Anthropogenic Atmospheric Emissions of Antimony and Its Spatial

Article pubs.acs.org/est

Anthropogenic Atmospheric Emissions of Antimony and Its Spatial Distribution Characteristics in China Hezhong Tian,*,† Dan Zhao,† Ke Cheng,† Long Lu,† Mengchang He,† and Jiming Hao‡ †

State Key Joint Laboratory of Environmental Simulation & Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China ‡ School of Environment, Tsinghua Unversity, Beijing 100084, China S Supporting Information *

ABSTRACT: An integrated inventory of atmospheric antimony (Sb) emissions from anthropogenic activities in China is compiled for the years 2005−2009. Emissions are estimated for all major anthropogenic sources for the first time. We estimate that the national emissions of antimony are 818 metric tons (t) in 2009, with the largest contribution from coal combustion at 61.8% of the total, while 26.7% of Sb is emitted from nonferrous metals smelting. Emissions are heaviest in Guizhou province, mainly due to small-scale combustion of high-Sb coal without emission control devices, and in Hunan province, where extensive smelting occurs. Furthermore, Sb emissions from 2188 large point sources and area sources are distributed within latitude/longitude-based grids with a resolution of 30 min × 30 min where Sb emissions are largely concentrated in highly populated and industrialized southwestern China, the east central region, and coastal areas. The uncertainties in our bottom-up inventory are quantified as −11% to 40% by Monte Carlo simulation. We recommend continuous field testing of coal combustors and smelters in China to improve the accuracy of these estimates.

1. INTRODUCTION Antimony (Sb) and its compounds are considered to be priority pollutants by the U.S. Environmental Protection Agency (EPA) and the European Union (EU).1 The International Agency for Research on Cancer (IARC) has assigned antimony trioxide (Sb2O3) to the group of substances that are suspected of being carcinogenic in humans.2 Antimony is potentially toxic at very low concentrations, and exposure to high levels of antimony can result in a variety of adverse health effects.3 After being emitted to the atmosphere, Sb has shown behavior very typical of long-range transport on both local and regional scales.4 Snow and ice from the Arctic provide unambiguous evidence that enrichment of Sb in Arctic air have increased 50% during the past three decades, elucidating the possible importance of Sb as a global pollutant.5 There is a considerable increasing concern about antimony because anthropogenic activities have resulted in an increasing concentration of this element in the environment. Atmospheric emissions of Sb from coal combustion and industrial processes are thought to be the primary sources of contamination of atmospheric, terrestrial and aquatic environments.6,7 For example, increased deposition of Sb was detected in biological samples collected within a few hundred meters of geothermal power plants in Tuscany.8 Also, industrial emissions from different forms of refining metallurgy (steel, stainless steel, copper, zinc) were linked to higher levels of Sb compared with rural background values.9 China possesses the most abundant Sb resource deposits of any country in the world. Due to Sb mining and smelting © 2012 American Chemical Society

processes, large quantities of Sb have been released, resulting in serious Sb contamination of the local environments. Antimony and its compounds have a large variety of industrial applications including a growing worldwide use of Sb in the manufacture of flame retardants (as Sb2O3) for plastics and textiles, most of which eventually ends up in a nonrecyclable waste stream. As municipal waste materials typically contain high concentrations of Sb impurities10 that are transformed during combustion, significant amounts of Sb can be released from waste incineration into the atmosphere. Antimony trisulfide (Sb2S3) is widely used as a lubricant in friction materials to reduce vibration and to improve friction stability. From vehicle transportation, antimony mainly comes from brake wear rather than from engine combustion.11 Considerable Sb concentrations are found in brake pads and dust, and a significant amount of brake dust is inhalable in the atmospheric environment.12,13 China plays an important role in global anthropogenic Sb emissions and its geochemistry cycle. High concentrations of Sb have been reported in the air of Chinese cities.14,15 However, an understanding of anthropogenic atmospheric emissions of Sb in China is quite limited compared with other trace elements such as Hg, As, and Se.16,17 In our previous study, atmospheric Sb emissions from coal combustion in Received: Revised: Accepted: Published: 3973

November 28, 2011 March 4, 2012 March 7, 2012 March 7, 2012 dx.doi.org/10.1021/es2041465 | Environ. Sci. Technol. 2012, 46, 3973−3980

Environmental Science & Technology

Article

China for the period of 1980−2007 were estimated.18 However, Sb discharged from other significant sources (such as nonferrous metals smelting, pig iron and steel production, municipal waste incineration, and brake wear) were not included. Thus, a comprehensive emission inventory of Sb with high spatial resolution information is urgently needed in China in order to know the source distribution characteristics of Sb emissions and to formulate appropriate control regulations and policies.

