Environ Geochem Health DOI 10.1007/s10653-013-9579-y
ORIGINAL PAPER
Occurrence and particle-size distributions of polycyclic aromatic hydrocarbons in the ambient air of coking plant Xiaofeng Liu • Lin Peng • Huiling Bai Ling Mu • Chongfang Song
•
Received: 2 February 2013 / Accepted: 29 October 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract The purpose of this study was to characterize the occurrence and size distributions of ten species of polycyclic aromatic hydrocarbons (PAHs) in the ambient air of coking plants. Particulate-matter samples of four size fractions, including B2.1, 2.1–4.2, 4.2–10.2, and C10.2 lm, were collected using a Staplex234 cascade impactor during August 2009 at two coking plants in Shanxi, China. The PAHs were analyzed by a gas chromatograph equipped with a mass-selective detector. The concentrations of total particulate-matter PAHs were 1,412.7 and 2,241.1 ng/m3 for plants I and II, and the distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm for plant II. The size distributions of individual PAHs (except fluoranthene) exhibited a considerable peak within the 0.1–2.1 lm size range in coking plant I, which can be explained by the gas–particle partition mechanism. The ambient air of the coking plant was heavily polluted by PAHs associated with fine particles (B2.1 lm), and benzo[b]fluoranthene made the largest contribution to total PAHs. The exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to PAHs
X. Liu L. Peng (&) H. Bai L. Mu C. Song College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, People’s Republic of China e-mail: [email protected]
associated with coarse particles. Benzo[b]fluoranthene, benzo[a]pyrene, and dibenzo[a,h]anthracene should be the primary pollutants monitored in the coking plant. This research constitutes a significant contribution to assessing the exposure risk of cokingplant workers and providing basic data for PAH standards for ambient air in coking plants. Keywords Polycyclic aromatic hydrocarbons Size distribution Ambient air Coking plant Size-resolved gas–particle partition coefficients (Kp) Equivalent concentration of benzo[a]pyrene
Introduction Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous semi-volatile organic compounds that contain two or more fused aromatic rings. Several PAHs are known to have carcinogenic, teratogenic, and mutagenic properties, and benzo[a]pyrene (BaP) is carcinogenic to humans according to IARC (2010). PAHs are often associated with suspended particulate matter (PM) in the air at ambient temperatures. Generally, lighter PAHs with 2–3 aromatic rings occur mainly in the gaseous phase, PAHs with 4 rings occur in the gaseous and particulate phases, and heavier ones (5–6 rings) are associated mainly with airborne particles (Hoff and Chan 1987).
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PAHs are widespread environmental contaminants which are emitted from incomplete combustion of organic materials (Bae et al. 2002), for example from coal and coke burners, diesel-fueled engines, grilled meats, and cigarettes. Coking is an important coalconversion process in which prepared coal is heated in an oxygen-free atmosphere. Large quantities of PAHs are released during the coking process. Studies on PAHs from coking emissions in various countries in the world have been conducted (Liberti et al. 2006; Liberti et al. 2004; Romundstad et al. 1998). These studies have identified and quantified several PAH compounds in samples collected from the coke-oven top, lorry-car operator, coke-car operator, and pushcar operator. The total PAH concentration (particulate and gaseous) from the coking process was 357 g/m3 as reported by Liberti et al. (2006). Six PAHs, naphthalene (Nap), pyrene (Pyr), benzo[b]fluoranthene (BbF), indeno[1,2,3-cd]pyrene (InP), BaP, and acenaphthylene (AcPy), contributed to approximately 77 % of total PAHs detected in emissions from coke batteries (Liberti et al. 2006). BaP and dibenzo[a,h]anthracene (DbA) are mostly responsible (approximately 85 %) for the powerful carcinogenicity of emissions from coke batteries (Liberti et al. 2006). The average concentration of total PAHs (particulate and gaseous) during the coking process is 500 lg/m3 as reported by Liberti et al. (2004). BaP is the typical primary contaminant emitted from the coking process. Near coke-oven batteries, levels of BaP may range from 100 to 200 lg/m3 on the machinery and discharge side of a battery roof and may be approximately 400 lg/m3 at the battery top (World Health Organization 2006). The total concentration of 20 species of PAHs, including gas- and solid-phase compounds collected 100 m directly downwind of a coking plant located in southeastern Chicago, was approximately 25 lg/m3 (Khalili et al. 1995). PAHs with two and three rings were responsible for 98 % of the total measured PAH concentration for a coke oven, as reported by Khalili et al. (1995). In the ambient air of the coke-oven top, PAH concentrations have been measured together with different particle sizes. A study of the size distribution of PAHs emitted from the coke-oven top illustrated that over 90 % of PAHs were found on particles smaller than 3 lm, which means that most of these compounds were within the respiratory size range (Broddin et al. 1977). Broddin et al. (1977)
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also reported that similar size-distribution curves were obtained for both lower and higher molecular weight compounds. To the best of our knowledge, the PAH size distribution in the ambient air of coking plants has been little investigated. The ambient air of coking plants is a special environment existing between the urban atmosphere and the coking pollution sources. The particle-bound PAHs in the atmospheric environment of the coking plant have unique characteristics. The PAHs associated with fine particles seriously affect the health of coking-plant workers; therefore, study of PAH size distributions in the ambient air of the coking plant is significant. To collect more information and experimental evidence, an investigation of the occurrence and size distribution of PAHs in the ambient air of the two coking plants was carried out. The aims of this work were to (1) characterize the distribution profile of PAHs associated with particles, (2) investigate the particle size-distribution characteristics of PM and PAHs, and (3) estimate the human health risk associated with respiratory exposure to PAHs using toxicity equivalency factors (TEFs). The results of this study are important for evaluating the risk of occupational exposure to particle-bound PAHs and for determining a concentration threshold for individual PAHs associated with fine particles.
Materials and methods Sample collection Size-segregated aerosol samples were collected from the two coking plants on 15 days between August 13 and 28, 2009 in Shanxi, China (Fig. 1). Sampling was conducted on days with little or no wind and a temperature range of 22 to 33 °C. Coking plant I is more than 1 km from G55 Erguang Expressway and 108 National Road. Coking plant II is next to Jiuyuan East Street, and its sampling site is located approximately 20 m south of Jiuyuan East Street and about 260 m east of Yunzhongshan North Road. The sampling sites were established at the dedusting ground stations of coking plants I and II, which were 5 and 4 m, respectively, above the ground. Basic information about the coking plants investigated is shown in Table 1.
Environ Geochem Health Fig. 1 Location map of the coking plants investigated, Shanxi, China
Table 1 Basic information about the investigated coking plants Coking plant
I
II
Annual capacity (9 103 t)
864.0
251.9
Technique for coal charging
Stamp charging
Stamp charging
Height of the coke oven (m)
4.3
3.2
Air pollution control device
Baghouse filter
Baghouse filter
Coking time (h)
24
24
Output rate (t/d)
2,376
690
Airborne particles were collected using a Staplex234 four-stage high-volume cascade impactor (made in the USA) at a flow rate of 0.565 m3/min. The cascade impactor can fractionate suspended particulates into as many as five size fractions. Impactor cut-points are nominally 10.2, 4.2, 2.1, and 1.4 lm, with the last stage collecting all particles smaller than 1.4 lm. To highlight the characteristics of PAHs associated with particles less than 2.1 lm in diameter, four categories, including B 2.1, 2.1–4.2, 4.2–10.2, and C 10.2 lm, were analyzed in this study. The size of the slotted media used between each impactor stage was 14.3 9 13.7 cm, and the size of the high-volume backup media was 20.3 9 25.4 cm. Glass fiber filters (GFFs) were used as a surrogate surface and placed on each impaction plate to collect the impacted particles of different sizes. The GFFs must be flat to collect the particles exiting the cascade impactor.
