Regional Characteristics of Sulfur and Lead Isotope Ratios in the

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Environ. Sci. Technol. 2001, 35, 1064-1071

Regional Characteristics of Sulfur and Lead Isotope Ratios in the Atmosphere at Several Chinese Urban Sites HITOSHI MUKAI,* ATSUSHI TANAKA, AND TOSHIHIRO FUJII National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki, 305-0053 Japan YIQIANG ZENG AND YETANG HONG Institute of Geochemistry, Chinese Academy of Sciences, No. 46 Guanshui Rd.,Guiyang, Guizhou 550002, P. R. China JIE TANG, SONG GUO, AND HUSHENG XUE Institute of Atmospheric Chemistry, Chinese Academy of Meteorological Sciences, No. 46, Baishiqiao Road, Beijing 100081, P. R. China ZHUOLIAN SUN, JITI ZHOU, AND DAMING XUE School of Chemical Engineering, Dalian University of Technology, 158 Zhong Shan Road, Dalian, 116012, P. R. China JING ZHAO, GUIHUA ZHAI, AND JINGLIANG GU Changchun Environmental Monitoring Center Station, Weisheng lu, Changchun, Jilin, P. R. China PINGYANG ZHAI The Environmental Protection Scientific Institute of Heilongjiang Province China, 356 Nanzhi Road Taiping District, Harbin, Heilongjiang Province, P. R. China

Sulfur and lead isotope ratios in the atmosphere were measured at several selected sites (Harbin, Changchun, Dalian, Waliguan, Shanghai, Nanjing, Guiyang) in China and Tsukuba (Japan), to reveal regional sources characteristics over Eastern Asia. Average S isotope ratios for SO2 and sulfate in the atmosphere in China were close to those of the coals used in each region, indicating a considerable contribution of coal combustion to the sulfur compounds in the atmosphere. Most northern cities had around 5‰ sulfur isotope ratio, while Guiyang, a southwestern city in China, showed a considerably lower sulfur isotope ratio (about -3‰) because of the unusually light sulfur isotope ratio of coals in this region. These were considerably different from the value (-1.4‰) for Tsukuba (Japan). Lead isotope ratios also suggested that coal combustion considerably contributed to atmospheric lead in some cases in China. At the same time, influences by the emission of Chinese lead ores were also observed in northern cities. Seasonal variations of both sulfur and lead isotope ratios indicated the existence of a certain amount of industrial sources other than coal combustion. In addition, fractionation effect between SO2 and sulfate showed a seasonal tendency (high in winter (0-6‰) and low in summer (-1-3‰)), suggesting the oxidation pathway of SO2 changed seasonally. 1064