2.1. Emission Factors of Sb. The source types for coal combustion, the release rates of Sb from different coal combustion facilities, and the removal efficiencies of Sb through PM and flue-gas desulfurization (FGD) control devices have been described previously.18 Thus, here we mainly focus on determination of the average Sb emission factors from noncoal sources. Nriagu and Pacyna6 were apparently the first to use aggregated emission factors to estimate trace metal emission inventories to air, water and soil on a global basis, and the emission factors of Sb for nonferrous metals smelting were assumed at 50−200 g/t (Cu), 50−100 g/t (Pb), and 10−20 g/t (Zn), respectively. The calculated Canadian Sb emission factors for 1993 given by Skeaff and Dubreuil19 were significantly lower than those reported earlier for worldwide6 and Canadian operations.20 Pacyna and Pacyna7 claimed that their emission factors of Sb are more accurate than those used by Skeaff and Dubreuil.19 The average emission factors applied for the calculation of smelter emissions are considered for developed countries and developing countries, respectively.7 However, one might anticipate that some detectable improvements in trace metals emission control may have occurred since then because these previous estimates were conducted for the 1980s (or 1990s). Indeed, the best solution for assessing the emissions of trace metals from smelters is to measure the actual discharge rate, particularly the stack emissions. But such specific field measurements are substantially lacking at present in China. Here, we presume the average emission factors (50 g/t Cu, 75 g/t Pb, 15 g/t Zn) for developing countries used in Pacyna and Pacyna7 report are reasonable for China before the year 2000. Since then, due to strengthening implementation of policies to eliminate backward production capacity and the energy-saving and pollution reduction by the Chinese government, many small-scale smelting enterprises with outdated smelting process have been shut down or retrofitted with advanced processes and equipment, gradually updating the level of nonferrous metals industrial technology. Environmental pollution in the nonferrous metals industry in China has been reduced with the expanded application of best available control technology (BACT),21 and since 2001, the rate of industrial dust emissions per metric ton of nonferrous metals production has been decreasing annually,22,23 as can be seen from Figure 1. Toxic air pollutant emissions (principally PM and SO2) are generated primarily from calcining and smelting furnaces. Copper, zinc, and lead oxides or sulfides are the significant constituents of the PM, but other metals such as As, Sb, and Hg may also be present.24,25 Considering that heavy metals have

2. METHODOLOGY, DATA SOURCES, AND KEY ASSUMPTIONS Atmospheric emissions of antimony were estimated for the following source categories: combustion of coal by power plant boilers, industrial burners, residential use and other uses; primary and secondary copper, lead, zinc, and antimony production; pig iron and steel production; municipal solid waste (MSW) incineration; and brake wear. Atmospheric emissions of Sb from coal combustion are calculated by combining the detailed coal consumption data, Sb content in coals, and the specific emission factors, which are classified into subcategories by different boiler configurations and the deployment and effectiveness of air pollution control devices (APCDs). The basic formula can be expressed as follows.18 E=

∑ ∑ Ci , jMi , jR i , j(1 − P PMj)(1 − P FGDj) i

j

(1)

where E is the atmospheric emissions of Sb; C is the averaged Sb content of coals as consumed in one province; M is the amount of coal consumption; R is the fraction of Sb released from a combustion facility; PPM and PFGD are the fraction of Sb removed by the existing particulate matter (PM) and SO2 control devices, respectively; j is the emission source classified by economic sectors, coal combustion facilities, and the equipped PM and SO2 control devices (the source classification can be seen in Table S1 in Supporting Information); and i is the province (autonomous region or municipality). The average content of Sb in raw coals as produced from 30 provinces (autonomous regions and municipalities) on the Chinese mainland are collected and compiled on the basis of a thorough review of available literature (please see Table S2, Supporting Information, for more details). For the algorithms to determine the Sb content in coals as consumed, cleaned coals, coal briquettes, and coke as produced, refer to our previous studies.17,18 Besides coal combustion, there are other combustion sources (MSW incineration) and noncombustion sources (ferrous and nonferrous metals smelting processes, brake wear) that contribute to atmospheric Sb emissions in China. Sb emissions from these non-coal categories are calculated by combining annual activity data (consumption/production) and specific Sb emission factors. The basic calculation is described by the following equation: E=