The GFFs were wrapped in aluminum foil and baked at 500 °C for 5 h to volatilize any organic contaminants before sampling. Size-separated samples were taken over periods of 3–4 h, and the total sampling volume was approximately 100–140 m3. All the experiments for each sampling point in each plant were repeated 3–4 times to make sure that the results were reproducible. In this study, all data shown are the average of measured results for each experiment. The GFFs were weighed before and after sampling to determine the amount of particles collected. The GFFs were equilibrated for 48 h at 25 °C and 50 % RH in a temperature and humidity chamber before weighing on a micro-balance (Sartorius LA130S-F) accurate to 0.1 mg. After sampling, the GFFs were removed from the impactor, folded with the adsorbed particulate matter on the inner side, wrapped in aluminum foil, and stored frozen at -20 °C for a maximum of 1 week before analysis. Extraction and analysis The extraction procedure for removing PAHs from the particulate matter used a Soxhlet apparatus. Surrogate deuterated PAHs (naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, and perylene-d12) were added before extraction. The filters were cut into strips and extracted for 48 h with dichloromethane (DCM). Then, the organic extracts were concentrated on a rotary evaporator and fractionated on a silica gel column. The elute of the PAH fraction was concentrated to 1 mL under a gentle stream of dry nitrogen, transferred to 1.5 mL vials, and preserved in a refrigerator at -20 °C until analysis.
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The internal standard pyrene-d10 was added for quantification of individual PAHs. The particle-bound PAHs were analyzed by a gas chromatograph equipped with a mass-selective detector (Thermo Fisher, Focus GC/ DSQII) and a computer workstation. A 30 m 9 0.25 mm i.d. DB-5MS (film thickness 0.25 lm) was used. The chromatographic conditions were as follows: injection volume 1 lL, splitless injection at 250 °C, and ion source temperature 300 °C. The temperature program was 50 °C for 3 min, then to 200 °C at a rate of 15 °C/min and hold for 5 min, then to 310 °C at a rate of 3 °C/min and hold for 10 min, for a total duration of 70 min. The masses of primary and secondary PAH ions were determined in the scan mode. Quantitation of PAHs was performed in the selected ion-monitoring (SIM) mode. The species of EPA’s 16 priority-controlled PAHs are as follows: naphthalene (Nap), acenaphthylene (AcPy), acenaphthene (Acp), fluorene (Flu), phenanthrene (PhA), anthracene (AnT), fluoranthene (FLuA), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DbA), indeno[1,2,3-cd]pyrene (InP), and benzo[ghi]perylene (BghiP). Based on their molecular weight and volatility, the 16 PAHs were divided into three groups: lighter PAHs with 2–3 aromatic rings and molecular weights less than 178 were denoted as PAHs(2,3), including NaP(2), AcPy(3), AcP(3), Flu(3), PhA(3), and AnT(3); medium PAHs with four rings and molecular weights ranging between 202 and 228 were denoted as PAHs(4), including FluA(4), Pyr(4), BaA(4), and Chr(4); and heavier PAHs with 5–6 rings and molecular weights of 252–278 were denoted as PAH(5,6) and consisted of BbF(5), BkF(5), BaP(5), DbA(5), InP(6), and BghiP(6). PAH vapor pressures are strongly correlated with molecular weight and decrease with increasing molecular weight. The PAHs(4,5,6) with higher molecular weight are easier to adsorb on particulate matter, while the PAHs(2,3) exist mainly in the gas phase. Therefore, the particle-size distributions of PAHs(4,5,6), including 10 species of PAHs, are discussed in this paper. The concentrations of individual PAHs were calculated by dividing their mass by the sampling volume and are expressed in ng/m3. The total PAH concentrations were defined as the sum of the concentrations of PAHs(4,5,6). BaP has been previously used as an indicator of carcinogenic PAHs, but BaP provides little information for most other PAHs. In recent years, the TEF methodology has been recommended to assess the risk
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associated with PAH exposure (Nisbet and Lagoy 1992; Petry et al. 1996; Bieniek and Lusiak 2012). The cancer incidence of different dose and group PAHs was obtained by testing on mice (Deutsch-Wenzel et al. 1983; LaVole et al. 1982; Habs et al. 1980; Pfeiffer 1977). The TEFs were calculated using the data from each study by applying the same mathematical model of the dose-response relationship to the data for each compound and comparing the results to those obtained for BaP (Clement 1988). The TEFs used in this paper were reported by Nisbet and Lagoy (1992), who modified the TEF approaches presented by Chu and Chen (1984) and Clement (1988). Stationary sampling data are, however, regarded as appropriate because there is no indication for the existence of a major difference in PAH profiles between stationary samples and personal samples (Petry et al. 1996). This study has focused on the assessment of workplace exposure for coking-plant workers using stationary sampling data. The potential toxicity of a mixture of 10 PAH species was determined by applying TEFs (Nisbet and Lagoy 1992) to the concentrations of individual PAHs and summing the equivalent concentrations. The total BaP equivalent concentrations (BaPeq) were defined as the sum of the BaPeq of PAHs(4,5,6). Quality assurance and quality control (QA/QC) The analytical recovery efficiencies of the 16 individual PAHs were determined by adding surrogate deuterated PAHs (naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, and perylene-d12) to all samples, which made it possible to monitor procedural performance and matrix effects. The mean recoveries of the 16 PAHs ranged from 75.2 to 108.7 % (SD = ±13 %). Blank samples were analyzed to quantify sample contamination from materials and equipment using the same procedure as the recovery-efficiency tests without adding the known standard solution before extraction. Analyses of field blanks revealed no detectable contamination.
Results and discussion PAH distribution profiles The average concentrations of total PAHs in the two coking plants are presented in Table 2. The total PAH
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levels associated with fine particles (B 2.1 lm) were significantly higher than those for other particle sizes. Whitey (2007) reported that fine particles were produced predominantly from gas-to-particle conversion and from incomplete combustion, whereas coarse particles originated mainly from mechanical processes which were originally only slightly contaminated. During the coking process, PAHs exist mainly in the gas phase or in association with fine particles. After emission, PAHs can become associated with coarse particles either during the growth of fine combustiongenerated particles or by volatilization from fine particles followed by condensation onto coarse particles (Allen et al. 1996). Therefore, the relative contributions of total PAHs in fine particles were high in the ambient air of the two coking plants, 93.4 and 70.1 % in coking plants I and II, respectively. This result was consistent with Broddin’s finding (1977) that over 90 % of PAHs were found on particles smaller than 3 lm on the coke-oven top. Table 2 also indicated that the average concentrations of total particulate-matter PAHs (B 10.2 lm) were 1,137.4 and 1,930.2 ng/m3 in coking plants I and II, respectively, which are significantly lower than those on the coke-oven top (6,800 and 2,100 ng/m3), but higher than that in the ambient air of steel plants (600 ng/m3) as reported by Tsai et al. (1996). The difference in total PAH concentrations between the two coking plants can be explained by the height of the coke ovens, their annual capacity, and the effect of road dust (Han et al. 2009). The concentrations of individual PAHs in differentsized particles in the two coking plants are listed in Table 3, and the contributions of individual PAHs relative to total PAHs in different-sized particles are presented in Fig. 2. In particles with diameters less
than 2.1 lm, the PAH distribution profiles were similar in plants I and II. BbF made the largest contributions (34.5 and 37.6 %) to the total amount of PAHs. Within the 2.1–4.2, 4.2–10.2, and C 10.2 lm size ranges, the contribution characteristics of individual PAHs were significantly different in the two coking plants. In coking plant I, the contributions of individual PAHs had similar characteristics in these three size ranges, and the largest contributor of PAHs was FluA, followed by Pyr. In coking plant II, the relative contributions of individual PAHs were similar in the three size ranges, but the contribution of BbF was slightly higher than those of other PAHs. The differences between the two coking plants described above are partly attributable to the influence of vehicular emissions. Coking plant I is relatively far from major transportation roads, while coking plant II is near Jiuyuan East Street and Yunzhongshan North Road, as can be seen in Fig. 1. Previous studies (Khalili et al. 1995; Manoli et al. 2002) reported that the contributions of FLuA, Pyr, BaA, and Chr from coke-oven emissions were significantly higher than those from vehicular emissions, while the contributions of BbF, BkF, BaP, InP, DbA, and BghiP from coke-oven emissions were significantly lower than those from vehicular emissions. The relative contribution characteristics of individual PAHs in coking plant II, shown in Fig. 2b), were the result of synthetic interaction between coke-oven emissions and vehicular emissions. The relative contributions of individual PAHs in the ambient air of coking plant I were similar to the source composition of coke-oven emissions as reported by Khalili et al. (1995); therefore, PAHs in plant I can be said to come mainly from coke-oven emissions. The characteristics of PAHs in coking plant I were minimally affected by
