A Comprehensive Global Inventory of Atmospheric Antimony

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A Comprehensive Global Inventory of Atmospheric Antimony Emissions from Anthropogenic Activities, 1995−2010 Hezhong Tian,*,†,§ JunRui Zhou,† Chuanyong Zhu,† Dan Zhao,† Jiajia Gao,† Jiming Hao,‡,§ Mengchang He,† Kaiyun Liu,† 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 10084, China § State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China S Supporting Information *

ABSTRACT: Antimony (Sb) and its compounds are considered as global pollutants due to their health risks and long-range transport characteristics. A comprehensive global inventory of atmospheric antimony emissions from anthropogenic activities during the period of 1995−2010 has been developed with specific estimation methods based on the relevant data available for different continents and countries. Our results indicate that the global antimony emissions have increased to a peak at about 2232 t (t) in 2005 and then declined gradually. Global antimony emissions in 2010 are estimated at about 1904 t (uncertainty of a 95% confidence interval (CI): −30% ∼ 67%), with fuel combustion as the major source category. Asia and Europe account for about 57% and 24%, respectively, of the global total emissions, and China, the United States, and Japan rank as the top three emitting countries. Furthermore, global antimony emissions are distributed into gridded cells with a resolution of 1° × 1°. Regions with high Sb emissions are generally concentrated in the Southeastern Asia and Western Europe, while South Africa, economically developed regions in the eastern U.S., and Mexico are also responsible for the high antimony emission intensity.



INTRODUCTION Antimony (Sb) and its compounds have been widely used in industrial production and daily life since the rapid development of industry in the 19th century.1 However, antimony is a chronic toxic element even at a very low concentration and is carcinogenic at long-time exposure.2 It commonly attaches to particulate matter in the form of Sb (III), Sb (V), and Sbcontaining nanoparticles.3 Previous studies indicated that ambient antimony concentrations in urban Canada, the United States, Europe and other areas were at ranges of 13−125 ng/ m3, 0.5−171 ng/m3, 2−470 ng/m3, and 7−36 ng/m3, respectively, dramatically higher than concentrations found in remote and rural areas (0.0008−7 ng/m3).4−7 Filella et al. indicated that about 58% of the total atmospheric antimony emissions originated from anthropogenic activities.8 In the nature, antimony is commonly enriched in coals and fossil fuels. Antimony concentrations in coals throughout the world are at a range of 0.05−10 ug/g,9,10 and the worldwide average concentration is estimated about 1 ug/g.11,12 As a kind of semivolatile elements, high temperature process helps to increase the evaporation rate of antimony.13 Therefore, fuel combustion is considered to be the most important anthropogenic activity emission source.8 With an atmosphere residence time of 1−2 weeks, anthropogenic activities have © 2014 American Chemical Society

imposed a substantial influence on the worldwide geochemical cycle of antimony.14−18 Antimony has aroused a wide concern among the public as a global pollutant. Studies of atmospheric emission inventories of antimony started in the early 1980s.19,20 Nriagu and Pacyna first calculated global emissions of 16 trace elements including antimony from industrial sources for the reference year of 1995.21 Some countries have established their national emission inventories (EI) for various hazardous air pollutants, however, only the national emission inventories (NEI) of U.S. and the National Pollutants Inventory (NPI) of Australia have covered the trace element antimony.22,23 Researchers from several countries have also carried out relevant quantitative researches about antimony emissions from various sources.24−28 During the past decade, the distribution pattern of the world economy and energy use has experienced a profound transformation. Nevertheless, the antimony emission inventory on a global scale has not been updated for a long time. The purpose of this article is to summarize the best currently Received: Revised: Accepted: Published: 10235