∑ ∑ Mi , j EFj i

i

(2)

where E is the emission of atmospheric Sb; M is the volume of municipal wastes burned, or output of ferrous and nonferrous metals products, or number of vehicles; EF is the assumed average emission factors; and j is the emission source classified by source category.

Figure 1. Trend of industrial dust emissions per metric ton of nonferrous metals production in China, 2001−2009.22,23. 3974

dx.doi.org/10.1021/es2041465 | Environ. Sci. Technol. 2012, 46, 3973−3980


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Table 1. Summary of Antimony Emission Estimates (in Metric Tons) by Province in 2009a coal combustion

nonferrous metals production

province

POW

IND

RES

OTH

Cu

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 China

3.6 0.8 1.2 1.3 0.9 7.4 6.0 8.8 0.2 3.5 3.5 2.1 1.7 2.3 7.0 7.3 2.6 3.3 4.2 0.6 0.3 4.9 9.2 1.7 5.9 4.2 1.2 2.4 2.4 5.4 105.7

11.8 1.3 11.2 4.2 1.9 11.9 23.0 28.3 0.2 20.2 4.6 9.4 12.5 18.4 7.1 11.7 7.4 5.8 9.1 1.4 0.8 12.2 20.6 2.8 17.1 23.5 2.8 4.0 8.3 6.3 299.7

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1

1.0 1.7 3.3 0.4 0.5 0.6 2.8 39.1 0.0 2.6 0.9 0.4 4.1 8.5 5.8 0.6 0.5 2.5 2.1 0.2 0.3 5.3 5.4 0.4 4.5 1.5 0.6 0.9 2.1 0.2 98.8

11.2 0.0 0.8 0.5 10.5 0.1

0.1 0.0 0.1 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.0 0.0 0.0 0.0 1.0

Pb

0.0 0.3 0.0 0.7 5.3 0.1 4.4 4.8 12.3 0.0 1.0

4.4

0.0

0.2 0.6 1.4 4.6 5.0 0.3

0.0 1.5 1.9 2.7 0.1

0.0 40.7 0.9 22.9 0.7 0.5 2.3

0.0 7.5 1.7 1.7 0.0 0.3 0.0 7.4 1.9 72.6

Zn

0.2

2.2 0.0 7.4 1.6 0.1 0.1

0.7 1.3 0.2 2.9 0.1 0.1

0.8 2.9

0.0

0.0 1.8 0.0

0.1 11.9 0.0 101.9

Sb

0.1 1.4 0.1

0.1 9.3

0.3

2.6

5.7 0.3 31.7

1.0 12.4

PISP

MSWI

BW

total

0.3 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.0 2.7 0.1 0.4 0.4 0.3 0.3 1.0 0.3 0.2 1.0 0.0 0.0 0.1 1.0 0.4 0.6 0.3 0.4 0.1 0.2 0.2 11.3

1.0 2.1 1.3 3.9

0.6 1.3 0.3 0.6 0.2 2.3 0.4 0.3 0.1 1.4 0.6 1.1 0.6 0.6 0.5 1.5 0.4 0.4 0.9 0.1 0.1 0.5 2.0 0.5 0.7 1.0 0.5 0.4 0.7 1.5 22.2

34.0 7.2 18.6 11.6 17.2 41.3 41.8 77.0 0.8 31.2 10.2 58.1 25.6 69.8 27.5 39.3 26.2 13.2 22.2 3.5 2.6 28.9 49.1 10.7 31.6 34.4 7.4 7.9 41.0 28.0 818.0