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Introduction Sulfur and Pb isotope ratios are useful tools for apportioning their sources in the environment. In general, SO2 sources such as coal combustion and metal smelting have a different sulfur isotopic composition depending on the isotope value of each raw material because they experience different isotopic fractionation effects through their formation processes. Similarly, Pb isotope ratios are also different from source to source, despite the fact that the process of isotopic composition change is due to the new production of three kinds of Pb isotopes (206Pb, 207Pb, and 208Pb) by the radiogenic decay of 238U, 235U, and 232Th, respectively. This is different from the case of sulfur. Lead isotope ratios could be an indicator of the age of lead ore formation (1). Many studies have been carried out in Europe (2-10), the Arctic (11-13), and America (14-16) to trace sulfate in the atmosphere and in precipitation by using sulfur isotope ratios. These researchers discussed the anthropogenic input of sulfur compounds to the atmosphere or soil environment through deposition. At the same time, some other source contributions such as biogenic sulfur compounds (e.g., dimethylsulfide and H2S) could be admitted from the sulfur isotopic signature (4, 9, 10, 12, 13, 16, 17). In China, coal is used as the main fuel and its combustion produces a large amount of SO2. Higashino et al. (18) estimated that 21 Tg of SO2 was emitted from China in 1990. In the atmosphere, sulfur dioxide is oxidized to sulfuric acid, which causes a serious acid rain problem in southern China (19-23). In particular, southern Chinese coal has a high sulfur content (over 1%), giving a high concentration of SO2 (19, 24). Hong et al. (25) measured the sulfur isotope ratio of Chinese coal and found wide variations for each region. He reported a very low sulfur isotope ratio (e.g., -7.52‰) for southern Chinese coal. This high sulfur content and low sulfur isotope ratio may be related. On the other hand, coal produced in northern China was found to have a high sulfur isotope ratio (1.4-11.22‰) but low sulfur content (under 1%). Some isotope ratio measurements have been carried out for atmospheric sulfate and sulfate in precipitation by the Hong group. Liu et al. (26) pointed out that sulfate in the atmosphere at a southern Chinese city (Guiyang) had a low sulfur isotope ratio similar to that of southern Chinese coal. Hong et al. (25) also reported a similar tendency (low sulfur isotope ratio in the southern area) in precipitation. In general, SO2 and sulfate in the atmosphere have several anthropogenic sources besides coal burning (27), such as metal smelter (28), oil combustion (29, 30), and sulfur industry (31). Furthermore, natural sources such as dimethyl sulfide (DMS) (32) and H2S (33), volcanic SO2 (34), and sea salt sulfate are also possible origins of sulfur compounds. Therefore, the sulfur isotope ratio of SO2 and sulfate in the atmosphere must be influenced by these source values. Because China is a large country, SO2 source characteristics are different from region to region. We should also pay attention to the isotopic fractionation effect between SO2 and sulfate, which occurs when SO2 is oxidized to sulfate. Saltzman et al. (14) pointed out that sulfate in the atmosphere is 0-4‰ heavier than SO2. The isotopic fractionation effect is said to be different from oxidation pathways. Heterogeneous oxidation on the surface of wet aerosol was considered to make the sulfur isotope ratio of sulfate, at a maximum, 16.5‰ heavier at 25 °C (35) because * Corresponding author e-mail: [email protected]. 10.1021/es001399u CCC: $20.00

 2001 American Chemical Society Published on Web 02/14/2001

FIGURE 1. Sampling Site Map. of the equilibrium process of SO2 between the gas phase and the water phase. On the other hand, Tanaka et al. (36) estimated that homogeneous oxidation would give about 9‰ lighter sulfate than original SO2. In this study, to expand the source characterization, lead isotope ratios in aerosol were also measured at the same time. Lead isotope ratios are good indicators of the sources of lead. Mukai et al. (37) showed the regional characteristics of lead isotope ratios at several urban sites in Asia. Because coal combustion can be a lead source, its contribution is bound to change lead isotope ratios in the atmosphere. In other cases, lead gasoline and industrial emission were major sources of lead in the atmosphere in Asia. Because lead ore has a regional difference based on the mother rock composition and its formation age, we can sometimes know the origin of ore lead by isotopic signature. For this study, several urban sites were selected in both northern and southern China. To clarify the seasonal differences of source contribution and the process of oxidation reactions, both SO2 and sulfate were collected in winter and summer. For reference, sampling was carried out at one background site in China and one Japanese site. These sulfur and Pb isotope data are discussed in terms of source appointments in the sampling areas.

