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Atmospheric Environment 77 (2013) 725e737Contents lists availableAtmospheric Environment

journal homepage: www.elsevier .com/locate/atmosenvFluoride and sulfur dioxide indoor pollution situation and control incoal-burning endemic area in Zhaotong, Yunnan, China

Yonglin Liu a,b, Kunli Luo a,*, Ling Li a,b, Muhammad Zeeshaan Shahid b,c

a Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, ChinabUniversity of the Chinese Academy of Sciences, Beijing 100049, Chinac Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, Chinah i g h l i g h t s To provide the gaseous F and SO2 pollution level in the coal-burning fluorosis areas. Gaseous F and SO2 pollution in the baking room with open stoves is serious. Use calcined dolomite instead of clay can reduce F and S release greatly. It is a useful way to control gaseous F and SO2 pollution in the fluorosis areas.a r t i c l e i n f o

Article history:Received 7 November 2012Received in revised form10 May 2013Accepted 17 May 2013

Keywords:Coal-burning endemic fluorosisGaseous fluoride and sulfur dioxidepollution levelControl researchCalcined dolomitic siliceous limestone* Corresponding author. Tel.: 86 10 64856503; faxE-mail addresses: liuyl.10b@igsnrr.ac.cn, liu3

kunliluo@sohu.com (K. Luo).

1352-2310/$ e see front matter 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.atmosenv.2013.05.043a b s t r a c t

The presented study aims to investigate the gaseous fluoride and sulfur dioxide (SO2) pollution level in thekitchen, traditional flue-curing barn and outdoor environment and to find economically feasible methodto reduce fluorine and sulfur release. The gaseous fluoride and SO2 concentrations in air of outdoorenvironment, kitchen and traditional flue-curing barn were determined in 56 households in coal-burningendemic fluorosis areas of Zhaotong. Among these, 21 households in Yujiawan Village, Zhenxiong County,Zhaotong City were chosen for this experiment to reduce gaseous fluoride and SO2 concentration intraditional flue-curing barn air by using calcined dolomitic siliceous limestone (CDSL) instead of claymixed with coal. The result showed that: (1) gaseous fluoride and SO2 concentration in the outdoor air inMangbu Township area was 0.51 mg dm2,day and

Table 1The parameters of the portable gas detector.

Parameter Range Parameter Range

Sucking rate ofaspiratorpump

300 ml min1 Operatingenvironment

Temperature: 10 Cto 45 CHumidity: 90% RH(non-condensing)

Detectingrange

0.02e200 ppm Span drift 5% (F.S)/4 h

Accuracy 5% (F.S) Zero drift 2% (F.S)/4 h

Table 2F and total S in the fine coal, clay, CDSL and coal slime.

Elements No. S (%) F (mg kg1)

Fine coal MB4 2.94 124.5MB7 2.73 106.0MB39 2.11 99.8LD2 2.30 95.5LD5 2.10 115.8LD12 2.00 40.3

Clay MB33 0.14 1303MB35 0.03 178.0MB38 B.D 1214.0LD9 0.82 1181.0LD14 0.13 1663.0LD15 B.D 2422.0

CDSL MB 0.10 137.0LD 0.41 78.8

Coal slime MB3 2.10 161.0MB15 1.80 145.0MB31 1.80 157.0

Note: MB: Mangbu Town, Zhenxiong County, Zhaotong City; LD: XiaolongdongTown, Zhaoyang District, Zhaotong City; B.D: Below detection; CDSL: Calcineddolomitic siliceous limestone.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737726gaseous fluoride, sulfur dioxide (SO2) and suspended particles areemittedduring the coal burning (Andoet al.,1998;Dai et al., 2004; Jinet al., 2006). Exposure to indoor air pollution from the combustion ofcoal can causemany diseases including endemic fluorosis, arseniasisand respiratory diseases (Liang et al., 1993a; Ando et al., 1998;Finkelman et al., 1999; Jin et al., 2006; Zhang and Smith, 2007). Theindoor gaseous fluoride pollution in coal-burning endemic fluorosisareas in China have been studied in many areas, such as LongliCounty (Ando et al., 1998, 2001; Dai et al., 2004), Guiding County(Yanget al., 2010) inGuizhouProvince,WushanCountyof ChongqingCity (Liang et al., 1993b; Ando et al., 1998, 2001) and SouthernShaanxi (He et al., 2005). Zhaotong City of Yunnan Province is thetypical coal-burning endemicfluorosis area in China (Ye et al., 2004a,2004b, 2005a, 2005b; Sun, 2005; Cao, 2001; Luo et al., 2007, 2008).Liang et al. (1993a) have reported the indoor and outdoor gaseousfluoride andSO2 pollution inXiaolongdongTownship, ZhaotongCity.25 gaseous fluoride samples (46 mg m3) and 99 SO2 samples(1.72 mg m3) in the kitchen were collected and measured. But thetypes of stove used by households were not introduced and thegaseousfluoride andSO2 pollution level in the traditionalflue-curingbarn (baking room) was not studied. Wang et al. (2001) have deter-mined 20 gaseous fluoride samples (1.5 mg m3) in the kitchenwiththe improved coal stove in Qinggangling Village, Qinggang Town-ship, Zhaotong City. But there is no data available about the gaseousfluoride and SO2 concentration in the traditional flue-curing barn airwith the open stove.