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power plant sector; industrial coal combustion sector; residential coal use sector; and other coal use sector. Then, the final discharge of Sb emissions from various fuel combustion facilities is estimated by considering the average antimony content in consumed coal, annual amount of consumed coal and the removal efficiencies of various installed air pollution control devices.24,25 The calculation methods for each region by source category are summarized in Table 2. 2.2. Temporal Varied Emission Factors. Although industrial production is growing dramatically each year, the technology for the industrial manufacturing processes has improved significantly and pollution controls have been popularized especially in the fuel combustion and industrial production process sectors. Consequently, it is necessary to adopt suitable dynamic emission factors to calculate annual antimony emissions so as to better reflect the temporal transition of emission factors during the past 15 years. Streets et al. developed a dynamic representation to reflect Hg emission factors as that sector undergoes a transition of industry process emission sources.33 Nevertheless, due to the absence of antimony emission levels and activity data in specified reference years, as well as the different characteristics between Sb and Hg, it is not fully appropriate to apply it to this study. During the high temperature process of fuel combustion or industrial production, antimony is generally released to the atmosphere attached to particulate matter, and it exhibits increasing enrichment with decreasing particle size. Most of the antimony compounds are released to the atmosphere accompany with fine particulate matter instead of coarse particulate matter.6,34−37 We know that fuel combustion and materials production has grown year-by-yearsometimes dramaticallybut at the same time combustion and process technology has improved and pollution controls with ever increasing efficiencies have been adopted. So the resulting level of emissions at any given time reduces to a competition between production growth and control technology improvemen.25,33 In response of the gradually slow declining tendency of emission factors and the relevant data availability we presume that emission factors for fuel combustion and industrial production emission sources (fuel combustion, pig iron and steel production and nonferrous metals production) from 1995 to 2010 have declined generally in accordance with the exponential regression curve of PM10 (region 1, 2, 4) or dust (region 3) emissions per unit of activity level (data sources see Supporting Information (SI) Table S1).25,38−42 Moreover,

available information on activity level and emission factors, establish a new global antimony emission inventory for the year of 2010 with high spatial resolution and present the historical trend of global antimony emissions from 1995 to 2010.

2. METHODOLOGY AND DATA SOURCES 2.1. Countries Classification and Estimate Methods. Generally, atmospheric antimony emissions from various anthropogenic activities can be assessed from 5 large source categories: fuel combustion (FC), nonferrous metals production (NMP), pig iron and steel production (PISP), waste incineration (WI), and brake wear (BW). In order to obtain a more accurate inventory, the appropriate countries are classified into four regions with similar levels of technology development (see Table 1). Antimony emissions of countries in each region are calculated by specified emission factors and estimation methods. Table 1. Countries Classification by Regions regions Region Region Region Region

1 2 3 4

countries United States Japan OECD Europe countries other developed countries except region 1 countries China other developing countries except China

The resultant Sb emissions from five emission source categories are estimated by using emission factor calculation equations; specific comprehensive emission factors (EF) are multiplied by annual activity data (fuel consumption or industrial products yields).21,24,25 With regard to fuel combustion, several specific estimate methods are employed for different regions. For regions 1 and 2, substantial installations of high-efficiency particulate matter (PM) and SOx control facilities have been adopted to reduce PM and SO2 emissions in coal-fired power plants.29−32 Therefore, antimony emissions from power plants are estimated separately according to the emission factors per unit of electricity generation for region 1 and 2. Emission factors per unit of coal consumption are adopted to calculate Sb emissions from other (nonpower plant) stationary coal combustion facilities in region 1 and 2, as well as Sb emissions from all coal combustion sources in Region 4. For Region 3 China, due to the detailed information available, coal combustion is further classified into four subcategories: the

Table 2. Methods of annual Sb Emissions Estimation for Regions by Source Categorya emission sources fuel combustion

world regions

estimation equation

Region 1, 2

electricity generation: E(t ) = MEG(t ) × EFEG(t )

(1)

other stationary coal combustion: E(t ) = MCC(t ) × EFCC(t ) Region 3

E(t ) =

∑ ∑ Ci ,j(t )Mi ,j(t )R i ,j(1 − PPMj)(1 − PFGDj) j

i

other four emission sources

Region 4

E(t ) = MCC(t ) × EFCC(t )

Region 1, 2, 3, 4

E=

∑ ∑ Mm,n(t )EFm,n(t ) m

n

(2)

(3)

(4) (5)

a E: Annual emissions of antimony; M: Annual activity level (material feed or industrial product yield); EF: Specific average emission factor. C: Average content of Sb in consumed coals; M: Amount of consumed coals; R: Release ratio of Sb in flue gas for each type of coal-fired facility; PPMj: Removal efficiency of Sb for each type of PM control equipment; PFGDj: Removal efficiency of Sb for each type of SO2 control equipment (flue gas desulfurization). EG: Electricity generation; CC: Coal combustion; i: Each province in China; j: Each subgroup classified with different configuration of coals, consumer sectors; m: Each world region; n: Each subcategory of emission sources; t: reference year.

