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Atmospheric Emission Inventory of Hazardous Trace Elements from China’s Coal-Fired Power PlantsTemporal Trends and Spatial Variation Characteristics Hezhong Tian,*,†,§ Kaiyun Liu,† Junrui Zhou,† Long Lu,† Jiming Hao,‡,§ Peipei Qiu,† Jiajia Gao,† Chuanyong Zhu,† Kun Wang,† and Shenbing Hua† †

State Key Joint Laboratory of Environmental Simulation & Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China ‡ Institute of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China § State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China S Supporting Information *

ABSTRACT: Coal-fired power plants are the important sources of anthropogenic atmospheric releases of various hazardous trace elements (HTE) because a large quantity of emissions can cause wide dispersion and possible long-distance transportation. To obtain the temporal trends and spatial variation characteristics of various HTE discharged from coalfired power plants of China, a multiple-year comprehensive emission inventory of HTE including Hg, As, Se, Pb, Cd, Cr, Ni, and Sb has been established for the period 2000−2010. Thanks to the cobenefit removal effects of conventional particulate matter/sulfur dioxide/nitrogen oxides (PM/SO2/NOx) control devices, emissions of these 8 toxic elements have shown a gradual decline since the peak in 2006. The total emissions of Hg, As, Se, Pb, Cd, Cr, Ni, and Sb are substantial and are estimated at about 118.54, 335.45, 459.4, 705.45, 13.34, 505.03, 446.42, and 82.33 tons (t), respectively, in 2010. Shandong, Jiangsu, Shanxi, and Hebei always rank among the top ten provinces with the highest emissions. Further, future emissions for 2015 and 2020 are projected with scenario analysis. Advanced technologies and integrated management strategies to control HTE are in great need.

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INTRODUCTION Anthropogenic atmospheric emissions of hazardous trace elements have been associated with a serious threat to human health and ecosystems.1,2 In the 1990 U.S. Clean Air Act Amendments, Sb, As, Cr, Pb, Cd, Hg, Ni, Se, Be, Mn, and Co (11 HTE) are listed as key toxic air pollutants because of their adverse effects on public health and the environment.3 The European Union has also listed As, Pb, Cd, Hg, and Ni as toxic air pollutants of prime environmental concern.4 Various HTE are normally released from anthropogenic sources both as suspended particulate matter and in a gaseous form at high temperature. They can attach themselves to fine particles, remain in the atmosphere for 5−8 days and even for 30 days when associated with very small particles.5,6 In China, with the extensive growth of industry and the economy, poisoning accidents associated with various HTE have increased, such as arsenic poisoning in Guizhou and children with excessive blood Pb levels in Qingyuan City of Guangdong province.7,8 Soil contaminated with heavy metals is eroding the foundation of China’s food safety and becoming a looming public health hazard. Information released at a news conference for the second National Soil Survey on Dec. 30, 2013 by Wang © 2014 American Chemical Society

Shiyuan, a deputy minister of the Ministry of Land and Resources of China (MLR) noted that more than about 2% of China’s total 1.2 million km2 (135.4 million hectares or 337 million acres) of arable land is too polluted with heavy metals and other chemicals to use for growing food.9−11 As the largest coal consumer in China, the coal-fired power plant sector is regarded as one of the most important contributors to anthropogenic HTE pollution due to large amounts of emissions passing through the elevated stacks at high velocity, which causes wide dispersion of fine particulates.12,13 By the end of 2010, coal use for electric generation amounted to 1591 Mt, accounting for about 50% of the national total coal consumption and resulting in a large amount of various HTE emissions.14 Some studies of anthropogenic emissions of various HTE have been conducted due to their significant impacts on human health and the ecosystems, especially Hg.15−22 For example, Received: Revised: Accepted: Published: 3575