Materials and Methods Sample Collection. Aerosol sulfate and sulfur dioxide were collected with a high-volume air sampler on a quartz fiber filter (2500QAT-UP, 8 × 10 in., PALLFLEX Pro. Co.) and an alkali-impregnated filter, respectively. The impregnated filter was prepared with quartz fiber filters dipped in 2% K2CO3 and 2% glyceline solution, followed by drying at 50 °C. A cellulose filter (No. 2, 8 × 10 in., Advantec, Japan) was inserted between the quartz filter and the alkali-impregnated filter in order to prevent contamination of the top quartz filter from the alkali filter. At the very base, another quartz filter was placed to protect the metal mesh of sampler from erosion. Air was usually sampled for 1 day with a flow rate of 5001000 L/min by a high-volume air sampler. Sampling sites are shown in Figure 1. For comparison, northern and southern cities that are highly populated and industrial were selected for this study. On the other hand, Waliguan in Qinghai province, one of the World Meteorological Organization (WMO)’s monitoring sites, was the background site. Sampling was usually carried out for 5 days in both winter and summer in 1996 and/or in 1997. Sampling days and site information are summarized in Table 1. As for Waliguan, a 3-day sampling was carried out because of the low SO2 level. In most cases, the sampler was placed at a city center (usually on the roof of the institute) to collect the regional pollution there. As for Beijing, only sampling for lead isotope ratio measurement was conducted.

After sampling, filter samples were carefully wrapped with aluminum foil separately, put in plastic bags, and kept in a refrigerator. S Isotope Analysis. Several small disks (2.5 cm dia.) of filter were punched out from the quartz filter sample for aerosol. Sulfate was extracted from one or two disks (depending on the sulfate amount) with 7 mL of distilled water. Sulfur dioxide trapped in the alkaline filter was extracted in a similar manner with 7 mL of distilled water containing 20 µL of H2O2 as sulfite was oxidized to sulfate. The extracted solution was filtrated, and major ions in the solution were measured by ion chromatography (Dionex model Quick). An aliquot (corresponding to 0.2-0.3 mg of the BaSO4 contained in it) was taken from the solution, and the sulfate in it was precipitated as BaSO4 by adding 200 µL of 2M BaCl2 solution. The precipitation of BaSO4 was filtrated using a small area (4 mm diameter) of a 0.45-µm Nuclepore filter. After rinsing with distilled water, the filtrated area was cut out and put into a tin cup together with 0.5 mg of V2O5 powder. This tin cup was crushed into a small size and set in the autosampler of an elemental analyzer (EA) (Calro Elba NA1500, Italy) connected with an isotope mass spectrometer (MASS). The combustion column (WO3 and Cu) for S analysis was set in an elemental analyzer, and the furnace temperature was kept at 1100 °C. Five milliliters of oxygen was introduced into the combustion column to burn BaSO4 and tin together. The separation column (2m PQS 50/80 mesh) for SO2 was kept at 80 °C, and its effluent was introduced first into an open splitter (Conflo II, ThermoQuest) and then into the ionization chamber of MAT252 (ThermoQuest, Germany), which was kept at a high temperature. A valve for pumping the ionization chamber was fully opened to evacuate SO2 quickly from the chamber and prevent unnecessary contamination of the chamber. The S isotope ratio of the SO2 peak from each sample was first calculated by using reference SO2 gas (38), which was calibrated against the standard (BaSO4, RM 8557(NBS-127), National Institute of Standards and Technology). Oxygen isotope correction was simply done by multiplying 1.09 by the ratio of 66/64. The isotope ratio was reported in the notation as ‰ deviation from the Canon Diablo Troilite (CDT) standard.

δ34S ) [ (Rsample/RCDT) - 1](1000) The SO2 production yield for BaSO4 was around 100% based on the usual S standard (sulfanylamide). However, a small systematic shift and drift (under 1.5‰), which can occur by various conditions of the EA analyzer (39), was corrected periodically by analyzing the standards (RM8554(NZ-1) (Ag2S) and RM8557(NBS-127) (BaSO4)) in the same way as the samples. Because the S isotope ratio observed was much lower than NBS-127 (20.3), the final calibration was done with NZ1 (-0.3). The combustion column was changed about every 80 samples. Pb Isotope Ratio Analysis. The punched filter disk was placed in a Teflon beaker. The filter was digested with 5 mL of HNO3 for 2 h and with 3 mL of HClO4 for several hours at 180 °C with a Teflon lid. After soot had been almost digested, 1 mL of HF was added to dissolve the quartz filter. The temperature was kept at 200 °C, and the solution was then evaporated and concentrated until near dryness. Then it was redissolved with 6 mL of 0.4 N HNO3 solution. Lead isotope ratios were measured by ICP-MS (Plasma Quad II, VG Elemental, U.K.). Prior to isotope measurement, lead concentrations in the sample solutions were adjusted in the range from 50 to 300 µg/L. Analytical conditions for lead isotope ratio analysis have been analyzed previously (40). Briefly, a mass spectrometer was scanned from 202 to 210 (512 channels; dwell time 80 µs per channel). The scanning was repeated 1600 times per measurement. This VOL. 35, NO. 6, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Sampling Sites and Other Parameters for Sampling. sampling site (province)