12.3 0.4 0.1 0.4 0.5 1.0

11.6 1.0 0.4

0.1 3.3 3.2 1.0 2.2 1.5 1.3 12.1 60.7

a

POW, power plant boilers; IND, industrial burners; RES, residential use; OTH, other uses; PISP, pig iron and steel production; MSWI, municipal solid waste incineration; BW, brake wear.

nonferrous metals in 2009 reached 2.53 million metric tons, accounting for about 10% of national nonferrous metals production.23 Here, the emission factor of secondary production is assumed at 3 g/t according to Nriagu and Pacyna.6 The emission factor of Sb from pig iron and steel smelting is relatively small: we use 0.01 g/t for our calculations.6,7 Antimony shows enrichment in MSW compared to its natural abundance in the earth’s crust with the average antimony concentration in MSW estimated to be about 10− 60 g/t.10,27,28 Paoletti et al.10 reported that about 50% of the Sb input remains in the grate ashes. Watanabe et al.28 indicated that the Sb distributions in fly ash were 33−74%. On the basis of these test results, the use of an emission factor of 3 g/t to calculate the emissions from MSW incineration is regarded as reasonable.7 For brake abrasion, atmospheric Sb distribution specifically depends on traffic density, traffic signal patterns, driving speed, and braking force.29 Limited by the lack of field test data for Chinese vehicles, we chose 0.59 g·car−1 ·year−1 as an approximation.30 For more details about the assumed emission factors and the relevant references, refer to Supporting Information Table S3. It is noteworthy that coal-related emissions are excluded when the Sb emissions are calculated from nonferrous metals, pig

always existed in the industrial dust and smoke from the nonferrous smelting processes, we presume that the average emission factors for nonferrous metals production from 2001 to 2009 in China declined generally in accordance with the declining rate of industrial dust emissions per unit nonferrous metals yield. As a result, the average emission factors for Cu, Pb, and Zn smelting are assumed at 25, 37.5, and 7.5 g/t respectively, by the end of 2009. Since China has the most abundant resources and largest production of Sb in the world, the emission from antimony production plays an important role in anthropogenic Sb emissions, which should not be ignored. Nevertheless, little information about atmospheric emissions from antimony production can be found. In this study, we determine the emission factor of Sb production mainly based on the draft of China National Standard-Emission Standards of Pollutants from Nonferrous Metals Industry-Sb.26 The emission factor is calculated at 75 g/t Sb in 2009, which is just a preliminary estimate. For the large-scale Sb smelting plants in China, the assumed emission factor may be suitable; for the small- and medium-scale smelters that are mainly scattered throughout Hunan province, it may underestimate the real Sb emission rate, which can be subject to a high level of uncertainty. In addition, great efforts have been taken to recycle nonferrous metals in recent years. The output of recycled 3975



