Ⅲ. Result and discussion
3.1. Concentration
3.1.2. PAS VOCs concentration
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Figure 16. (a) Seasonal variation and (b) spatial variation of AVOCs and BVOCs
(a) (b)
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Table 6. Min, max and mean concentration of Σ24 VOCs from PAS, MDL and Detection ratio (μg/m3, %)
No. VOC species Summer Autumn Winter
MDL Detection
ratio Category
Min Max Mean Min Max Mean Min Max Mean
1 Isoprene 0.13 0.63 0.35 0.07 0.23 0.12 0.03 0.32 0.07 0.23 100 BVOC
2 MTBE 0.21 3.07 0.77 0.56 5.92 2.44 0.73 4.04 2.14 0.26 100 AVOC
3 Benzene 0.53 6.64 1.46 1.76 14.3 3.46 2.83 16.6 4.66 0.20 100 AVOC
4 Toluene 1.84 11.6 5.34 4.41 38.4 10.5 3.09 23.0 7.04 0.13 100 AVOC
5 Ethylbenzene 1.21 9.32 3.40 1.20 17.8 5.00 0.93 15.1 3.07 0.05 100 AVOC
6 m,p-Xylenes 1.61 9.19 4.05 1.25 20.4 6.14 1.14 14.0 3.41 0.1 100 AVOC
7 o-Xylene 1.43 7.91 3.49 1.02 12.4 4.34 1.09 10.9 2.86 0.1 100 AVOC
8 α-Pinene 0.49 7.76 3.12 0.00 1.89 0.72 ND 0.06 0.01 0.53 90 BVOC
9 Camphene 0.25 1.41 0.75 0.03 0.39 0.21 0.00 0.05 0.02 0.31 100 BVOC
10 1,3,5-Trimethylbenzene 0.22 0.96 0.46 0.20 1.78 0.63 0.16 1.04 0.35 0.18 100 AVOC
11 β-Pinene 0.29 2.35 1.03 0.05 0.68 0.32 0.01 0.10 0.04 0.27 100 BVOC
12 1,2,4-Trimethylbenzene 1.04 3.58 1.90 0.86 5.95 2.19 0.66 3.54 1.36 0.27 100 AVOC
13 Myrcene 0.02 0.13 0.06 0.00 0.02 0.01 ND 0.01 0.00 0.77 98 BVOC
14 d-3-Carene 0.01 0.03 0.02 0.00 0.03 0.01 ND 0.02 0.01 0.54 99 BVOC
15 α-Terpinene 0.01 0.06 0.02 0.00 0.01 0.01 0.00 0.01 0.00 0.11 100 BVOC
16 p-Isopropyltoluene 0.16 0.71 0.39 0.05 0.19 0.10 0.02 0.04 0.03 0.56 100 BVOC
17 Limonene 0.14 0.52 0.33 ND 0.20 0.10 ND 0.04 0.02 0.65 98 BVOC
18 Eucalyptol 0.12 0.38 0.21 0.01 0.64 0.22 ND 0.02 0.00 0.61 78 BVOC
19 γ-Terpinene 0.01 0.03 0.02 0.00 0.04 0.01 0.00 0.01 0.00 0.28 100 BVOC
20 Terpinolene 0.01 0.03 0.02 0.00 0.01 0.01 0.00 0.01 0.00 0.21 100 BVOC
21 Linalool ND ND ND ND ND ND ND ND ND 0.74 0 BVOC
22 Camphor 0.17 0.49 0.32 0.09 0.22 0.15 0.02 0.06 0.03 0.83 100 BVOC
23 Naphthalene 0.40 0.91 0.59 0.21 0.62 0.33 0.13 0.30 0.20 0.73 100 AVOC
24 α-Humulene 0.10 0.22 0.14 0.01 0.04 0.02 ND 0.02 0.01 0.42 99 BVOC
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The spatial distribution of AVOCs and BVOCs concentrations at each sampling site is shown in Figure 16. Industrial sites showed the highest AVOCs than urban and rural sites. The concentrations of AVOCs were 34.7 µg/m3 in industrial sites, 22.63 µg/m3 in urban sites, and 20.24 µg/m3 in rural sites.
AVOCs concentration in industrial sites was statistically higher than in urban and rural sites (Rank-sum test, p < 0.001). Regarding BVOCs, rural sites showed higher BVOCs than in industrial and urban sites.
The concentration of BVOCs was 5.87 µg/m3 in rural sites, 4.91 µg/m3 in urban sites, and 2.78 µg/m3 in industrial sites. But there was not statistically different between rural and urban sites (Rank-sum test, p > 0.05).