The fluoride (F) content in coal in Zhaotong City was 77mg kg1

(Luo et al., 2007), that is similar to the Chinese average of 82mgkg1

(Luo et al., 2004; Ren et al., 2006), to the F average of 83 mg kg1 inWestern Guizhou (Dai et al., 2004) and to the world average of80 mg kg1 (Swaine, 1990). Therefore, the coal used by householdsin Zhaotong City is the low-fluorine coal. The F sources in endemicfluorosis area in Zhaotong City are the high fluorine clay as an ad-ditive for coal-burning and as a binder for briquette-making (Li et al.,1995; Luo et al., 2007, 2008). So, we need to know the gaseousfluoride and SO2 concentrations caused by low-fluorine coal (LFC)mixed with high-fluorine clay (HFCL) in Zhaotong City.

Ando et al. (1998, 2001) indicated that direct inhalationaccounted for 1.9e3.4% of total fluoride dose, 94.5e97.3% of totalfluoride exposure was caused from dietary food consumption andonly 0.8e2.1% of total fluoride dosewas caused fromdrinkingwaterin the coal-burning fluorosis area in Longli County of GuizhouProvince and Pengshui County of Chongqing City.

Therefore, it is clear that the F sources in endemic fluorosis areain Zhaotong City are the high fluorine clay as an additive for coal-burning and as a binder for briquette-making (Li et al., 1995; Luoet al., 2007, 2008). So, theoretically, if abandon the high-fluorineclay (HFCL) as an additive for coal-burning and as a binder forbriquette-making, the gaseous fluoride pollution in the traditionalflue-curing barn would be reduced dramatically in Zhaotong City.So, the gaseous fluoride and SO2 pollution levels in the traditionalflue-curing barn need to be determined.

Zhaotong City is one of the main areas of middle and high sulfur(S) coal producing area, and average S content of coal in Zhaotong is2.36% (Table 2). So, in the coal-burning endemic fluorosis areas, thesulfate SO42 and inorganic anions change to acidic compoundsvery easily in the moisture containing atmosphere, which is moreharmful to human respiratory system (Zhao, 1992; Liang et al.,1993a; An et al., 1995; Yan, 1996). Liang et al. (1993a) studied thatif high concentration of gaseous fluoride and SO2 coexisted in air, itwould exacerbate the endemic fluorosis. Thus SO2 pollution levelalong with the fluorine pollution from coal burning in coal-burningendemic fluorosis in Zhaotong also needs to study.

The technology of fluorine and sulfur retention with calcium-based materials in coal combustion had been studied in differentyears (Cao, 1992; Zhang et al., 2002; Liu et al., 2006; Yamada et al.,2008; Chen et al., 2009; Yang et al., 2010) and satisfactory resultshad been achieved.

Coal briquette in previous study is all honeycomb briquettes. Butin the rural area of Zhaotong City, local resident are more perfect touse the briquette that is only mixture of clay and coal together(Fig.A.1, Fig. 1), not shape up them as a special model like thehoneycomb briquettes, to bake the corn and chili, or for living used.

Domestic coal in Zhaotong is mainly crushed coal, accountingfor more than 70% of coal yield, and the price is only 1/3e1/2 of thelump coal. If the crushed coal is directly added into the coal stove inthe practical operation, it can cut off from the air, resulting in thefire to extinguish. Therefore, binder has to be added into thecrushed coal.

There is abundant carbonate rock-dolomite, dolomitic limestoneand limy dolomite in Zhaotong (Fig.A.2), which contain low con-tents of fluorine (Luo et al., 2007). We try to use the local lowfluorine calcined carbonate rock to instead of clay as a binder forbriquette-making. Theoretically, if using the low fluorine calcineddolomitic siliceous limestone (CDSL) instead of high fluorine claymixed with coal, the gaseous fluoride and SO2 concentration in thetraditional flue-curing barn air would declined markedly. So, weneed to know the both gaseous fluoride and SO2 concentrations inindoor air by low-fluorine coal (LFC) mixed with low-fluorine cal-cium-based materials in Zhaotong City.

