Temporal and spatial distribution of atmospheric antimony emission inventories from coal combustion in China

Environmental Pollution 159 (2011) 1613e1619

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Temporal and spatial distribution of atmospheric antimony emission inventories from coal combustion in China H.Z. Tian*, D. Zhao, M.C. He, Y. Wang, K. Cheng State Key Joint Laboratory of Environmental Simulation & Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China

A multiple-year inventory of atmospheric antimony emissions from coal combustion in China for the period of 1980e2007 has been calculated for the first time.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 23 November 2010 Received in revised form 16 February 2011 Accepted 26 February 2011

A multiple-year inventory of atmospheric antimony (Sb) emissions from coal combustion in China for the period of 1980e2007 has been calculated for the first time. Specifically, the emission inventories of Sb from 30 provinces and 4 economic sectors (thermal power, industry, residential use, and others) are evaluated and analyzed in detail. It shows that the total Sb emissions released from coal combustion in China have increased from 133.19 t in 1980 to 546.67 t in 2007, at an annually average growth rate of 5.4%. The antimony emissions are largely emitted by industrial sector and thermal power generation sector, contributing 53.6% and 26.9% of the totals, respectively. At provincial level, the distribution of Sb emissions shows significant variation. Between 2005 and 2007, provinces always rank at the top five largest Sb emissions are: Guizhou, Hunan, Hebei, Shandong, and Anhui. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Antimony Emission inventory Coal combustion Atmosphere

1. Introduction Antimony is designated as an acute toxic substance by many government agencies, such as the US EPA, the European Union and the Ministry of Health, Labor, and Welfare of Japan. Although US EPA has not classified antimony for carcinogenicity, it is potentially toxic at very low concentrations and some antimony compounds are considered to be hazardous e or even carcinogenic e to human health (Gebel, 1997). Recently, the topic about trace elements has drawn more and more interest from scientists because of the great concern for their toxicological and negative environmental impacts. Antimony has an estimated average abundance of 0.4 ppm in the earth’s upper continental crust (Rudnick and Gao, 2004), and the coal Clarke value is 0.92 ppm (Ketris and Yudovich, 2009). This trace element is ubiquitously present in the environment as a result of human activities and natural processes. Major anthropogenic sources are fossil fuel combustion, non-ferrous metals refining, waste incineration, and incineration of sewage sludge. Besides, natural sources (volcano eruption, rock weathering, soil runoff, etc.) are also responsible for Sb emissions into the environment (Filella et al., 2002).

* Corresponding author. E-mail address: [email protected] (H.Z. Tian). 0269-7491/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2011.02.048

High-temperature processes, such as coal combustion in electric power stations and heat and industrial plants, gasoline combustion, smelting of ores, refuse incineration emit various trace metals, which enter the atmosphere and the aquatic and terrestrial ecosystems. Combustion of coal in electric power plants and industrial, commercial, and residential burners was a significant source of Sb (Nriagu and Pacyna, 1988). In comparison to the Hg, As, and Se, the concern about the fate of Sb during coal combustion (i.e., partitioning, environmental impacts, emission control, etc.) is a relatively new subject. Although antimony is not the major pollutant in the atmosphere, its toxicological and environmental effects can’t be ignored. There are two primary pathways to release Sb to the environment during coal combustion. These are directly, via atmospheric emissions of volatile phases, and indirectly, through the leaching of solid combustion by-products, during their disposal (they usually are ponded or landfilled) or after their deposition on the soil and water of the surrounding area from the atmospheric emissions (Llorens et al., 2001). When released into the air, antimony can attach itself to fine particles (Song et al., 2003), which most easily pass through conventional particulate control devices, and may stay in the atmosphere for many days. It may be possible for these particles to be transported over long distances before they eventually settle down (Shotyk et al., 2005). Agricultural soils may become polluted with Sb through wet and dry deposition from mining, sewage sludge, and fly ash. It is believed that Sb pollution from Xikuangshan Sb mine and from Sb