Table 2 Concentrations and contributions of total PAHs and total BaPeq for different-sized particles in the two coking plants Size range (lm)
Total PAHs
Total BaPeq
Concentration (ng/m3)
Contribution (%)
Concentration (ng/m3)
Contribution (%)
Plant I
Plant II
Plant I
Plant II
Plant I
Plant II
Plant I
Plant II
1,082.7
1,439.9
93.4
70.1
169.1
265.4
90.7
56.9
2.1–4.2
28.9
304.9
2.5
14.8
6.7
112.5
3.6
24.1
4.2–10.2
25.8
185.4
2.2
9.0
4.2
53.4
2.3
11.4
C10.2
21.6
123.9
1.9
6.0
6.4
35.3
3.4
7.6
B2.1
123
123
30.7
65.3
154.4
95.2
373.8
93.9
38.8
98.0
11.2
121.4
Pyr
BaA
Chr
BbF
BkF
BaP
InP
DbA
BghiP
B2.1
Plant I
0.3
0.7
1.3
2.3
3.6
1.0
3.4
2.5
4.6
9.2
2.1–4.2
0.9
0.4
1.4
1.6
2.3
1.2
3.3
0.0
4.7
10.0
4.2–10.2
PAH concentration (ng/m3)
FLuA
Particle size (lm)
0.9
0.9
1.5
1.4
1.7
1.1
2.6
0.0
3.8
7.7
C10.2
7.8 17.4 5.5 16.0
41.9 14.5 38.3
154.7 26.9 147.8
29.9
43.3
541.3 17.4
23.9
30.3
216.9 18.8
25.6
35.3
154.9
25.3
16.9
24.8
30.8
25.0
32.4
7.7 45.9
113.0
4.2–10.2
2.1–4.2
B2.1
Plant II
9.8 56.0 1.2
3.5 14.4
37.4
21.4
14.6
1.0
13.4 9.4
15.4
14.5
38.8
0.1
9.9
5.1
0.0
15.2
11.9
B2.1
C10.2
Plant I
0.0
3.5
0.1
2.3
0.4
0.1
0.0
0.3
0.0
0.0
2.1–4.2
0.0
2.0
0.1
1.6
0.2
0.1
0.0
0.0
0.0
0.0
4.2–10.2
0.0
4.5
0.2
1.4
0.2
0.1
0.0
0.0
0.0
0.0
C10.2
BaPeq concentration (ng/m3)
Table 3 Concentrations of individual PAHs and individual BaPeq in the ambient air of the two coking plants
1.5
134.5
15.5
30.8
11.3
54.1
2.2
15.5
0.0
0.0
B2.1
Plant II
0.4
72.5
4.2
25.3
1.9
4.3
0.3
3.5
0.0
0.0
2.1–4.2
0.2
27.5
1.7
17.4
0.8
3.0
0.2
2.6
0.0
0.0
4.2–10.2
0.1
17.5
1.5
11.9
0.5
2.1
0.1
1.5
0.0
0.0
C10.2
0.01
5
0.1
1
0.1
0.1
0.01
0.1
0.001
0.001
TEF(Nisbet and Lagoy 1992)
Environ Geochem Health
Fig. 2 Relative contributions of individual compounds to total investigated PAHs for different-sized particles: a coking plant I; b coking plant II
other pollution sources, and consequently, the relative contributions of individual PAHs in plant I were representative.
Toxic equivalent concentrations of PAHs
The corresponding BaPeq of different size ranges, obtained on the basis of TEFs as suggested by Nisbet and Lagoy (1992), are presented in Table 2. In the B 2.1 lm size range, the BaPeq concentrations of total PAHs were considerably higher than those in other stages in the two coking plants. Consequently, the exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to those associated with coarse particles. The considerable differences in the BaPeq concentration contribution of PAHs for particles of different size ranges are shown in Fig. 3. For particles less than 2.1 lm, the
Environ Geochem Health
contributions of DbA, BaP, and BbF equivalent concentrations were the highest among the BaPeq of the PAHs. The contributions were 33.1, 23.0, and 22.1 %, respectively, in coking plant I and 50.7, 11.6, and 20.4 % in coking plant II. In the 2.1–4.2, 4.2–10.2, and C 10.2 lm size ranges, the BaPeq contributions of DbA and BaP were significantly higher than those of other PAHs, which were 48.2–70.6 and 22.0–38.6 %, respectively, in coking plant I and 49.6–64.5 and 22.5–33.8 % in coking plant II. Compared with the concentration contributions of individual PAHs, the concentration contributions of BbF, Pyr, and FluA were higher than those of other PAHs, but their BaPeq contributions were lower than the others. The BaPeq contributions of DbA and BaP were higher than those of other PAHs. The BaPeq contribution profile was similar to that of PAHs on the coke-oven top as reported by Petry et al. (1996). Consequently, DbA, BaP, and BbF should be the primary pollutants
monitored in the ambient air of coking plants to reduce the exposure risk of coking-plant workers. PAH particle-size distributions To describe PAH size distributions, the commonly used approach is to plot a histogram of the relative mass of DC/(CtotalDlogDp) versus Dp on a logarithmic scale, where DC/Ctotal is the mass percentage of PAHs on each filter and DlogDp is the size interval for each impactor stage (Hien et al. 2007; Aceves and Grimalt 1993; Venkataramant and Friedlander 1994; Alves et al. 2000; Kawanaka et al. 2004; Whitby et al. 1972). Aceves and Grimalt (1993) and Cancio et al. (2004) took 0.08 and 30 lm as the lower and upper limits of particle size to present the size distribution. In this study, the diagrams shown in Fig. 4 were constructed by taking 0.1 and 30 lm as the lower and upper particle-size limits, respectively. The lower limit was selected based on the results of urban aerosol studies involving size-fraction partitioning devices of 0.01–0.1 lm resolution (Whitby et al. 1972); the upper limit was taken from reported data for aerosols of different origins (Slinn 1983). The mean normalized distributions of PAHs and PM with particle size for the two coking plants are presented in Fig. 4. PM size distribution
Fig. 3 Relative contribution of individual BaPeq to total BaPeq for different-sized particles: a coking plant I; b coking plant II
PM concentrations (four stages plus post-filter) were 1.8 and 2.9 mg/m3 in coking plants I and II, respectively, which were lower than the particle concentrations (10.2 in spring, 6.4 mg/m3 in fall) at the battery top (Bjørseth et al. 1978) and higher than the 470 lg/ m3 obtained from Vietnam (roadside site) in the dry season by Hien et al. (2007). The PM in the ambient air of the coking plant was emitted mainly from the coking process and diluted by diffusion processes. Consequently, PM concentrations in the coking plants were significantly lower than in emissions from the coke oven. The sampling sites were close to the coke oven, and the high particle concentrations were significantly elevated by emissions from chimneys and leaks from the stack area; therefore, the measured PM levels in the coking plants were much higher than at the urban roadside site. Different-sized particles affect the environment and human health differently. To obtain a deep understanding of the atmospheric-pollution situation in the
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Fig. 4 Particle-size distribution of PAHs and PM in the ambient air of the two coking plants. Solid line coking plant I; dotted line coking plant II
coking plant and to establish reasonable preventive countermeasures, it is very important to study particlesize distributions. The PM size distributions from the two coking plants are shown in Fig. 4(l). PM from the two coking plants exhibited a unimodal distribution with a peak in the 0.1–2.1 lm size range. This can be partly explained by the collection efficiency of the baghouse filter used in these coking plants, which is higher for coarse particles than for fine ones. These data indicated that the fine-particle pollution and respiration exposure risk in the coking-plant area were
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severe. The percentage cumulative mass of particulates smaller than 3 lm corresponds to approximately 50 % of the total particulate weight on the coke-oven top (Broddin et al. 1977). The particle-size distribution in the coking-plant area was similar to that on the coke-oven top. The size distribution gives important information about the health effects of inhaled particles in the coking-plant area. Particles less than 3 lm in diameter will penetrate the upper respiratory tract and settle in bronchia and alveoli (Wu et al. 2006). From Fig. 4(l), it is evident that almost all the particles