This studywill focus on the following problems: 1), what are theindoor and outdoor gaseous fluoride and SO2 pollution level in theendemic fluorosis areas in the improved stove used area in Zhao-tong City. 2), what are the gaseous fluoride and SO2 pollution levelin traditional flue-curing barn (baking room) by open stoves tobake the corn and chili in Zhaotong City. 3), the gaseous fluorideand SO2 concentration in the traditional flue-curing barn in the

Fig. 1. The mode of baking corn and chili and building structure of traditional flue-curing barn.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737 727households after use the calcined dolomitic siliceous limestone(CDSL) instead of clay mixed with coal in Zhaotong City.

1.1. Study areas

Zhaotong is the typical karst region (Fig.A.2) in the Southwestarea of China. The major strata are Early and Later Paleozoic strataand Early Mesozoic strata, which are thousands meter carbonatedeposits (dolomite and limestone mainly). If this natural carbonaterock can be utilized, it not only makes full use of local materials, butalso reduces cost and secondary pollution in the industrial Ca-based sorbent production process. The Ca-based and Mg-basedmaterials are suitable for inconvenient traffic and economic less-developed mountainous areas in the Southwestern area of China.Fig. 2. Location map of the experimental sites. Note: Administrative division of China is dCounty (District), Township, Village (Administrative Village) and Natural Village (group).Yujiawan Village (Fig. 2) is located in Mangbu Township, about1 km northwest of Mangbu Town with average elevation 1625.8 m,mean annual temperature 10.8 C, annual rainfall 1388mmand frost-free period more than 250 days. Xiaolongdong Township (Fig. 2) islocated in the eastern of Zhaoyang District, Zhaotong City, about10.3 km from Zhaotong Urban Area. The elevation is from 1910 m to3152 m. The annual temperature is 11 C and the annual rainfall is750 mm. The frost-free period is more than 200 days. So, the town-ship is a typical cold indigent area. Group 22 (Fig. 2) is located in thesoutheast of Xiaolongdong Township, about 12 km from the Xiao-longdong Town. In two severe endemic fluorosis areas in Zhaotongthe improvedcoal stovewithchimney isused forheatingandcookingfrom1990s. Thepopularization test on reducingfluorine and sulfur influorosis areas was done in Yujiawan Village, Zhaotong City.ivided into six government levels, that is, Province, Prefecture-level city (Prefecture),

42

35

6

78

910

12

1113

1

1- colorimetric cylinder; 2-condensing tube; 3- high-temperature combustion furnace; 4-silica boat; 5-quartz tube; 6-push rod; 7-water mouth;8-explosion-

proof ball; 9-distillation flask;10-temperature adjusting slot;11-thermocouple;12-temperature controller;13-oxygen bottle

abc

Fig. 3. Combustion hydrolysis set to determine F content in solid samples.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e7377281.2. The mode of cooking and heating and baking foodstuffs

In most households of coal-burning fluorosis area, including thestudy households, fuels such as coal briquettes are burned inimproved stove (with furnace cover and chimney leading out of theroof) all day in the whole year for cooking and heating (Fig.A.3).Some households use the open furnace for cooking and heating.The corn and chili are usually baked by the open furnace (Fig.A.1) inthe traditional flue-curing barn (Fig. 1). Meanwhile, the study areais the indigent area in China. The study area is typical karstmountain area and has a complicated landform and physiognomy(Fig.A.2). The house structure is generally 2e3 m high ranch housewith 3 rooms connecting to each other, and each room is about 10e20 m2. Most of kitchen in many households are the living-room.The kitchen in some households is not only the living-room butalso the sleeping room. Even if the kitchen, the living-room and thebedroom are not the same room, they usually connect to each otherfor heating and saving energy. For the most part, the traditionalflue-curing barn (baking room) in Zhaotong City, Yunnan Provinceis separate and does not connect with other rooms. In addition, thekitchen is closed and is used as temporary traditional flue-curingbarn and it also does not connect with other rooms in the harvestseason.