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H.Z. Tian et al. / Environmental Pollution 159 (2011) 1613e1619

mining activities in China in general is very severe, resulting in significant environmental problems in China (He, 2007). Coal, as an important world energy component, will be continuously and widely used in this century due to its relatively abundant reserves and lower price than oil and natural gas. With increasing consumption of coal, large amounts of antimony will be emitted into the environment. Therefore, it is very necessary to know the situation and distribution characteristics of Sb emissions from coal combustion. By now, there have been no published estimates of atmospheric antimony emissions from coal in China. In this paper, applying the emission factor method based on provincial coal consumption and average Sb concentration in coal, a comprehensive inventory of atmospheric antimony emissions from coal combustion in China for the period of 1980e2007 is established. Specially, the temporal and spatial distribution of atmospheric emission inventories of Sb is developed and discussed in detail by economic sectors and regions.

Table 1 Results of averaged content of Sb in raw coal as produced and consumed by province in China, 2007 (mg/g).

2. Methodology, data sources, and key assumptions Emissions are calculated using fuel consumption data and the specified Sb emission factors grouped by different combustion facilities and the equipped particulate matter (PM) and SO2 control devices. The emissions are firstly estimated by province and sector, as the product of activity levels (coal combustion), the average content of Sb in coal as consumed, the average fraction of Sb released from boilers, one minus the removal efficiency of dust collectors, and one minus the removal efficiency of flue gas desulfurization (FGD) system, then aggregated to obtain the national total level. The basic concept of the Sb emission calculation can be described by the following equations:




Ei;j ¼ Ci;j Mi;j Ri;j 1  PPMði;jÞ Ei ¼ ET ¼

X




1  PFGDði;jÞ



Ei;j

X

Ei

(1) (2) (3)

where E is the emission of atmospheric Sb; C is the averaged Sb content of coal as consumed in one province; M is the amount of coal consumption; R is the fraction of Sb released from combustion facility; PPM and PFGD are the fraction of Sb removed by the existing PM and SO2 pollution control devices, respectively (some of Sb released from coal combustion facilities can be removed from flue gas by the equipped PM collectors and FGD scrubbers); j is the emission source classified by economic sectors, combustion facilities, and the equipped PM and SO2 control devices; i is the province (autonomous region or municipality); and T is the national totals. 2.1. Averaged content of Sb in raw coal as mined The content of Sb in coal mined from different places varies substantially due to the coal-forming plants and the coal-forming geological environments. Table 1 shows the provincial Sb content of raw coal, as mined in China. We have compiled Sb abundance of 1612 Chinese coal samples from domestic published literature data (See Table S1 in the supplementary material for more details) and obtained a national average of 1.48 mg/g. Among these 30 provinces, the lowest mean concentration of Sb is 0.04 mg/g in Gansu province while the highest concentration is 76.2 mg/g in Guizhou province. The average Sb content in coals from Guizhou, Hunan, and Guangxi is much higher than the national averaged value of Chinese coals. The Sb content in most world coals is between 0.05 and 10 mg/g (Swaine, 1990), and the average Sb content in U.S. and Australian

Provincea

Raw coal production (Mt)b

Raw coal consumption (Mt)b

SbP

SbC

SbS

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

92.66 6.49 42.94 20.50 39.49 0 7.21 108.64 0 86.63 100.65 192.87 10.84 62.17 354.38 24.80 29.97 33.54 63.49 37.72 9.64 203.54 145.18 0 630.21 95.58 0 49.16 77.55 0.12

97.84 29.85 40.79 61.17 44.55 125.94 47.72 106.30 4.14 245.49 98.53 231.71 105.35 102.77 185.32 199.52 51.70 78.47 152.24 41.35 10.58 78.94 317.03 52.60 292.03 94.50 39.27 49.44 76.20 130.24

2.95 1.19c 1.50 0.38 0.70 2.40c 3.67 3.97 0.00d 1.19 0.90 0.65 1.17 3.76 1.67 0.39 1.79 1.02 2.01 0.19 0.35 2.25 0.53 0.00d 1.21 1.83 0.00d 0.78 0.74 0.82