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by the power plants in these provinces has to be generally transported long-distances from the several domestic coalproducing provinces or even imported from coal-exporting countries. In order to meet the individual boiler’s combustion performance needs, most coal-fired boilers throughout the country use a blend of coals, which are prepared by mixing several types of coals from different coal mines located in one or several provinces. Moreover, China has become a net coalimporting country with the rapid economic growth and huge fossil-fuel demand. In 2010, China imported 130 Mt coal from Indonesia, Australia, Vietnam, Mongolia, and Russia, where the concentration of various HTE in coals is remarkably varied from that in Chinese coals due to different coal-forming environments (see Supporting Information (SI) Table S1 and Figure S1).24 The concentration of HTE in coal mined from different regions of the Chinese mainland varies substantially owing to the significant distinction of coal-forming plants or coal-forming geological environments.25,26 As a result, there is a remarkable variation between the concentration of HTE in coal produced and consumed in a single province, which must be taken into consideration when developing a reliable HTE emission inventory for Chinese coal-fired power plants. To obtain reliable estimates of various HTE emissions from coal-fired power plants scattered throughout the Chinese mainland, it is essential to know the HTE concentration of coal as burned. The averaged concentration of Hg, As, Se, Pb, Cd, Cr, Ni, and Sb in raw coals as produced from 30 provinces (autonomous regions and municipalities) on the Chinese mainland has been elaborately reviewed and assessed with multiple statistical mean calculation methods in Tian’s previous research (2013).25 Table S2 in the SI illustrates the average concentrations of various HTE by each province. Based on the official statistical data obtained from China Energy Statistical Yearbook (2011) and China Coal Industry Yearbook (2011), a coal flow matrix is established among 30 provinces and other coal-exporting countries (see SI Table S3 and Figure S2).27,28 Then, combined with the provincial and international average content of HTE in raw coal as produced, the provincial weighted-average concentrations of various HTE in consumed coal are determined, as illustrated in SI Table S4. 2.2. Coal Consumption. The installed capacity, electricity generation and coal consumption data for Chinese coal-fired power plants from 2000 to 2010 is compiled from China Energy Statistical Yearbooks, China Power Statistical Yearbook and Edition Commission of Chinese Power Statistical Yearbook (see SI Table S5 and Figure S3).14,23,27,28 In this study, a new refined activity database is established that contains ∼1800 coal-fired power plants with detailed information about geographical location, installed capacity, annual electricity generation, annual coal consumption, and the installed flue gas pollution control devices. 2.3. Emission Factors (EFs) of Various HTE. In this study, coal combustion devices are divided into three types: pulverized-coal (PC) boiler, stoker fired boiler and circulating fluidized bed (CFB) boiler. Owing to the higher furnace temperature, the release ratios of HTE from PC boilers are higher than those from CFB boilers and stoker fired boilers. Presently, the major coal combustion facilities in coal-fired plants are pulverized-coal boilers in most of the provinces in China, taking a share of over 85%; stoker fired boilers are a relatively small proportion and the proportion declines annually due to energy-saving and pollution reduction policies.28 The CFB boiler has being rapidly developed since 1980s in China

Nansai et al. developed a high-resolution inventory of Japanese anthropogenic mercury emissions,22 and Tian et al. estimated the emissions of Hg, As, and Se from the coal-fired power plants of China for the year 2007.13 However, the status of coalfired power plants, such as the mix of coal-fired boilers with different burner patterns and the installation of conventional air pollution control devices (APCDs), has changed substantially during the past decade, especially the wide application of flue gas desulfurization (FGD) and the increasing installation of selective catalytic reduction (SCR). For Chinese coal-fired power plants, a detailed and integrated emission inventory that simultaneously addresses the up-to-date emission status of 8 hazardous trace elements (Hg, As, Se, Pb, Cd, Cr, Ni, and Sb) is still limited. Little is known about the annual temporal variation and the geo-spatial distribution characteristics of various HTE emissions from power plants. In this article, a multiple-year comprehensive emission inventory of Hg, As, Se, Pb, Cd, Cr, Ni, and Sb from coalfired power plants for the period 2000−2010 in China is presented. Spatial distribution characteristics and emission trends in the near future are analyzed.

2. METHODOLOGIES AND KEY PARAMETERS In this study, atmospheric emissions of 8 toxic elements, including Hg, As, Se, Pb, Cd, Cr, Ni, and Sb, were calculated by applying a new unit-based bottom-up methodology with a refined activity database and an upgraded specific emission factors database. All of the plants were subgrouped into 17 categories by taking into account the different patterns of boiler facilities and APCDs. The basic calculation equation of a bottom-up emission inventory could be expressed as follows: E Total =

∑ Ei i

=

∑ ∑ ∑ ∑ Ci × Mi ,k × R m × (1 − ηPM ) i

k

m

n

× (1 − ηSO ) × (1 − ηNOx ) × (1 − ηHg ) 2

n

(1)

where E is the annual atmospheric emissions of Hg, As, Se, Pb, Cd, Cr, Ni, or Sb (tons/year) in China; C is the provincial average concentration of one hazardous trace element in feed coal (μg/g); M is the amount of coal burned (tons/year); R is the average release ratio of one hazardous trace element in flue gas compared with the element concentration in feed coal from different types of coal-fired boilers (%); ηPM, ηSO2 and ηNOx represent the averaged fraction of one hazardous trace element cobenefit removed from flue gas by the conventional PM/SO2/ NO x emission control devices, respectively, while η Hg represents the added Hg removal efficiency by the specialized Hg control technologies such as activated carbon injection (ACI) (%) if any; i, k, m, and n stand for province (municipality, autonomous region), power plant, boiler type, and PM emission control technology type. 2.1. Averaged Concentration of Various HTE in Feed Coals by Province. Coal reserves in the Chinese mainland are very unevenly distributed; coal is predominantly deposited in western and northern China. In 2010, about 65% of coal output was mined from Inner Mongolia, Shanxi, Shaanxi, Guizhou, Hebei, Xinjiang, and Yunnan province.23 However, huge coal consumers are always the coastal provinces with large numbers of coal-fired power plants, such as Shandong, Jiangsu, Guangdong, Zhejiang, Fujian, and Shanghai. Coal consumed 3576