winter or summer

sampling date

flow rate (l/min)

Harbin (Heilongjiang)

W S W S W S W S W S W S W S W S W

1997, Feb 22-26 1997, Jul 22, 23, 28, 30, Aug 4 1997, Feb 11-15 1997, Jul 16-21 1997, Mar 24-28 1997, Jul 14-18 1997, Apr 6-9, 10-13, 13-16, 16-19, 19-22 not sampled 1997, Jan 27-29 1997, Aug 5-9 1997, Jan 28, 29 1997, Jul 28-31, Aug 1, 4 1996, Dec 8, 9, 10-12,12-15,16-17, 17-19, 19-23, 23-25, 25-27 1997, Aug 8-15 1997, Mar 11, 12, 18 1997, Aug 7, 12,19-21 1997, Mar 13, 14

520 1050 500 500 800 800 800

Changchun (Jilin) Dalian (Liaoning) Waliguan (Qinghai) Shanghai Nanjing (Jiangsu) Guiyang (Guizhou) Tsukuba, Japan Beijing

measurement was done five times per sample and then averaged. The intensity of mass of 204 was corrected by subtracting the 204Hg contribution, which was calculated by 202Hg intensity. Filter blank was measured at the same time, and the blank intensity of each mass was subtracted from the sample intensity. Analytical precision was under 0.5% for 207Pb/206Pb and 208Pb/206Pb, while 0.8% was the precision for 206Pb/204Pb. Lead isotope ratios were calibrated against the lead standard SRM981 (National Institute of Standards and Technology).

Results and Discussion Comparison of EA-MASS Analysis to the Conventional Method. The precision of the S isotope measurement by the EA-MASS method was about 0.5‰. Because a small shift (up to 1‰) was observed when the sample amount was small, below 100 µg of BaSO4, sample size was adjusted within the range from 100 to 400 µg. To evaluate the EA-MASS method for S isotope analysis, both conventional dual-inlet measurement (by Mitsubishi Material Co.) and the EA-MASS method were compared using the same samples. For this comparison, several samples were specially selected and a sufficient amount (about 1 mg as BaSO4) of sulfate was extracted from the sample filters for both methods. The conventional method was performed based on the method of Yanagisawa and Sakai (41). Although they used different standards, the observed values were well matched with a slight sift (about 0.6‰). On the basis of the precision of EA-MASS, the small shift may be negligible. Therefore, it was concluded that the analytical technique used in this work was creditable within a sub ‰ range. Overview of the S Isotope Ratio for SO2 and Sulfate. The isotopic fractionation effect between gaseous SO2 and particulate sulfate has been reported previously (14, 36). Therefore, to relate the S isotope value to those of the sources, we have to compute the atmospheric average S isotope ratio by the concentration-weighted average of SO2 and sulfate (SO4).

