make sure all the flue gas was vented through the chimney. Flue gas was sampled at the chimney outlet using the Ontario Hydro Method to separate three Hg species (Figure S2),23 Hg0, Hg2+ and Hg(p). Hg(p) is first captured on the glass fiber filter with pore size of 0.45 μm (WatermanTM) and then Hg2+ is absorbed by three impingers of KCl solution (1 mol/dm3). Hg0 is collected by one impinger with H2O2 + HNO3 (10% v/v +5% v/v) and three impingers of H2SO4 + KMnO4 solution (10% v/v +4% m/v). In the end, an impinger with silica gel is used to remove moisture. The teflon sampling line, with a PTFE funnel in 3 cm in diameter mounted in the front side, was inserted 50 cm inside the outlet of chimney pipe to ensure the sampling accuracy and 8 ACS Paragon Plus Environment

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representative. Both the probe and the filters were heated to above 120°C to avoid water condensation and Hg adsorption on the tubing walls.

2.2. Analysis and Quality Control The absorption solutions for gaseous Hg was prepared, recovered and analyzed on site. The pretreatment of different solutions was as follows. 5% w/v KMnO4 was added into the KCl and H2O2 + HNO3 impingers until an enduring purple color was appeared, while 10% w/v NH2OH·HCl solution was added into the H2SO4 + KMnO4 impingers until a pink or slight purple color was obtained. Hg2+ in each impinger was reduced to Hg0 by SnCl2 and measured by Cold Vapor Atomic Absorption Spectrophotometry (CVAAS, F732S, Shanghai Huaguang Instrument Corp.) at least twice. Solid materials, such as lump coal, honeycomb briquette and slag, were collected in zip-zag bags and brought back to laboratory, where they were air-dried, homogenized and grounded to less than 150 μm. The US EPA Method 7473 was adopted to determine Hg concentrations in different solid sample including the flue gas filter samples, which heats solid samples at 800ºC and measures the released Hg0 by CVAAS (Lumex RA915+, Russia) with a detection limit of 0.1 μg/kg. Proximate analysis for each solid sample was conducted with the Chinese national standard method GB/T 212-2008.24 The temperature for ash yield measurement was 815±10ºC, which was similar to coal burning temperature of domestic stoves with ca. 800ºC and maximum temperature up to 1000ºC.25 Total sulfur in coal was detected by the Eschka method according to GB/T 214-2007.26 9 ACS Paragon Plus Environment

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Before the flue gas sampling, all the sampling lines (quartz glass and teflon tubings), impingers and bottles were soaked in 20% HNO3 overnight and washed with deionized water in the laboratory. Hg concentrations of reagents used in the experiments were below the detection limit, except H2SO4 (ca. 1.2 ng Hg/cm3 concentrated), which compromised about 80% of the systematic blank. Certified reference materials stand for coal (NIST SRM 1632d), fly ash (NIST SRM1633c and GBW 08401) and soil (GBW 07405) were used to guarantee the analytical quality, and the recovery of Hg was found to be in the range of 98-105%. For proximate and ultimate analysis, certified reference materials (GSB06-2105-2007 for anthracite and GSB06-2113-2007 for bituminous coal) were detected along with coal samples at the same time, and the measured mean values were close to the certified contents and variation coefficients were lower than 5%.

2.3. Calculation and Statistical Methods The mercury emission ratio (MER) represents the ratio of mercury emitted into the atmosphere to the total mercury in feed coal. MER was calculated based on the difference in Hg quantities between the feed coal and the resulting slag, as shown in eq 1. Fly ash generated from lump coal and honeycomb briquette was very little and thus not taken into consideration.