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Table 1. Average Release Ratio and Cobenefit Removal Efficiency of 8 HTE from Coal-Fired Power Plants release ratio, R (%)a,b

coremoval efficiency, η (%)b

category

Hg

As

Se

Pb

Cd

Cr

Ni

Sb

pulverized-coal boiler fluidized-bed furnace stoker fired boiler ESP FFs cyclone WFGD SCR ACI

99.42 98.92 83.15 33.17 67.92 6.00 57.22 11.92 90.00

98.46 75.60 77.18 86.20 99.00 43.00 80.38

96.22 98.05 80.95 73.78 65.00 40.00 74.87

96.25 77.33 40.10 97.17 99.00 12.10 78.40

94.94 91.50 42.53 96.47 97.63 22.90 80.50

84.50 81.33 26.74 98.54 95.13 30.05 86.00

56.53 68.36 10.46 92.92 94.83 39.93 80.00

89.40 74.38 53.52 83.46 94.25 40.00 82.10

a

Release ratio is comparing with the total amount of the corresponding hazardous trace element in feed coal. bDifferences of release ratio and cobenefit removal among provinces are neglected since they are mainly technology related.

the speciation of Hg and promote the oxidation of some of elemental Hg to Hg2+, especially for those boilers firing coals with high Cl content.34 Table 1 summarized the averaged release ratios of various HTE from different types of utilities and the cobenefit removal efficiencies from different types of flue gas control devices. Details for release ratios and removal efficiencies of various HTE from coal-fired boilers can be seen in SI Table S6−S7. There are rarely control devices that are dedicated to remove HTE from flue gas in power plants of China, although Hg discharged from coal-fired power plants has gained worldwide concern owing to the possible long-distance transportation through elevated stacks. Normally, mercury (Hg) emitted from coal-fired power plants exists in three primary forms, namely, elemental mercury (Hg0), gaseous oxidized mercury (Hg2+), and particle-bound mercury (HgP). Hg2+ and HgP remain in the atmosphere for only a few days, whereas Hg0 could stay in the atmosphere for more than 1 year and thus can be transported long-distances before settling out by dry and wet deposition processes. As a specialized Hg control technology, activated carbon injection (ACI) can greatly reduce mercury emissions; ACI systems are now considered to be the most robust technology for Hg control in coal-fired power plants and can achieve about 90% mercury reduction.35,36 In addition to ACI, the injection of bromine into the flue gas has been demonstrated to further improve Hg removal efficiency.37,38 There is still no commercial ACI system in operation in China’s coal-fired power plants. Instead, part of Hg in flue gas is removed by the additional cobenefit reduction effects of conventional APCDs (ESP/FFs, WFGD and SCR). However, several industrial-scale pilot experiments are in progress, and it is anticipated that future power plants will install ACI to further abate Hg in the next 10 years, especially for those boilers burning coal with high Hg and low Cl content.34,39 To identify the current status of Hg emissions and to estimate the fate and behavior of Hg from coal burned by power plants, an estimation of Hg speciation is of great significance. In this article, we adopted the average proportion of Hg0, Hg2+ and HgP in total Hg emissions for the boilers installed with ESP, FFs, ESP+WFGD, and SCR+ESP +WFGD on the basis of field tests conducted inside and outside China (Table 2).35,40−47 2.4. Scenario Projections on HTE Emissions for 2015 and 2020. Based on projections of installed capacity and electricity generation from thermal power plants for 2015 and 2020, which were released in the Report on “12th Five-YearPlan” of the Electric Power Industry, we assumed three different scenarios for the target years 2015 and 2020 to analyze

and has become a key clean coal technology used in power generation, especially for SO2 and NOx emission reduction. By the end of 2010, the total capacity of CFB boilers grew to 80 GWe.23,28 With rising furnace temperature during the combustion processes, various HTE bound with coal will be released and redistributed along with the flue gas, and then react with surrounding gases. The release ratios of HTE varied with different boiler types, which are mainly associated with coal combustion technologies.29 Field tests have demonstrated that the application of conventional air pollution control devices has significant impacts on the removal of not only PM/SO2/NOx but also the final HTE emissions from the exhaust.30−32 Different types of PM/SO2/NOx control devices will behave varied performance of this add-on synergic removal (we call it as a “co-benefit” in this article) for various elements owing to the varied physical and chemical properties under the flue gas conditions. Currently, all coal-fired boilers in China have adopted particulate control devices, and electrostatic precipitators (ESP) are now the most widely applied PM abatement devices in power plants throughout China. By the end of 2010, about 95% of the total installed capacity coal-fired units have been equipped with ESP, while the remaining 5% employ fabric filters (FFs) or combined ESP-FFs. FFs and ESP+FFs are more effective for fine particle capture and accordingly result in greater HTE emissions reduction.33 Consequently, in response to the more stringent PM emission standard, more and more FFs or combined ESP-FFs are installed on newly built or retrofitted coal-fired boilers, especially for those boilers burning lignite (in this case, the performance of traditional ESP will deteriorate owing to the high-resistivity of fly ash) and equipped with dry or semidry FGD systems.33 In spite of the worsening urban air quality, SO2 emissions have been reduced gradually through wide application of FGD during the “11th five-year-plan (2006−2010)”. According to the Ministry of Environmental Protection of China (MEP), the capacity of power plants with installed FGD devices is 526.9 GWe which account for about 75% of the total installed capacity (707 GWe) of thermal power plants in 2010.14 Within these units equipped with FGD systems, about 96.1% adopted wet FGD (WFGD) and about 90% use limestone as the desulfurization agent. Furthermore, NOx reduction has become one of atmospheric pollutants reduction by the Chinese central government during the “12th five-year-plan (2011−2015)”. The capacity of units with SCR devices installed which are intended to diminish NOx emissions amounted to 69.2 GWe by the end of 2010. SCR catalysts, which are installed with boilers to transform NOx in the flue gas into unreactive N2, can alter 3577