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estimate the yearly variation of Sb-containing brake pads since 2000 by assuming a declining exponential regression curve based on available information for all regions,25,27,50 which is shown in SI Figure S2. With regard to Region 3 (China), various parameters used in eq 3 can be referred to our previous works.24,25 The calculated emission factors for various source categories in 2010 from regression equations in this work are summarized in SI Table S2. 2.3. Statistical Activity Level Data. The annual consumption of raw materials and the annual production of industrial products from 1995 to 2010 are collected and compiled from statistics of relevant countries or international organizations. The sources of statistical data on the annual activity level are listed in SI Table S3. Detailed statistical data of each continent and the top 50 emitting countries in 2010 are also summarized in SI Table S4 and Table S5; statistical data of various source categories for various continents from 1995 to 2010 are illustrated in SI Figure S3−Figure S8. 2.4. Quantifying Uncertainty. Monte Carlo simulation is adopted to quantify the uncertainties in our global Sb emission inventory depending on available activity data and emission factors distribution.24−26,51 The input parameters of specific activities and emission factors, with corresponding statistical distributions, are determined based on the uncertainties method introduced in EEA/EMEP emission inventory guidebook 2013 or related published literatures.51−53 By means of 1000 times repeated sampling, uncertainties of statistic data on activity level and emission factors are transmitted to the output via simulation equations. Detailed information about the input parameters and results (expressed as the lower and upper bounds around a central estimate) are listed in SI Table S6 and Table 4.

Sb emissions from various fuel combustion sources in China are estimated by integrating our previous work with eq 3 in Table 2.24 Figure 1 presents the annual temporal variation trend of

Figure 1. Annual temporal trend of PM10 or dust emissions from nonferrous metals production per products output for varied regions22,23,43−45

PM10 or dust emissions from nonferrous metals production per products output for varied regions. Annual temporal variation trend of PM10 or dust emissions from other source categories per unit of activity level for varied regions during the period of 1995 to 2010 are put in the separate SI Figure S1.22,23,43−45 According to the development level of different regions, emission factors of fuel combustion, pig iron and steel production and nonferrous metals production in each world region for the initial reference years are assumed and shown in SI Table S1. From these, we can estimate the value of emission factors in each year with the regression curves shown in Figure 1, SI Figure S1. The average concentration of antimony in municipal solid waste (MSW) is estimated at a range of 10−60 g/t. When wastes are being incinerated, about 50% of the antimony stays in the bottom ash while 33−74% of antimony is discharged along with fly ash into the atmosphere.46,47 An emission factor of 3 g/t for municipal solid waste is regarded as a suitable assumption.21,25 Sb2S3 is widely used in brake linings as lubricant of friction materials and a high temperature binder. Previous studies demonstrated that antimony emissions from traffic sources mainly come from brake wear rather than vehicle fuel combustion.48 However, use of the mileage-based emission factor is not really practical because the release of the brake abrasion dusts occurs only during braking.49 Therefore, we assume an emission factor of 0.59 g/car/year which is deduced by analysis of abrasion dusts.27 Non-Sb brake pads have been introduced to the vehicle market since 2000, however, few studies have estimated their use on in-use vehicles.50 We

3. RESULTS AND DISCUSSION 3.1. Comparison with Estimates of Other Studies.21−23 By combining the annual activity levels of various source categories and specific temporal-varied emission factors, the historical trend of global Sb emissions from 1995 to 2010 are estimated. The comparison with estimates from other studies is shown in Table 3. The difference of global Sb emissions estimation in 1995 between Pacyna et al. and this work can be due to two main reasons. (1) New classification of the world regions and specific emission factors are applied in this work. Since the installation of emission control equipment in developed countries has a significant development, particularly highly efficient electrostatic precipitators beginning

Table 3. Estimate of Annual Sb Emissions from Various Studies (t/yr)a estimation in this study

a b

Pacyna et al.(2001)