(1) Where QMcoal and QMslag are the quantities of mercury in feed coal and slag (μg), 10 ACS Paragon Plus Environment

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respectively; MCcoal and MCslag are mercury concentrations in feed coal and slag (μg/kg), respectively; Qcoal is the quantity of the coal burnt (kg); and Aad is the ash yield of feed coal based on air-dried basis (%). The estimated quantity of mercury emissions (QME) from RCC in Guizhou province was calculated with the following eq 2. (2) Where MCave is the average Hg concentration in Guizhou coal (μg/kg), Qcoal is the quantity of the coal burnt in Guizhou (kg), and MERave is the average mercury emission ratio (%) of RCC. A Pearson correlation analysis was performed with Hg concentrations to establish the relationship between feed coal and flue gas. P < 0.05 was considered statistically significant. Linear regression analysis was applied to examine the predictive ability of QME in terms of MER.

3. RESULTS AND DISCUSSION 3.1. Mercury Emission Ratio (MER) in Guiyang Out of the 27 families investigated in Guiyang, coal used in 19 families was produced in Bijie and in the other 8 families produced in Guiyang. Small chimneys were installed in all but four families. One lump coal was determined to be anthracite and all the others were subbituminous coal based on their volatile matter. Some of the slags were agglomerated while others were burnt into fine ash, indicating their different coal quality, 11 ACS Paragon Plus Environment

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such as the content of main minerals and tar, as well as the ash fusion point,27 since all the investigated stoves were similar to each other as shown in Figure 3b. Hg concentrations in lump coal ranged from 14 to 1050 μg/kg (N = 26) with an average of 378±300 μg/kg, and those in slag ranged from 0.0 to 18.0 μg/kg with an average of 3.9±4.8 μg/kg (Table 1). Hg concentration in honeycomb briquette was 172 μg/kg (N = 1), and in the corresponding slag, 0.7 μg/kg. The MERs of domestic lump coal in Guiyang ranged from 96.2 to 100.0% with a mean value of 99.6±0.8%. The MER of the domestic honeycomb briquette was determined to be 99.8%, close to that of lump coal. Collectively, the average MER of RCC in Guiyang is 99.6%, similar to the value of 99.8% reported by Li et al. in suburb Beijing,16 but much higher than those reported in the other studies (54-84%, Table 2). Thus, Hg emissions from RCC were likely underestimated in the majority of the previous studies.

3.2. Mercury Speciation in Exhausted Flue Gas Results of proximate and ultimate analysis of coal samples collected from Guizhou province are presented in the Table S1 of Supporting Information. The ash yield of honeycomb briquette in Shuicheng is 56.8%, while those in the other four lump coal are in a much lower range of 9.89-23.72%. The net calorific value is 11.2 MJ/kg for honeycomb briquette and range from 25.1 to 30.3 MJ/kg, or 2-3 times higher, for the lump coal. Carbon content in honeycomb briquette is 28.8%, significantly lower than those in lump coal (63.6-79.9%). The sulfur content ranges from 0.47-4.04%, with higher 12 ACS Paragon Plus Environment

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values for lump coal than honeycomb briquette, and coal in east Guizhou (Dejiang county, Tongren city) has more sulfur than that in central (Guiyang) and west Guizhou (Bijie, Liupanshui and Xingren). Chlorine content in Guizhou coal is 274 μg/g,28 similar to the mean value of that in Chinese coal (255 μg/g),29 but greatly lower than that in USA coal (614 μg/g).30 Chlorine has an essential effect on the oxidation of Hg in flue gas, therefore, the low concentration of chlorine may contribute to a higher proportion of Hg0 in flue gas. Also, Hg content in lump coal from Dejiang (east Guizhou) presents a remarkable higher level (230 μg/kg) compared to the range of 84-103 μg/kg in the other areas. The average Hg content in flue gas is 9.4±3.5 μg/m3, ranging from 5.4 to 18.5 μg/m3. The average proportions of Hg0, Hg2+ and Hg(p) are 91.2%:7.6%:1.2%, and with the range of 83.0-96.1%, 3.2-15.9%, and 0.1-6.8%, respectively (Table 3). As shown in Figure 4, the main species of Hg is uniformly in Hg0 for all five families. In contrast, a previous report showed particulate mercury (Hg(p)) as the dominant species, in which the proportions of Hg0, Hg2+ and Hg(p) were 9%:3%:88%.8 The high proportion of Hg0 in our on-site study was likely explained by the low Cl content in feed coal and the extremely short time which was insufficient for Hg0 oxidation and adsorption on particles in flue gas to form Hg2+ and Hg(p) before being exhausted into ambient environment. Therefore, we believe Hg emitted into the atmosphere from RCC is mainly in the form of Hg0. The MERs of RCC in these five families in Guizhou were also determined. Hg concentrations in fueled coal ranged from 60-240 μg/kg with an average of 113±49 μg/kg, 13 ACS Paragon Plus Environment