2.59 1.02 1.54 0.67 0.69 1.55 2.75 3.96 0.71 1.10 0.98 0.68 1.05 3.07 1.56 1.06 1.89 1.19 1.57 0.49 0.49 1.92 0.80 0.96 1.19 1.86 1.01 0.73 0.91 1.09

1.34 1.08 e 0.55 1.25 0.41 2.12 1.87 e 1.2 0.9 1.35 1.55 1.55 0.88 1.03 0.87 1.04 0.79 1.18 1.39 1.33 0.84 1.12 1.25 1.13 1.18 1.02 1.75 1.18

stands for raw coal as produced, C stands for raw coal as consumed, and S stands for background concentration in soils. The data of Sb background concentrations in Chinese soils come from Zeng and Zeng (2002). a Xizang, Taiwan province, Hong Kong and Macau Special Administrative Region are not included in this table. b The values come from China energy statistical yearbook 2008. c Beijing and Guangdong lack of corresponding date, in this study, we choose the Sb content of Hebei and the average Sb content of surrounding province (Guangxi, Fujian, Jiangxi and Hunan, respectively). d No raw coal produced in Hainan, Shanghai, and Tianjin, thus the values of Sb content are assumed to be zero. P

coals are 1.2 mg/g and 0.5 mg/g, respectively (Finkelman, 1993; Swaine, 1990). As can be seen, the average Sb abundance in Chinese coals is comparable with that in U.S. coals while much higher than that in Australian coals. No significant difference in trace elements content in coal samples among different years has been reported. Therefore, we assume that the averaged content of Sb of raw coal as produced did not change during the period of this study. 2.2. Averaged content of Sb in raw coal and coal products as consumed The geographical distribution of coal resources in China is extremely unbalanced, less in the southern and eastern areas while abundant in northern and western areas. As a result, large quantities of coal produced have to be transported long distance from production areas to consumption areas, leading to remarkable difference between the trace elements content in coal as produced and consumed in one province. In order to obtain reliable estimates of the magnitude and spatial distribution of Sb emissions, it is essential to know the Sb content of the coal as burned, not just as mined. Therefore, it is necessary to relate the coal produced (mined) in particular provinces to its consumption in each province. As a result, a transportation matrix is required to quantify in-province

H.Z. Tian et al. / Environmental Pollution 159 (2011) 1613e1619

coal use and inter-province coal flows (Streets et al., 2005; Tian et al., 2010). According to the statistical data retrieved from China Energy Statistical Yearbooks (1997e2008) and China Coal Industry Yearbooks (2005e2008), annual coal flow matrixes among 30 provinces are established to quantify in-province coal use and inter-province coal flows from 2004 to 2007. From 1995 to 2003, only 1996 and 1999 coal flow matrixes are set up due to statistical data restrictions. It has been proven that the inter-province coal supply patterns were relatively steady for the majority of provinces between 1996 and 1999, resulting in a small change in Sb content in coal as burned for most of the provinces (Streets et al., 2005). Therefore, we apply the 1996 flow matrix to 1995, 1997 and 1998, and the 1999 matrix to the other years (2000e2003). For the years before 1995, the patterns of coal output by province and inter-province coal flow have changed little (DITS, 1992, 1998), thus we use the average Sb content calculated from 1996 flow matrix instead due to lack of detailed interprovince coal transportation statistical data. In China, coal briquettes and coke are produced from both raw coal and the cleaned coal. The methodologies for calculating the Sb content of cleaned coal, coal briquettes, and coke as produced are calculated based on the following equation (Tian et al., 2010):