Average S isotope ratio ) SO2 × δ34S-SO2 + SO4 × δ34S-SO4 SO2 + SO4 If sea salt is included in aerosol, it causes a plus bias to the S isotope value of sulfate because of its high isotope ratio value (e.g., 20.3: NBS-127). Usually sea salt sulfate is estimated from sodium concentration; however, in the inland area of China, the contribution of sea salt is low while the contribution from coal combustion and soil can be much higher than 1066

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500 940 1000 520 500 600 600 500 5

from sea salt. If all observed sodium were estimated to be from sea salt, its contribution to the S isotope ratio would be calculated to be 1.4‰ at most. However, because sulfate concentration was extremely high compared with the expected sea salt concentration, the estimated maximum contribution was, in most cases, under 0.8‰ even in a seaside city like Shanghai. Since it was also difficult to separate sea salt Na and Na from other sources such as coal combustion and soil, sea salt correction was not carried out except on the samples from Tsukuba, where no contribution of Na from coal combustion exists. Average S isotope ratios for both gaseous SO2 and particulate sulfate are plotted with one standard deviation at each site in Figure 2, including the data at Tsukuba City in Japan. Data for the isotope ratios and the concentrations are also summarized in Table 2. Concerning the Harbin summer samples, since both SO2 and sulfate were unfortunately collected by one filter by accident, only average data are shown in the figure. Regional differences in the average S isotope ratio are clearly seen in Figure 2. High S isotope ratios (around 5‰ in atmospheric average) were observed in northern China (Harbin, Changchung, and Dalian), and low isotope values were observed in southern China, especially in Guiyang (around -3‰). Shanghai and Nanjing seemed to be within those ranges (about 3‰ in average). Tsukuba (Japan) had lower isotope values than cities in northern China. These differences are basically attributable to the differences in the characteristics of fuels as S sources. In general, northern Chinese coals have been reported to have higher S isotope ratios than southern Chinese coals (25). Therefore, the tendency of regional average S isotope ratios observed here is considered to correspond well to the values of source coals. As for Japanese fuel sources, Ohizumi et al. (42) reported that the oil and coal used in Japan have isotope ratios lower than 0 on average (-2.7‰ in Niigata Prefecture). Observed average values in Tsukuba were found to be similar to those. Concerning seasonal differences in average S isotope ratios, small differences (1-3‰) were seen in all Chinese sites, although the Japanese site (Tsukuba) had a very small seasonal variation (0.4‰). In addition, Guiyang showed large temporal variations (lager than 10‰, one standard deviation was listed in Table 2, individual data is plotted in Figure 6) in both seasons, while the variations for the other sites were less than 5‰, which suggested that some variety of SO2 sources might be present in Guiyang. Regarding the S isotope ratios of SO2 and sulfate, the S isotope ratios of sulfate were 0-7‰ heavier than those of SO2 except for the Dalian summer sample (2‰ lighter). In

sulfate. We may estimate the reaction pathways from the fractionation factor observed, based on the difference between homogeneous oxidation (e.g. 0.991 (36)) and heterogeneous reaction (e.g. 1.0165 (35)). In Figure 3, average isotopic fractionation factors from all sites and seasons are plotted. This graph clearly shows differences of the fractionation factor between seasons. In summer, R was about 1.001, suggesting that homogeneous oxidation was dominant rather than heterogeneous oxidation. Only Guiyang showed a relatively high R value even in summer. It may be related to high aerosol concentration and high humidity in summer there, which are both preferable to heterogeneous reaction. On the other hand, in most cases, R was high (1.0021.006) in winter, except in Dalian and Waliguan, suggesting that heterogeneous reactions with cloud droplets and/or wet aerosols surfaces became relatively important. The contribution may increase up to roughly 50%. The fractionation factor for heterogeneous oxidation was reported to increase with decreasing temperature: for example, the value at 0 °C was estimated to be 1.021 (14). Such temperature dependency can possibly affect seasonal difference on isotope fractionation factor R. Harbin and Changchun, located in the northern part of China, however, had rather small R values compared to other sites despite being colder than other sites such as Tsukuba and Shanghai. This may be related to very dry conditions at those sites.

FIGURE 2. Sulfur isotope ratios for SO2, sulfate, and their average in the atmosphere at Chinese sites and Tsukuba (Japan) in winter (a) and summer (b). general, sulfate can have a heavier isotope ratio than original SO2 when it is produced by a heterogeneous reaction of SO2 (14, 36). In Figure 3, the difference between SO2 and sulfate was found to be smaller for summer samples than for winter samples. This seemed to have some relationship with the oxidation ratio (1 - f).