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Table 2. Average Proportion of Hg0, Hg2+, and HgP in Total Hg Emissions from Coal-Fired Power Plants FFs FFs+WFGD SCR+FFs+WFGD ESP ESP+WFGD SCR+ESP+WFGD

Hg0

Hg2+

HgP

refs

0.274 0.657 0.633 0.524 0.810 0.793

0.613 0.271 0.290 0.458 0.186 0.202

0.113 0.072 0.077 0.018 0.004 0.005

45−47 35,40,42,45−47 35,40−42,45−47 35,40,43−47 35,40,42,43,45,47 35,41,45,47

in Table 3, the national total emissions of most HTE have decreased substantially from 2006 to 2010, with an annual averaged decline rate of about 4% for Hg and about 10−15% for the other seven elements. The national total emissions of Hg, As, Se, Pb, Cd, Cr, Ni, and Sb are estimated at 118.54, 335.45, 459.4, 705.45, 13.34, 505.03, 446.42, and 82.33 t in 2010, respectively. The differences in the declining rates among these toxic elements can be mainly explained by the variation of integrated cobenefit effects of these elements by the installed conventional ACPD systems, as illustrated in Table 1 and Table 2. Because of the policy of replacement of small coal-fired plant units with large units and installation and operation of advanced ESP, FFs, WFGD, and SCR systems, the final discharge rates of hazardous trace elements into the atmosphere per ton of coal combustion by power plants have been reduced significantly from 2000 to 2010 (Table 3). Notably, total Hg emissions have increased during 2000 to 2006 with the rapid increase of coal consumption, whereas it began to decline gradually during 2006−2010 (peak in 2006) along with the widespread application of WFGD although coal consumption has kept growing. This is mainly due to the attributes of WFGD scrubber that can achieve cobenefit removal of gaseous oxidized Hg in flue gas (see Tables 1 and 3). Hg2+ is water-soluble and can be retained in WFGD, while Hg0 is insoluble and cannot be retained effectively in the scrubber. Therefore, the proportion of Hg2+ in the discharged total Hg has been decreasing continuously. However, Hg0 stays in the atmosphere longer than Hg2+ and HgP, and is much easier to transport long distances even causing trans-boundary concerns. Thus, the potential environmental problems due to the variations of Hg speciation should be highlighted, while the rapid growth of total Hg emissions has been restrained effectively in China. The transfer of HTE from the atmosphere and accumulation in the water and soil environment through dry and wet deposition should also be noted, because the elements may transform to more toxic species and endanger the ecosystem and human health.53 3.2. Spatial Distribution Characteristics of HTE Emissions in 2010. As shown in Figure 1, most power plants are concentrated in or near the coastal provinces, such as Shandong, Hebei, and Jiangsu. Because of the implementation of programs to “Transfer Electricity from West to East and the “Western Development Strategy”, primary coal-producing provinces such as Inner Mongolia, Guizhou, and Shanxi stand out as large point sources. To combat the worsening urban air quality, SO2 emissions from power plants have been reduced

the potential influence of cobenefit removal efficiency of conventional air pollution control devices for hazardous trace elements (see details in SI Table S8).33,48−52 The first is a baseline scenario called business-as-usual (BAU), second is a scenario with best-available-control-technology (BACT), and the third is an intensive scenario with advanced high- efficiencycontrol-technology and specialized Hg control technology (HECT). Energy conservation and air pollutant emission reduction from coal-fired power plants were addressed in the “12th fiveyear-plan” period and the coming “13th five-year-plan” period and this information was included in the three scenarios. The main differences among the three scenarios come from the assumptions of the installed capacity of various PM/SO2/NOx/ Hg control devices in the coal-fired power plants (please see details in SI Table S8). For 2020 scenarios, CFB boilers are considered to be equipped with WFGD and/or SCR to meet the new emission standard limits. Furthermore, as the largest Hg emitter in the world, we anticipate that some demonstration projects and commercially operational devices of ACI systems will be initiated to further abate Hg emissions in response to the global Minamata Convention on Mercury during 2015− 2020.