 Ccc=b=c;i ¼

 Crc;i Mrc;i þ Ccc;i Mcc;i ð1  FÞ Pcc=b=c;i

(4)

where Ccc/b/c is the averaged content of Sb in the cleaned coal, briquettes or coke; Mrc and Crc are the amount and averaged Sb content of raw coal input in the production; Mcc and Ccc are the amount and averaged content of cleaned coal input in the production of briquettes or coke; F is the fraction of Sb removed by the coal washing process, briquette production or coke making process; Pcc/b/c is the amount of cleaned coal, briquettes or coke as produced; and i is the province (autonomous region or municipality). We assume an average coal cleaning Sb removal efficiency of 35.67% (Akers, 1995; Bai, 2003; DeVito et al., 1994; Quick and Irons, 2002; Wang et al., 2003, 2004) that is independent of the Sb content, and 30% of the Sb contained in a given coal remains in coke after the coking process (Helble et al., 1996). Because no evidence shows that there is Sb removal during the briquette production process, we assume that 100% of the antimony in the raw coal or cleaned coal is transferred to the briquettes. 2.3. Coal consumption and emission factors of Sb Multiple-year coal consumption data by sectors and types of coal products is provincial-level statistical data compiled from the China Energy Statistical Yearbooks from 1980 to 2007 (DITS, 1992, 1998; NBS, 2001, 2004; NBS and NDRC, 2005e2009). Taiwan province, Hong Kong and Macau Special Administrative Region are not considered tentatively. The total energy consumption in China has increased from 602.75 million metric tons of standard coal equivalent (Mtce) in 1980 to 2655.83 Mtce in 2007. Among the major coal-consuming sectors, the power sector is the leading sector in coal growth, increasing 9.7% annually. The industrial sector has a moderate increase in coal use, 6.0% annually. Similarly, coal consumption for other uses has no discernible increase (1.5% annual rate). However, coal use for the residential sector has been slightly decreasing (0.3% annual rate) due to fuel transitions to cleaner gaseous fuels and electricity in many regions of China. Because the release rates of Sb depend greatly on combustion technology and operation conditions, it is necessary to develop a detailed specification of the ways in which coal is burned in China. Our model contains 62 individual source types for coal combustion,

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38 of which are for coal-fired power plants, 16 for industrial use, 4 for residential use, and 4 for other uses (See Table S2 in the supplementary material for more details). A fraction of the antimony contained in the fuel is not emitted into the air but is retained in the bottom ash and disposed of as solid waste. The release rates of Sb emissions are different for different boiler types. Some studies (Álvarez-Ayuso et al., 2006; Ito et al., 2006; Llorens et al., 2001; Nodelman et al., 2000) indicate approximately 78e96% of Sb release into the air for pulverized-coal (PC) boilers; while the ratio may reduce to about 34e68% for stokers and 62e95% for fluidized-bed furnace (FBF) (Åmand and Leckner, 2004; Klika et al., 2001; Song et al., 2005; Zhang et al., 2003a,b). The selected average release rates of different boiler types used for Sb emissions calculation are listed in Table 2. Control technologies used to reduce criteria air pollutant emissions (e.g., particulate matter, SO2) from combustion boilers can also remove some of the Sb from the flue gas; however, the removal efficiencies vary widely. Electrostatic precipitator (ESP) and fabric filter (FF) have high Sb removal efficiencies of 56e100% (Brekke et al., 1995; Helble et al., 1996; Ito et al., 2006; Klika et al., 2001; Llorens et al., 2001; Meij and Winkel, 2007; Miller et al., 1998; Nodelman et al., 2000); cyclones show very little benefit, with Sb removal efficiency about 40% (Gogebakan and Selçuk, 2009). In addition, wet flue gas desulfurization (WFGD) can reach a high Sb removal efficiency (Meij and Winkel, 2007). However, there is no published data for wet scrubbers. Fortunately, many studies showed that, antimony and arsenic share some chemical and physical properties in coals and both of them can be enriched in the finer particles (Clarke, 1993; Song et al., 2003). So, here we use the arsenic removal efficiency (Ondov et al., 1979) to substitute it. Table 3 presents the assumed Sb removal efficiencies of WFGD and four predominant types of PM control devices equipped with coal-fired boilers in China. Residential use is also an important coal-consuming sector in China. The major combustion types for residential cooking and heating are traditional cookstoves and improved cookstoves, both of which are without any PM and SO2 control devices. However, there is very little information about Sb emissions through residential use. Here, we choose to use the emission factor for coal combustion provided by NPI (1999), and the emission factor of Sb through residential use is assumed at 9.0  106 kg/t. In addition, the major combustion devices for other uses are medium and small scale stoker fired boilers, which are mainly used for supplying hot water and heating. Hence, we use the average emission factor of stoker fired boilers to calculate Sb emissions from other uses sector.

