Real-Time Gas-Phase Analysis of Mono- to Tri-Chlorobenzenes

Jun 15, 2010 - The VUV light (1014 photons cm−2 s−1) is introduced through a MgF2 ... and 360 ppb (BF), and 2300, 230, and 110 ppb (ESP), respecti...
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Environ. Sci. Technol. 2010, 44, 5528–5533

Real-Time Gas-Phase Analysis of Mono- to Tri-Chlorobenzenes Generated from Heated MSWI Fly Ashes Containing Various Metal Compounds: Application of VUV-SPI-IT-TOFMS T A K A S H I F U J I M O R I , †,⊥ M A S A K I T A K A O K A , * ,† SHIGENORI TSURUGA,‡ KAZUYUKI OSHITA,† AND NOBUO TAKEDA§ Department of Urban and Environmental Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nisikyo-ku, 615-8540, Kyoto, Japan, Advanced Technology Research Center, Yokohama Research & Development Center, Mitsubishi Heavy Industries, Ltd., 1-8-1 Sachiura, Kanazawa-ku, Yokohama, 236-8515, Kanagawa, Japan, and Eco-Technology Research Center, Ritsumeikan University, Noji Higashi 1, 1-1 Kusatsu, 525-8577, Shiga, Japan

Received March 19, 2010. Revised manuscript received June 7, 2010. Accepted June 7, 2010.

We measured sensitive real-time change of low-chlorinated (Cl1-Cl3) benzenes in gas phase from heated model and real solid samples using the recently developed vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap timeof-flight mass spectrometer (VUV-SPI-IT-TOFMS). Model solid samples that contained activated carbon, potassium chloride, silicon dioxide, and trace metallic compounds (copper, iron, lead, and zinc) were used to simulate fly ash at a municipal solid waste incinerator (MSWI). The concentrations of chlorobenzenes determined by integrating the area for 30 min using VUV-SPI-IT-TOFMS were correlated with gasphase concentrations analyzed by GC/MS. Real-time changes had characteristic patterns dependent on metal species and compounds. Comparing gas-phase real-time patterns of lowchlorinated benzenes between real and model fly ashes, copper chloride- and oxide-like compounds in real fly ash at the postcombustion zone in a MSWI may play key factors in the formation of low-chlorinated benzenes. Lead and zinc compounds and iron oxide in solid phase did not affect the formation of low-chlorinated benzenes in gas phase. VUVSPI-IT-TOFMS can be applied to the time-dependent characterization of volatile low-chlorinated benzenes in gas phase in various artificial and environmental processes.

* Corresponding author e-mail: [email protected]. kyoto-u.ac.jp. † Kyoto University. ‡ Mitsubishi Heavy Industries, Ltd. § Ritsumeikan University. ⊥ Present address: Research Center for Material Cycles and Waste Management, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506, Ibaraki, Japan. 5528

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Introduction High-chlorinated benzenes, such as hexa- and pentachlorobenzenes, are involved in persistent organic pollutants (POPs) and are of worldwide concern due to their toxicity and biomagnification (1). Moreover, low-chlorinated benzenes (mono-, di-, and tri-) also show harmful effects on human health and the environment (2). Volatile organic compounds (VOCs) defined by the World Health Organization (boiling point, 50-260 °C) (3) contain low-chlorinated benzenes. Chlorobenzenes from mono- to tri- scattered from natural and anthropogenic sources have high mobility in atmospheric, soil, and water environments, respectively, and accumulate in the food chain (2, 4, 5). Moreover, such lowchlorinated benzenes are known to be precursors of polychlorinated dibenzo-p-dioxins/furans and are indicative of dioxin formation because their concentrations are correlated with dioxin concentrations in the gas phase in thermal processes such as municipal solid waste incinerators (MSWIs) (6, 7). Recently, a real-time measurement technique of gasphase low-chlorinated (Cl1-Cl3) benzenes was developed (7, 8). Various types of real-time measurement techniques are expected to have novel applications for the study of timedependent formation of gas-phase chlorinated organic compounds (9-11). Chlorinated aromatic compounds such as dioxins and chlorobenzenes are known to be emitted from anthropogenic thermal processes. Homo- and heterogeneous formations of chlorinated aromatic compounds from macromolecular carbons have been suggested in many studies (12-14). Fly ash collected from the postcombustion zone in MSWIs has the highest potential for forming chlorinated aromatic compounds (12, 13). Recently, the authors reported that metal species and their chlorides and oxides strongly affect the formation path of chlorinated aromatic compounds in the solid phase of fly ash (15). Thus, gas-phase real-time formations of low-chlorinated benzenes are implied to also depend on metallic forms, which provide instantaneous time scale knowledge about VOCs such as low-chlorinated benzenes based on the presence of particular metallic compounds. However, typically, the fine time scale measurement of chlorinated organic compounds has been difficult because conventional gas chromatography/mass spectrometry (GC/ MS) analysis required too much time to measure and analyze the compounds under a single experimental condition. Here, we report the availability of sensitive real-time gasphase measurement to estimate the formation mechanism of low-chlorinated benzenes during the heating of real and model fly ash mixed with various metal species using the recently developed vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS) (7). Comparing four species of metal (copper, iron, lead, and zinc) and their oxides, chlorides, and other forms, we show that metallic compounds identify the real-time formation of low-chlorinated benzenes from model fly ash under the same experimental conditions. Realtime change pattern features of many types of samples mixed with metal species suggest the main factor for the generation of gas-phase chlorobenzenes and other chlorinated organic compounds, such as dioxins scattered from real fly ash in MSWIs.