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operations are known to be a significant source of antimony.6,7 Mining and smelting industries produce huge amounts of waste and release large quantities of Sb into the environment.34 We estimate that these nonferrous smelting operations emit about 218.7 t of Sb. At the provincial level, the highest emissions from nonferrous metals industry are found in Henan (43.6 t), followed by Hunan (39.6 t) and Yunnan (26.0 t) provinces. The national emissions estimates for pig iron and steel production are 11.3 t. The top three provinces with high emissions are Hebei (2.7 t), Shandong (1.0 t), and Jiangsu (1.0 t). In general, however, emissions of Sb from iron and steel production are substantially lower than those from coal combustion and the nonferrous metal industry. This may be somewhat due to the lower emission factors assumed for iron and steel production as compared to other major source categories. 3.1.3. Sb Emitted from MSW Incineration. With increasing amounts of municipal waste produced during the rapid urbanization in China, more efficient technologies for waste reduction and disposal are urgently needed. Incineration of solid waste contributes significantly to the overall global emission of antimony. Pacyna and Pacyna7 estimated that the atmospheric Sb emissions from MSW incineration were 235 t in mid-1990, accounting for 15% of the global emissions. In 2009, the statistical volume of the consumption of municipal wastes collected and transported are 157 million metric tons, but only 12.9% (about 20 million metric tons) are disposed of by incineration.22 Here, we estimate that Sb emissions from MSW incineration are 60.7 t (Table 1), accounting for only 7.4% of the national total Sb emissions. 3.1.4. Brake Wear. With the gradual removal of asbestos from brake pads in the 1980s and its partial replacement by Sb2S3, antimony has become one of the most highly enriched elements in urban dusts.12,35 Antimony emissions from mobile sources has been reported as an important source. In Stockholm, for the year 2005, it is reported that the Sb emissions from brake linings were 710 kg/year.35 Iijima et al.30 estimated that the amount of Sb emitted to the ambient air in Japan may be 21 t in 2005. Increased concentration of Sb in soil, sediment, and biota which is associated with road traffic has been reported.36,37 The use of Sb in friction material is even suspected to pose a human cancer risk.38 In 2009, there were 62.7 million civil vehicles owned in China,22 and we assume that brake pads containing Sb account for 60% of the total pads.39 Thus, the number of vehicles with Sb-containing brake pads is estimated to be 37.6 million, and 22.2 t (Table 1) of Sb may be emitted to the ambient air as brake abrasion dust from vehicles. Therefore, with the rapid expansion of vehicle volume in China,22 we should pay more attention to vehicular traffic, which is one of the main sources of antimony in urban areas. For example, the present vehicle ownership rate is 229 per 1000 inhabitants in Beijing, and the total vehicle population is estimated to have exceeded 5 million by the end of 2011.22 Thus, brake pad wear has become the leading local source category for Sb emissions. 3.1.5. Total Antimony Atmospheric Emissions. The aggregated estimates for antimony emissions from all anthropogenic sources in 2009 are summarized in Table 1 by province. As can be seen, the final national gross emissions of Sb are calculated at 818.0 t, and the five provinces with largest emissions are demonstrated to be Guizhou (77.0 t), Hunan (69.8 t), Henan (58.1 t), Shandong (49.1 t), and Guangxi (41.8 t). The largest source contribution, 61.8% of the total Sb, comes

iron and the steel smelting processes, to avoid double-counting with the emissions from the coal combustion category. 2.2. Data Sources of Activity Levels. Coal consumption by sectors and types of coal products is provincial-level data compiled from China Energy Statistical Yearbooks.31 Materialyield data by provinces (e.g., the output of ferrous/nonferrous metals products, volume of municipal wastes burned, and number of vehicles) are compiled from China Statistical Yearbooks and the Yearbook of Nonferrous Metals Industry of China.22,23 Trends of activity levels by different sectors in China between 2005 and 2009 can be seen in Supporting Information Figures S1−S5.

3. RESULTS AND DISCUSSION 3.1. Estimates of Antimony Atmospheric Emissions in 2009. 3.1.1. Sb Emitted from Coal Combustion. The concentration of antimony in coal is generally low (the Sb content in most of the world’s coals is between 0.05 and 10 μg/g,32 only parts per million), but in light of the large throughputs of coal in combustion, the potential environmental risk may be significant. Here, the national total emissions of Sb from coal combustion in 2009 are estimated at 505.3 t (see Table 1). By the end of 2009, the total installed power capacity in China reached 874 GWe, and 74% are coal-fired power plants.33 Coal consumption of coal-fired power plants is 1633 million metric tons, and the resultant atmospheric Sb emissions are estimated at 105.7 t (Table 1). At the provincial level, the five provinces with largest Sb emissions from coal-fired power plants are Shandong, Guizhou, Guangdong, Jiangsu, and Inner Mongolia. This is due to the very substantial coal consumption (e.g., Shandong, Inner Mongolia, and Jiangsu) and high Sb content in the raw coals produced and consumed (e.g., 6.01 μg/g for Guizhou and 2.33 μg/g for Guangdong; see Table S2 in Supporting Information). Industrial coal burning is the largest single sector, with Sb emissions of 299.7 t (Table 1), accounting for 36.6% of the total Sb emissions in 2009. This may be attributed to the following reasons: coal consumption of the industrial sector reached 1777 million metric tons by 2009, and the sector contains a significantly higher share of boilers with inadequate air pollution control devices compared to power plants, leading to the high final discharge rate of Sb from the stacks. Coal consumption for the residential sector decreased slightly in recent years, mainly due to fuel substitution with natural gas, liquefied petroleum gas, and electricity, especially in urban areas. The major combustion sources for residential sectors are cook stoves firing briquettes or lump coal and with very few SO2 or PM control devices installed. However, there is little information about the emission factor of Sb from Chinese residential cook stoves. The emission factor we use18 is cited from AP-42, which is suitable for the United States or Australia and so is considered to be of low reliability when applied to the Chinese situation. Because of the reasons above, the residential sector contributed only 0.1% of total Sb emissions in 2009. Coal consumption for farming, construction, transportation, and commerce are combined together as other uses. We estimate that the combined Sb emissions from other uses in 2009 are 98.8 t (Table 1). Therein, Guizhou Province is featured with the highest Sb emission from other uses sector (39.1 t) at the provincial level, mainly owing to both the high Sb content in the raw coals and the large magnitude of coal use. 3.1.2. Sb Emitted from Nonferrous Metals Smelting and Pig Iron and Steel Production. Nonferrous smelting 3976



