Characteristics of PCDD/Fs in PM2.5 From Emission Stacks and The Nearby Ambient Air in Taiwan


 This study aimed to find the characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in fine particulate matter from different stationary emission sources (coal-fired boiler, CFB; municipal waste incinerator, MWI; electric arc furnace, EAF) in Taiwan and the relationship between PM2.5 and PM2.5-bound PCDD/Fs with Taiwanese mortality risk. PM2.5 was quantified using gravimetry and corresponding chemical analyses were done for PM2.5-bound chemicals. Mortality risks of PM2.5 exposure and PCDD/Fs exposure were calculated using Poisson regression. The highest concentration of PM2.5 (0.53±0.39 mg/Nm3) and PCDD/Fs (0.206±0.107 ng I-TEQ/Nm3) was found in CFB and EAF, respectively. Higher proportions of PCDDs over PCDFs were observed in the flue gases of CFB and MWI whereas it was reversed in EAF. For ambient air, PCDD/F congeners around the stationary sources were dominated by PCDFs in vapor phase. Positive matrix factorization (PMF) analysis found that the sources of atmosphere PCDD/Fs were 14.6% from EAF (r=0.81), 52.6% from CFB (r=0.74), 18.0% from traffic (r=0.85) and 14.8% from MWI (r=0.76). For the dioxin congener distribution, PCDDs were dominant in flue gases of CFB and MWI, PCDFs were dominant in EAF. It may be attributed to the different formation mechanisms among wastes incineration, steel-making, and coal-burning processes.

1. Introduction PM 2.5 exposure could lead to adverse health impacts [1][2][3][4] . Studies found association between monthly PM 2.5 levels and all-cause mortality, death caused by cardiovascular (CVD) and respiratory diseases 5,6 . Signi cant correlation between PM 2.5 and hospitalization of asthma, arrhythmia, and myocardial infarction was also found in previous research 7 . Quantitatively, each 10 μg/m 3 increase of PM 2.5 concentrations lead to increment of all-cause mortality (1.18%), CVD (1.03%-1.76%), and respiratory disease deaths (1.71%) 8 . Retainment of ne particles in the lungs could cause in ammations 9 which are enhanced by some PM 2.5bound chemicals.
Polychlorinated dibenzo-p-dioxin and furans (PCDD/Fs) were persistent organic pollutants (POPs) announced by United Nations Environment Programme (UNEP). PCDD/Fs have long half-life and exible mobility in the atmosphere. Atmospheric PCDD/Fs by dry and wet deposition could land on the topsoil surface and eventually through the food chain entered the human body. Oh, et al. 10 found PCDD/Fs of municipal waste incinerator at atmospheric and soil area in Korea to be 0.66 pg I-TEQ/m 3 (35.6 pg/m 3 ) and 19.1 pg I-TEQ/g (1077.11 pg/g). Yu, et al. 11 found PCDDs in the electric arc furnace (EAF) plant to be dominated by 2,3,4,6,7,8-HpCDD and OCDD when PCDFs were dominated by 1,2,3,4,6,7, 8-HpCDF and OCDF. Previous studies observed PCDD/Fs emission from EAF was higher than municipal waste incinerators 12,13 . According to the inventory of PCDD/Fs showed that incinerators (19.4%) and steelmaking process (54.6%) was the major source of emission. The major PCDD/F emission in Taiwan were from stationary sources including boiler combustion (24.1%), fugitive emission sources (20.8%), sinter plant (15.3%) and electric arc furnaces (14.4%) 14 . Therefore, it is crucial to understand the characteristics of this source of emission. In this study, we monitor PCDD/Fs and PM 2.5 emitted from stationary sources and atmospheric measurements in the vicinities. We also aim to study the relationship between PM 2.5 and PM 2.5 -bound PCDD/Fs with Taiwanese mortality risk.