Materials and Methods Real and Model Fly Ash. Real fly ashes were collected from a bag filter (BF) and electrostatic precipitator (ESP) at a MSWI. Any organic compounds in activated carbon (Takeda Phar10.1021/es1008888

 2010 American Chemical Society

Published on Web 06/15/2010

maceutical Co., Ltd., Osaka, Japan) were removed by heating at 500 °C for 60 min under a 100% nitrogen gas stream (100 mL/min), and removed activated carbon was referred to as “AC” in this report. The AC contained few metal species. To determine the effect of metal species, model fly ashes were prepared and mixed by grinding the following in a mortar for about 10 min: AC (3.0 wt %), potassium chloride (KCl; 10 wt % Cl), metal compounds (0.2 wt % metal), and silicon dioxide (SiO2; remainder). Note that model fly ash without metal compounds, a mixture of AC+KCl+SiO2, was called a “blank” in the previous report. Metal species included CuCl2 · 2H2O (purity 97%), Cu2(OH)3Cl known as atacamite (high purity; Nichika Corp., Kyoto, Japan), CuCl (95%), CuO (97.5%), Cu2O (99.5%), Cu(OH)2 (>95%), CuCO3 · Cu(OH)2 · 2H2O (55% as Cu), FeCl3 (97%), FeCl3 · 6H2O (99%), FeCl2 · 4H2O (>99%), Fe2O3 (95%), PbCl2 (99%), PbO (99%), ZnCl2 (98%), and ZnO (99%). Low-Chlorinated Benzenes Monitored by VUV-SPI-ITTOFMS. A 5.0 g portion of real or model fly ash was inserted on a quartz boat into a quartz tube (120 cm × 4 cm i.d.) filled with 10% oxygen (90% nitrogen) gas at 50 mL/min and heated for 30 min in an electronic furnace preheated to 300 °C. Connected to VUV-SPI-IT-TOFMS at the outlet of the quartz tube, we measured real-time changes in low-chlorinated benzenes in the outlet gas, as illustrated in Figure S1 in the Supporting Information (SI). Low-chlorinated benzenes in gas phase were ionized by a single photon of vacuum ultraviolet, Lyman R light (wavelength, 121.6 nm; photon energy, 10.2 eV), and the target ions were trapped and ionized in the ion trap, and detected by a time-of-flight mass spectrometer. The VUV light (1014 photons cm-2 s-1) is introduced through a MgF2 window into the ion trap in the vacuum chamber. The ionization efficiency by VUV-SPI-ITTOFMS did not decrease, as reported previously in detail (6). As the ionization intensity is maintained by integration, highly sensitive real-time measurements can be made. Achieved one-measurement time was ca. 18.3 s. By controlling the temperature at 300 °C and inserting the quartz boat as quickly as possible, we monitored mono-, di-, and trichlorobenzenes, called M1CBz (monochlorobenzene), D2CBz (1,4-dichlorobenzene), and T3CBz (1,2,4-trichlorobenzene), per 20 s in the outlet gas from the connection at 50 mL/min (see Figure S2b). The lower detection limit was determined to be ca. 10 ppt level of T3CBz. In the following figures, the dashed and bold lines indicate data per 20 s and the moving average data of 11 points (i.e., 0, (20, (40, (60, (80, (100 s each time). Toluene in an impinger trapped organics in the outlet gas (also 50 mL/min) and was also analyzed by GC/MS for D2 and T3CBz. The GC/MS analysis procedure has been reported elsewhere (15).