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efficiency and production technology in the process of nonferrous metals smelting in China. Currently, MSW incineration installation in China is growing rapidly, especially in the last five years, which has caused the Sb emissions from waste incineration to increase rapidly. Because waste materials typically contain high concentrations of Sb impurities that will be transformed during combustion, the flue gases need to be cleaned effectively in order to avoid harmful heavy metals release to the environment. In view of the potential adverse effects on human health and the gradually growth trend of Sb emissions during the past years, comprehensive control policies should be promulgated and implemented to further restrain Sb discharge from fuels combustion and industrial production processes, especially to obtain Sb abatement cobenefit by strengthening further PM and SO2 control from coal combustion in industrial boilers and the nonferrous metals smelting enterprises. 3.3. Spatial Distribution. Compared with point sources, the location of area sources is difficult to determine. Area source pollution in the atmosphere can better reflect the regional background value, while the most polluted areas are always concentrated around the large point sources (such as large coal-fired power plants, steel mills, and nonferrous metal smelters).41,42 Consequently, emissions of Sb from large point sources should be highlighted for their potential harmful impacts on the local environment and public health. In this study, antimony emissions from point and area sources were spatially distributed within the grid system of 30 min × 30 min, according to the following procedures. It should be noted that (1) the point sources are all precisely located at their latitude/longitude coordinates; (2) about these point sources, we distribute the total emissions of each province to each plant evenly based on the activity levels (coal consumption, smelting capacity, output of metals, MSW treatment capacity) of individual plant, and accounted for the specific combustion and control technology configuration for power plants (source: China Pollution Source Census); and (3) here the calculations of the Sb emissions from large ferrous/ nonferrous smelting plants have incorporated the associated coal combustion emissions due to coal consumption for these point sources, accounting for a significant portion of industrial coal consumption. 3.3.1. Point Sources. The geological distribution of point sources is illustrated in Supporting Information Figure S6. In this study, most power generation units (∼1800 power plants) with capacity larger than 6000 kW in China are identified as point sources, which contribute about 80% of the total coal used in power plants, while other miscellaneous plants are treated as area sources. These point source power plants were estimated to emit 86.4 t of Sb, and most of them are located in the east central, northeast, and coastal regions of industrialized China (especially in Shandong province). The total Sb emissions from copper smelting in 2009 are estimated at 72.6 t. Here, we deal with 47 large copper smelting plants as point sources, which contribute about 61% of the total copper smelting capacity, while other miscellaneous plants are treated as area sources. Most of these large point plants are located in Shandong, Anhui, Yunnan, and Jiangsu provinces. These large-scale copper smelting plants emitted 44.5 t of Sb altogether. Guixi Smeltery, located at Jiangxi province, is the largest copper smelting plant in China and has been active for over 20 years, resulting in significant pollution to the local environment.43

from coal combustion, followed by 26.7% from nonferrous metals smelting and 7.4% from MSW incineration. 3.2. Historical Trend of Sb Emissions in China and Possible Control Measures. The historical trend of Sb emissions by different economic sectors from 2005 to 2009 is summarized in Figure 2. Since the introduction of 11th five-

Figure 2. Historical trend of atmospheric Sb emissions by sectors in China, 2005−2009. CCIB, combustion of coal by industrial burners; CCPP, combustion of coal by power plant boilers; CCRS, combustion of coal by residential sectors; CCOS, combustion of coal by other sectors; CS, copper smelting; LS, lead smelting; ZS, zinc smelting; AS, antimony smelting; PISP, pig iron and steel production; MSWI, municipal solid waste incineration; BW, brake wear.