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and Hg in slag ranged from 1-8 μg/kg with an average of 2±2 μg/kg (Table S1 of Supporting Information). Accordingly, the MERs of these five families ranged from 97.799.9% with a mean value of 99.4%, consistent with what was obtained in Guiyang city in this study (99.6%). Although Hg concentrations in feed coal, which were randomly sampled and originally produced in different regions, differed significantly between the two campaigns, the MERs observed were almost the same (> 99%).

3.3. Estimated Quantity of Mercury Emissions (QME) from Residential Coal Combustion (RCC) in Guizhou The correlation analysis and linear regression using SPSS come to a conclusion that the total mercury emission has a highly positive relationship (p < 0.01) with the total Hg content in domestic coal (Figure 5), confirming that nearly all of the mercury in coal was emitted into the atmosphere. This positive correlation was also reported in biomass fuel combustion process, during which Hg was essentially completely emitted.33 The average Hg concentration of coal in Guizhou is considered to be 201 μg/kg based on about over 150 coal mines.34-36 The annual coal consumed by residential use ranged from 6.15-11.50 Tg with an average of 9.05 Tg during 1990 to 2016, according to the Guizhou Province Statistical Yearbook.37 Using eq 2 mentioned above, annual Hg emissions from RCC in Guizhou were estimated to be 1.2-2.3 Mg/yr from 1990 to 2016 (Figure 6), with the accumulated emissions totaling 48.9 Mg Hg during this period. More than 90% of these emissions were in the form of Hg0, which can be transported to places 14 ACS Paragon Plus Environment

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far away from the sources and thus have long-lasting negative effects on various ecosystems in large spatial scales. Atmospheric Hg emissions from CFPPs in Guizhou have been remarkably reduced in the recent several years,38 e.g., to a level lower than 0.5 Mg/yr (our unpublished data). As a result, emissions from RCC surpassed those from the coal-fired power plants by 2-4 times in Guizhou. Similar situation could have also occurred in other provinces that heavily rely on coal as residential energies, such as Hebei and Shanxi. Furthermore, the actual amount of coal consumption in the residential sector might be more than twice of that reported by the Statistical Yearbook according to a multitude field investigations.39,40 Therefore, Hg emissions from RCC might be even higher than the estimates provided above. More detailed surveys on RCC and accurate estimation of associated Hg emissions are needed on the national scale. It should also be noted that much more Hg was emitted from RCC than residential biomass fuel combustion in Guizhou in 2007 (0.3 Mg/yr).41

4. CONCLUSIONS Mercury emission ratios from residential coal combustion in Guizhou were observed to be 96.2-100.0%, and mostly in the form of Hg0 (91%). The total atmospheric Hg emitted from residential coal combustion in Guizhou province was estimated to be 1.2 to 2.3 Mg/yr in the past three decades. The city government of Guiyang has released policies forbidding RCC in some urban areas since 2017, but no action has been taken for 15 ACS Paragon Plus Environment

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rural areas at provincial level. RCC has caused seriously endemic arsenosis and fluorosis in western and central Guizhou where coal and coal biding clay are enriched with As and F, respectively.42 Hg emissions from this source should be paid more attention in this sector. It is recommended to provide clean energy sources to rural areas with high population density, noting this will require substantial support from government policies and economic incentive. It is also recommended to quantify Hg emissions from this much neglected source sector across China (particularly Hebei and Shanxi) so the Hg emission database can be improved, which are urgently needed for meeting the goals set in the Minamata Convention on Mercury.