Results and Discussion Formation of Gas-Phase Low-Chlorinated Benzenes from Heated Real Fly Ashes. We succeeded at monitoring the high-resolution real-time change of CBzs in gas phase. When two real fly ashes were heated at 300 °C for 30 min in an electric furnace, low-chlorinated benzenes generated in gas phase (Figure 1). Two-type raw fly ashes contained 10 ng/g levels of D2 and T3CBz, respectively. Reheating fly ashes generated two or more order higher contents of D2 and T3CBz. Although volatilization of remaining low-chlorinated benzenes was partly thought to influence real-time measurement, we assessed its effect as negligible. As the concentration of M1CBz had a higher baseline than that of D2 and T3CBz, its precise concentration was determined by deduction of the baseline as explained in Figure S2a. Focusing attention on the position and height of the first peak defined as the time (min) and height (ppb) of the first appearance of peaks in the real-time pattern, the first peak positions of M1, D2, and T3CBz were 4.0, 14.2, and 15.0 min

FIGURE 1. Gas-phase real-time change patterns of lowchlorinated benzenes generated from reheating real fly ashes captured at a bag filter (left side) and electrostatic precipitator (ESP; right side) at 300 °C for 30 min as measured by VUV-SPI-IT-TOFMS.

TABLE 1. Various First Peak Positions and First Peak Heights of Real-Time Change Patterns of Model and Real Fly Ashesa first peak position (min) first peak height (ppb) metal compounds M1CBz D2CBz T3CBz M1CBz D2CBz T3CBz A. oxide-like compounds of copper CuO 11.0 14.8 16.0 400 Cu2O 13.1 14.5 15.9 410 15.5 14.0 15.3 340 Cu(OH)2 CuCO3 · Cu(OH)2 · 10.0 12.9 14.3 320 2H2O CuCl2 · 2H2O Cu2(OH)3Cl CuCl

620 550 230 580

520 390 250 550

B. chloride-like compounds of copper 10.8 20.0 22.5 5500 1200 11.8 11.6 14.0 3300 3000 13.2 19.1 22.0 1200 700

850 2000 350

FeCl3 FeCl3 · 6H2O FeCl2 · 4H2O

C. chlorides of iron 11.0 12.5 13.5 6300 11.2 12.1 13.1 4500 11.8 12.5 14.8 6100

1300 310 430

230 20 30

blank Fe2O3 PbO ZnO PbCl2 ZnCl2

D. blank-like compounds 6.0 n.d. n.d. 200 10.0 n.d. n.d. 180 10.0 n.d. n.d. 90 11.0 n.d. n.d. 160 12.5 n.d. n.d. 120 12.2 n.d. n.d. 200

n.d. n.d. n.d. n.d. n.d. n.d.

n.d. n.d. n.d. n.d. n.d. n.d.

fly ash (BF) fly ash (ESP)

4.0 12.8

370 230

360 110

real fly ashes 14.2 15.0 15.8 16.2

1300 2300

a

These two values clearly divided the real-time change patterns into four group types: (A) oxide-like compounds of copper, (B) chloride-like compounds of copper, (C) chlorides of iron, and (D) blank-like compounds. n.d. ) not detected.

(captured by BF), and 12.8, 15.8, and 16.2 min (ESP), respectively; first peak heights showed 1300, 370, and 360 ppb (BF), and 2300, 230, and 110 ppb (ESP), respectively (Table 1). Then, we needed to specify causative elements to generate gas-phase low-chlorinated benzenes from the heated solid phase of real fly ash. However, real fly ash contains numerous elements. As chlorinated benzenes have chlorine in their chemical structure, a chlorine source in real fly ash is thought to be important to assess the promoting factor in gas-phase formation of low-chlorinated benzenes. Inorganic chlorines, such as KCl and NaCl, were the main chemical forms of chlorine in real fly ash reported by Zhu et al. (16). So, we prepared a simple model fly ash, calling it the blank, containing KCl as the chlorine source, a carbon source (AC), and SiO2 matrix. Although the first peak height of the blank was detected as 200 ppb at 6.0 min in M1CBz, D2 and T3CBzs were not detected (Figure 2a and Table 1). VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 2. Real-time change in low-chlorinated benzenes from model fly ashes without metal compounds (blank) (a) and with copper oxides (b and c), hydroxide (d), basic copper carbonate dehydrate (e), and ferric, lead, and zinc oxides (f, g, and h, respectively) detected by VUV-SPI-IT-TOFMS.