1-f)

SO4 SO2 + SO4

The oxidation ratio, which is the ratio of sulfate to total sulfur compounds (SO2 + sulfate), is calculated in Table 2 with atmospheric average concentrations of SO2 and sulfate at seven Chinese sites and Tsukuba (Japan). Both concentrations were found to be higher in winter than in summer because of high coal combustion in winter in China. The oxidation ratio was generally high in summer and low in winter, suggesting that SO2 was oxidized more quickly in summer. Waliguan, one of the background monitoring stations of WMO, showed considerably low concentrations for both species. In particular, SO2 concentration was much lower than that of sulfate. Therefore, sulfate was the most abundant species in the atmosphere in Waliguan. Isotope fractionation factor R was calculated based on the Rayleigh equation shown by Saltzman et al. (14). This fractionation factor (R) principally means overall apparent kinetic fractionation during oxidation reaction, despite that it is neglecting the effect of SO2 continuous emission and the process of deposition of both SO2 and

Dalian showed relatively low fractionation factors compared to other sites in both summer and winter, which may be explained in several ways. Because Dalian City is located near the Bo Hai Sea, the chance of aerosol accumulation by the inversion layer is not high and there is more oxidation by homogeneous reaction than at other sites. If light sources of sulfate other than SO2 are present, such as H2S, sulfate may have a relatively light S isotope ratio. Some reports have pointed out the possibility of the contribution of H2S to sulfate (17). In addition, there is also a possibility that transported sulfate contributes to the values in Dalian because the areas around the Bo Hai Sea had strong emission intensities of SO2 (18, 43). Overview of Pb Isotope Ratios. Pb isotope ratios from all the sampling sites are plotted in Figure 4 (a and b) with the lead growth curve presented by Cumming and Richards (1). Wide variations in Pb isotope ratios were obvious in both seasons. Guiyang was characterized by lower 207Pb/206Pb and 208Pb/206Pb than other sites, suggesting that younger lead, such as lead from coal (44), was emitted in the atmosphere. Because the major lead ore in China did not show such low lead isotope ratios (usually older than coal’s values) (45) as shown in Figure 4c, the observed lead isotope ratios in Guiyang were considered to be contributed by coal combustion. On the other hand, Dalian had higher values in those ratios, suggesting ore lead from old age mines was being introduced in the atmosphere. The total trend of the Chinese sites showed lines that were slightly shifted upward from the lead growth curve except Guiyang data, as seen in Figure 4 parts a and b. This tendency in lead isotope ratios is common for Chinese and Korean lead (45, 46), which were influenced by continental Th rich crust. In Figure 4c, the lead isotope ratios for Chinese ore leads (45) and northern Chinese coals (37) are plotted. The figure shows that Chinese ore lead was along a straight line, while coal had a large variation. If we add this Chinese lead line to Figure 4 parts a and b as a dotted line, the isotope ratios observed in this work are along this line as well. Therefore, the observed leads are considered to originate from Chinese domestic leads. On the other hand, it was recognized that Tsukuba (Japan) showed a relatively VOL. 35, NO. 6, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Summary of Observed Values for S Isotope Ratios in Chinaa sampling site Harbin Changchun Dalian Waliguan Shanghai Nanjing Guiyang Tsukuba (Japan) a

season

sulfate (µg-S/m3)

SO2 (µg-S/m3)

total (µg-S/m3)

δ34S-sulfate (‰)

δ34S-SO2 (‰)

δ34S-average (‰)

1-f (%)

winter summer winter summer winter summer winter summer winter summer winter summer winter summer winter summer

7.0 ( 2.4 ND 4.2 ( 1.1 5.1 ( 2.3 10.9 ( 5.8 6.1 ( 2.4 0.9 ( 0.2 ND 7.9 ( 2.4 7.8 ( 1.7 7.3 ( 2.1 10.1 ( 4.8 22.6 ( 12 10.5 ( 2.7 1.4 ( 0.2 2.8 ( 1.5

