| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 107 === Precipitation is one of the important sedimentation mechanisms of pollutants in the atmosphere, but the literature of Dibenzo-p-dioxin and Dibenzofuran (PCDD/Fs) deposition in cloud/fog water is still absent. However, droplets of cloud/fog water are much smaller and have a much higher surface-to-volume ratio compared to rain which might make it more efficiency in PCDD/F sedimentation. Therefore, we investigate PCDD/Fs scavenged by cloud/fog water in this study in order to figure it out.
Sequential cloud/fog water samples were collected for each cloud event during January 17th to February 24th, 2018 and January 15th to February 16th, 2019. The cloud water samples were combined into one to reach 20 L for PCDD/F measurement due to the low solubility of PCDD/Fs in water. There were 3 and 11 events happened during collecting period in 2018 and 2019, respectively, but only 8 events were analyzed in 2019 because of too short cloud/fog water event period or too low liquid water content. On the other hand, the ambient air sample were collected during January 14th and 28th, 2019, with 7 samples. Total PCDD/F-WHO-TEQ concentration collected by active fog collector in cloud/fog water samples in 2019 (mean: 1.35±1.80 pg WHO-TEQ L-1) averaged higher than the values of passive one (mean: 0.769±1.23 pg WHO-TEQ L-1). There might mix with a little bit rain in cloud/fog water sample collected by passive fog collector, which made liquid water content (LWC) for passive fog collector larger than LWC for active one.
Compared to scavenging coefficient of PCDD/F-WHO-TEQ of passive fog collector (mean: 2.24×105±2.96×105), scavenging coefficient (C-cloud/C-air) of PCDD/F-WHO-TEQ of active one was larger (mean: 4.20×105±3.60×105) in 2019. The cause of PCDD/F scavenging coefficient difference contributed to cloud/fog water sample mixing with rain which collected by passive fog collector. Besides, scavenging coefficient of PCDD/F-WHO-TEQ of passive fog collector in 2018 (mean: 3.20×105±3.26×105) averaged higher than the results of passive one in 2019 due to rich cloud and fog during collecting period in 2018. Then, compared to PCDD/F scavenging coefficient of precipitations (around 1.9×105), the scavenging coefficient of cloud/fog water in 2019 was larger. On the other hand, compared to scavenging ratio of PCDD/F-WHO-TEQ of passive fog collector (mean: 0.056±0.074), scavenging ratio (C-cloud/C-air *LWC) of PCDD/F-WHO-TEQ of active one was lower (mean: 0.033±0.029) in 2019. The reason might connect with higher LWC of passive fog collector where PCDD/Fs in the atmosphere could be scavenged by more cloud/fog water and rain. Besides, scavenging ratio of PCDD/F-WHO-TEQ of passive fog collector in 2018 (mean: 0.254±0.236) averaged higher than the results of passive one in 2019 due to higher LWC and rich cloud and fog during collecting period in 2018. Additionally, PCDD/F scavenging ratio of cloud/fog water was smaller than that of trace elements (ranged from 0.11- 0.56) since trace elements are easier to dissolve in water than PCDD/Fs. In conclusion, the obtained scavenging ratios of PCDD/Fs by cloud/fog water are crucial for clarifying the effect of cloud/fog water on the deposition of atmospheric PCDD/Fs.
|
|---|