year-plan after 2005, atmospheric emissions of Sb in China have begun to grow at a more moderate pace in spite of the continuing rapid coal consumption and the increased output of industrial products. The national total atmospheric emissions of Sb in China from 2005 to 2009 are estimated at 716, 726, 742, 774, and 818 t, respectively. As can be seen, Sb emissions from coal-fired power plants have declined in the period from 2005 to 2009. We believe this is mainly due to the substantial installation of FGD in power plants to reduce SO2 emissions under new requirements of central and local government since the introduction of 11th five-year-plan after 2005. By the end of 2009, the FGD installed capacity reached 461 GWe, accounting for about 71% of total coal-fired power plants installed capacity. In comparison, the FGD installed capacity was only about 39 GWe by the end of 2005.40 As mentioned in our previous study, Sb emissions from large-scale power plants can be effectively abated by the existing dust collectors and FGD systems.18 Accordingly, the final discharge of Sb from power plants has decreased substantially during these recent years, even as the amount of coal burned by power plants has caught up with that burned by the industrial sector. In contrast, the emissions from industrial coal burning sectors are still experiencing a rapid increase, at an annual growth rate of 8.1% from 2005 to 2009, owing to the growing coal use and lower penetration of advanced PM and SO2 control devices. For nonferrous metals smelting, despite the increasingly significant production in recent years, Sb emissions from this category show a slowdown in growth. This can be mainly attributed to significant improvement of emission control 3977



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point sources are highly concentrated in Henan, Hunan, Yunnan, Guangdong, and Jiangsu provinces, where extensive smelting activities occur. Although these point sources contribute less than half (41.2%) of national total Sb emissions, they will substantially elevate the local Sb concentration in the atmosphere and easily cause poisoning accidents and human health problems in the vicinity of these industry and combustion sources, because workers and inhabitants normally receive long-time exposure to relatively higher local Sb concentrations compared to the widespread Sb release from area sources. 3.3.2. Area Sources. Apart from the emissions from 2188 point sources discussed above, the remaining emissions from other combustion and industrial sources are all treated as emissions from area sources on the provincial level. Sb emissions from area sources are 481.1 t altogether, accounting for 58.8% of national totals. Unlike the point sources, area source emissions cannot be directly assigned to any specific geographical location due to lack of specific location and activity information. Figure 4 shows the spatial distribution of

Some large-scale lead and zinc smelting plants (50 plants for lead and 59 plants for zinc) in China are identified as point sources, which contribute about 71% and 68% of the total lead and zinc smelting capacities and were estimated to emit 72.0 and 22.0 t of Sb, respectively. Most of these point-source lead and zinc smelting plants are located in Henan, Yunnan, Hunan, and Guangxi provinces. All other small-scale plants are treated as area sources. China is the largest producer of Sb, with approximately 90% of the world’s share in 2009.44 Antimony reserves in China are concentrated in Guangxi, Hunan, Yunnan, and Guizhou provinces. Xikuangshan, located near Lengshuijiang City, Hunan Province, is the largest Sb producing area in the world and is well-known as the “World Capital of Sb”. It is believed that Sb pollution from this particular area is very severe, resulting in serious Sb contamination and posing significant health threats to the local inhabitants.45,46 In this study, all of the antimony smelting plants (about 180) are identified as point sources, and most of these smelting plants are concentrated in Hunan, Guangxi, Yunnan, and Guizhou provinces. We deal with 39 large iron and steel plants as point sources, and other plants are treated as area sources. These large iron and steel plants together emitted 38.9 t of Sb, mainly owing to coal consumption for this category, accounting for a significant portion of industrial coal (especially coke) consumption.31 Stack gas generated from Sb products released by MSW incineration also becomes a very important source of Sb emissions in China. The first incineration plant in China was put into operation in 1987 at Shenzhen. By the end of 2009, there have been a total of about 90 MSW incineration plants, with treatment capacities of approximately 0.07 million metric tons per day.22 Most of these plants are concentrated in Zhejiang, Jiangsu, and Guangdong Provinces. Here, all of the MSW incineration plants are identified as point sources. Through careful location determination and verification, all point source emissions are allocated into the various grid cells according to their geographical coordinates. Figure 3 shows the spatial distribution of point antimony emissions in China in 2009 at a resolution of 30 min × 30 min. A total of 2188 point sources are described in the emission inventories with total associated emissions of 336.9 t of Sb in 2009. Emissions from