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in the coking-plant area were less than 2.1 lm in diameter. Emission standard of pollutants for coking chemical industry (GB16171-2012) provides only a concentration limit for PM at the boundary of the coking plant. Fine particles penetrate easily into the respiratory system and cause a serious health risk (Kameda et al. 2005). Therefore, the regulation and monitoring of fine particles should be strengthened to improve working conditions for coking-plant workers. This study provides basic fine-particle concentration data for ambient air in a coking plant. PAH size distributions Figure 4 shows the size distributions of individual and total PAHs in the two coking plants. In coking plant I, the size distributions of individual PAHs (except FluA) exhibited a considerable peak within the 0.1–2.1 lm size range. FluA showed a unimodal distribution in the 2.1–4.2 lm size range, which may have been caused by its low molecular weight. These size distributions show an increase in the fraction of PAHs associated with smaller aerosols as ring number and molecular weight increase. The observation that higher molecular weight PAHs were adsorbed to fine particles while more volatile PAHs were associated with larger particles has been supported by many studies (Venkataraman and Friedlander 1994; Venkataraman et al. 1994; Venkataraman et al. 1999; Allen et al. 1996). Substantial differences were observed for individual PAHs in coking plants I and II (see Fig. 4). In coking plant II, FluA and Pyr exhibited a peak in the 2.1–4.2 lm size range; Chr, BbF, and BkF exhibited a peak in the 0.1–2.1 lm size range; and BaP, InP, DbA, and BghiP exhibited a peak in the 2.1–4.2 lm size range. The two coking plants are in different geographic locations; coking plant I is relatively far from major transportation roads, while coking plant II is close to Jiuyuan East Street and Yunzhongshan North Road. The difference in PAH size distributions in the two plants can be partly attributed to the influence of vehicular emissions. The PAH size distributions, especially PAH(5,6), in coking plant II were affected by vehicular emissions nearby. Pyr, InP, and BghiP were abundant in urban aerosols at the roadside, as reported by Hien et al. (2007). Sheu et al. (1996) reported that InP, DbA, and BghiA exhibited higher fractions in the 1.8–3.2 lm size range in the vicinity of
traffic intersections. Consequently, PAHs emitted from vehicles substantially affected the distribution of high molecular weight PAHs in coking plant II. The PAH size distribution in coking plant I was minimally affected by other pollution sources, and consequently, the PAH characteristics in plant I are representative. The average concentrations of total particulatematter PAHs were 1,412.7 and 2,241.1 ng/m3 for coking plants I and II, respectively. Total PAH size distributions in the ambient air of the two coking plants are shown in Fig. 4(k). The distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm size range for plant II. This result was consistent with the study of Bjørseth et al. (1978), who reported that the largest amounts of PAHs were found in particles within the 0.9–3 lm diameter range on the battery top. The total PAH size distribution in the ambient air of the coking plant was somewhat different from that at the urban site (Wu et al. 2006; Hien et al. 2007). The total PAH size distributions in the urban environment were bimodal, with one peak in the fine particle-size range (0.4–0.7 lm) and the other peak in the coarse particle-size range (4.7–5.8 lm) (Hien et al. 2007). This may have resulted from the fact that the PAHs from the urban site came from diverse sources (heating, cooking, rainwater, and others), while the PAHs from the coking plant were mainly derived from the coking process. Mechanisms to explain PAH characteristics for different particle sizes Several possible mechanisms might explain the observed PAH characteristics for different particle sizes, such as the different subcooled liquid vapor pressures of individual PAHs, different emission sources, chemical affinities between PAHs and different particle sizes, and reactivity of different PAHs on photooxidation (Venkataraman et al. 1999; Allen et al. 1996; Venkataraman and Friedlander 1994). Particlebound PAHs emitted from the coke oven are almost always associated with fine particles (Broddin et al. 1977; Tsai et al. 1996). If no other processes affected the state of these PAHs, all PAHs would be found on fine particles. However, this was not observed in this study or in previous studies (Broddin et al. 1977; Hien et al. 2007; Allen et al. 1996). It has been reported that PAHs can associate with coarse particles during the
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growth of fine particles or through volatilization from fine particles followed by condensation onto coarse particles (Allen et al. 1996; Hien et al. 2007). If coagulation of particles were the main mechanism creating coarse particle-bound PAHs, the PAH profiles for different particle sizes would be similar. Previous studies (Hien et al. 2007; Allen et al. 1996) have demonstrated that this hypothesis does not hold, and similar results were found in this study. PAHs(5,6) with high molecular weights have low vapor pressure and are nonvolatile. They probably do not volatilize or redistribute appreciably to different-sized particles during short-range atmospheric transport to the monitoring stations; therefore, they tend to remain on fine particles. Previous studies also reported the same tendency (Poster et al. 1995; Kiss et al. 1998; Bi et al. 2005). As for PAHs(3,4), they are semi-volatile compounds with higher vapor pressure than PAHs(5,6). PAHs(3,4) can easily volatilize from fine particles and then condense on other particles during the diffusion process. The redistribution of PAHs among different particle sizes is affected by meteorological conditions, especially ambient temperature. During the sampling period, the average temperature was fairly high (22–33 °C), resulting in easier evaporation of semi-volatile PAHs to bring about a wider PAH distribution shifted toward larger particle sizes. PAHs dissolve weakly in water; their solubility decreases with an increase in the number of aromatic rings (Skupin´ska et al. 2004), which may also have affected the redistribution of PAHs to different particle sizes. The PAH size distribution can also be explained by a gas–particle partition mechanism. A study of sizeresolved gas–particle partition coefficients (Kp) in an urban atmosphere has revealed that the highest Kp values of individual PAHs are associated with fine particles and the lowest Kp values with coarse particles (Yu and Yu 2012). The Kp values can be determined simultaneously in both phases according to the relationship proposed by Yamasakl et al. (1982). Kp is the ratio of the PAH content per unit mass of particles to the gas concentration of PAHs. For individual PAHs, the gas concentration is a certain value (Yamasakl et al. 1982). Because the Kp of individual PAHs associated with fine particles is higher than that for PAHs associated with coarse particles, the PAH content per unit mass of fine particles is higher than that per unit mass of coarse
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particles. Assuming that Kp values in the ambient environment of the coking plant are in accordance with this variation tendency, the relative contribution of individual PAHs associated with fine particles is higher than of PAHs associated with coarse particles. The peaks of individual PAHs (except FLuA) occurred in the 0–2.1 lm size range in coking plant I, as shown in Fig. 4. The size distribution of FLuA is different from that described above; the reasons for this remain to be explored in future research. Investigation of the PAH size distributions in the ambient air of a coking plant is important, and the sizedistribution results presented in this study give useful information about the health effects of particle-bound PAHs on coking-plant workers. Fine particles penetrate easily into the respiratory system and cause a serious health risk (Kameda et al. 2005). The lung cancer risk of high molecular weight PAHs such as BaP, BghiP, BbF, InP, BkF, and DbA is enhanced in combination with fine particles (Hien et al. 2007; Kameda et al. 2005). A concentration limit for BaP at the coking-plant boundary has been provided in emission standard of pollutants for coking chemical industry (GB16171-2012). It is necessary to create an additional air-quality standard for individual PAHs associated with fine particles, especially PAHs(5,6), in the ambient air of the coking plant. This study provides additional PAH data for the coking plant, which may serve as reference values for future evaluations of PAH reduction in the coking process.
Conclusions In this study, the concentrations and particle-sizedistribution characteristics of PAHs have been studied in two coking plants in Shanxi, China. The concentrations of total particulate-matter PAHs were 1,412.7 ng/m3 and 2,241.1 ng/m3 for plants I and II, and the distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm size range for plant II. Substantial differences were observed for individual PAHs in coking plants I and II because of the influence of vehicle emissions on plant II. In coking plant I, the size distributions of individual PAHs (except FluA) exhibited a considerable peak within the 0.1–2.1 lm size range. The PAH size distribution can be explained by a gas–particle partition mechanism.
Environ Geochem Health
The ambient air of the coking plant was heavily polluted by PAHs associated with fine particles (B 2.1 lm), with BbF making the largest contribution to total PAHs. The exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to PAHs associated with coarse particles. BbF, BaP, and DbA should be the primary pollutants monitored in the coking plant. These results give useful information about the health effects of particlebound PAHs on coking-plant workers and can serve as reference values for future evaluations of PAH reduction in the coking process. Acknowledgments This research work was supported by the R&D Special Fund for Public Welfare Industry of China (Grant 200809027) and the Project of National Natural Science Foundation of China (Grand 41173002).