3. RESULTS AND DISCUSSION 3.1. Temporal Trend of HTE Emissions from CoalFired Power Plants. From 2000 to 2010, the total electricity generation by coal-fired power plants in China increased from 1114.2 to 3222.1 TWh.14 Meanwhile, the volume of coal burned about tripled from 545.9 to 1591.0 Mt during 2000− 2010.28 However, peak values of the annual national total of Hg, As, Se, Pb, Cd, Cr, Ni and Sb emissions occurred in 2006, the first year of “11th five-year-plan” period under which FGD devices are required to be installed in many more power plants in order to reduce SO2 emissions substantially. As can be seen

Table 3. HTE Emissions from Coal-Fired Power Plants in China, 2000−2010 (Tons/Year)

a

HTE

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2006−2010a

Hg Hg0 Hg2+ HgP As Se Pb Cd Cr Ni Sb

79.00 41.95 35.65 1.39 354.01 451.85 820.00 23.47 650.00 480.29 96.75

82.14 43.62 37.05 1.48 371.98 474.93 860.00 22.73 680.00 501.59 104.10

92.94 49.48 41.83 1.63 408.45 525.26 952.00 22.85 740.00 544.42 111.76

110.08 58.70 49.42 1.96 480.25 599.95 1074.74 26.28 822.97 633.09 131.03

126.91 68.40 56.27 2.25 540.19 676.89 1170.00 29.94 916.57 709.82 145.63

141.34 76.72 64.48 2.43 593.39 760.14 1190.48 31.64 955.35 775.23 158.82

146.81 86.40 58.07 2.34 615.70 818.26 1189.10 30.56 965.21 794.43 166.35

135.29 88.88 44.69 1.73 523.11 737.54 1019.38 24.85 806.83 677.68 150.50

120.66 85.35 34.01 1.29 424.23 618.24 860.40 18.04 674.68 545.29 122.80

114.12 83.23 29.70 1.19 369.14 514.80 760.93 15.97 571.55 477.34 99.39

118.54 86.64 30.66 1.23 335.45 459.40 705.45 13.34 505.03 446.42 82.33

−4.19 0.06 −11.99 −12.07 −11.44 −10.90 −9.92 −15.28 −12.15 −10.89 −13.12

The annual averaged decline rate for hazardous trace elements from 2006 to 2010 (unit: %). 3578

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Olympic Games, 2010 World Expo, and 2010 Asian Games, while in other provinces SCR/SNCR devices have been installed in most newly built coal-fired units after 2007 voluntarily or under pressure from the local environmental authorities. Because of the differences in volume of fired coal units, the average HTE concentration in feed coals, as well as the application of conventional air pollution control devices, remarkable unevenness can be seen among provincial inventories (see Table 4). With their large coal consumption, Shandong, Jiangsu, Shanxi, and Hebei are generally among the top 10 provincial emitters of HTE. Although the volume of coal consumed by power plants in Inner Mongolia is the largest among the 30 provinces, the resultant HTE emissions in Inner Mongolia rank below second. In particular, emissions of Se, Cd, Cr and Sb in Inner Mongolia are much lower than those in the other large coal-fired provinces, such as Shanxi, Anhui, and Guizhou. This is mainly due to the relatively lower average HTE content in coal mined from Inner Mongolia located in the Early-Middle Jurassic period coal bearing area compared to other coal basins.25 On the other hand, with less feed coal combusted in power plants, emissions of Hg, As, Pb, Cd, Cr, and Ni in Yunnan are always high, due to the relatively higher average HTE concentration in coal from Yunnan than in coal from other provinces. For the similar reasons, Se emissions in Anhui and Cd emissions in Sichuan are relatively high.

Figure 1. Geographical distribution of coal-fired power plants and provincial installed WFGD and SCR capacity, 2010.

gradually through wide application of FGD and the replacement of coal by other lower sulfur fuels during the “11th five-year-plan (2006−2010)”. By the end of 2010, the proportion of WFGD capacity exceeded 75% in most provinces. Furthermore, NOx reduction at power plants is now required by the Chinese central government during the “12th five-year-plan (2011−2015)”. Many SCR devices were installed or retrofitted in the newly built and in-use power plants in Beijing, Shanghai, and Guangdong prior to the 2008

Table 4. HTE Emissions from Coal-Fired Power Plants by Province in China, 2010 (Tons/Year) province

total Hg

Hg0

Hg2+

HgP

As

Se

Pb

Cd

Cr

Ni

Sb

Anhui Beijing Chongqing Fujian Gansu Guangdong Guangxi Guizhou Hainan Hebei Heilongjiang Henan Hubei Hunan Inner Mongolia Jiangsu Jiangxi Jilin Liaoning Ningxia Qinghai Shaanxi Shandong Shanghai Shanxi Sichuan Tianjin Xinjiang Yunnan Zhejiang total