2. Experiment and analytical method

2.1. Sampling method of gaseous fluoride and SO2 in air

To determine gaseous fluoride in the air, lime-paper sampling(LTP) was used (Li et al., 1989). Lime suspension liquidwas preparedusing followingmethod: 56 g calcium oxidewasmixedwith 250mldistilled water in the 2000 ml beaker, meanwhile, slowly adding250 ml of 72% perchloric acid under stirring. A mixed solution washeated until white smoke emitting. After cooling, 200 ml distilledwater was added, and then mixture was heated until white smokeemit. The whole procedure was repeated three times. After cooling,mixture was filtered by glass sand funnel (G3). Then, 1000 ml of2.5 M sodium hydroxide solution was added to the filtrate understirring. The solution was depositing, keeping static, dumping su-pernatant into 5000mlvolumetricflask. Every time the supernatantmust be dumped into 5000 ml volumetric flask. 1% calcium hy-droxide suspension liquid was finished at last. Lime filter paper wasprepared using following method: 12.5 cm qualitative filter paperwas placed into the first glass culture dish with 1% calcium hy-droxide suspension liquid. After soaking and draining filter paper(calcium hydroxide suspension liquid must be replaced afterimpregnating 5e6 pieces of filter paper), it was placed into thesecond glass culture dish with 1% calcium hydroxide suspensionliquid. Drained filter paper was spread on a big qualitative filterpaper (cleanliness and no-fluoride). The impregnated filter paperwasbakedat 60 C in electric dryingoven. Thebakedfilterpaperwasplaced in a plastic sealed bag, and then it was put into dry cabinet.

The method of hanging the lime filter paper in outdoor air is asfollows: a piece of lime filter paper should be place on the bottom ofthe sampling box and be fixed by the circlip. The sampling box withfilter paper should be far away from the chimney of the stove and isfastened above a fixed object, about 3.5w4 m away from theground. The method of hanging the lime filter paper in indoor was:a piece of lime filter paper should lie on the bottom of the samplingbox and be fixed by the circlip (Fig.A.4). The sampling box withfilter paper should be 1.5 m away from the stove and about 1.5 maway from the ground. Two pieces of lime filter paper should befixed in every room. The surface of lime filter paper must facedown. The top of sampling box should be covered, in order toprevent fly ash from falling on the filter paper. The lime filter papermust be exposed to air more than 7 days. When the sampling boxwas collected, the lime filter paper was put into a plastic seal bagimmediately. After that the lime filter paper should be put into drycabinet in the lab. The determination of F content must be finishedwithin 6 weeks. The specific sampling method may be referred toMinistry of Environmental Protection of the Peoples Republic ofChina (2003).

The method of sampling SO2: Because the temperature in thetraditional flue-curing barn is very high, air sampler and aspiratorpump would be damaged while SO2 is sampled by the method offormaldehyde absorbing-pararosaniline spectrophotometry. There-fore, the portable gasdetector (BeijingXinhualaoScience&TradeCo.,Ltd) was used to determine the indoor and outdoor SO2 concentra-tion. Table 1 is the parameters of portable gas detector. In order toensure measurement accuracy, zero correction and range correctionmust be done.

Zero correction:When the digital readout display is stable in theclean air, it shows the value on the liquid crystal display (LCD)screen is 000 through adjusting the zero potentiometer. Rangecorrection: whether the show value returns to zero, the digitalreadout display is stable in the clean air. The bag filled up withstandard SO2 gasmust be connected to the instrument inlet with anair duct, and dont adjust the potentiometer S until the indicationvalue stays stable, then stop gas input when the value shows nodifference with the sample concentration value. This procedureshould be repeated once. If the difference between two values iswithin error, the correction is finished. If the difference exceeds theerror range, the corrective procedure should be repeated. When theSO2 concentration is determined in situ, the gas detector should be1 m away from the stove, about 1 m high from the ground (Fig.A.5).Evacuation time must be more than 45 min. Meanwhile, the tem-perature and pressure in situ should be recorded.

2.2. Analytical methods

2.2.1. Analytical method of fluoride in airThe gaseous fluoride content was determined by fluoride ion-

selective electrode (ISE) method. 0.1, 0.2, 0.4, 1.0, 2.0, 4.0, 8.0, 16.0and 40 mg ml1 of fluoride standards were prepared using the100 mg ml1 of fluoride standard solution. The standard curve wasdrawn by using semi logarithmic chart. Related coefficient of theregression equation was greater than 0.999; Slope was within the(54 0.2t) mv.

Determination of sample: The lime filter paper was cut insquares of 5 mm by 5mm, and put into 100ml plastic beaker. 25 mlof total ionic strength adjustment buffer (TISAB) and 25 ml ofdistilled water were added into 100 ml plastic beaker. Mixture wascleaned 30 min in the ultrasonic cleaner. The 100 ml plastic beaker

Table 3Gaseous fluoride and SO2 concentration in outdoor air in Yujiawan village, MangbuTownship and Group 22, Xiaomi Village.

Study areas Number ofsamples

Gaseous fluoride(mg dm2 day)(daily average)

SO2 (mg m3)(one-hour average)

Min Max Mean Min Max Mean

Yujiawan 9

Table 4Gaseous fluoride and SO2 concentration in the traditional flue-curing barn air inZhaotong City.