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ORIGINAL PAPER
Occurrence and particle-size distributions of polycyclic aromatic hydrocarbons in the ambient air of coking plant Xiaofeng Liu • Lin Peng • Huiling Bai Ling Mu • Chongfang Song
•
Received: 2 February 2013 / Accepted: 29 October 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract The purpose of this study was to characterize the occurrence and size distributions of ten species of polycyclic aromatic hydrocarbons (PAHs) in the ambient air of coking plants. Particulate-matter samples of four size fractions, including B2.1, 2.1–4.2, 4.2–10.2, and C10.2 lm, were collected using a Staplex234 cascade impactor during August 2009 at two coking plants in Shanxi, China. The PAHs were analyzed by a gas chromatograph equipped with a mass-selective detector. The concentrations of total particulate-matter PAHs were 1,412.7 and 2,241.1 ng/m3 for plants I and II, and the distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm for plant II. The size distributions of individual PAHs (except fluoranthene) exhibited a considerable peak within the 0.1–2.1 lm size range in coking plant I, which can be explained by the gas–particle partition mechanism. The ambient air of the coking plant was heavily polluted by PAHs associated with fine particles (B2.1 lm), and benzo[b]fluoranthene made the largest contribution to total PAHs. The exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to PAHs
X. Liu L. Peng (&) H. Bai L. Mu C. Song College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, People’s Republic of China e-mail: [email protected]
associated with coarse particles. Benzo[b]fluoranthene, benzo[a]pyrene, and dibenzo[a,h]anthracene should be the primary pollutants monitored in the coking plant. This research constitutes a significant contribution to assessing the exposure risk of cokingplant workers and providing basic data for PAH standards for ambient air in coking plants. Keywords Polycyclic aromatic hydrocarbons Size distribution Ambient air Coking plant Size-resolved gas–particle partition coefficients (Kp) Equivalent concentration of benzo[a]pyrene
Introduction Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous semi-volatile organic compounds that contain two or more fused aromatic rings. Several PAHs are known to have carcinogenic, teratogenic, and mutagenic properties, and benzo[a]pyrene (BaP) is carcinogenic to humans according to IARC (2010). PAHs are often associated with suspended particulate matter (PM) in the air at ambient temperatures. Generally, lighter PAHs with 2–3 aromatic rings occur mainly in the gaseous phase, PAHs with 4 rings occur in the gaseous and particulate phases, and heavier ones (5–6 rings) are associated mainly with airborne particles (Hoff and Chan 1987).
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PAHs are widespread environmental contaminants which are emitted from incomplete combustion of organic materials (Bae et al. 2002), for example from coal and coke burners, diesel-fueled engines, grilled meats, and cigarettes. Coking is an important coalconversion process in which prepared coal is heated in an oxygen-free atmosphere. Large quantities of PAHs are released during the coking process. Studies on PAHs from coking emissions in various countries in the world have been conducted (Liberti et al. 2006; Liberti et al. 2004; Romundstad et al. 1998). These studies have identified and quantified several PAH compounds in samples collected from the coke-oven top, lorry-car operator, coke-car operator, and pushcar operator. The total PAH concentration (particulate and gaseous) from the coking process was 357 g/m3 as reported by Liberti et al. (2006). Six PAHs, naphthalene (Nap), pyrene (Pyr), benzo[b]fluoranthene (BbF), indeno[1,2,3-cd]pyrene (InP), BaP, and acenaphthylene (AcPy), contributed to approximately 77 % of total PAHs detected in emissions from coke batteries (Liberti et al. 2006). BaP and dibenzo[a,h]anthracene (DbA) are mostly responsible (approximately 85 %) for the powerful carcinogenicity of emissions from coke batteries (Liberti et al. 2006). The average concentration of total PAHs (particulate and gaseous) during the coking process is 500 lg/m3 as reported by Liberti et al. (2004). BaP is the typical primary contaminant emitted from the coking process. Near coke-oven batteries, levels of BaP may range from 100 to 200 lg/m3 on the machinery and discharge side of a battery roof and may be approximately 400 lg/m3 at the battery top (World Health Organization 2006). The total concentration of 20 species of PAHs, including gas- and solid-phase compounds collected 100 m directly downwind of a coking plant located in southeastern Chicago, was approximately 25 lg/m3 (Khalili et al. 1995). PAHs with two and three rings were responsible for 98 % of the total measured PAH concentration for a coke oven, as reported by Khalili et al. (1995). In the ambient air of the coke-oven top, PAH concentrations have been measured together with different particle sizes. A study of the size distribution of PAHs emitted from the coke-oven top illustrated that over 90 % of PAHs were found on particles smaller than 3 lm, which means that most of these compounds were within the respiratory size range (Broddin et al. 1977). Broddin et al. (1977)
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also reported that similar size-distribution curves were obtained for both lower and higher molecular weight compounds. To the best of our knowledge, the PAH size distribution in the ambient air of coking plants has been little investigated. The ambient air of coking plants is a special environment existing between the urban atmosphere and the coking pollution sources. The particle-bound PAHs in the atmospheric environment of the coking plant have unique characteristics. The PAHs associated with fine particles seriously affect the health of coking-plant workers; therefore, study of PAH size distributions in the ambient air of the coking plant is significant. To collect more information and experimental evidence, an investigation of the occurrence and size distribution of PAHs in the ambient air of the two coking plants was carried out. The aims of this work were to (1) characterize the distribution profile of PAHs associated with particles, (2) investigate the particle size-distribution characteristics of PM and PAHs, and (3) estimate the human health risk associated with respiratory exposure to PAHs using toxicity equivalency factors (TEFs). The results of this study are important for evaluating the risk of occupational exposure to particle-bound PAHs and for determining a concentration threshold for individual PAHs associated with fine particles.
Materials and methods Sample collection Size-segregated aerosol samples were collected from the two coking plants on 15 days between August 13 and 28, 2009 in Shanxi, China (Fig. 1). Sampling was conducted on days with little or no wind and a temperature range of 22 to 33 °C. Coking plant I is more than 1 km from G55 Erguang Expressway and 108 National Road. Coking plant II is next to Jiuyuan East Street, and its sampling site is located approximately 20 m south of Jiuyuan East Street and about 260 m east of Yunzhongshan North Road. The sampling sites were established at the dedusting ground stations of coking plants I and II, which were 5 and 4 m, respectively, above the ground. Basic information about the coking plants investigated is shown in Table 1.
Environ Geochem Health Fig. 1 Location map of the coking plants investigated, Shanxi, China
Table 1 Basic information about the investigated coking plants Coking plant
I
II
Annual capacity (9 103 t)
864.0
251.9
Technique for coal charging
Stamp charging
Stamp charging
Height of the coke oven (m)
4.3
3.2
Air pollution control device
Baghouse filter
Baghouse filter
Coking time (h)
24
24
Output rate (t/d)
2,376
690
Airborne particles were collected using a Staplex234 four-stage high-volume cascade impactor (made in the USA) at a flow rate of 0.565 m3/min. The cascade impactor can fractionate suspended particulates into as many as five size fractions. Impactor cut-points are nominally 10.2, 4.2, 2.1, and 1.4 lm, with the last stage collecting all particles smaller than 1.4 lm. To highlight the characteristics of PAHs associated with particles less than 2.1 lm in diameter, four categories, including B 2.1, 2.1–4.2, 4.2–10.2, and C 10.2 lm, were analyzed in this study. The size of the slotted media used between each impactor stage was 14.3 9 13.7 cm, and the size of the high-volume backup media was 20.3 9 25.4 cm. Glass fiber filters (GFFs) were used as a surrogate surface and placed on each impaction plate to collect the impacted particles of different sizes. The GFFs must be flat to collect the particles exiting the cascade impactor.