59.3 ( 12 ND 27.5 ( 4 2.8 ( 1.2 25.5 ( 14 10.7 ( 6.3 0.2 ( 0.3 ND 35.4 ( 8.0 13.2 ( 10 14.9 ( 0.6 7.1 ( 4.5 46.7 ( 39 76.1 ( 29 2.9 ( 0.5 2.5 ( 1.2

66.3 ( 14 3.8 ( 2.0 31.6 ( 5 7.9 ( 3.2 36.4 ( 19 16.8 ( 7.6 1.1 ( 0.2 ND 43.3 ( 8.8 21.0 ( 11 22.2 ( 1.5 17.2 ( 8.4 69.2 ( 39 86.6 ( 30 4.2 ( 0.5 5.2 ( 2.4

6.4 ( 0.5 ND 8.1 ( 1.3 3.7 ( 2.6 5.9 ( 1.6 3.8 ( 3.0 4.2 ( 1.1 ND 6.3 ( 0.6 5.4 ( 1.8 6.9 ( 0.6 3.0 ( 1.7 1.2 ( 0.9 -1.3 ( 1.8 3.4 ( 1.3 -0.7 ( 1.1

4.0 ( 0.8 ND 6.1 ( 0.8 3.0 ( 1.2 6.2 ( 1.3 5.7 ( 1.5 3.1 ( 0.5 ND 0.7 ( 0.9 4.4 ( 2.3 2.6 ( 0.6 0.8 ( 2.4 -4.1 ( 2.0 -4.5 ( 4.0 -3.4 ( 0.5 -2.5 ( 0.3

4.2 ( 0.7 6.0 ( 1.0 6.4 ( 0.5 3.3 ( 1.6 6.1 ( 1.2 4.9 ( 2.3 4.2 ( 0.7 ND 1.7 ( 0.8 4.9 ( 2.0 4.0 ( 0.1 2.1 ( 1.4 -2.2 ( 1.8 -4.0 ( 3.6 -1.2 ( 0.9 -1.6 ( 0.6

11 ND 13 65 30 36 80 ND 18 37 33 59 33 12 32 53

Note: One standard deviation was shown with an average. ND ) not determined.

FIGURE 3. Fractionation factors between SO2 and sulfate at Chinese and Japanese sites in each season.

ln R)

δ34S-SO2 + 103 δ34S-average + 103 +1 ln f

low 208Pb/206Pb ratio compared to the Chinese lead line. Chinese coal has been reported to have wide variations in Pb isotope ratio (37). Some northern coals did not show such a young age as that of Guiyang, as seen in Figure 4c. The average isotope ratio of 207Pb/206Pb for northern coal seemed to be 0.84-0.86, which was similar to the values observed in Nanjing (winter and summer), Shanghai (summer and winter), Changchun (winter), Harbin (winter), and Waliguan (winter), as summarized in Table 3. Because Dalian (winter and summer), Beijing (winter), Harbin (summer), and Changchun (summer) showed isotope ratios higher than 0.86 in 207Pb/206Pb, other lead sources, such as leaded gasoline and industrial lead from smelters and metal industries, must be considered. China has regulated leaded gasoline since 2000; however, although the samples in this work were collected before that date, some influence from leaded gasoline is possible despite the fact that lead concentration in lead gasoline in China seemed to be low (e.g., 0.0167 Pb g/L (47)). In Table 3, large seasonal variations of Pb isotope ratios were seen in Changchun and Harbin, where coal combustion is frequently used, especially in winter. Because coal has a relatively low 207Pb/206Pb ratio, the contribution in winter could reduce the original ratio toward low figures such as 0.85. On the other hand, these two sites had fairly high 2071068

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FIGURE 4. Lead isotope ratios observed in Chinese and Japanese sites in each season (a and b). Lead growth curve was from Cumming and Richards (1). Dotted line was Chinese ore lead line as illustrated in c, which is data for northern Chinese coals (37) and major lead mines in China (45). Chinese coal showed more radiogenic nature than ore leads. Pb/206Pb ratios (over 0.87) in summer, suggesting that sources other than coal combustion contribute considerably in both cities, especially in Changchun, because high Pb concentration was observed even in summer.