9.00 0.32 1.54 1.10 2.13 5.19 0.96 5.20 0.12 6.07 3.39 6.35 1.85 1.39 10.71 11.43 1.61 4.37 5.04 1.87 0.43 3.11 11.05 2.82 5.73 3.66 1.24 0.83 5.19 4.83 118.54

7.02 0.27 1.22 0.80 1.57 3.99 0.56 4.19 0.09 4.52 2.27 4.97 1.41 1.10 7.95 8.83 1.28 2.94 3.64 1.35 0.30 2.44 7.55 2.23 4.30 2.61 0.98 0.51 3.87 3.80 88.58

1.90 0.05 0.31 0.29 0.53 1.15 0.37 0.99 0.03 1.49 1.07 1.33 0.42 0.28 2.65 2.48 0.32 1.36 1.35 0.50 0.12 0.65 3.36 0.56 1.38 1.01 0.25 0.30 1.27 0.98 28.74

0.08 0.00 0.01 0.01 0.02 0.05 0.02 0.02 0.00 0.06 0.05 0.05 0.02 0.01 0.11 0.11 0.01 0.06 0.06 0.02 0.01 0.03 0.15 0.03 0.06 0.04 0.01 0.01 0.05 0.05 1.22

7.96 0.89 2.76 4.29 4.18 17.72 4.72 8.52 0.28 20.09 14.96 9.53 3.83 9.90 34.54 22.17 5.28 20.65 21.49 3.75 0.66 5.98 42.45 6.20 16.34 9.17 2.98 6.48 15.96 11.72 335.45

45.14 1.93 4.43 5.44 1.15 28.93 3.12 12.03 0.67 17.79 7.37 39.15 10.42 11.15 16.57 44.40 15.15 13.08 10.45 9.81 0.58 13.16 51.16 7.88 36.71 13.25 6.63 1.20 7.21 23.44 459.40

16.12 2.61 6.38 6.46 3.61 36.00 4.57 13.54 0.86 46.11 33.37 30.68 14.72 13.60 68.29 61.15 10.03 29.52 36.70 6.82 1.10 22.64 80.62 13.02 46.37 21.34 8.76 2.65 32.91 34.96 705.45

0.18 0.07 0.25 0.12 0.03 1.04 0.07 0.43 0.02 0.43 0.18 0.91 0.30 0.35 0.30 1.04 0.28 0.17 0.28 0.45 0.02 0.51 1.36 0.10 1.32 1.37 0.21 0.12 0.69 0.74 13.34

25.26 1.49 3.78 4.86 7.49 26.96 9.89 9.51 0.42 25.16 17.70 25.64 8.74 11.49 25.64 41.50 10.65 16.31 27.10 3.44 1.80 13.43 51.67 6.42 28.17 20.68 4.58 6.21 47.74 21.34 505.03

22.87 1.50 4.49 5.33 8.43 26.01 3.20 12.39 0.47 18.59 14.50 20.01 7.82 7.52 19.05 38.97 9.12 12.70 28.93 4.75 1.09 12.23 56.77 5.86 29.04 17.02 4.83 8.64 23.97 20.28 446.42

0.81 0.23 1.02 0.36 0.85 6.63 1.46 7.75 0.09 2.81 2.81 2.30 2.32 1.72 4.57 8.57 1.84 2.50 3.31 0.39 0.18 4.34 6.48 0.90 4.98 3.29 0.81 1.62 2.43 4.97 82.33

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the combination of SCR + ESP/FFs + WFGD configuration, most HTE emissions from coal-fired power plants in the BACT scenario will be reduced by about 15% compared with the baseline emissions in 2010. On the other hand, along with the promotion of demonstration projects and commercial application of ACI systems, coal fired power plants will emit less than 100 t Hg in 2020 BACT scenario and 2020 HECT scenario. As for the other 7 elements, the ESP/FFs + WFGD system is the best choice to control various HTE emissions up to now. In the future, innovative multipollutant control technology may be available as the more cost-effective way to further diminish HTE emissions. 3.5. Uncertainty Analysis. With regard to the uncertainties in the estimates, we have conducted sensitivity analysis on the total emissions of various HTE by using Monte Carlo simulation. Normal distribution with a coefficient of variation (CV, the standard deviation divided by the mean) of 5% is assumed for coal consumption and average concentration of HTE. Triangular distribution is assumed for the release ratio and removal efficiency in this article.19,21,55 Supporting Information Table S9 illustrates the uncertainties (95% confidence interval around the arithmetic mean value) in atmospheric emissions of HTE from Chinese coal-fired power plants in 2010. As can be seen, the uncertainties of most HTE are estimated at about −40% to 90%, which are mainly the result of poor investigation and inadequate field test data for the release ratio and cobenefit removal efficiency of various HTE. Although there are still some uncertainties due to the lack of adequate original field test data in Chinese coal-fired power plants, this new comprehensive HTE emission inventory and the temporal and spatial distribution characteristics provide indispensable input data for atmospheric transport, deposition and future abatement strategies. 3.6. Proposals for Future HTE Control. With continued energy mix restructuring, cleaner energy is projected to generally increase in the coming 10 years, but still not enough to alter the coal-dominated electricity generation structure.56 To control HTE emissions from Chinese coal-fired power plants, control strategies and specific countermeasures noted below could be implemented. Large coal consumption provinces in the east and the coast of China which are densely populated and suffering from complex regional air pollution and lack of local coal reserves, such as Shandong, Jiangsu, Zhejiang, Guangdong, and