The GFFs were wrapped in aluminum foil and baked at 500 °C for 5 h to volatilize any organic contaminants before sampling. Size-separated samples were taken over periods of 3–4 h, and the total sampling volume was approximately 100–140 m3. All the experiments for each sampling point in each plant were repeated 3–4 times to make sure that the results were reproducible. In this study, all data shown are the average of measured results for each experiment. The GFFs were weighed before and after sampling to determine the amount of particles collected. The GFFs were equilibrated for 48 h at 25 °C and 50 % RH in a temperature and humidity chamber before weighing on a micro-balance (Sartorius LA130S-F) accurate to 0.1 mg. After sampling, the GFFs were removed from the impactor, folded with the adsorbed particulate matter on the inner side, wrapped in aluminum foil, and stored frozen at -20 °C for a maximum of 1 week before analysis. Extraction and analysis The extraction procedure for removing PAHs from the particulate matter used a Soxhlet apparatus. Surrogate deuterated PAHs (naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, and perylene-d12) were added before extraction. The filters were cut into strips and extracted for 48 h with dichloromethane (DCM). Then, the organic extracts were concentrated on a rotary evaporator and fractionated on a silica gel column. The elute of the PAH fraction was concentrated to 1 mL under a gentle stream of dry nitrogen, transferred to 1.5 mL vials, and preserved in a refrigerator at -20 °C until analysis.
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The internal standard pyrene-d10 was added for quantification of individual PAHs. The particle-bound PAHs were analyzed by a gas chromatograph equipped with a mass-selective detector (Thermo Fisher, Focus GC/ DSQII) and a computer workstation. A 30 m 9 0.25 mm i.d. DB-5MS (film thickness 0.25 lm) was used. The chromatographic conditions were as follows: injection volume 1 lL, splitless injection at 250 °C, and ion source temperature 300 °C. The temperature program was 50 °C for 3 min, then to 200 °C at a rate of 15 °C/min and hold for 5 min, then to 310 °C at a rate of 3 °C/min and hold for 10 min, for a total duration of 70 min. The masses of primary and secondary PAH ions were determined in the scan mode. Quantitation of PAHs was performed in the selected ion-monitoring (SIM) mode. The species of EPA’s 16 priority-controlled PAHs are as follows: naphthalene (Nap), acenaphthylene (AcPy), acenaphthene (Acp), fluorene (Flu), phenanthrene (PhA), anthracene (AnT), fluoranthene (FLuA), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DbA), indeno[1,2,3-cd]pyrene (InP), and benzo[ghi]perylene (BghiP). Based on their molecular weight and volatility, the 16 PAHs were divided into three groups: lighter PAHs with 2–3 aromatic rings and molecular weights less than 178 were denoted as PAHs(2,3), including NaP(2), AcPy(3), AcP(3), Flu(3), PhA(3), and AnT(3); medium PAHs with four rings and molecular weights ranging between 202 and 228 were denoted as PAHs(4), including FluA(4), Pyr(4), BaA(4), and Chr(4); and heavier PAHs with 5–6 rings and molecular weights of 252–278 were denoted as PAH(5,6) and consisted of BbF(5), BkF(5), BaP(5), DbA(5), InP(6), and BghiP(6). PAH vapor pressures are strongly correlated with molecular weight and decrease with increasing molecular weight. The PAHs(4,5,6) with higher molecular weight are easier to adsorb on particulate matter, while the PAHs(2,3) exist mainly in the gas phase. Therefore, the particle-size distributions of PAHs(4,5,6), including 10 species of PAHs, are discussed in this paper. The concentrations of individual PAHs were calculated by dividing their mass by the sampling volume and are expressed in ng/m3. The total PAH concentrations were defined as the sum of the concentrations of PAHs(4,5,6). BaP has been previously used as an indicator of carcinogenic PAHs, but BaP provides little information for most other PAHs. In recent years, the TEF methodology has been recommended to assess the risk
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associated with PAH exposure (Nisbet and Lagoy 1992; Petry et al. 1996; Bieniek and Lusiak 2012). The cancer incidence of different dose and group PAHs was obtained by testing on mice (Deutsch-Wenzel et al. 1983; LaVole et al. 1982; Habs et al. 1980; Pfeiffer 1977). The TEFs were calculated using the data from each study by applying the same mathematical model of the dose-response relationship to the data for each compound and comparing the results to those obtained for BaP (Clement 1988). The TEFs used in this paper were reported by Nisbet and Lagoy (1992), who modified the TEF approaches presented by Chu and Chen (1984) and Clement (1988). Stationary sampling data are, however, regarded as appropriate because there is no indication for the existence of a major difference in PAH profiles between stationary samples and personal samples (Petry et al. 1996). This study has focused on the assessment of workplace exposure for coking-plant workers using stationary sampling data. The potential toxicity of a mixture of 10 PAH species was determined by applying TEFs (Nisbet and Lagoy 1992) to the concentrations of individual PAHs and summing the equivalent concentrations. The total BaP equivalent concentrations (BaPeq) were defined as the sum of the BaPeq of PAHs(4,5,6). Quality assurance and quality control (QA/QC) The analytical recovery efficiencies of the 16 individual PAHs were determined by adding surrogate deuterated PAHs (naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, and perylene-d12) to all samples, which made it possible to monitor procedural performance and matrix effects. The mean recoveries of the 16 PAHs ranged from 75.2 to 108.7 % (SD = ±13 %). Blank samples were analyzed to quantify sample contamination from materials and equipment using the same procedure as the recovery-efficiency tests without adding the known standard solution before extraction. Analyses of field blanks revealed no detectable contamination.
Results and discussion PAH distribution profiles The average concentrations of total PAHs in the two coking plants are presented in Table 2. The total PAH
Environ Geochem Health
levels associated with fine particles (B 2.1 lm) were significantly higher than those for other particle sizes. Whitey (2007) reported that fine particles were produced predominantly from gas-to-particle conversion and from incomplete combustion, whereas coarse particles originated mainly from mechanical processes which were originally only slightly contaminated. During the coking process, PAHs exist mainly in the gas phase or in association with fine particles. After emission, PAHs can become associated with coarse particles either during the growth of fine combustiongenerated particles or by volatilization from fine particles followed by condensation onto coarse particles (Allen et al. 1996). Therefore, the relative contributions of total PAHs in fine particles were high in the ambient air of the two coking plants, 93.4 and 70.1 % in coking plants I and II, respectively. This result was consistent with Broddin’s finding (1977) that over 90 % of PAHs were found on particles smaller than 3 lm on the coke-oven top. Table 2 also indicated that the average concentrations of total particulate-matter PAHs (B 10.2 lm) were 1,137.4 and 1,930.2 ng/m3 in coking plants I and II, respectively, which are significantly lower than those on the coke-oven top (6,800 and 2,100 ng/m3), but higher than that in the ambient air of steel plants (600 ng/m3) as reported by Tsai et al. (1996). The difference in total PAH concentrations between the two coking plants can be explained by the height of the coke ovens, their annual capacity, and the effect of road dust (Han et al. 2009). The concentrations of individual PAHs in differentsized particles in the two coking plants are listed in Table 3, and the contributions of individual PAHs relative to total PAHs in different-sized particles are presented in Fig. 2. In particles with diameters less
than 2.1 lm, the PAH distribution profiles were similar in plants I and II. BbF made the largest contributions (34.5 and 37.6 %) to the total amount of PAHs. Within the 2.1–4.2, 4.2–10.2, and C 10.2 lm size ranges, the contribution characteristics of individual PAHs were significantly different in the two coking plants. In coking plant I, the contributions of individual PAHs had similar characteristics in these three size ranges, and the largest contributor of PAHs was FluA, followed by Pyr. In coking plant II, the relative contributions of individual PAHs were similar in the three size ranges, but the contribution of BbF was slightly higher than those of other PAHs. The differences between the two coking plants described above are partly attributable to the influence of vehicular emissions. Coking plant I is relatively far from major transportation roads, while coking plant II is near Jiuyuan East Street and Yunzhongshan North Road, as can be seen in Fig. 1. Previous studies (Khalili et al. 1995; Manoli et al. 2002) reported that the contributions of FLuA, Pyr, BaA, and Chr from coke-oven emissions were significantly higher than those from vehicular emissions, while the contributions of BbF, BkF, BaP, InP, DbA, and BghiP from coke-oven emissions were significantly lower than those from vehicular emissions. The relative contribution characteristics of individual PAHs in coking plant II, shown in Fig. 2b), were the result of synthetic interaction between coke-oven emissions and vehicular emissions. The relative contributions of individual PAHs in the ambient air of coking plant I were similar to the source composition of coke-oven emissions as reported by Khalili et al. (1995); therefore, PAHs in plant I can be said to come mainly from coke-oven emissions. The characteristics of PAHs in coking plant I were minimally affected by