TABLE 3. Summary of Observed Values for Lead Isotope Ratios in Chinaa sampling site Harbin Changchun Dalian Waliguan Shanghai Nanjing Guiyang Tsukuba(Japan) Beijing a

season

Pb concentrated (ng/m3)

winter summer winter summer winter summer winter summer winter summer winter summer winter summer winter summer winter

282 ( 101 57 ( 21 177 ( 188 191( 129 485 ( 160 266 ( 236 13 ( 11 ND 466 ( 250 208 ( 41 317 ( 28 200 ( 113 784 ( 881 203 ( 88 16 ( 2 36 ( 5 119 ( 15

206Pb/204Pb

(-)

18.22 ( 0.14 17.92 ( 0.09 18.09 ( 0.13 17.85 ( 0.09 17.69 ( 0.12 17.74 ( 0.11 18.02 ( 0.15 ND 18.06 ( 0.09 18.08 ( 0.23 18.20 ( 0.08 18.26 ( 0.10 18.60 ( 0.20 18.65 ( 0.18 17.98 ( 0.13 18.02 ( 0.10 17.78 ( 0.14

207Pb/206Pb

(-)

0.853 ( 0.004 0.871 ( 0.003 0.858 ( 0.005 0.873 ( 0.003 0.881 ( 0.003 0.879 ( 0.005 0.862 ( 0.003 ND 0.865 ( 0.003 0.863 ( 0.007 0.861 ( 0.001 0.858 ( 0.003 0.844 ( 0.009 0.841 ( 0.008 0.867 ( 0.001 0.863 ( 0.000 0.871 ( 0.002

208Pb/206Pb

(-)

2.098 ( 0.006 2.122 ( 0.003 2.113 ( 0.009 2.131 ( 0.009 2.151 ( 0.006 2.146 ( 0.012 2.114 ( 0.005 ND 2.118 ( 0.002 2.114 ( 0.017 2.118 ( 0.004 2.111 ( 0.003 2.077 ( 0.020 2.073 ( 0.020 2.119 ( 0.014 2.107 ( 0.004 2.129 ( 0.007

Note: One standard deviation was shown with an average. ND ) not determined.

FIGURE 5. Comparison of regional sulfur isotope ratio in the atmosphere (Plots) to fuels (horizontal dotted lines) produced there (25,42,49) with a lead isotope ratio as a horizontal axis. Similarly, the observed isotope ratio in Dalian in the Liaoning province was fairly high in both 207Pb/206Pb and 208Pb/206Pb. Lead produced in northern China (e.g., Liaoning province) was reported to have very high values, as shown in Figure 4c. One lead ore has 0.93 in 207Pb/206Pb and 2.22 in 208Pb/206Pb; another lead ore has 0.85 and 2.1 in 207Pb/ 206Pb and 208Pb/206Pb, respectively (45). Because the Pb isotope ratios observed in Dalian, Harbin (summer), and Changchun (summer) were between those of the two lead ores (i.e., 0.870.88 in 207Pb/206Pb), the lead isotope ratio values there were considered to be the result of the mixing of leads that have high lead isotope ratios, such as leads from Liaoning, with some other leads that have low isotope ratios (e.g., coal combustion). Regional Characteristics. (1) Southern China. Low S isotope values were observed in southern China, especially in Guiyang. Liu et al. (26) previously reported that sulfate in aerosol in Guiyang had a low sulfur isotope ratio (-7.8‰ to 7.48‰) because of the low values of the coal used there ( -7.5‰ on average) (25). They observed that a smaller particle (