Study areas Parameters Min Max Mean S.D Skew

Yujiawan F (mg m3) (daily average) 1.92 28.0 10.1 9.78 1.57SO2 (mg m3) (one-houraverage)

2.62 57.3 14.4 18.5 2.24

Group 22,XiaomiVillage

F (mg m3) (daily average) 1.21 20.7 7.2 7.54 1.40SO2 (mg m3) (one-houraverage)

2.37 14.8 6.8 4.00 1.08

Note: S.D: standard deviation.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e7377302.3.2. Conversion formula of sulfur dioxideThe conversion formula of sulfur dioxide is:

mg m3 M=22:4 ppm 273=273 T Ba=101325

M: Molecular weight of SO2 (64 g mol1); T: temperature values(C); Ba: the values of atmospheric pressure (Pa).

2.4. Experimental methods for popularization test on reducingfluorine and sulfur

The popularization test on reducing fluorine and sulfur influorosis areas was done in Yujiawan Village, Zhaotong City(Fig.A.2). First, dolomitic siliceous limestone near experimentalvillages was calcined into powder (CDSL) in lime factory, and thentransported to experimental households. Experimental groups(EGs) (Fig.A.6) substituted local CDSL for clay (Fig.A.7) mixed withlow-fluorine coal. The mixing ratio of CDSL to coal was 3:7, namely,there had 30 kg CDSL and 70 kg coal in 100 kg mixed fire coal(Fig.A.8). But the contrast groups (CGs) (Fig.A.1) still did cookingand baked the food with the traditional mixed fire coal-low-fluorine coal mixed with high-fluorine clay.

3. Results and analysis

3.1. Fluoride and total S content in solid

F and total S content in fine coal, coal slime (coal slime: it is theresidue through coal washing technology), clay and CDSL are listed(Table 2). The Table 2 shows that the F content in fine coal ismaximum of 124.5 mg kg1, with average of 96.9 mg kg1, which isslightly higher than the Chinese average of 82 mg kg1 (Luo et al.,2004). And the F content in clay (Fig.A.7) is maximum of2422 mg kg1, with average of 1327 mg kg1, which is close to thatFig. 5. The gaseous fluoride (a) and SO2 (b) concentration in the trad(1516 mg kg1) in clay reported by Luo et al. (2007). So, thehouseholds use the LFC mixed with HFCL as their domestic energyfor cooking, heating and baking foodstuffs.

On the basis of classification for coal quality (GAQS and IQPRC,2004), total S content in the middle and high S coal is 1.5e3.0%,high S coal with>3.0% and low S coal with

Fig. 6. Comparison of experimental results between in Guiding, Guizhou Province (GG) and in Zhaotong City, Yunnan Province.

Table 5F content (mg kg1) in fresh and roasted corn in 2010.

Study areas Sampleproperties

Fresh Baked(in EGs)

Baked(in CGs)

Yujiawan, MangbuTown

Corn 1.1 5.1 10.2Chili 0.8 9.0 35.2

Group 22, XiaomiVillage

Corn 1.7 4.7 10.5Chili 2.5 43.7 144.1

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737 731et al., 2001; Ye et al., 2004b). Therefore, through determining thegaseous fluoride and SO2 pollution level before and afterimprovement, the fluorine and sulfur removal effect (Fig.4) of theimproved coal stove was studied.

Daily average of gaseous fluoride concentration in the kitchenwith open furnacewas 11.5 mgm3 (Fig.4(a)) (reference value (Lianget al., 1992) is 10 mgm3). One-hour average of SO2 concentration inthe kitchen with open furnace was 14.8 mg m3 (Fig.4(b)) that wasmuch higher than indoor SO2 standard (0.5 mg m3). Afterimproving the stove, the daily average of gaseous fluoride concen-tration in the kitchenwith improved coal stovewas 3.7 mgm3, withone-hour average of SO2 concentration of 0.94 mg m3. Comparingbefore and after improvement, the average value of gaseousfluorideconcentration in the kitchen air was decreased by 68.3% and waswithin the reference value (10 mgm3) (Fig. 4(a)). The average valueof SO2 concentration in the kitchen air was decreased by 93.7% andwas still higher than the standard value (0.5 mg m3) (Fig.4(b)).Although the SO2 concentration in the kitchen air had decreasedmarkedly, the SO2 concentration in the kitchen with improved coalstove was still higher than the indoor air standard (0.5 mg m3).Hence, decreasing the SO2 concentration in indoor airmust be comeinto notice. From the above, the improved coal stove with chimneygreatly improved the indoor and outdoor air quality.

3.4. The gaseous fluoride and SO2 pollution in the traditional flue-curing barn

The time for hanging lime filter paper in the traditional flue-curing barn was from October 30th or 31st, 2010 to November8th, 2010 in Yujiawan Village, Zhenxiong County. The time wasfrom November 19th or 20th, 2010 to December 3rd or 4th, 2010 inGroup 22, Xiaomi Village, Zhaoyang District. The exposed time oflime filter paper exceeded 7 days.