Table 2 The release rates of Sb from coal combustion. Boiler type Pulverized-coal boiler Pulverized-coal boiler

Release rate (%) 86 93

Literature cited

Ito et al., 2006 Álvarez-Ayuso et al., 2006 Pulverized-coal boiler 96, 94 Nodelman et al., 2000 Pulverized-coal boiler 78 Llorens et al., 2001 Stoker fired boiler 34.47 Zhang et al., 2003b Stoker fired boiler 53.50, 67.50 Zhang et al., 2003a Stoker fired boiler 58.63 Song et al., 2005 Fluidized-bed furnace 85, 95 Klika et al., 2001 Fluidized-bed furnace 55, 62.5 Åmand and Leckner, 2004 In this study Pulverized-coal boiler 89.4 Averaged value Stoker fired boiler 53.5 Averaged value Fluidized-bed furnace 74.4 Averaged value 5 Coke furnace 6.310 kg/mg US EPA, 1992

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H.Z. Tian et al. / Environmental Pollution 159 (2011) 1613e1619

Table 3 Removal efficiencies of Sb by PM and SO2 control devices. Control device

Release rate (%)

Literature cited

ESP ESP ESP ESP ESP ESP FF FF FF In this study

69.8 92, 97 98.9 72 56 98.5 87 98, 100 92 83.5 94.3 40 82.1 96.3

Ito et al., 2006 Brekke et al., 1995 Meij and Winkel, 2007 Klika et al., 2001 Llorens et al., 2001 Helble et al., 1996 Klika et al., 2001 Nodelman et al., 2000 Miller et al., 1998 Averaged value Averaged value Gogebakan and Selçuk, 2009 Meij and Winkel, 2007 Ondov et al., 1979

ESP FF Cyclone WFGD Wet scrubber

3. Results and discussion 3.1. Trends of Sb emissions by sector The trends of Sb emissions by different economic sectors from 1980 to 2007 are summarized in Fig. 1. The national total emissions of Sb from coal in China in 1980 are estimated at 133.19 t, and increasing to 546.67 t by 2007, at an annually average growth rate of 5.4%. As can be seen, the accumulated total Sb emissions into the atmosphere are 8061.53 t during the period from 1980 to 2007. Industrial use is the biggest single sector, contributing 53.6% of the total Sb emissions. This is attributed to two major reasons: (1) it is the largest coal-consuming sector in China; and (2) it contains a significantly higher share of uncontrolled or poorly controlled boilers compared to the power plants sector. Thermal power generation sector is the second biggest source, contributing 26.9% of the national totals. Coal consumption for residential decreased during the period due to fuel substitution with cleaner fuels such as natural gas and electricity, especially in urban areas, resulting in the emissions of Sb dropped down (the residential sector contributed only 0.4% of total Sb emissions). Coal consumption for farming, construction, transportation, and commerce are combined together as other uses. We estimate that the total accumulated Sb emissions of other uses from 1980 to 2007 are 1540.63 t. Nriagu and Pacyna (1988) estimated that the global Sb emissions from coal combustion were 353e2255 t per year. Pacyna and Pacyna (2001) estimated that the input of Sb from anthropogenic activities to the global atmosphere were about 1600 t per year, while the emissions of Sb from combustion of fuels in stationary

sources in 1995 were 730 t in which the Asian countries emitted 308 t. In this study, we estimate that the Sb emissions from coal combustion are about 300 t in 1995, a relatively higher value, which can be mainly attributed to the higher average content of Sb in coal and the different scope of activity levels. Until now, the comprehensive and detailed studies on Sb emissions in China are quite limited, thus the further research about Sb emission are very necessary.