In Figure 17, there is a spatial distribution of AVOCs and BVOCs in each season. Seasonal contour plots of each season for AVOCs and BVOCs concentration were drawn by using a geographic information system (ArcGIS 10.4.1, ESRI Inc., USA) with using inverse distance weighting (IDW) interpolation method to visualize the distribution of concentration and sampling sites. Contour plots imply that there are different sources of AVOCs and BVOCs in each site. AVOCs showed complicated spatial distribution in industrial, urban, and rural sites in all seasons. There was high AVOCs concentration in I3 and I4 which are located nearby petrochemical industries. Those sites showed high benzene concentration in I3 and high toluene concentration in I4. Benzene and toluene are known to be emitted from petrochemical processes (Lv et al., 2021; Watson et al., 2001). Also, I5 and U3 showed high concentration of ethylbenzene, xylenes, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene.
Those sites are located next to shipbuilding industries and those compounds are reported to be emitted from painting and coating processes (Datta & Philip, 2012; Yuan et al., 2010). Between the petrochemical and shipbuilding industries, there is another industrial site I3 which had a high concentration of BTEX. I3 site could be affected by those industries with easterly wind and northwesterly wind (Figure S3). In a previous study in Ulsan, four major industrial complexes (petrochemical, non-ferrous, automobile, and shipbuilding industries) were clearly to be primary sources of VOCs (Kim et al., 2019). In urban sites, there were high concentrations of AVOCs in U5 and U6. There were estimated to be affected by local solvent and paint use near sampling sites.
Especially in rural site (R2), there was high AVOCs concentration with high toluene concentration.
Around the R2 site, there were registered toluene emission industries in PRTR (MOE, 2020c). The concentration of AVOCs in R2 suggests that even rural sites can be affected by human activity or industrial sources.
On the other hand, from Figure17 and Table S5, BVOCs showed high concentration around rural sites and some urban sites near the forest in summer and there was no spatial distribution in autumn and winter. In summer, there was a high concentration of industrial, urban, and rural sites. In I3 near petrochemical industries, there was a high concentration of isoprene. Isoprene is known to be produced
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by a chemical reaction in industries to synthesize rubber products and exhaust from vehicles (Li et al., 2023; Wagner & Kuttler, 2014). With the anthropogenic use of isoprene, registered isoprene emission facilities were also confirmed in Ulsan (MOE, 2020c). Isoprene concentration was also high in urban U2 and U10 sites. Isoprene is known to be mainly emitted from broad-leaves plants (Aydin et al., 2014;
Chang et al., 2021). Those sites are surrounded by broad-leaves forests and could be affected by isoprene. Among rural sites, R2, R4, and R5 sites showed high isoprene concentrations. In Figure 5 and 6, those sites are related to isoprene emission from near broad-leaves forests. Regarding monoterpenes, there were high concentrations around urban and rural sites in summer. As there is no report information on the monoterpenes production process in industrial facilities, there was a low concentration around the industrial area. Among urban areas, U1 and U7 sites showed high concentrations of monoterpenes in summer. U1 and U7 sites are located near coniferous plants which are known to mainly emit monoterpene (Aydin et al., 2014; Chang et al., 2021). In R1, R2, R3, and R4 rural sites, there were high concentrations of monoterpenes in summer. Their monoterpenes concentration (10.48 µg/m3) was two times higher than those of industrial (4.29 µg/m3) and urban sites (5.76 µg/m3). These measured data were also supported by the forest-type map from Korea Forest Service (http://fgis.forest.go.kr).