Figure 4. Gridded Sb emissions from area sources for the year 2009 (30 min × 30 min resolution; units, kilograms per year per grid cell).

area antimony emissions in China in 2009 at a resolution of 30 min × 30 min from all area sources combined. Normally, most grids are composed of part or all of several counties. The emissions from industrial sectors (include the area sources of coal combustion from industrial sector, nonferrous metal production sector, and pig iron and steel production sector) are first divided into each county with the proportion of industrial GDP in one province, and then allocated to each grid according to the share of each county area in one grid. The emissions from residential coal use, other coal use sectors, and brake wear are first divided into each county according to the proportion of populations in one province and then allocated to each grid with the share of each county area in one grid. As can be seen from Figures 3 and 4, antimony emissions in China are distributed very unevenly due to the remarkable difference in economic and energy consumption structure, degree of development, and density of population, as well as regional point and area sources distribution of each province. We find that Sb emissions are mainly concentrated in the southwestern (particularly Guizhou province), eastern, and coastal provinces in China. Besides, several provinces such as

Figure 3. Gridded Sb emissions from point sources for the year 2009 (30 min × 30 min resolution; units, kilograms per year per grid cell). 3978



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Table 2. Uncertainties of Sb Emissions by Sectors in China, 2009a uncertainties

a

uncertainties

category

mean

range

category

mean

range

coal combustion nonferrous metals smelting pig iron and steel production

505 219 11

399−604 (−21%, 20%) 143−417 (−35%, 90%) 6−113 (−49%, 907%)

municipal wasters incineration brake wear total

61 22 818

55−139 (−10%, 129%) 5−47 (−77%, 113%) 730−1142 (−11%, 40%)

Emissions are given in metric tons per year. The percentages in parentheses indicate the 95% confidence interval (CI) around the central estimate.

anonymous reviewers for their valuable comments and suggestions on our paper.

Guizhou, Hunan, and Guangxi stand out in coal-related Sb emissions due to the high Sb content of raw coal mined and consumed in these provinces. Mainly owing to the distinct variation of the Sb content of raw coal in different districts, the allocation of the total Sb emissions is very different between one district and another. Thus, strengthening Sb emissions reduction is urgently needed from coal-burning sources and nonferrous smelting plants in these high Sb coal regions. 3.4. Uncertainty Analysis. Monte Carlo simulation is used to quantify the uncertainty in our Sb emission estimates depending on available activity data and emission factors distribution. The input parameters of activity levels and emission factors, with corresponding statistical distributions, are determined depending on the authors’ judgment or to the related published literature.47,48 See the Supporting Information for more details. The ranges of Sb emissions from all major categories with uncertainties are listed in Table 2. The overall uncertainties in our inventories are estimated at −11% to 40%. The coal combustion category is estimated to have the smallest uncertainty due to narrow classification of source types and relatively high data quality. In contrast, relatively higher uncertainties can be observed in the remaining categories. The high Sb emission uncertainties for these industrial processes mainly results from inadequate source information and limited field test data in China. Owing to the large variety of smelting processes and installed pollution control technologies, adopting an average value of emission factors for these industrial processes provides just a preliminary estimate and may lead to under- or overestimation of the Sb emissions from some specific sources. For a more reliable estimation of atmospheric Sb emissions, long-term field testing and continuous monitoring at all kinds of combustion facilities and industrial processes in China should be considered.

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ASSOCIATED CONTENT

S Supporting Information *

Four tables and six figures as described in the text. This material 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 funded by the National Natural Science Foundation of China (20677005, 40975061, 21177012) and the Beijing Natural Science Foundation (8113032). We are grateful to Mr. Freed, C.N. of US EPA for providing helpful advice to improve our paper. Also, we thank the editors and the 3979



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Anthropogenic Atmospheric Emissions of Antimony and Its Spatial

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