With the wide application of WFGD in coal-fired power plants in the eastern and coastal economically well-developed provinces, the majority of Hg species emitted from coal-fired power plants is dominated by Hg0. Additionally, because of the easier absorption of Hg2+ by the downstream WFGD scrubbers, SCR technology provide an additional cobenefit in the Hg reduction of coal-fired power plants since SCR catalysts can promote the oxidation of some elemental Hg into Hg2+ and thus alter the speciation of Hg in flue gas.34 3.3. Comparison with Other Inventories. Until now, the comprehensive and detailed studies on various HTE (except Hg) emissions in China are quite limited. Therefore, only Hg emission estimates have been compared with other investigations.13,15−18,34,54 In this study, on the basis of previous research and some newly published field test results as mentioned before, the national averaged Hg concentration in coal of China is determined to be about 0.21 mg/kg, a little higher than 0.19 mg/kg in Wu et al.17 and 0.20 mg/kg in Jiang et al.16 As a result, the trend of Hg emissions in this study agrees well with other studies while the values for same-year calculations are somewhat higher as shown in Figure 2, which maybe represent an upper estimation of Hg emissions from coal-fired power plants in China.

Figure 2. Comparison of Hg emission estimates from coal-fired power plants in China.

3.4. Scenario Analysis for 2015 and 2020. As illustrated in Table 5 and SI Figure S4−S5, based on the assumptions made in the three scenarios, the level of HTE emissions is still high. Most HTE emissions would increase by about 5% in 2015 BAU scenario compared with that in 2010 with 21% increase of the amount of coal consumption. Especially for Se, even the emissions under BACT and HECT scenarios are still higher than those in 2010 mainly due to the relatively lower cobenefit removal efficiency of ESP/FFs and WFGD as illustrated in Table 1. At the end of 2020, with the widespread application of

Table 5. Projected HTE Emissions (Tons) from Chinese Coal-Fired Power Plants in 2015 and 2020 under Three Scenarios Based on the Reference Year 2010 2010