For the most part, the traditional flue-curing barn (Fig.1) in Zhao-tong City, Yunnan Province is separate and do not connect with otherrooms. But hitherto, there is no report on gaseous fluoride and sulfurdioxide indoor pollution level in the traditional flue-curing barn.

Table 4 showed that gaseous fluoride and SO2 indoor pollutionin the traditional flue-curing barnwas very serious. So, the gaseousfluoride, SO2 and other harmful elements polluted the corn andchili in the traditional flue-curing barn. Luo et al. (2011) have alsoinvestigated the stove-improving effects in Zhenxiong County,Zhaotong City, Yunnan Province in 2011 and again indicated thatthe dental fluorosis (Fig.A.9) rate of childrenwas still high (82.7%) inthe coal-burning fluorosis areas in Zhaotong City after improvingthe stove. The main reason is that the residents use open furnace tobake corn and chili in the traditional flue-curing barn in the harvestseason.Consequently, in order to solve the coal-burning endemic fluo-rosis in Zhaotong areas radically, the gaseous fluoride, SO2 andother toxic substance pollution in the traditional flue-curing barnmust be reduced dramatically.

4. Effectiveness evaluation for reducing fluorine and sulfur

4.1. Study areas

There are 150 total households and 673 total populations inYujiawan Village (elevation of 1600 m), Zhenxiong County and 80total households and 280 total populations in Group 22 (elevation of2076 m), Xiaomi Village, Zhaoyang District. The area is the seriousfluorosis areas (Ye et al., 2004a, 2005a, 2005b). There are 21 experi-mental groups (EGs) and19contrast groups (CGs) inYujiawanVillage,Zhenxiong County. The experimental time which was the harvestseason of corn is from October 20th, 2010 to December 6th, 2010.

4.2. The F and SO2 pollution in the traditional flue-curing barn

Fig.5(a) shows that the F release has been decreased aftersubstituting CDSL for clay mixed with coal in Yujiawan Village,Zhenxiong County. The gaseous fluoride concentration (5.5 mgm3)in the traditional flue-curing barn air in EGs in Yujiawan Village is45.27% less than that (10.1 mg m3) in CGs. It proved that thegaseous fluoride pollution in the traditional flue-curing barn hadbeen reduced markedly. The SO2 concentration (1.3 mg m3) in thetraditional flue-curing barn air (Fig.5(b)) in EGs in Yujiawan Villageis 91% less than that (14.4 mg m3) in CGs.

Comparison of experimental results between in Guiding County,Guizhou Province (Yang et al., 2010) and in Zhaotong City, YunnanProvince (Fig.6), the indoor gaseous fluoride concentration(1.4 mg m3) in EGs in Guiding County, Guizhou Province was lowerthan that (5.5 mg m3) in the traditional flue-curing barn in Yujia-wan Village, Zhaotong City (Fig.6(a)). The indoor SO2 concentration(0.17 mg m3) in EGs in Guiding County, Guizhou Province waslower than that (1.3 mg m3) in the traditional flue-curing barn inYujiawan Village, Zhaotong City (Fig.6(a)). The indoor gaseousfluoride (3.6 mg m3) concentration in CGs in Guiding County,

Fig. 7. The F content in the baked corn (A) and chili (B) of 2009 and 2010 in fluorosis area.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737732Guizhou Province was lower than that in the traditional flue-curingbarn air in Yujiawan Village, Zhaotong City (10.1 mg m3) (Fig.6(b)),and SO2 (0.45 mg m3) concentration was also lower than that inYujiawan Village, Zhaotong City (14.4 mg m3) (Fig.6(b)). The Fcontent in the bitumite, anthracite, clay and lime in Guiding County,Guizhou Province was 2170 mg kg1, 231 mg kg, 2098 mg kg1 and850 mg kg1, respectively (Yang et al., 2010). The F content in finecoal, coal slime, clay and CDSL in Zhaotong City, Yunnan Provincewas 91 mg kg1, 154 mg kg1, 1327 mg kg1 and 108 mg kg1,respectively. The reason for this difference was different ventilatedconditions. All houses in Guiding County, Guizhou Province had anattic above the cooking/living and sleeping rooms, used for fooddrying and storage (He et al., 2005; Yang et al., 2010). So, there wasno separate traditional flue-curing barn in Guiding County, GuizhouProvince. Therefore, the indoor ventilation in Guiding County,Guizhou Province was very well and that was beneficial to gaseousfluoride and SO2 dispersion. But the traditional flue-curing barn inZhaotong City, especially in Mangbu Township, Zhenxiong County,was separate and did not connect with other rooms, and the vol-ume of traditional flue-curing barn was small (9e18 m3). So, thebuilding structure of flue-curing barn was not beneficial to gaseousfluoride and SO2 dispersion. It is clear that the gaseous fluoride andSO2 pollution in the traditional barn in Zhaotong City had greatinfluence on F and S content in corn and chili (Table 5; Fig. 8).