Table 2 Concentrations and contributions of total PAHs and total BaPeq for different-sized particles in the two coking plants Size range (lm)
Total PAHs
Total BaPeq
Concentration (ng/m3)
Contribution (%)
Concentration (ng/m3)
Contribution (%)
Plant I
Plant II
Plant I
Plant II
Plant I
Plant II
Plant I
Plant II
1,082.7
1,439.9
93.4
70.1
169.1
265.4
90.7
56.9
2.1–4.2
28.9
304.9
2.5
14.8
6.7
112.5
3.6
24.1
4.2–10.2
25.8
185.4
2.2
9.0
4.2
53.4
2.3
11.4
C10.2
21.6
123.9
1.9
6.0
6.4
35.3
3.4
7.6
B2.1
123
123
30.7
65.3
154.4
95.2
373.8
93.9
38.8
98.0
11.2
121.4
Pyr
BaA
Chr
BbF
BkF
BaP
InP
DbA
BghiP
B2.1
Plant I
0.3
0.7
1.3
2.3
3.6
1.0
3.4
2.5
4.6
9.2
2.1–4.2
0.9
0.4
1.4
1.6
2.3
1.2
3.3
0.0
4.7
10.0
4.2–10.2
PAH concentration (ng/m3)
FLuA
Particle size (lm)
0.9
0.9
1.5
1.4
1.7
1.1
2.6
0.0
3.8
7.7
C10.2
7.8 17.4 5.5 16.0
41.9 14.5 38.3
154.7 26.9 147.8
29.9
43.3
541.3 17.4
23.9
30.3
216.9 18.8
25.6
35.3
154.9
25.3
16.9
24.8
30.8
25.0
32.4
7.7 45.9
113.0
4.2–10.2
2.1–4.2
B2.1
Plant II
9.8 56.0 1.2
3.5 14.4
37.4
21.4
14.6
1.0
13.4 9.4
15.4
14.5
38.8
0.1
9.9
5.1
0.0
15.2
11.9
B2.1
C10.2
Plant I
0.0
3.5
0.1
2.3
0.4
0.1
0.0
0.3
0.0
0.0
2.1–4.2
0.0
2.0
0.1
1.6
0.2
0.1
0.0
0.0
0.0
0.0
4.2–10.2
0.0
4.5
0.2
1.4
0.2
0.1
0.0
0.0
0.0
0.0
C10.2
BaPeq concentration (ng/m3)
Table 3 Concentrations of individual PAHs and individual BaPeq in the ambient air of the two coking plants
1.5
134.5
15.5
30.8
11.3
54.1
2.2
15.5
0.0
0.0
B2.1
Plant II
0.4
72.5
4.2
25.3
1.9
4.3
0.3
3.5
0.0
0.0
2.1–4.2
0.2
27.5
1.7
17.4
0.8
3.0
0.2
2.6
0.0
0.0
4.2–10.2
0.1
17.5
1.5
11.9
0.5
2.1
0.1
1.5
0.0
0.0
C10.2
0.01
5
0.1
1
0.1
0.1
0.01
0.1
0.001
0.001
TEF(Nisbet and Lagoy 1992)
Environ Geochem Health
Fig. 2 Relative contributions of individual compounds to total investigated PAHs for different-sized particles: a coking plant I; b coking plant II
other pollution sources, and consequently, the relative contributions of individual PAHs in plant I were representative.
Toxic equivalent concentrations of PAHs
The corresponding BaPeq of different size ranges, obtained on the basis of TEFs as suggested by Nisbet and Lagoy (1992), are presented in Table 2. In the B 2.1 lm size range, the BaPeq concentrations of total PAHs were considerably higher than those in other stages in the two coking plants. Consequently, the exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to those associated with coarse particles. The considerable differences in the BaPeq concentration contribution of PAHs for particles of different size ranges are shown in Fig. 3. For particles less than 2.1 lm, the
Environ Geochem Health
contributions of DbA, BaP, and BbF equivalent concentrations were the highest among the BaPeq of the PAHs. The contributions were 33.1, 23.0, and 22.1 %, respectively, in coking plant I and 50.7, 11.6, and 20.4 % in coking plant II. In the 2.1–4.2, 4.2–10.2, and C 10.2 lm size ranges, the BaPeq contributions of DbA and BaP were significantly higher than those of other PAHs, which were 48.2–70.6 and 22.0–38.6 %, respectively, in coking plant I and 49.6–64.5 and 22.5–33.8 % in coking plant II. Compared with the concentration contributions of individual PAHs, the concentration contributions of BbF, Pyr, and FluA were higher than those of other PAHs, but their BaPeq contributions were lower than the others. The BaPeq contributions of DbA and BaP were higher than those of other PAHs. The BaPeq contribution profile was similar to that of PAHs on the coke-oven top as reported by Petry et al. (1996). Consequently, DbA, BaP, and BbF should be the primary pollutants
monitored in the ambient air of coking plants to reduce the exposure risk of coking-plant workers. PAH particle-size distributions To describe PAH size distributions, the commonly used approach is to plot a histogram of the relative mass of DC/(CtotalDlogDp) versus Dp on a logarithmic scale, where DC/Ctotal is the mass percentage of PAHs on each filter and DlogDp is the size interval for each impactor stage (Hien et al. 2007; Aceves and Grimalt 1993; Venkataramant and Friedlander 1994; Alves et al. 2000; Kawanaka et al. 2004; Whitby et al. 1972). Aceves and Grimalt (1993) and Cancio et al. (2004) took 0.08 and 30 lm as the lower and upper limits of particle size to present the size distribution. In this study, the diagrams shown in Fig. 4 were constructed by taking 0.1 and 30 lm as the lower and upper particle-size limits, respectively. The lower limit was selected based on the results of urban aerosol studies involving size-fraction partitioning devices of 0.01–0.1 lm resolution (Whitby et al. 1972); the upper limit was taken from reported data for aerosols of different origins (Slinn 1983). The mean normalized distributions of PAHs and PM with particle size for the two coking plants are presented in Fig. 4. PM size distribution
Fig. 3 Relative contribution of individual BaPeq to total BaPeq for different-sized particles: a coking plant I; b coking plant II
PM concentrations (four stages plus post-filter) were 1.8 and 2.9 mg/m3 in coking plants I and II, respectively, which were lower than the particle concentrations (10.2 in spring, 6.4 mg/m3 in fall) at the battery top (Bjørseth et al. 1978) and higher than the 470 lg/ m3 obtained from Vietnam (roadside site) in the dry season by Hien et al. (2007). The PM in the ambient air of the coking plant was emitted mainly from the coking process and diluted by diffusion processes. Consequently, PM concentrations in the coking plants were significantly lower than in emissions from the coke oven. The sampling sites were close to the coke oven, and the high particle concentrations were significantly elevated by emissions from chimneys and leaks from the stack area; therefore, the measured PM levels in the coking plants were much higher than at the urban roadside site. Different-sized particles affect the environment and human health differently. To obtain a deep understanding of the atmospheric-pollution situation in the
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Fig. 4 Particle-size distribution of PAHs and PM in the ambient air of the two coking plants. Solid line coking plant I; dotted line coking plant II
coking plant and to establish reasonable preventive countermeasures, it is very important to study particlesize distributions. The PM size distributions from the two coking plants are shown in Fig. 4(l). PM from the two coking plants exhibited a unimodal distribution with a peak in the 0.1–2.1 lm size range. This can be partly explained by the collection efficiency of the baghouse filter used in these coking plants, which is higher for coarse particles than for fine ones. These data indicated that the fine-particle pollution and respiration exposure risk in the coking-plant area were
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severe. The percentage cumulative mass of particulates smaller than 3 lm corresponds to approximately 50 % of the total particulate weight on the coke-oven top (Broddin et al. 1977). The particle-size distribution in the coking-plant area was similar to that on the coke-oven top. The size distribution gives important information about the health effects of inhaled particles in the coking-plant area. Particles less than 3 lm in diameter will penetrate the upper respiratory tract and settle in bronchia and alveoli (Wu et al. 2006). From Fig. 4(l), it is evident that almost all the particles
Environ Geochem Health
in the coking-plant area were less than 2.1 lm in diameter. Emission standard of pollutants for coking chemical industry (GB16171-2012) provides only a concentration limit for PM at the boundary of the coking plant. Fine particles penetrate easily into the respiratory system and cause a serious health risk (Kameda et al. 2005). Therefore, the regulation and monitoring of fine particles should be strengthened to improve working conditions for coking-plant workers. This study provides basic fine-particle concentration data for ambient air in a coking plant. PAH size distributions Figure 4 shows the size distributions of individual and total PAHs in the two coking plants. In coking plant I, the size distributions of individual PAHs (except FluA) exhibited a considerable peak within the 0.1–2.1 lm size range. FluA showed a unimodal distribution in the 2.1–4.2 lm size range, which may have been caused by its low molecular weight. These size distributions show an increase in the fraction of PAHs associated with smaller aerosols as ring number and molecular weight increase. The observation that higher molecular weight PAHs were adsorbed to fine particles while more volatile PAHs were associated with larger particles has been supported by many studies (Venkataraman and Friedlander 1994; Venkataraman et al. 1994; Venkataraman et al. 1999; Allen et al. 1996). Substantial differences were observed for individual PAHs in coking plants I and II (see Fig. 4). In coking plant II, FluA and Pyr exhibited a peak in the 2.1–4.2 lm size range; Chr, BbF, and BkF exhibited a peak in the 0.1–2.1 lm size range; and BaP, InP, DbA, and BghiP exhibited a peak in the 2.1–4.2 lm size range. The two coking plants are in different geographic locations; coking plant I is relatively far from major transportation roads, while coking plant II is close to Jiuyuan East Street and Yunzhongshan North Road. The difference in PAH size distributions in the two plants can be partly attributed to the influence of vehicular emissions. The PAH size distributions, especially PAH(5,6), in coking plant II were affected by vehicular emissions nearby. Pyr, InP, and BghiP were abundant in urban aerosols at the roadside, as reported by Hien et al. (2007). Sheu et al. (1996) reported that InP, DbA, and BghiA exhibited higher fractions in the 1.8–3.2 lm size range in the vicinity of