Mass concentrations of PM 2.5 , PCDD/F levels and chemical compounds in the ue gas of different stationary sources
Highest concentration of PM 2.5 was found in CFB ue gas at 0.53±0.39 mg/Nm 3 (n=5). The ue gas average concentration of PM 2.5 were 0.34±0.06 and 0.35±0.12 mg/Nm 3 in MWI (n=3) and EAF (n=3), respectively. In ue gas of CFB, the average PCDD/Fs concentrations were 0.003±0.003 and 0.0005±0.0003 ng I-TEQ/Nm 3 in vapor and solid phase, respectively (Table 1). In MWI ue gas, the average PCDD/F concentrations were 0.021±0.011 and 0.004±0.002 ng I-TEQ/Nm 3 in vapor and solid phase, respectively.
The highest concentrations of PCDD/F were found in EAF ue gas, the average concentrations were 0.204±0.071 and 0.001±0.0003 ng I-TEQ/Nm 3 in vapor and solid phase, respectively. All of ue gas samples were lower than the emission standards for stationary sources in Taiwan (CFB: 1.0, MWI: 0.1, EAF: 0.5 ng I-TEQ/Nm 3 ). The lowest PCDD/F concentrations measured in CFB ue gas maybe attributed to the sulfur content in coal the fuel of CFB. However, previous study found PCDD/Fs from coal combustion to be relatively low 15 . Research of Tuppurainen, et al. 16 found how phenolic precursors converted into sulfuric compounds (ex: dibenzothianthrene and dibenzthiophene) which were similar to PCDD/Fs. Ogawa, et al. 17 and Tuppurainen,et al. 16 elucidated the mechanism of inhibiting PCDD/F formation by adding sulfur.
The chemical compounds of PM 2.5 measured in ue gases at different emission sources were shown in Table S1. In CFB, the PM 2.5 in ue gas had major species of metals as Ca (821,060 ng/m 3 ), Al (220,790 ng/m 3 ), Fe (171,460 ng/m 3 ), the highest water-soluble ions as SO 4 2-(112±29.7 μg/m 3 ), and OC/EC ratio as 0.78. In both of MWI and EAF ue gas PM 2.5 , the major species of metals were Ca and Zn, the dominant water-soluble ions were Cl -, and OC/EC ratios were greater than 2.0 ( Fig.2). A large OC/EC ratio (>2.0-2.2) was footprint of secondary organic aerosols 18,19 . It indicated the industrial boiler PM 2.5 came from primary emitted aerosols. Fig.S1 showed the different contribution of ue gas in PCDD/Fs with CFB, MWI and EAF. Due to the result that ΣPCDD in ue gas was contributed to both phase in CFB and MWI.      In the next step, the PCDD/Fs congener pro le of total twenty-eight air samples were analyzed via PMF model and compared with other study. PMF analysis of atmospheric PCDD/Fs in the vicinity of stationary sources indicated that around 14 (Table S4).
The people who live in site C2 with a higher concentration of PCDD/F showed the signi cantly higher relative risk for all causes of death for both males and females than people who live in site M1 PCDD/F ( Compared with previous study 21 , it was also showed the similar result with the relative risk of mortality between the highest and lowest concentrations of PCDD/Fs and PM 2.5 . Difference of this study was higher correlation with relative risk of mortality in PM 2.5 .
The reason was believed that PM 2.5 contains more hazardous pollutants and leads the difference result with relative risk of mortality in PCDD/Fs and PM 2.5 .

Discussion
In the section 2.1, we kmown the proportion of PCDD/Fs measured in CFB and MWI was different from EAF. The difference can be explained by different air pollution control devices adopted in EAF. The control system in EAF might even generate PCDD/Fs at the temperature window between 200 o C-500 o C via de novo synthesis. In EAF, the ue gas cooling system provides su cient retention time (2-5 seconds) with the operating temperature between 300 o C and 500 o C. On the other hand, ΣPCDF in ue gas was also contributed to both phase in EAF. Previous study 22 indicates that mostly generates PCDFs in y ash by the de novo synthesis that was similar with higher PCDFs measured in PM 2.5 and TPM in the ue gas of EAF. In general, vapor and solid phase distribution of PCDD/F congeners is affected by the temperature variation and removal mechanism in ue gas. Because of the higher vapor pressures of PCDFs compared with PCDDs, the distributions of solid-phase PCDDs in ue gases are higher than that of PCDFs. In EAF, the removal mechanism of solid-phase PCDD/Fs relies on ltration of the bag lter resulting in the increase of PCDF congener distribution observed in stack gas. In addition, the vapor-phase PCDFs in the ue gases of MWI can be effectively removed by the activated carbon injection with bag lter that resulted the lowest PCDF distribution in vapor phase of MWI. Moreover, previous study found that the PCDD/Fs appeared to be present mainly in the solid phase during winter, spring and autumn, while during summer it mostly allocated in gas phase 23 in the ambient air. All the measurements indicated that the atmospheric PCDD/Fs measured in this study were all lower than the air quality standards for dioxins in Japan (0.6 pg-TEQ/m 3 ).
Furthermore, for the limitation of source apportionment, even though the possible sources with the PMF model analysis were given the advice which about sample size (>100). However in this study with a stable adjusting on model and higher correlation between emissions sources and contribution sources pro le, the result of source apportionment was still valid.