2015

2020

HTE

basic line

BAU

BACT

HECT

BAU

BACT

HECT

Hg Hg0 Hg2+ HgP As Se Pb Cd Cr Ni Sb

118.54 86.64 30.66 1.23 335.45 459.4 705.45 13.34 505.03 446.42 88.8

120.49 96.66 22.98 0.85 355.55 490.58 725.36 14.23 554.73 486.2 85.27

112.74 93.88 17.96 0.89 340.89 480.44 699.6 13.76 535.46 466.4 84.06

106.08 89.51 15.68 0.9 330.4 475.1 689.66 13.2 525.01 454.85 72.54

106.09 90.74 14.53 0.82 257.16 459.57 601.45 12.67 489.79 386.23 66.34

99.54 86.18 12.61 0.74 240.92 445.03 564.41 11.48 441.57 347 62.75

93.54 80.99 11.85 0.7 215.57 439.01 535.24 10.65 410.46 328.25 88.8

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(4) EMEP/EEA. Air pollutant emission inventory guidebook, Technical report No. 9/2009, 2009. http://www.eea.europa.eu/ publications/emep-eea-emission-inventory-guidebook-2009. (5) Song, D. Y.; Qin, Y.; Wang, W. F. Burning and migration behavior of trace elements of coal used in power plant. J. China Univ. Min. Technol. 2003, 32, 316−320 in Chinese. (6) Mukherjee, A. B. Nickel: A review of occurrence, uses, emissions, and concentration in the environment in Finland. Environ. Rev. 1998, 6, 173−187. (7) Xiao, T.; Zhang, A.; Wang, Z. Effects of toxic trace elements on arsenic poisoning caused by coal-burning. China Public Health 2011, 27, 305−307 in Chinese. (8) Chen, J.; Tong, Y.; Xu, J.; Liu, X.; Li, Y.; Tan, M.; Li, Y. Environmental lead pollution threatens the children living in the Pearl River Delta region, China. Environ. Sci. Pollut. Res. 2012, 19, 3268− 3275. (9) ABC News. Chinese official: Soil pollution hurts farming. http:// abcnews.go.com/International/wireStory/chinese-official-soilpollution-hurts-farming-21365375. (accessed Jan. 3, 2014) (10) The Ministry of Land and Resources of the People’s Republic of China (MLR). The news conference on the Second Land National Survey. http://www.mlr.gov.cn/zwgk/zytz/201312/t20131230_ 1298865.htm (accessed Jan. 3, 2014). (11) China Daily News. Tainted farmland to be restored. http://usa. chinadaily.com.cn/china/2013-12/31/content_17206152.htm (accessed Jan. 3, 2014). (12) Helble, J. J. A model for the air emissions of trace metallic elements from coal combustors equipped with electrostatic precipitators. Fuel Process. Technol. 2000, 63, 125−147. (13) Tian, H. Z.; Wang, Y.; Xue, Z. G.; Qu, Y. P.; Chai, F. H.; Hao, J. M. Atmospheric emissions estimation of Hg, As, and Se from coal-fired power plants in China, 2007. Sci. Total Environ. 2011, 409, 3078− 3081. (14) China Electricity Council. China Editorial Power Industry Statistics (2000−2010); China Power Press: Beijing, China, 2001− 2011 (in Chinese). (15) Streets, D. G.; Hao, J. M.; Wu, Y.; Jiang, J. K.; Chan, M.; Tian, H. Z.; Feng, X. B. Anthropogenic mercury emissions in China. Atmos. Environ. 2005, 39, 7789−7806. (16) Jiang, J. K.; Hao, J. M.; Wu, Y.; Streets, D. G.; Duan, L.; Tian, H. Z. Development of mercury emission inventory from coal combustion in China. Environ. Sci. 2005, 26, 34−39 in Chinese. (17) Wu, Y.; Wang, S. X.; Streets, D. G. Trends in anthropogenic mercury emissions in China from 1995 to 2003. Environ. Sci. Technol. 2006, 40, 5312−5318. (18) Wang, S. X.; Zhang, L.; Li, G. H.; Wu, Y.; Hao, J. M.; Pirrone, N.; Sprovieri, F.; Ancora, M. P. Mercury emission and speciation of coal-fired power plants in China. Atmos. Chem. Phys. 2010, 10, 1183− 1192. (19) Tian, H. Z.; Cheng, K.; Wang, Y.; Zhao, D.; Lu, L.; Jia, W. X.; Hao, J. M. Temporal and spatial variation characteristics of atmospheric emissions of Cd, Cr, and Pb from coal in China. Atmos. Environ. 2012a, 50, 157−163. (20) Tian, H. Z.; Lu, L.; Cheng, K.; Hao, J. M.; Zhao, D.; Wang, Y.; Jia, W. X.; Qiu, P. P. Anthropogenic atmospheric nickel emissions and its distribution characteristics in China. Sci. Total Environ. 2012b, 417−418, 148−157. (21) Tian, H. Z.; Zhao, D.; Cheng, K.; Lu, L.; He, M. C.; Hao, J. M. Anthropogenic atmospheric emissions of antimony and its spatial distribution characteristics in China. Environ. Sci. Technol. 2012c, 46, 3973−3980. (22) Nansai, K.; Oguchi, M.; Suzuki, N.; Kida, A.; Nataami, T.; Tanaka, C.; Haga, M. High-resolution inventory of Japanese anthropogenic mercury emissions. Environ. Sci. Technol. 2012, 46, 4933−4940. (23) National Bureau of Statistics of China. China Energy Statistical Yearbook (2001−2011); China Statistical Press: Beijing, China, 2001− 2011 (in Chinese).

Shanghai, should control their total coal consumption. Electricity demand in these areas could be fulfilled with China’s national strategies of “Transforming Electricity from West to East” and locally built of natural gas fired power plants, instead of long-distance coal transmission. Because of technical feasibility and favorable cost-benefit for coal-fired power plants, the combination of SCR + ESP/FFs + WFGD configuration may be the best available choice for China, especially for coal-electricity exporting provinces, which can also enhance substantial cobenefit HTE reduction. However, even with widespread application of SCR, FGD and ESP/FFs, not all of the Hg can be removed and the proportion of Hg0 in total Hg emissions is increasing. Thus, as a positive response to meeting the objective of the Minamata Convention on Mercury (signed by 92 countries and regions in October 2013), some demonstration and commercial projects involving advanced technologies such as ACI with high removal efficiency would be especially helpful to further abate Hg emissions in the future. In addition, the majority of power plants in China presently burn raw coal directly. The removal efficiency of coal washing for various HTE is about 30−60%, and thus coal washing before burning may be another effective way to reduce Hg and the other HTE emissions.13,19,21 Moreover, innovative multipollutant control technology and fine particle control technology may be other effective ways to enhance the control of HTE emissions. Controlling total coal use and substituting clean energy and renewable energy power plants for coal-fired plants should be considered to further eliminate the HTE emissions. However, it is a very complex issue involving resource availability, supply stability, energy price, and markets that will require thoughtful analysis.

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ASSOCIATED CONTENT

S Supporting Information *

Tables S1−S9 and Figures S1−S5. This information is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 86-10-58800176. Fax: 86-1058800176. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is fund by the National Natural Science Foundation of China (40975061, 21177012, and 21377012), State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex (No.SCAPC201305) and the special fund of the State Key Joint Laboratory of Environmental Simulation and Pollution Control (No.13L02ESPC).

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