3.2. Trends of Sb emissions by provinces and regions The total emissions of Sb by provinces in China for 1995, 2000, 2005, 2006, and 2007 are summarized in Table 4. At the provincial level, the trends of total Sb emissions show significant differences. For most provinces (e.g., Shandong, Shanxi, Inner Mongolia, Henan), the annual average growth rates show increased first and then decreased during these three periods; but Hubei and Ningxia provinces show the opposite trend; the rates of some provinces (e.g., Beijing, Shanghai and Anhui) show reduced tendency gradually; however, some other provinces (e.g., Liaoning and Xinjiang) show increased Sb emissions over these periods. Sb emissions for each province are strongly affected by specific source-related trends. For example, (1) Sb emissions reductions in Beijing (6.0% annually from 2005 to 2007) are primarily due to the reduced coal consumption in the industrial sector and the fast penetration of advanced PM and SO2 control technologies, such as ESP and FGD, in the power sector; (2) the rapid increase in antimony emissions from 2000 to 2005, 27.4% annually, for Shandong province is primarily attributed to the greatly increased coal consumption in the power and industrial sector; (3) the 65.2% increase in annual antimony emissions from 2005 to 2007 in Ningxia province is driven by the increased Sb content of coal as produced, because the source of raw coal between 1995 and 2005 mainly came from itself, while from 2006 the consumed coal mainly came from ShenfuDongsheng coal field, where the Sb content in coal as mined is high. It should be noted that up to the end of 2008, the share of ESP and FGD in power plants has reached more than 96% and 60%, respectively (NDRC, 1998; 2008). The fast penetration of advanced control technologies contributed the reduction of Sb emissions since 2005. For a specific Sb emission source type, the Sb emission trends can be quite different from one province to another. Between 2005 and 2007, provinces always ranked in the top five largest Sb emissions are: Guizhou, Hunan, Hebei, Shandong, and Anhui. This is mainly owing to the high Sb content in the raw coal produced and/or consumed in Guizhou and Hunan province, and most of which (e.g., Hebei and Shandong) are located in the east and are traditional industry-based or economically intensive areas in China.

Fig. 1. Trend of atmospheric Sb emissions by sectors from coal combustion in China, 1980e2007.

H.Z. Tian et al. / Environmental Pollution 159 (2011) 1613e1619 Table 4 Summary of total Sb emission estimates (t) by province, 1995, 2000, 2005, 2006, and 2007. Province/region 1995 2000 2005 2006 2007 AAGRa 1995e 2000e 2005e 2000 (%) 2005 (%) 2007 (%) North China Beijing 5.2 5.9 5.8 5.4 5.1 Tianjin 4.5 4.2 6.6 6.0 6.0 Hebei 17.7 21.2 37.4 33.8 35.4 Shanxi 13.1 18.0 26.8 28.8 28.8 Inner Mongolia 12.3 15.8 26.5 28.0 30.7 Northeast China Liaoning 22.6 24.7 28.8 31.6 31.4 Jilin 9.5 8.5 16.1 16.7 16.6 Heilongjiang 7.3 7.7 12.3 11.8 11.2 East China Shanghai 5.1 7.6 8.2 7.6 7.7 Anhui 18.5 27.7 30.9 32.9 32.3 Jiangsu 11.0 13.8 27.3 24.2 24.7 Zhejiang 7.3 9.8 17.4 16.5 16.2 Fujian 1.7 2.1 5.2 5.2 5.7 Jiangxi 7.3 6.6 10.8 12.0 12.1 Shandong 10.5 10.5 35.1 35.0 35.0 Central China Henan 7.1 9.0 17.9 17.6 19.5 Hubei 8.7 12.3 15.6 17.6 18.4 Hunan 33.6 20.0 46.0 50.7 50.7 South China Guangdong 18.0 19.6 22.4 21.6 20.3 Guangxi 15.3 15.1 18.7 19.0 19.8 Hainan 0.2 0.2 0.4 0.3 0.5 Southwest China Guizhou 22.9 29.5 49.3 52.4 49.6 Sichuan 20.2 12.1 19.6 16.3 18.5 Chongqing 0.0 10.4 8.9 9.1 8.5 Yunnan 3.1 3.1 9.1 10.2 9.8 West China Gansu 2.6 2.6 4.0 4.3 4.4 Ningxia 0.3 0.9 0.9 2.2 2.5 Qinghai 0.3 0.4 0.6 0.6 0.6 Shanxi 11.1 8.2 17.5 17.1 18.5 Xinjiang 3.1 3.6 4.9 5.6 6.2 Total 300.1 330.8 530.9 540.2 546.7 a