4.3. Fluoride and sulfur content in baked foodstuffs

Table 5 shows F content in corn and chili. The F content inroasted corn and chili in the CGs using clay as binder was 2e4 timesFig. 8. The S content in the baked corn andhigher than that of EGs using CDSL as binder. Luo et al. (2010) re-ported that the F content (3.0 mg kg1) in the roasted corn inMuxuan Township, Zhaotong City which was the non-fluorosis areawas higher than the permitted level of fluoride content in foods(1.5 mg kg1) (NSPRC, 1984). But there was not dental and skeletalfluorosis. Luo et al. (2010) made the safety line (less than4.0 mg kg1) of fluoride content in roasted corn in coal-burningfluorosis areas. The F content (Table 5) in corn baked by coalmixed with CDSL was close to the safe line of 4 mg kg1 (Luo et al.,2010). The F content (Table 5) in chili baked by coal mixed withCDSL was still much higher than the safe line of 4 mg kg1, butsignificantly lower than that of CGs using clay as binder. Therefore,the gaseous fluoride pollution in the traditional flue-curing barnwas reduced markedly after CDSL instead of clay as binder.

Local residents in the fluorosis areas in Zhaotong largely eat thebaked corn and chili of last year before harvesting fresh corn andchili. Fig. 7 showed that the F content in the baked corn of 2009 wasobviously higher than that of 2010 (Fig.7(A)). But the F content inthe baked chili of 2009 had no significant difference as comparedwith that of 2010 (Fig.7(B)).

Sulfur (S) that constitutes the cell protein, tissuefluid, andvariousimportant component of coenzyme is an essential human chemicalelement. But excessive intake of Swould increases lipid peroxidationand may cause damage to the visual system (Parcell, 2002; Ozturket al., 2011). Fig. 8 showed S content in corn and chili. The S con-tent (Fig. 8) in roasted corn (mean: 0.28 102) and chili (mean:0.45 102) in the CGs using clay as binder was much higher thanfresh corn (mean: 0.14 102) and fresh chili (mean: 0.4 102).The mixture of clay and middle and high sulfur coal, which ischili of 2009 and 2010 in fluorosis area.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737 733produced by localmines, is used as amain household energy to bakethe foodstuffs. Because of this traditional baking method, the cornand chili are contaminated by the SO2 emitted during the coalburning. The S content (Fig. 8) in roasted corn (mean: 0.14 102)and chili (mean: 0.35 102) in the EGs using CDSL as binder wasmuch lower than roasted corn (mean: 0.28 102) and roasted chili(mean: 0.45 102) in the CGs using clay as binder, and they wasequivalent to the S content in fresh corn and fresh chili. Therefore, theSO2 pollution in the traditional flue-curing barn was reduced mark-edly after CDSL instead of clay as binder.

The S content in the baked corn (mean: 0.34 102) and chili(mean: 0.6 102) of 2009 was higher than that in the baked corn(mean: 0.28 102) and chili (mean: 0.45 102) of 2010. As thegrain is stored with long time, the corn and chili continue to adsorbthe sulfide emitted during the coal burning.

5. Conclusions

Based on the systematic study of the gaseous fluoride and SO2pollution level in outdoor environment, the kitchen and thetraditional flue-curing barn, as well as the experiment for fluorineand sulfur retention, main conclusions in this study have beensummarized as follows:

1) Meanvalueof gaseousfluoride inoutdoor air inYujiawanVillage,Zhenxiong County (0.51 mg dm2 day) and in Group 22, XiaomiVillage, ZhaoyangDistrict (2.7 mg dm2 day)was both lower thanthe ambient air quality standard (3 mg dm2 day). But somewerehigher than the ambient air standard. So, to some extent, theoutdoor air was polluted by fluoride emitted by coal-burning.

2) The households in Zhaotong City use LFC mixed HFCL as do-mestic energy. By comparing before and after improving coalstove, the gaseousfluoride and SO2 concentration in the kitchenair has been declined markedly. The gaseous fluoride concen-tration (3.7 mg m3) in the kitchen air is much lower thanambient air quality (7 mg m3) and reference value (10 mg m3).Although the SO2 concentration in the kitchen air has decreasedFig. A.1. Corns and chilies (corns are placed in the attic) are baked by the mixmarkedly, it is still higher (0.94mgm3) than indoor SO2 qualitystandard (0.5 mg m3). So, reducing the SO2 pollution in thekitchen with improved coal stove is main direction from nowon. The epidemiological survey should be carried out.