Figure 17. Seasonal variation of AVOCs in (a) summer, (b) autumn, (c) winter and BVOCs in (d) summer, (e) autumn and (f) winter
(a)
(d)
(b) (c)
(e) (f)
31 Table 7. Summer PAS concentration in 21 sampling sites (µg/m3)
No. VOC species I1 I2 I3 I4 I5 I6 U1 U2 U3 U4 U5 U6 U7 U8 U9 U10 R1 R2 R3 R4 R5
1 Isoprene 0.29 0.31 0.54 0.24 0.14 0.21 0.24 0.58 0.13 0.21 0.22 0.22 0.28 0.36 0.41 0.63 0.28 0.49 0.43 0.47 0.61 2 MTBE 0.91 1.22 0.68 3.07 0.75 0.53 0.59 0.38 0.85 0.73 0.95 0.46 0.53 0.81 0.47 0.27 0.43 1.36 0.68 0.32 0.21 3 Benzene 0.96 1.35 6.64 3.33 1.19 1.16 1.09 0.53 0.58 1.01 1.22 1.46 1.44 1.88 0.68 1.51 0.91 0.89 1.22 0.87 0.75 4 Toluene 8.92 7.82 7.95 10.41 5.06 11.60 4.15 1.84 4.98 5.01 5.38 3.15 4.99 6.91 2.72 2.39 3.58 7.35 3.24 2.36 2.32 5 Ethylbenzene 3.34 3.21 4.23 4.08 6.06 4.84 1.96 1.37 9.32 5.64 2.48 1.92 5.85 3.46 1.50 2.21 3.06 2.60 1.61 1.44 1.21 6 m,p-Xylenes 3.84 4.07 4.66 5.77 9.19 7.66 2.74 1.90 8.07 4.27 3.07 2.47 5.33 4.18 1.91 4.12 2.73 3.38 2.01 2.02 1.61 7 o-Xylene 3.38 3.52 3.99 3.70 7.91 6.27 2.58 1.78 6.58 3.27 2.66 2.24 4.99 3.65 1.81 4.47 2.40 2.97 1.93 1.75 1.43 8 α-Pinene 2.65 2.11 1.95 0.49 3.45 1.21 5.39 3.61 1.35 1.90 2.33 1.32 4.27 2.90 2.91 1.82 4.37 7.76 6.06 4.61 3.02 9 Camphene 0.67 0.57 0.52 0.25 0.51 0.36 1.27 0.77 0.28 0.50 0.55 0.45 1.04 1.06 0.54 0.49 0.95 1.30 1.41 1.20 1.00 10 1,3,5-Trimethylbenzene 0.57 0.58 0.67 0.66 0.96 0.81 0.39 0.31 0.60 0.38 0.40 0.25 0.53 0.48 0.26 0.26 0.27 0.49 0.29 0.29 0.22 11 β-Pinene 1.03 0.94 0.81 0.29 0.55 0.54 2.08 1.04 0.68 0.72 1.20 0.44 1.19 0.96 1.03 0.74 1.18 2.35 1.79 1.23 0.80 12 1,2,4-Trimethylbenzene 2.25 2.54 2.71 2.58 3.58 3.14 1.60 1.31 2.22 1.68 1.74 1.21 2.12 2.08 1.13 1.10 1.26 1.97 1.25 1.30 1.04 13 Myrcene 0.05 0.03 0.06 0.05 0.05 0.06 0.06 0.05 0.02 0.04 0.03 0.04 0.10 0.08 0.03 0.03 0.08 0.13 0.06 0.10 0.07 14 d-3-Carene 0.02 0.02 0.02 0.01 0.02 0.01 0.03 0.01 0.01 0.02 0.03 0.01 0.02 0.02 0.02 0.01 0.03 0.02 0.03 0.02 0.01 15 α-Terpinene 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.01 0.06 0.02 0.01 0.02 0.01 0.02 0.02 0.02 0.01 0.03 16 p-Isopropyltoluene 0.33 0.28 0.33 0.19 0.27 0.24 0.71 0.33 0.16 0.25 0.28 0.24 0.51 0.71 0.22 0.27 0.44 0.69 0.65 0.52 0.51 17 Limonene 0.31 0.25 0.28 0.14 0.36 0.26 0.39 0.33 0.20 0.30 0.30 0.19 0.50 0.31 0.32 0.25 0.44 0.52 0.51 0.43 0.27 18 Eucalyptol 0.38 0.19 0.23 0.13 0.19 0.23 0.26 0.14 0.13 0.18 0.20 0.12 0.29 0.18 0.16 0.14 0.21 0.35 0.28 0.21 0.19 19 γ-Terpinene 0.03 0.02 0.02 0.01 0.01 0.03 0.02 0.01 0.01 0.02 0.02 0.01 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.02 0.01 20 Terpinolene 0.02 0.01 0.02 0.01 0.01 0.02 0.03 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.02 0.03 0.03 0.02 0.02
21 Linalool ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
22 Camphor 0.36 0.30 0.26 0.18 0.24 0.21 0.48 0.27 0.17 0.27 0.27 0.25 0.40 0.41 0.24 0.23 0.35 0.42 0.49 0.44 0.42 23 Naphthalene 0.64 0.67 0.61 0.54 0.71 0.62 0.53 0.40 0.45 0.64 0.91 0.86 0.70 0.83 0.44 0.52 0.45 0.52 0.55 0.47 0.41 24 α-Humulene 0.22 0.12 0.12 0.14 0.13 0.15 0.12 0.13 0.11 0.15 0.13 0.16 0.21 0.15 0.11 0.17 0.11 0.11 0.15 0.11 0.10
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