2.3 1.3 3.7 6.6 5.1

0.3 9.3 12.1 8.3 10.9

6.0 4.5 2.7 3.8 7.7

1.7 2.2 1.1

3.2 13.6 9.9

4.4 1.8 4.2

8.4 8.4 4.6 6.0 5.0 2.1 0.0

1.6 2.2 14.6 12.2 19.6 10.3 27.4

3.2 2.2 4.8 3.4 5.0 6.2 0.2

4.7 7.0 9.9

14.9 5.0 18.2

4.2 8.4 5.1

1.8 0.2 4.0

2.7 4.4 16.1

4.7 2.7 10.0

5.2 9.7 e 0.1

10.8 10.1 3.1 23.9

0.3 3.1 2.4 3.9

0.1 25.4 6.0 5.8 2.6 2.0

9.5 0.4 9.4 16.4 6.7 9.9

4.1 65.2 3.6 2.7 12.7 1.5

Annual average growth rate.

Fig. 2 shows the distribution of the total Sb emissions intensity from coal combustion in China in 2007. It can be seen that the emissions of hazardous element from coal combustion in China distributed very unevenly due to the great difference in economic and energy consumption structure, degree of economic development, density of population as well as regional area of each province. The emissions of Sb from coal combustion in China are mainly concentrated in the Eastern Central and Southern areas. Antimony background concentrations in Chinese soils vary between 0.41 and 2.12 mg/g (Zeng and Zeng, 2002). The background values of Sb in Guangxi, Guizhou, Yunnan, Hubei and Hunan

Fig. 2. The distribution of the total Sb emission intensity from coal combustion in China in 2007, kg/km2.

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province soils are high (Table 1). At the same time, the contents of Sb in raw coal as consumed in 2007 and raw coal as produced in Guizhou, Hunan, and Guangxi province also show a high value (see Table 1). The correlation coefficient of SbP and SbS is 0.403, while the correlation coefficient of SbC and SbS is 0.451. In addition, some other factors (such as the coal consumption, atmospheric dry and wet deposition, soil conditions, etc.) can have much impact on the soil Sb content. Hence, much more field investigations and longterm studies are necessary to fully demonstrate the correlation between the Sb content of soil, Sb content of coal, and the Sb emissions. As can be seen from Fig. 3, from 2000 to 2007, the annual average growth rate of Sb emissions and coal consumption from industrial sector, and the total Sb emissions from coal combustion conform exactly. It indicates that industrial sector is the most important contributor to Sb emissions. That is to say, the decrease/increase in the total Sb emissions is basically consistent with the variation trend of the industrial coal use. The main reason is that the proportion of industrial coal use is very large, and the net emission rate is relatively high owing to the lower co-benefit removal by the poorly equipped PM and SO2 control devices. 3.3. Uncertainties Several factors influence the estimation of Sb emissions, including emission factor and activity level. Firstly, there are large discrepancies in estimates of the typical Sb content of coal and concentrate ore in many provinces. The abundance of Sb in Chinese coals did not receive much attention until 1990s. Some scholars have investigated the abundance and distribution of Sb in Chinese coals systematically, but the results vary widely. Ren et al. (1999) reported that the average Sb abundance in 133 samples of Chinese coals being 2.56 mg/g. Zhao et al. (2002) gave an average value of 2 mg/g Sb in 446 samples of Chinese coals. Similarly, Bai (2003) obtained an average value of 1.08 mg/g from 1018 samples. Recently, Qi et al. (2008) obtained a mean of 2.27 mg/g. Geological setting of China (e.g., Guizhou, Inner Mongolia, Yunnan) is very complex, and some coals in these areas have a high Sb content (Dai et al., 2006; Du et al., 2009; Hu et al., 2009). For example, Dai et al. (2006) reported that Sb is significantly enriched in Xingren, Guizhou province, and the content is as high as 3860 mg/g. Du et al. (2009) reported that the high-Ge coals in the Shengli coal field, Inner Mongolia, highly enriched in Sb. A high content of Sb (2382 mg/g) in the high-Ge coals was found. Similarly, the Ge-rich coals in Lincang germanium deposit, Yunnan province, are notably rich in Sb (Hu et al., 2009). However, most coals from these provinces still contain a normal amount of Sb. Because of the huge volume of coal consumption in China, the Sb content in coal is very critical to the estimation of Sb emissions in order to assess the reliability and accuracy of the Sb data. We have conducted a thorough review for available domestic published literatures, and neglected the abnormal samples with extremely high or low values which taking into account of the representatives of coal samples and their small output, then we determined the arithmetic average values for coal as produced by province as well as the national average value of 1.48 mg/g (Table 1). However, in view of a better assessment of geochemistry and mineralogical characteristics of coals and a reliable Sb emission inventory, more detailed field tests are very necessary, especially in some provinces such as Ningxia, Xinjiang, Gansu, Fujian and Zhejiang. Besides the Sb content of coal, there are some other uncertainties in our knowledge of antimony emissions from coal combustion into the atmosphere. By now, the field measurements