3) Based on the above explained experiments for fluorine andsulfur reducing, the indoor gaseous fluoride and SO2 pollutionin traditional flue-curing barn have obvious decrease afterCDSL instead of clay as binder. Therefore, the food adsorptioncapacity to fluorine and sulfur is reduced.

4) The mean fluorine content in clay is 1327 mg kg1, yet in theCDSL is less than 100 mg kg1, which suggests that the overallfluorine content in the system of coal plus 30% of this lowfluorine CDSL is far less than that in coal with ordinary clay.Therefore, abandoning the hundreds of years traditional wayof mixed clay with coal will make the gaseous fluoride con-centration in indoor air greatly reduced.

The cost of adding calcined dolomitic siliceous limestoneinstead of clay as a binder for briquette-making.

The calcined dolomitic siliceous limestone has some cohesive-ness and can be used as a binder for fine coal burning in ZhaotongCity. The calcined dolomitic siliceous limestone in the residentialcoal combustion is not only a binder, but also sulfur-fixing agent andcombustion improver. If the calcined dolomitic siliceous limestoneis added into the residential coal combustion, the cost of 1000 kgcoal will increase 5e10 (1e2 US$) Yuan (RMB). Also, about 4000 kgcoals are burned every year by people living in fluorosis area inSoutheast China for baking food, half of them are lump coal, whoseprice is twice of fine coal, 100 Yuan (RMB) (14 US $) more than finecoal. Thus, increased cost of the briquettes is offset by using less orno lump coal. Actually, the cost of baking foodstuffs does not in-crease by using the calcined dolomitic siliceous limestone.

This method is simple, and drawing the carbonate material inlocal is very easy, but let local people substitute the calcined car-bonate for the clay, which added in the coal for hundreds of years isnot easy. Therefore, the promotion of this method needs time anddepends on the vigorous propaganda and support of government.ture of coal and clay, and improved coal stove is treated as open furnace.

Fig. A.3. Edibility method of baked corn.

Fig. A.2. Carbonate rocks widely distributing in coal-burning endemic fluorosis area in Zhaotong.

Fig. A.4. Sampling method of indoor gaseous fluoride.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737734

Fig. A.6. Corn and chili are baked by the mixture of coal and calcined dolomitic siliceous limestone.

Fig. A.5. Sampling method of indoor SO2.

Fig. A.7. The outcrop of fire-resistant clay around Group 22 in Xiaolongdong Township.

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737 735

Fig. A.8. The mixture of coal and calcined dolomitic siliceous limestone in the EGs.

Fig. A.9. A child suffering dental fluorosis in Yuqing Village in Zhenxiong County(10 years old).

Y. Liu et al. / Atmospheric Environment 77 (2013) 725e737736Acknowledgments

This work is supported by the National High-Tech R&D Program(863 Program) (Nos. 2004AA601080 and 2006AA06Z380) and Na-tional Natural Science Foundation of China (No. 40872210,41172310). Special thanks are given to Science and TechnologyBureau of Zhaotong and local personnel for their support in sam-pling and collection of clay, calcined dolomitic siliceous limestoneand coal samples. We thank Dr. Huijie Li for their selfless help insampling. Many thanks are also given to Dr. Yongxin Xu and Ms.Wulan Tan for their help in the fluorine and sulfur determinations.Thank Ms Yuling Zhang for crushing samples.

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Fluoride and sulfur dioxide indoor pollution situation and control in coal-burning endemic area in Zhaotong, Yunnan, China1 Introduction1.1 Study areas1.2 The mode of cooking and heating and baking foodstuffs

2 Experiment and analytical method2.1 Sampling method of gaseous fluoride and SO2 in air2.2 Analytical methods2.2.1 Analytical method of fluoride in air2.2.2 Analytical method of solid sample

2.3 Method of calculation2.3.1 Calculation formula of fluoride2.3.2 Conversion formula of sulfur dioxide

2.4 Experimental methods for popularization test on reducing fluorine and sulfur

3 Results and analysis3.1 Fluoride and total S content in solid3.2 The outdoor gaseous fluoride and SO2 pollution3.3 The gaseous fluoride and SO2 pollution in the kitchen3.4 The gaseous fluoride and SO2 pollution in the traditional flue-curing barn

4 Effectiveness evaluation for reducing fluorine and sulfur4.1 Study areas4.2 The F and SO2 pollution in the traditional flue-curing barn4.3 Fluoride and sulfur content in baked foodstuffs

5 ConclusionsAcknowledgmentsReferences