FIGURE 3. Real-time change in low-chlorinated benzenes from model fly ashes with cupric chloride dehydrate (a), atacamite (b), cuprous chloride (c), ferric chloride (d), and hexahydrate (e), ferrous chloride tetrahydrate (f), lead chloride (g), and zinc chloride (h) detected by VUV-SPI-IT-TOFMS.

The influence of KCl on the formation of gas-phase lowchlorinated benzenes was much less than that of real fly ashes. As for the formation of solid-phase chlorinated aromatics, inorganic chloride also showed little influence (15, 17, 18). To estimate the effective element, we should study other chlorine sources or catalysts such as trace metal compounds in real fly ash. Metal Species Specify the Real-Time Change Patterns of Exhausted Chlorobenzenes. Model fly ashes containing various metal compounds consisting of Cu, Fe, Pb, and Zn showed characteristic gas-phase real-time change patterns during heating at 300 °C for 30 min (Figures 2 and 3, Table 1). Some metal compounds had a stronger influence than real fly ashes on the formation of chlorinated benzenes in gas phase. Hence, some trace metal compounds in real fly ash were concluded to be the causative elements to promote gas-phase low-chlorinated benzenes. In this section, we discuss the real-time change patterns characterized by metal compounds. The metal compounds could be divided clearly into four major groups by comparing the shapes of the real-time change patterns: (A) oxide-like compounds of copper, (B) chloride-like compounds of copper, (C) chlorides of iron, and (D) blank-like compounds. First, however, we verified the accuracy of the real-time VUV-SPI-IT-TOFMS measurements by correlation with the concentrations of D2 and T3 benzenes in a toluene trap as analyzed by GC/MS. Calculating the area of real-time change excluding the baseline, we estimated the amounts of M1, D2, and T3CBz in gas phase for 30 min during the heating of each model fly ash (Figure S3). Figure S4 shows that the order of the area calculated

indicated a positive correlation with the order of concentrations of D2 (r ) 0.79) and T3CBz (0.83) as determined by GC/MS. The group D blank-like compounds contained the blank (Figure 2a), ferric, lead, and zinc oxides (Fe2O3, PbO, and ZnO; Figure 2f, g, and h, respectively), and lead and zinc chlorides (PbCl2 and ZnCl2; Figure 3g and h, respectively). The first peak heights of M1CBz were the smallest and between 90 and 200 ppb appeared at 6.0-12.5 min (Table 1). For D2 and T3CBz, the first peak heights were not detected by VUV-SPI-IT-TOFMS because the detection limit was thought to be less than 10 ppb in the present study. When model fly ash with added zinc chloride (ZnCl2) and one of the blank-like compounds was heated at 300 °C for an expanded 120 min, gas-phase low-chlorinated benzenes were hardly detected, except for a little formation of M1CBz until around 20 min (Figure 4c). Blank-like compounds had little effect on gas-phase formation of low-chlorinated benzenes during heating. So, we estimated these compounds in real fly ash to have little impact on the generation of gas-phase low-chlorinated benzenes. Causative metal compounds associated with the generation of low-chlorinated benzenes in gas phase were considered to belong to three groups: A, B, and C. Copper forms bonded to an oxygen atom, not to chlorine (oxide-like compounds of copper in group A), cupric oxide (CuO; Figure 2b), cuprous oxide (Cu2O; Figure 2c), cupric hydroxide [Cu(OH)2; Figure 2d], and basic copper carbonate dihydrate [CuCO3 · Cu(OH)2 · 2H2O; Figure 2e], showed the same original real-time change patterns. The first peak positions (mean values) of real-time changes in M1, D2, and T3CBz appeared at 12.4, 14.1, and 15.4 min, respectively; first peak heights of