ACKNOWLEDGMENT The authors greatly appreciate the three anonymous reviewers for their constructive suggestions. This work is financially supported by K.C.Wong Education Foundation, the Natural Science Foundation of China (No. U1612442, 41373056) and the Guizhou Science and Technology Foundation (No. Qian-Ke-He J Zi [2008]2246).

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Energy & Fuels

LIST OF FIGURES Figure 1. Proportions of families using different energy in rural China (left) and Guizhou province (right), based on data compiled from Guizhou Bureau of Statistics.18 Figure 2. Sampling sites in this study: (a) 5 families (A-E) in different areas in Guizhou province sampled with the exhausted flue gas and the corresponding feed coal and slag in 2012, and (b) 27 families with paired feed coal and slag in Guiyang City in 2011. Figure 3. On site sampling photos in winter 2012: (a) coal combustion in the stove, (b) household stove and chimney in the common rural families, and (c) flue gas sampling using the Ontario Hydro Method Figure 4. Hg concentration (a) and percentage of different Hg species (b) in the exhausted flue gas from five families in Guizhou (A-E indicates different families) Figure 5. Linear regression of Hg concentrations between exhausted flue gas and feed coal Figure 6. Estimation of atmospheric Hg emissions from residential coal combustion in Guizhou province from 1990 to 2016


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

Figure 1. Proportions of families using different energy in rural China (left) and Guizhou province (right), based on data compiled from Guizhou Bureau of Statistics.18 The percentage of biogas, electricity and others in rural China are 0.7%, 0.8% and 0.3%, respectively, and the percentage of gas/natural gas, biogas, electricity and others in Guizhou are 0.58%, 0.83%, 1.47% and 0.02%, respectively.


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Energy & Fuels

Figure 2. Sampling sites in this study: (a) 5 families (A-E) in different areas in Guizhou province sampled with the exhausted flue gas and the corresponding feed coal and slag in 2012, and (b) 27 families with paired feed coal and slag in Guiyang City in 2011.


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

Figure 3. On site sampling photos in winter 2012: (a) coal combustion in the stove, (b) household stove and chimney in the common rural families, and (c) flue gas sampling using the Ontario Hydro Method


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Energy & Fuels

Figure 4. Hg concentration (a) and percentage of different Hg species (b) in the exhausted flue gas from five families in Guizhou (A-E indicates different families)


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

Figure 5. Linear regression of Hg concentrations between exhausted flue gas and feed coal


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Energy & Fuels

Figure 6. Estimation of atmospheric Hg emissions from residential coal combustion in Guizhou province from 1990 to 2016


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

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TABLES Table 1. MERs from 27 families in Guiyang city Family No.

Coal type

Aad (%)*

Vdaf (%)*

Hg in coal Hg in slag MER (%) (μg/kg) (μg/kg)