NEI

NPI

regions and years

global 1995

U.S. 2008

Australia 2010

global 199521

U.S. 200822

Australia 201023

FCc NMP PISP BW WI other total

829 584 9 357 299

9 7 1 91 86

2 5 0b 5 1

730 553 7

8.7 4 0.5

0.6 2.3 0b

272

2080

194

13

1562

0.4 49.6 63.2

0b 4.6 7.5

FC: fuel combustion; NMP: nonferrous metals production, PISP: pig iron and steel production; WI: waste incineration; BW: brake wear. Emissions are under the significant digit of the tabulated data instead of no emission. cOil combustion is not considered. 10237

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in the 1980s and FGD technologies toward the end of the 1980s while the implementation of emission control devices in power plants in the developing countries started in the second half of the 1990s.54 It is obvious that emission factors used to calculate different regions present significant difference from each other. However, Pacyna et al. calculated each emission source mainly based on average emission factors for all countries of the world. This would possibly underestimate emissions of developing countries, especially for coal combustion. (2) Brake wear is not included in the former studies by Pacyna et al. However, it has been confirmed to be the main source of antimony emissions from traffic, and cannot be ignored for the global antimony emissions calculation.27,28,48 With regard to nonferrous metals production category, Sb production is also taken into consideration in this work, but is not considered in Pacyna et al., 2001.21 In general, Sb emissions from fuel combustion, nonferrous metals production and pig iron and steel production of the United States in 2008 that are estimated in this work are considered consistent with those reported by NEI within the range of estimation uncertainties. However, brake wear is also not included in NEI studies. As the country with the largest vehicle population, the United States is estimated to be the largest global emitter of brake wear particles in this research, which may need further investigation for improved reliability. Meanwhile, a waste incineration assessment conducted by the United States only covers medical incineration rather than municipal solid waste. This is an important omission and may lead to the possible underestimation of antimony emissions in United States. The situation is similar for the NPI in Australia. It is worth mentioning that Sb emissions from other emission sources are included in the NEI and NPI, including other fuel combustion pathways, NEC (not elsewhere classified) industrial process, nonindustrial NEC, solvent and more. However, owing to data unavailability, these miscellaneous emission sources are not discussed in this research but should be investigated in depth in the future work. 3.2. Historical Trends of Global Sb Emissions. During the past 15 years, antimony emissions on a global scale have fluctuated slightly from about 2008 tons in 1995 to about 2035 tons in 2002 due to the Asia financial crisis, and then increased to an emission peak at about 2232 tons in 2005, but decreased gradually to about 1904 tons in 2010 (see Figure 2). Transition of Sb emissions is mainly influenced by the variation of Sb emissions from fuel combustion and nonferrous metals production. With the strengthening of atmospheric contamination control in developing countries, especially China and India in the recent 5 years, emissions from fuel combustion have declined steadily. Emissions from nonferrous metals production have decreased gradually mainly because of the development of manufacturing technologies and the popularization of emission control devices during these 15 years from 1995 to 2010. Emissions from brake wear have been declining since 2001 with the increasing use of non-Sb containing brake pads. With the generation volume of world municipal waste and the proportion of MSW incineration growing steadily, emissions from waste incineration have continued rising. In terms of continental contribution variation, Asia dominates the global antimony emissions trend and it is responsible for over 45% of the total antimony emissions. Over half of the Asian Sb emissions are emitted in the Chinese mainland. The historical trend of Sb emissions by sectors in

Figure 2. Trends of Sb emissions by (a) sectors and (b) world regions.

China during 1995−2010 is available in SI Figure S9. The fossil fuel demand in Asian countries has been increasing, but Sb emissions from fuel combustion have been gradually reduced in the past 5 years. This is directly related to the increased application of advanced PM and SO2 pollution control devices in Asia countries, especially the substantial installation of FGD in power plants and industrial boilers in China since the introduction of 11th five-year-plan after 2005. As mentioned above, most of the antimony compounds are adhered with fine particulate matter, which are partially escaped from ESP/FFs while some of them can be captured by the downstream FGD scrubber. Meij et al. (2007) reported that the average Sb capture efficiency by wet FGD were about 82.1% and the overall synergistic removal efficiency on Sb combining ESP with wet FGD can reached about 99.81%.30 3.3. Global Total Antimony Emissions in 2010. Estimates of global anthropogenic atmospheric antimony emissions for various continents are summarized in Table 4 and SI Figure S10. The largest antimony emissions component to the global atmosphere is from fuel combustion, mainly coal burned in power plants and other stationary combustion boilers. Fuel combustion is calculated to release about 803 t of antimony, which account for 42.2% to the worldwide total emissions of 1904 t in 2010. Of this, Asia with 625 t of antimony emissions contributes the majority of global antimony emissions from fuel combustion, mainly due to the enormous amount of coal consumed (about 65% of world total coal consumption). Waste incineration ranks as the second largest antimony emission source, which contributes about 23.9% to the global antimony emissions in 2010. With regard to the nonferrous metals production, antimony emissions mainly come from Cu production (∼173 t), followed by Zn (∼69 t), Pb (∼68 t) and Sb production (∼10 t) in 2010. Sb emissions from Cu production processes are mainly generated in Asia and South America while Sb emissions 10238