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H.Z. Tian et al. / Environmental Pollution 159 (2011) 1613e1619

30% Sb Emissions from Industrial Sector

Annual Rates, 2000-2007

25%

Total Sb Emssions

20%

Coal Consumption of Industrial Sector

15% 10% 5% 0% -5%

Ningxia

Xinjiang

Gansu

Qinghai

Yunnan

Shaanxi

Sichuan

Guizhou

Hainan

Chongqing

Guangxi

Guangdong

Hubei

Hunan

Henan

Jiangxi

Shandong

Anhui

Fujian

Jiangsu

Zhejiang

Shanghai

Jilin

Heilongjiang

Liaoning

Inner Mongolia

Hebei

Shanxi

Beijing

Tianjin

-10%

Fig. 3. Annual growth rates of Sb emissions and coal consumption growth at provincial level, 2000e2007.

of Sb emission rates from Chinese combustors/smelters and the capture of Sb in Chinese emission control devices are still very limited. Residential coal use in rural areas may be under-reported in Chinese statistics. For a better reliable estimation of Sb emissions from coal combustion in China, long-term field testing and continuously monitoring for all kinds of coal combustion facilities in China, deserve further investigation. 4. Conclusions An inventory of Sb emissions from coal combustion in China is carried out for the year 1980e2007. The calculated national total atmospheric emissions of Sb from coal combustion in China have rapidly increased from 133.19 t in 1980 to 546.67 t in 2007, at an annually averaged growth rate of 5.4%. Industrial use is the biggest single sector, contributing 53.6% of the total Sb emissions. Thermal power generation sector is the second biggest, contributing 26.9% of the totals. At the provincial level, the trends of total Sb emissions show significant variation, the top 5 provinces with the heaviest antimony emissions in 2007 are Hunan (50.74 t), Guizhou (49.56 t), Hebei (35.39 t), Shandong (34.98 t), and Anhui (32.30 t). In general, atmospheric emissions of Sb caused by coal combustion are mainly concentrated in the more populated and industrialized areas of China, i.e., the Eastern Central and Southeastern areas. Although there are still some uncertainties introduced by the lack of original data in China, the emissions inventory and temporal, spatial distribution of Sb emissions provide indispensable input data for atmospheric transport, deposition and abatement strategies for China in future research. Acknowledgments This work is fund by the National Natural Science Foundation (NSFC) of China (20677005, 40975061), and the special program on environmental protection of the Ministry of Environment Protection (MEP) (200909024). The authors thank the editors and the anonymous reviewers for their valuable comments and suggestions on our paper. Appendix. Supplementary material Supplementary material related to this article can be found online at doi:10.1016/j.envpol.2011.02.048.

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