2003年夏季東海海域大氣汞的分布和成因

Abstract

本研究主要是針對東海大氣汞進行研究，以瞭解其在空間分布及時間上之特性。利用海研一號於2003年夏季在東海海域上執行兩次航行任務，分別為OR1_686 (2003年6月19日到6月26日) 和OR1_691 (2003年8月13日到8月23日) 。大氣汞之採樣及測定，是採用本實驗室自製的汞分析儀系統，以現場連續採樣和即時監測方式進行，根據二階段汞齊濃縮法 (Two-Stage Amalgamation) 原理來測定汞的濃度。本研究顯示，OR1_686大氣元素汞 (GEM) 平均濃度為 4.5 ± 1.8 ng/m3 (2.1~13.2 ng/m3，n=123)，OR1_691為 3.6 ± 2.0 ng/m3 (1.8~11.8 ng/m3，n=78)。GEM之空間分佈變化很大，主要受物質來源的影响；其亦有日夜變化之情形，亦即是GEM白天高，晚上低，日夜差異於OR1_686和OR1_691二個航次平均為3 ng/m3左右。由氣流軌跡回推圖來看，較污染的氣團來源有來自日本 (GEM 6.8 ± 1.6 ng/m3) 、大陸地區 ( 5.3 ± 1.1 ng/m3) 、台灣海峽 ( 5.0 ± 1.5 ng/m3) 和台灣地區 ( 4.2 ± 0.4 ng/m3) ，也有自南海 ( 3.5 ± 0.2 ng/m3) 和太平洋 ( 2.5 ± 0.9 ng/m3) 較為乾淨的海洋氣團，說明邊緣海大氣汞的濃度受到周圍人為污染源的影響很大。颱風後的西南氣流，也影響了東海夏季大氣汞的分佈。

The concentration and distribution of gaseous elemental mercury (GEM) over the surface air of the East China Sea were investigated to characterize its spatial and temporal variations by using Ocean Research 1 in summer 2003 e.g. OR1-686 (June 19~26, 2003) and OR1-691 (August 13~23, 2003). The sampling and analysis of the GEM were performed on board ship by an semi-automated GEM analyzer (GEMA) which analytical principle was based on the two-stage amalgamation technique. The GEM averaged 4.5 ± 1.8 (n=123) and 6.1 ± 2.0 (n=78) ng/m3 with the range of 2.1~13.2 and 1.8~11.8 ng/m3 for OR1-686 and OR1-691 , respectively. There were significantly spacial GEM variation likely associated with the sources of Hg from surrounding areas of the ECS. Additionally, the two-cruise average magnitude of diurnal variation in GEM overall was about 3 ng/m3 .According to source tracking by air-backward trajectory analysis, we found air masses in summer were from Japan (GEM concn. 6.8 ± 1.6 ng/m3) , China (5.3 ± 1.1 ng/m3) , Taiwan Strait (5.0 ± 1.5 ng/m3) ,and Taiwan (4.2 ± 0.4 ng/m3) which exported the terrestrial and industrially anthropogenic materials to the ECS. On the other hand, air masses were from the Pacific Ocean (2.5 ± 0.9 ng/m3) with the clean marine materials and the South China Sea (SCS) (3.5 ± 0.2 ng/m3) with less Hg emission. The results show the GEM in marginal sea was significantly influenced by transportation of terrestrial and anthropogenic materials. Additionally, the special weather event, like the typhoon, would alter the distribution of GEM in ECS.