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Table 4. Constitution of Global Anthropogenic Emissions of Sb in 2010 and Their Uncertainties (In Tons)a continents

FC

NMP

PISP

WI

BW

total

Africa Asia Oceania Europe (including Russia) South America North America total

42 (31, 55) 625 (524, 781) 2 (1, 7) 114 (89, 138) 8 (6, 12) 11 (7, 21) 803 (675, 1011)

7 (3, 9) 173 (102, 228) 6 (4, 13) 45 (24, 61) 68 (18, 79) 21 (15, 35) 320 (209, 416)

0b (0b, 2) 7 (5, 13) 0b (0b, 1) 2 (1, 4) 0b (0b, 3) 0b (0b, 2) 9 (8, 19)

0b (0b, 3) 194 (73, 458) 0b (0b, 1) 177 (67, 403) 0b (0b, 2) 83 (30, 195) 455 (171, 1048)

3 (1, 5) 80 (28, 143) 6 (2, 12) 111 (41, 207) 16 (6, 31) 100 (38, 193) 318 (118, 589)

52 (29, 87) 1079 (874, 1329) 14 (9, 26) 448 (311, 689) 93 (45, 171) 216 (141, 351) 1094 (788, 1827)

a

FC: Fuel combustion; NMP: Nonferrous metals production, PISP: Pig iron and steel production; WI: Waste incineration; BW: Brake wear. Uncertainties are expressed as the lower and upper bounds around a central estimate. bEmissions data is under the significant digit of the tabulated data instead of no emission.

waste in weight and volume, incineration of waste has been extensively adopted in the regions where the economy is developed and the country’s land territory is relatively small. This leads to it to be the largest emitting sector in Japan and Germany. India has witnessed a tremendous increase of energy consumption in the last decades with its rapid economic development and population growth. Coal consumption in India has increased from 298.8 million tons in 1995 to 601.2 million tons in 2010. Further, approximately 70% of electricity generation in India comes from coal-based thermal power plants, and few plants are equipped with flue gas desulfurization (FGD) system.58 Consequently, antimony emissions from coal combustion also occupy the largest fraction in the total Sb emissions of India. More details about antimony emissions from the top 20 countries (accounting for about 87% of the global total emissions) and their uncertainties in 2010 are presented in SI Table S7. 3.5. Geographical Distribution of Global Sb Emissions. The worldwide antimony emission inventory is geospatially distributed within a global 1° × 1° latitude/ longitude grid; emissions of countries with vast geographical area like China, the United States, Russia, Canada and India are divided into state or province level units according to relevant surrogates, such as regional GDP by industry and population, as shown in Figure 3.

