Chapter 3: Identification of source areas of polycyclic aromatic hydrocarbons in Ulsan, Korea
3.3. Results and discussion
3.3.3. Application of gas/particle partitioning for the identification of source areas
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In winter, both PSCFm and CWTm validated north of China (i.e., Hebei, Tianjin, and Beijing) could be the source areas of the particulate PAHs in Ulsan (Figures 3-9d and 3-10d). These areas could contribute to 77% of the transported particulate PAHs in Ulsan during winter. An increase in PAHs emitted from combustion (i.e., coal/biomass combustion for heating) (Figure 3-6) combined with the greater aerosol levels in those areas during winter, especially in February (Figure 3-11j), could lead to higher levels of the particulate PAHs by coagulation and/or condensation (Indarto et al., 2010). Moreover, the particulate PAHs, especially the 4- to 6-ring species, mainly sorb to organic matters of fine particles having aerodynamic diameter lower than 1 µm (Park et al., 2007). Such particles can be removed from the air by wet deposition (i.e., in-cloud and below cloud deposition) (Baek et al., 1991b). However, an absence of rainfall when air parcels passed over north of China in winter (Figure 3-7) could lead to the long-range transport of particulate PAHs emitted from these areas.
The CBPF plot of the particulate phase was also checked to more clarify the effect of non-local and local emission sources on the particulate PAHs in Ulsan. Two sources with high wind speed (5–6 m/s) located in the south and northwest of the sampling site were identified (Figure 3- 12d). The source at the south was expected to be stack emission (Uria-Tellaetxe and Carslaw, 2014) in the industrial complexes at the east and southeast of Ulsan. Noticeably, the prevailing wind direction in Ulsan during winter is northwesterly, leading to a transport of PAHs derived from the industrial area to the East Sea (Figure 3-1). However, the low mixing height and an increase of the particulate PAHs in Ulsan during winter (Nguyen et al., 2018) could promote the horizontal dispersion of PAHs within the local scale. The other source at the northwest could be a distinct source and might have a contribution from the regional emissions (e.g., long-range transport from northern China). The high probabilities (> 0.8) of the distant and local sources suggest their simultaneous influence on the particulate PAHs in Ulsan during the winter.
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northern China (i.e., Hebei, Beijing, Tianjin, and Shandong) were suggested as source areas for the particulate PAHs in Ulsan. Interestingly, the north of China (i.e., Hebei, Beijing, and Shandong) were neglected and moderately highlighted as source areas for the particulate PAHs by the PSCFm and CWTm, respectively (Figures 3-9a and 3-10a). An explanation could be that the PAH concentrations declined by high rainfall events (Figure 3-7a) when the air parcels crossed over the north of China and the Yellow Sea. However, mass fractions of the particulate PAHs at the receptor site were still high, leading to the greater FWT in northern China, especially in Hebei, Beijing, and Tianjin.
Figure 3-13. Fraction-weighted trajectory (FWT) values in the (a) spring, (b) summer, (c) fall, and (d) winter. The CWTm was calculated for the ratio of the particulate to the total (gas + particle) concentrations.
In summer, the FWT values were high in eastern China (i.e., Shanghai, Jiangsu, Henan, and Zhejiang), but they obviously declined in the Korean Peninsula (Figure 3-13b). This result suggests that the levels of particulate PAHs emitted from the regional sources could decline during the atmospheric transport of PAHs. In other words, the local emission sources, rather
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than the distant ones, could keep an important contribution to the PAHs in Ulsan in the summer.
This observation is also consistent with the discussion in Section 3.3.2.2.
For the fall, the FWT confirmed that the particulate PAHs emitted in western Korea could be brought to the sampling site (Figure 3-13c). Emission sources in this area could be several industrial complexes and large-scale coal power plants located at the west coast and open burning after harvest (Ryu et al., 2004) in the fall. However, the low FWT (< 0.4) in fall suggests a less influence of the non-local sources on the particulate PAHs in Ulsan, which was already mentioned in Section 3.3.2.2.
The emission source areas suggested by the FWT in the winter (Figure 3-13d) were similar to those suggested by the PSCFm and CWTm for the particulate PAHs (Figures 3-9d and 3-10d).
These areas include northeastern China (i.e., Liaoning and Jilin) and northern China (i.e., Hebei, Beijing, and Tianjin). In addition, the other source areas in South Korea and North Korea were more emphasized in the FWT. Indeed, the west and northwest areas of the Korean Peninsula are upwind of Ulsan in the winter; therefore, air parcels could trap the emitted PAHs in these areas and then brought them to Ulsan. However, emission inventories of PAHs in South Korea were much lower than those in China (Shen et al., 2013), implying a large contribution of the trans-boundary transport of PAHs in Ulsan in winter.
Comparing to the PSCFm and CWTm, the FWT could validate more appropriately the source areas of particulate PAHs, which could be more affected by the long-range transport. Especially, the FWT would differentiate the source scale (i.e., local and distant sources) more effectively in summer and fall, when the local sources were more important. This result demonstrates that the FWT using both the gaseous and particulate data can more clearly identify the source- receptor relationship.
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