traffic intersections. Consequently, PAHs emitted from vehicles substantially affected the distribution of high molecular weight PAHs in coking plant II. The PAH size distribution in coking plant I was minimally affected by other pollution sources, and consequently, the PAH characteristics in plant I are representative. The average concentrations of total particulatematter PAHs were 1,412.7 and 2,241.1 ng/m3 for coking plants I and II, respectively. Total PAH size distributions in the ambient air of the two coking plants are shown in Fig. 4(k). The distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm size range for plant II. This result was consistent with the study of Bjørseth et al. (1978), who reported that the largest amounts of PAHs were found in particles within the 0.9–3 lm diameter range on the battery top. The total PAH size distribution in the ambient air of the coking plant was somewhat different from that at the urban site (Wu et al. 2006; Hien et al. 2007). The total PAH size distributions in the urban environment were bimodal, with one peak in the fine particle-size range (0.4–0.7 lm) and the other peak in the coarse particle-size range (4.7–5.8 lm) (Hien et al. 2007). This may have resulted from the fact that the PAHs from the urban site came from diverse sources (heating, cooking, rainwater, and others), while the PAHs from the coking plant were mainly derived from the coking process. Mechanisms to explain PAH characteristics for different particle sizes Several possible mechanisms might explain the observed PAH characteristics for different particle sizes, such as the different subcooled liquid vapor pressures of individual PAHs, different emission sources, chemical affinities between PAHs and different particle sizes, and reactivity of different PAHs on photooxidation (Venkataraman et al. 1999; Allen et al. 1996; Venkataraman and Friedlander 1994). Particlebound PAHs emitted from the coke oven are almost always associated with fine particles (Broddin et al. 1977; Tsai et al. 1996). If no other processes affected the state of these PAHs, all PAHs would be found on fine particles. However, this was not observed in this study or in previous studies (Broddin et al. 1977; Hien et al. 2007; Allen et al. 1996). It has been reported that PAHs can associate with coarse particles during the
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growth of fine particles or through volatilization from fine particles followed by condensation onto coarse particles (Allen et al. 1996; Hien et al. 2007). If coagulation of particles were the main mechanism creating coarse particle-bound PAHs, the PAH profiles for different particle sizes would be similar. Previous studies (Hien et al. 2007; Allen et al. 1996) have demonstrated that this hypothesis does not hold, and similar results were found in this study. PAHs(5,6) with high molecular weights have low vapor pressure and are nonvolatile. They probably do not volatilize or redistribute appreciably to different-sized particles during short-range atmospheric transport to the monitoring stations; therefore, they tend to remain on fine particles. Previous studies also reported the same tendency (Poster et al. 1995; Kiss et al. 1998; Bi et al. 2005). As for PAHs(3,4), they are semi-volatile compounds with higher vapor pressure than PAHs(5,6). PAHs(3,4) can easily volatilize from fine particles and then condense on other particles during the diffusion process. The redistribution of PAHs among different particle sizes is affected by meteorological conditions, especially ambient temperature. During the sampling period, the average temperature was fairly high (22–33 °C), resulting in easier evaporation of semi-volatile PAHs to bring about a wider PAH distribution shifted toward larger particle sizes. PAHs dissolve weakly in water; their solubility decreases with an increase in the number of aromatic rings (Skupin´ska et al. 2004), which may also have affected the redistribution of PAHs to different particle sizes. The PAH size distribution can also be explained by a gas–particle partition mechanism. A study of sizeresolved gas–particle partition coefficients (Kp) in an urban atmosphere has revealed that the highest Kp values of individual PAHs are associated with fine particles and the lowest Kp values with coarse particles (Yu and Yu 2012). The Kp values can be determined simultaneously in both phases according to the relationship proposed by Yamasakl et al. (1982). Kp is the ratio of the PAH content per unit mass of particles to the gas concentration of PAHs. For individual PAHs, the gas concentration is a certain value (Yamasakl et al. 1982). Because the Kp of individual PAHs associated with fine particles is higher than that for PAHs associated with coarse particles, the PAH content per unit mass of fine particles is higher than that per unit mass of coarse
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particles. Assuming that Kp values in the ambient environment of the coking plant are in accordance with this variation tendency, the relative contribution of individual PAHs associated with fine particles is higher than of PAHs associated with coarse particles. The peaks of individual PAHs (except FLuA) occurred in the 0–2.1 lm size range in coking plant I, as shown in Fig. 4. The size distribution of FLuA is different from that described above; the reasons for this remain to be explored in future research. Investigation of the PAH size distributions in the ambient air of a coking plant is important, and the sizedistribution results presented in this study give useful information about the health effects of particle-bound PAHs on coking-plant workers. Fine particles penetrate easily into the respiratory system and cause a serious health risk (Kameda et al. 2005). The lung cancer risk of high molecular weight PAHs such as BaP, BghiP, BbF, InP, BkF, and DbA is enhanced in combination with fine particles (Hien et al. 2007; Kameda et al. 2005). A concentration limit for BaP at the coking-plant boundary has been provided in emission standard of pollutants for coking chemical industry (GB16171-2012). It is necessary to create an additional air-quality standard for individual PAHs associated with fine particles, especially PAHs(5,6), in the ambient air of the coking plant. This study provides additional PAH data for the coking plant, which may serve as reference values for future evaluations of PAH reduction in the coking process.
Conclusions In this study, the concentrations and particle-sizedistribution characteristics of PAHs have been studied in two coking plants in Shanxi, China. The concentrations of total particulate-matter PAHs were 1,412.7 ng/m3 and 2,241.1 ng/m3 for plants I and II, and the distributions showed a peak within the 0.1–2.1 lm size range for plant I and the 0.1–4.2 lm size range for plant II. Substantial differences were observed for individual PAHs in coking plants I and II because of the influence of vehicle emissions on plant II. In coking plant I, the size distributions of individual PAHs (except FluA) exhibited a considerable peak within the 0.1–2.1 lm size range. The PAH size distribution can be explained by a gas–particle partition mechanism.
Environ Geochem Health
The ambient air of the coking plant was heavily polluted by PAHs associated with fine particles (B 2.1 lm), with BbF making the largest contribution to total PAHs. The exposure levels of coking-plant workers to PAHs associated with fine particles were higher than to PAHs associated with coarse particles. BbF, BaP, and DbA should be the primary pollutants monitored in the coking plant. These results give useful information about the health effects of particlebound PAHs on coking-plant workers and can serve as reference values for future evaluations of PAH reduction in the coking process. Acknowledgments This research work was supported by the R&D Special Fund for Public Welfare Industry of China (Grant 200809027) and the Project of National Natural Science Foundation of China (Grand 41173002).
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