from Pb, Zn and Sb production largely come from Asia (see SI Figure S11 and Figure S12). The number of vehicles in use worldwide has reached about 943.3 million by the end of 2010. Because non-Sb brake pads have been adopted gradually since 2000, we assume that the Sbcontaining brake pads account for about 57% of the total pads in the reference year of 2010. As a consequence, 318 t of antimony is estimated to have been discharged to the atmosphere from worldwide brake wear. From a continental perspective, Asian countries emit 1079 tons of antimony, contributing about 56.7% of the global antimony emissions in 2010, followed by Europe (∼23.5%) and South America (∼11.3%). Moreover, there are great differences of contribution by various emission sources in each continent (see SI Figure S10). This may be mainly attributed to the diversity of economic and energy structures, difference of industrial capacities and advancement of pollution control technology among various continents. 3.4. Top 10 Largest Emitting Countries. The top 10 largest emitting countries (China, the United States, Japan, India, Germany, Russia, Chile, France, Poland, South Africa) account for about 73% of the global antimony emissions in 2010 (see SI Figure S13). China is the largest emitter of antimony worldwide, with about 649 t of antimony emissions in 2010. Among the fuel combustion sources, the industrial coal combustion sector with 214.4 t of antimony emissions contributes most, followed by other coal uses and power plant sectors. It is noteworthy that, even though the coal consumption by power plants in 2010 is 10.6 million tons more than that in 2009, antimony emissions from the power plant sector in 2010 are nearly equal to the emissions in 2009.25 This can be mainly attributed to the proportion of installed wet FGD capacity of power plants that grew from 71% in 2009 to 77% in 2010.55 Furthermore, as regard to the emissions of nonferrous metals production, Sb production is important in China. Currently, there are 114 Sb mines in 18 provinces or autonomous regions which make China the largest Sb producer in the world.56 There are about 246.7 million vehicles in use in the United States 2010, the largest vehicle stock of the world. Emissions from brake wear are calculated to be the leading Sb source in the United States in 2010. Meanwhile, the generation of MSW in the United States has grown steadily. At present, 88 waste-toenergy plants are located in 25 U.S. states and serve a population of 30 million.57 As a result, waste incineration is thought to be another important emission source in the United States, contributing about 80 t of Sb emissions. As a promising waste management practices which can generate energy and simultaneously reduce a large amount of

Figure 3. Global distribution of anthropogenic atmospheric emissions of Sb in 2010.

As can be seen, the regions with high Sb emission intensity are all concentrated in Southeastern Asia and Western Europe. As the largest emitter, China shows an obvious regional distribution characteristic of antimony emissions. High antimony emissions intensity mainly occurs in densely populated and industrialized regions of Mideastern and Southwestern China where most of thermal power plants and 10239

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nonferrous metals smelting plants are concentrated.20 Detailed information about the spatial distribution of point sources and the total antimony emissions of China in 2010 are available in SI Figure S14. In terms of countries with relatively small land area, Germany (71 t) and Poland (42 t) suffer from high atmospheric antimony contamination. This is mainly attributed to fuel combustion and waste incineration. In addition, due to nonferrous metals production, antimony pollution is also serious in coast countries of the Western South America such as Chile (51 t). Beyond that, South Africa, economically developed regions in the eastern U.S., and the Mexico are also responsible for the high antimony emission intensity. 3.6. Uncertainty Analysis. In this study, uncertainties of antimony emissions in 2010 have been quantified with Monte Carlo simulation. The overall uncertainty is estimated at a range of 788−1827 tons. Fuel combustion category and Asia are estimated to have the smallest uncertainties in various source categories and continents respectively (see Table 4). As regard to the brake wear category, the proportion of Sb-containing brake pads is another critical factor except for activity level data and emission factors. It is estimated to contribute uncertainties of emissions from brake wear at a range of 124−550 tons in 2010. As a result of statistics information limitation, emission factors for brake wear over the years have merely been calculated with the same variation trend for each region of the world, similarly, the emission factors for waste incineration are also simply considered as constant during the concerned time periods. These assumptions may bring large uncertainties for these two emission sources which merits further investigation in the future. This new updated comprehensive global Sb emission inventory as well as the temporal trend and spatial distribution characteristics, will provide indispensable input data for worldwide atmospheric transport, deposition and future abatement strategies of this important global toxic air pollutant. Nevertheless, much work on future emission scenarios projection and air quality modeling to link our inventory with the in situ observations is still needed in depth for the following research in order to obtain a more comprehensive understanding of the global atmospheric antimony contamination.



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ASSOCIATED CONTENT

S Supporting Information *

Tables S1−S7 and Figures S1−S14. This material is available free of charge via the Internet at http://pubs.acs.org/.



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AUTHOR INFORMATION

Corresponding Author

*Phone: 86-10-58800176; fax: 86-10-58800176; e-mail: [email protected]. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work is jointly funded by the National Natural Science Foundation of China (40975061, 21177012, and 21377012), the Open fund of 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). 10240

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dx.doi.org/10.1021/es405817u | Environ. Sci. Technol. 2014, 48, 10235−10241