1

Lump

8.58

12.6

122

8.6

99.40

2

Lump

10.81

13.8

454

4.8

99.89

3

Lump

12.79

12.1

243

0.5

99.97

4

Lump

26.52

20.0

637

2.1

99.91

5

Lump

34.41

26.7

748

1.2

99.95

6

Lump

21.98

20.9

689

1.2

99.96

7

Lump

11.06

10.5

22

0.0

100.00

8

Lump

16.88

14.9

380

1.5

99.93

9

Lump

10.13

12.6

14

0.0

100.00

10

Lump

12.64

12.3

332

0.8

99.97

11

Lump

18.87

17.5

666

9.0

99.75

12

Lump

14.11

9.0

175

0.8

99.94

13

Lump

16.65

13.1

882

10.0

99.81

14

Lump

23.76

19.8

1050

0.5

99.99

15

Lump

16.74

13.9

439

3.7

99.86

16

Lump

25.63

18.5

142

0.3

99.95

17

Lump

29.98

16.4

337

2.5

99.78

18

Lump

19.57

19.2

104

0.0

100.00

19

Lump

18.10

17.2

124

4.0

99.42

20

Lump

29.49

18.7

139

7.0

98.53

21

Lump

16.26

15.1

439

3.8

99.86

22

Lump

30.44

26.2

143

18.0

96.17


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Energy & Fuels

23

Lump

32.70

26.1

345

15.5

98.53

24

Lump

20.95

19.2

947

0.5

99.99

25

Lump

12.65

11.0

153

3.6

99.70

26

Lump

10.58

14.5

103

1.5

99.85

27

Honeycom b Briquette

47.89

15.6

172

0.7

99.81

Minimum

8.58

9.0

14

0.0

96.17

Maximum

47.89

26.7

1050

18.0

100.00

Mean

20.38

16.6

370

3.9

99.63

SD

9.15

4.7

291

4.8

0.79

Note: * Aad and Vdaf are ash yield and volatile matter based on air-dried and dry ash-free basis, respectively.


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Table 2. Comparison of MERs between this and earlier studies on household coal combustion worldwide Study area

Type of coal

MER (%)

Reference

Poland

Hard coal

52

Pyka et al.31

Guiyang, Guizhou

n.d.

61.7

Qu15

Zhaotong, Yunnan

Briquette

83.61

Wang and Luo12

Daxing, Beijing

Lump coal

83.7

Hong et al.32

Honeycomb briquette

83.7

Lump coal

83

Briquette

98

Suburb Beijing

Honeycomb briquet

99.76

Li et al.16

Guiyang, Guizhou

Lump coal

99.62

This study

Honeycomb briquette

99.81

Chinaa

Streets et al.8

Notes: n.d.- no data; a: included 30 provinces, autonomous regions, and municipalities in China. Tibet, Hong Kong, Macao, Taiwan are excluded.


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Energy & Fuels

Table 3. Hg concentrations in feed coal and slag, ash yield in coal, MERs and Hg speciation in exhausted flue gas in Guizhou

Family ID.

Sample No.

Hg in Hg in Aad coal slag (%) (μg/kg) (μg/kg)

#1

105

4.4

56.63

#2

101

2.9

#3

89

#4

MER (%)

Hg in Hg species (%) in flue gas discharged flue gas (μg/m3)

Hg2+

Hg0

Hg(p)

97.65

9.53

9.9

89.6

0.5

57.41

98.35

8.10

7.8

91.2

1.0

1.7

56.38

98.95

8.12

6.3

92.8

1.0

81

1.6

n.d.

n.d.

10.29

15.8

83.5

0.6

#5

84

1.4

19.07

99.69

5.43

8.5

91.1

0.4

#6

107

1.0

15.56

99.86

7.48

6.0

93.3

0.8

#7

60

n.d.

17.82

n.d.

7.83

4.3

95.6

0.1

#8

127

2.0

10.54

99.83

8.77

4.6

93.4

2.0

#9

64

2.1

10.57

99.65

5.45

13.9

83.0

3.2

#10

111

n.d.

9.32

n.d.

10.73

5.3

93.9

0.8

#11

108

2.2

10.47

99.79

8.18

4.5

95.3

0.2

#12

99

8.4

10.08

99.15

7.61

9.2

90.6

0.2

#13

101

1.2

10.76

99.88

8.27

9.7

89.8

0.5

#14

220

1.4

25.03

99.84

18.49

4.6

88.6

6.8

#15

240

1.4

22.81

99.87

16.90

3.2

96.1

0.7

Minimum

60

1.0

9.32

97.65

5.43

3.2

83.0

0.1

Maximum

240

8.4

57.41

99.88

18.49

15.9

96.1

6.8

Mean

113

2.4

23.75

99.38

9.41

7.6

91.2

1.2

SD

49

2.0

18.59

0.72

3.55

3.5

3.8

1.7

A

B

C

D

E

Notes: n.d.- no data. 31 ACS Paragon Plus Environment

Atmospheric Mercury Emissions from Residential Coal Combustion in

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