桃園大氣汞分布與沈降暨顆粒汞粒徑分布特徵

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題名:	桃園大氣汞分布與沈降暨顆粒汞粒徑分布特徵
作者:	林祐瑄;Lin, Yu-Hsuan
貢獻者:	大氣科學學系
關鍵詞:	大氣汞;汞沉降;顆粒汞;顆粒汞粒徑篩分;atmospheric mercury;mercury deposition;particle-bound mercury;size-fractionated particulate mercury
日期:	2021-10-22
上傳時間:	2021-12-07 11:09:30 (UTC+8)
出版者:	國立中央大學
摘要:	汞(Hg)是一種具有神經毒性的重金屬，可藉由大氣傳送到世界各地。台灣位於全球人為汞排放最多的東亞地區，關於台灣平地大氣汞分布的研究仍有限，且缺乏長時間的連續觀測資料，因此本研究探討台灣平地大氣汞特徵，包含氣態元素汞(gaseous elemental mercury, GEM)、氣態氧化汞(gaseous oxidized mercury, GOM)以及顆粒汞(particle-bound mercury, PBM)濃度的時序變化、顆粒汞粒徑分布以及大氣汞沈降量。本研究使用2018-2020年桃園市國立中央大學校園的大氣汞連續監測觀測資料、雨水汞資料以及氣象資料，進行大氣汞濃度與乾溼沈降的特徵分析，其中乾沈降量是透過表面阻力參數化模式(surface resistance model, SRM)進行估算。此外，本研究於2020年6月至2021年5月在相同測站使用微粒分階衝擊式採樣器(Dekati PM10 Impactor)採集四種粒徑顆粒(PBM>10、PBM2.5-10、PBM1-2.5、PBM1)進行總汞分析，以探討顆粒汞濃度的粒徑分布特徵。 2018至2020年間，GEM、GOM及PBM的平均濃度(±標準差)分別為2.32 ± 4.60 ng m-3、7.1 ± 21.6 pg m-3及13.1 ± 51.4 pg m-3。整體而言，因為地區性的排放源，當風向為南或南南西時，容易出現較高的大氣汞濃度，來自該方向的氣團平均GEM濃度為4.45 ng m-3，為整體GEM平均濃度的1.8倍。同期間雨水汞權重平均濃度為10.08 ng L-1，平均年濕沈降量為15.15 μg m-2 yr-1，且呈現夏季汞沈降量較高，冬季較低的趨勢，而利用模式推估的年平均乾沈降總量為36.5 μg m-2 yr-1，桃園郊區的大氣汞沈降以乾沈降為主。顆粒汞分徑採樣分析結果，PBM>10、PBM2.5-10、PBM1-2.5、PBM1的平均濃度分別是0.6±0.3、3.7±1.92、4.1±2.2、6.6±5.3 pg m-3，分析結果顯示顆粒汞主要分布在細粒徑顆粒，且也會受到當地排放源影響，在風向為西南風時各階層顆粒汞濃度皆會上升。造成本站大氣汞濃度升高的主要事件可分為長程傳輸霾害事件、長程傳輸沙塵事件、當地弱風累積事件及當地排放源影響事件，連續監測與分徑採樣結果皆顯示當地事件通常比長程傳輸事件帶給本站更高的大氣汞濃度。 ;Mercury is a global toxicant transported primarily via atmospheric circulation. Since the majority of anthropogenic mercury emissions in the world occurred in East and South-east Asia, and Taiwan is located in the downwind region in this area, it is meaningful to examine the atmospheric mercury level in Taiwan. As previous studies in this aspect are limited and long-term observations are scarce, the present study aims to understand the characteristics of atmospheric mercury at ground level in Taiwan, including: 1) gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) concentrations; 2) particle size distribution of PBM; and 3) atmospheric mercury deposition. Findings showed that between 2018 and 2020, the mean concentrations of GEM, GOM, and PBM were 2.44 ± 4.19 ng m-3, 7.1 ± 21.6 pg m-3, and 13.1 ± 51.4 pg m-3, respectively. On the whole, because of regional emissions, when the wind direction was south to south-southwest, higher mercury concentrations were observed. The GEM average concentration of air masses from SSW winds was twice the overall GEM average. The volume-weighted mean (VWM) concentration of mercury in rainwater was 10.08 ng L-1. The annual mercury wet deposition was 15.15 μg m-2 yr-1, and the total annual mercury dry deposition estimated by the model was 36.5 μg m-2 yr-1. It can be inferred that the atmospheric mercury deposition at ground level in Taiwan was dominated by dry deposition while the mercury deposition flux in summer was higher than that in winter. Furthermore, the sample of size-fractionated particulate mercury was collected between June 2020 and May 2021. The mean (± S.D.) concentrations of PBM>10, PBM2.5-10, PBM1-2.5 and PBM1 were 0.6±0.3, 3.7±1.92, 4.1±2.2 and 6.6±5.3 pg m-3, respectively. Results showed that particle-bound mercury was mainly distributed in fine particles, with PBM2.5 usually accounting for more than 70% of the total particulate mercury concentration.
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