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FIGURE 4. Three types of real-time change patterns for 120 min. Atacamite [Cu2(OH)3Cl] (a), ferric chloride (b), and zinc chloride (c) represent chloride-like compound of copper, iron chlorides, and blank-like compounds, respectively. One representative real-time change pattern by oxide-like compounds of copper (b-e, as shown in Figure 2) was not measured for the 120-min span. M1, D2, and T3CBz showed the same level at 320-410, 230-620, and 250-550 ppb, respectively (Table 1). Therefore, low-chlorinated benzenes were distributed in the sequence M1 (12.4 min) f D2 (14.1 min) f T3CBz (15.4 min), at the same level at 430 ( 132 (standard deviation) ppb (n ) 12) in the case of mixtures of the group A oxide-like compounds (Figure 5a). Although the chlorine source was only KCl in the model fly ash of group A, the amounts of chlorobenzenes in group A were higher than those of the group D, blank-like compounds (Table 1 and Figure S3). This is because gasphase low-chlorinated benzenes were thought to be catalyzed by copper oxide, and oxide-like forms catalyzed via Deaconlike reaction (19, 20) using KCl as a chlorine source in solid phase. Copper compounds connected to chlorine, called chloridelike compounds of copper (group B in this paper) such as cupric chloride dihydrate (CuCl2 · 2H2O), atacamite (Cu2(OH)3Cl), and cuprous chloride (CuCl), showed characteristic real-time change patterns and strongly affected the gas-phase formation of low-chlorinated benzenes. Chlorobenzenes in gas phase changed with first maximum peaks at around 11.9 (M1CBz), 16.9 (D2), and 19.5 (T3) min and ordered M1 (3300 ppb, mean) > D2 (1600 ppb) > T3CBz (1100 ppb) during heating for 30 min (Table 1 and Figure 3a-c). Figure 5b shows the features of first peak positions and heights of M1, D2, and T3CBz of chloride-like compounds in group B. Note that concentrations of chlorobenzenes for 30 min from Cu(II) chlorides were much higher than those from Cu(I) chloride, according to Figure S3. When the heating time was expanded over 30 min, the amounts of low-

FIGURE 5. Characteristic features of the first peak positions and heights of oxide-like compounds of copper (a), chloridelike compounds of copper (b), and chlorides of iron (c), respectively. chlorinated benzenes in gas phase inverted from M1 > D2 > T3 to T3 > D2 > M1CBz generated from heated model fly ash mixed with Cu2(OH)3Cl in group B, as shown in Figure 4a. A small wave of real-time change was thought to be derived from a temperature fluctuation (10 °C caused by the control mode of stable temperature at 300 °C of the electric furnace. The CuCl2 · 2H2O in Figure 3a and CuCl in Figure 3c also show that M1CBz decreased gradually, D2CBz remained stable, and T3CBz increased gradually over 20 min. Generally, the boiling points of chlorobenzenes are positively proportional to the number of chlorines bonded with benzene (M1CBz, 132.0 °C; 1,4-(D2)CBz, 174.0 °C; 1,2,4-(T3)CBz, 213.5 °C) (21). However, in the case of chloride-like compounds of copper, the volatilization of low-chlorinated benzenes showed the inverse property (T3 > D2 > M1CBz) over 30 min under heating at 300 °C. This was thought to be intimately linked with the chlorination mechanism of carbon in solidphase fly ash. Our previous X-ray spectroscopic study (22) revealed that the immediate reduction of copper, Cu(II) f Cu(I), at around 300 °C plays a key role in the chlorination mechanism of the carbon matrix in the solid phase of a fly ash, and the consumption of organic carbon increased rapidly VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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during heating for 30 min. These results implied that the second gas-phase real-time formation pattern over 30 min, T3 > D2 > M1CBz (Figure 4a), was caused by the thermal destruction of carbon. Chlorides of iron have been reported to be effective promoters of the formation of chlorinated aromatic compounds in solid phase such as fly ash (15, 23). In gas phase, chlorides of iron also had a strong effect on the generation of chlorinated aromatics from the real-time measurements using VUV-SPI-IT-TOFMS. Without the valence of Fe(II) or Fe(III), chlorides of iron (ferric chloride, FeCl3; ferric chloride hexahydrate, FeCl3 · 6H2O; and ferrous chloride tetra-hydrate, FeCl2 · 4H2O) in group C promoted the same level of lowchlorinated benzenes (Figure S3) and exhibited an original pattern of real-time change, as shown in Figure 3d, e, and f, respectively. The first peak positions of M1, D2, and T3CBz occurred at about 11.3, 12.4, and 13.8 min, respectively. Specifically, these were distinguished from other metal compounds in that more lower chlorinated benzenes were generated in gas phase during heating, i.e., M1 (5600 ppb, first peak height) . D2 (680 ppb) . T3CBz (93 ppb) (Table 1, Figures S3 and 5c). Heating for 120 min, the real-time amounts of low-chlorinated benzenes, M1, D2, and T3CBz, remained stable at around 4000, 300, and 100 ppb, respectively, over 30 min (Figure 4b). According to these results, the lower chlorinated benzene in gas phase was preferentially promoted by iron chlorides. Promotion of chlorinated aromatic compounds in fly ash (solid phase) by oxychlorination of iron chloride (24) is thought to cause the formation of low-chlorinated benzenes in gas phase. Effect of Metal Species in Real Fly Ash Analyzed by RealTime Features. According to the real-time changes of M1, D2, and T3CBz in the model system categorized into four groups, we attempted to infer the contribution to the gasphase formation of low-chlorinated benzenes from real fly ash. We plotted first peak positions and heights from groups A through D in a two-dimensional plane (Figure 6) to identify the metal compounds causing the formation of gas-phase low-chlorinated benzenes from heated real fly ashes collected by BF and ESP (Figure 1). If a plot of a real fly ash was included in the area composed of each group, low-chlorinated benzenes in gas phase were estimated to be influenced mainly by the metal compounds in each group. Figure 6a shows that the plot of M1CBz from real fly ash collected by ESP was included in group B. The first peak height of M1CBz from real fly ash collected by BF had the same level of chloridelike compounds of copper, although real fly ash (BF) showed the most rapid first peak position, 4.0 min, in all samples (Table 1). More real-time patterns of real and model fly ashes were needed by VUV-SPI-IT-TOFMS to reveal the correct factors. Yet, trace chloride-like compounds of copper in real fly ash were implied to affect mainly the formation of gasphase M1CBz. The area of group A for D2 and T3CBz (Figure 6b and 6c, respectively) contained the plot of real fly ash collected by BF and located the nearest plot of real fly ash collected by ESP. So, oxide-like compounds of copper (group A) in real fly ash were thought to be the main causative metallic compounds in the catalytic formation of D2 and T3CBz in gas phase. The amount of copper (0.20-0.26 wt %) was less than that of Fe (0.47-1.0 wt %), Pb (0.52-0.75 wt %), and Zn (1.4-1.7 wt %) in these real fly ashes, which we have measured before (25). However, the relatively trace copper compounds (e.g., oxides, chlorides) in a real fly ash seemed to make the most powerful contribution to the gasphase formation of low-chlorinated benzenes. The influences of lead and zinc compounds (oxides and chlorides) in real fly ash on the formation of gas-phase low-chlorinated benzenes were thought to be rather weak in terms of the real-time measurement of model fly ashes (Table 1). Although iron chlorides showed strong contributions to the formation 5532