Conclusions
For the dioxin congener distribution, PCDDs were dominant in ue gases of CFB and MWI, PCDFs were dominant in EAF. It may be attributed to the different formation mechanisms among wastes incineration, steel-making, and coal-burning processes.
Ca, Al, and Fe were major metals in CFB ue gas when Ca and Zn dominated in MWI and EAF. In CFB, SO 4 2was found to be major ion when in MWI and EAF, Clwas main ion. OC/EC ratio showed primary origin in CFB (OC/EC = 0.78) and secondary origin in MWI and EAF (OC/EC>2.0).
In the surrounding ambience, the highest level of PM 2.5 was at site E2 (35.1±4.75 μg/m 3 ), the highest dioxin level was at site C2 (31.1±16.3 fg I-TEQ/m 3 ). The health relative risk for all causes of death (RR=1.432, p-value = < 0.0001) were higher in the high PM 2.5 exposed group (Site E2). Signi cant elevation of all cause mortality risk was observed at high PCDD/F exposed group (RR=1.236, p-value=0.003).

Sampling site
In this study, the sampling areas for stationary emission were situated in North and Central Taiwan were located about 8 km from the plant. The upwind and downwind sampling sites were located nearby power plant and farmland, respectively. On the other hand, the background station was located at Mt. Lulin (23.51-o N, 120.92-o E; 2,862 m above mean sea level) in Jade Mountain National Park. Its high elevation kept it away from all local pollution sources.

Sampling method
The sampling procedures of stack gases of different facilities were performed following the main guideline of the Taiwan EPA NIEA A212.10B for ue gas collection 24 . The vapor-phase PCDD/Fs in ue gas was collected via XAD-2 while the PM 2.5 and total particulate matter (TPM) was collected by the cyclone splitter with quartz ber lter. Isokinetic sampling was ensured to collect representative samples. For ue gas sampling, one TPM sample and ve PM 2.5 samples were collected in CFB; in MWI and EAF, three TPM and three PM 2.5 samples were collected in each stack.
Additionally, three ambient air samples were collected at each upwind and downwind site of CFB, MWI and EAF, respectively. For ambient air samples, both vapor phase and solid phase (PM 2.5 ) samples of PCDD/F compounds were collected using high volume sampling instruments (Analitica HVS-PM 2.5 ) and at ow rate of 500L min -1 . The air sample with total volume was over 700 m 3 for a typical 24-hour sampling duration. Whatman quartz ber lters and polyurethane foam (PUF) plugs were used for collecting particles and vapor PCDD/F compounds, respectively. The lters were heated at 900 °C (5 hours). Gravimetric analysis was done after stabilizing the lter at constant humidity (45% ± 5%) and temperature (18°C) for at least 24 h. On the other hand, polyurethane foam (PUF) was cleaned using Toluene by Soxhlet puri cation for 4 h.

Chemical analysis
In this study, the congeners of seventeen 2,3,7,8-substituted PCDD/F were analyzed with high-resolution gas chromatography After Soxhlet extraction and puri cation, high-resolution gas chromatograph/mass spectrometer was used for PCDD/Fs analysis.
The detailed protocol can be found elsewhere 25 . A laboratory blank and led blank were analyzed for quality control. Furthermore, a matrix spike sample (2.0-20 pg µL -1 PCDD/Fs) also were analyzed after every eight samples. The injection volume was 1 µL and the sample volume was 1 mL.

Enrichment factor
In order to evaluate the enrichment of each element relative to the crust composition, this study calculated the enrichment factor (EF) for each element, which was calculated by equation (1).

EF= (E/Al) Sample/ (E/Al) Crust (1)
Where E is the enrichment value of the element relative to the source of crust (Al), (E/Al) Sample is the ratio that element E to the content of Al in the sample, (E/Al) Crust is the ratio that element E to the content of Al in average composition of crust.
EF value equal to 1.0 means that the element is mainly from the source of crust. When the EF value is more than 10, it means that the element mainly come from other sources of anthropogenic pollution. When the EF value ranges from 2.0 to 10, it means that the element might have a mixed source of crust and anthropogenic pollution.

Source apportionment
To identify the sources of the atmosphere PM 2.5 , principal component analysis (PCA) and the Positive Matrix Factorization (PMF, version 5.0) which available from U.S. EPA (2014) were used to identify and quantify sources that contribute to ambient PCDD/F concentrations in the vicinity of stationary pollution sources.
We used PCA to reduce the dimension of original PCDD/Fs into different major principal components with different loading scores. On the other hand, PMF was used to decompose PCDD/Fs into different factors. PMF can result in PCDD/F ngerprints of different factors. These ngerprints can be used to compare with other known ngerprint from emission sources to identify the possible sources of PCDD/Fs.