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FIGURE 6. Two-dimensional plots between first peak positions and first peak height of M1CBz (a), D2CBz (b), and T3CBz (c). Groups A, B, C, and D are characteristic groups of oxide-like compounds of copper, chloride-like compounds of copper, chlorides of iron, and blank-like compounds, respectively. of gas-phase low-chlorinated benzenes, iron oxide had a weak contribution. The main chemical form of iron in real fly ash has been summarized as oxides (Fe2O3 and FeO) by Kirby and Rimstidt (26). Thus, we suggest that iron compounds in real fly ash did not have a great influence on the generation of gas-phase low-chlorinated benzenes. Nonetheless, some part of the chemical form of iron in real fly ash may exist in a chloride form to strongly promote gas-phase low-

chlorinated benzenes. These results using real-time features such as the first peak position and height indicate the importance of trace metal compounds, especially chlorideand oxide-like compounds of copper, in real fly ash on the generation of gas-phase low-chlorinated benzenes. Our novel research using VUV-SPI-IT-TOFMS provides useful and original knowledge to characterize the gas-phase formation of low-chlorinated benzenes. We concluded that real-time sensitive measurements of M1, D2, and T3CBz offer not only real-time features, but also the identification of causative factors by comparing model and real samples. The thermal process is thought to be a major anthropogenic source of gas-phase low-chlorinated benzenes. Thus, the monitoring and characterization of thermal processes by VUV-SPI-IT-TOFMS may contribute more detailed scientific information to protect the environment from pollution by low-chlorinated benzenes.

Acknowledgments We thank S. Morisawa, N. Matsuyama, J. S. Komatsu, and A. Shiono for supporting this study; N. Senba and other staff for helping with VUV-SPI-IT-TOFMS measurement at Mitsubishi Heavy Industries, Ltd.

Supporting Information Available Four supporting figures. This information is available free of charge via the Internet at http://pubs.acs.org.

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