High-Resolution Inventory of Japanese Anthropogenic Mercury Emissions

Heavy metals like mercury that are emitted into the environment remain there indefinitely, posing a long-term threat to both the environment and human health. Elemental mercury is volatile and is in gaseous form, and because of the long residence time, transported over long distances. Comprehensive control of mercury emissions therefore remains an important international issue. The crucial steps for designing effective approaches for such control include the quantification of mercury emissions by sources and the identification of geographical characteristics of the emissions. In this study a detailed, high-resolution inventory of Japanese mercury emissions in 2005 was developed to improve understanding of their geographical distribution. Proceeding from a national emissions inventory per source category, emissions were spatially allocated with increasing geographical resolution in a stepwise procedure using statistics from geographic information resources, yielding mercury emissions per prefecture, per municipality and per grid cell of approximately 1 × 1 km. The five prefectures with the highest emissions were Fukuoka, Yamaguchi, Hyogo, Oita, and Hokkaido, accounting for 35.2% of all emissions. In each prefecture a small number of municipalities account for a major share of emissions. Distribution by grid cell is characterized by a concentration of 50% of all emissions in a mere 32 of the 255 954 grid cells over which emissions are distributed in this study. It was also quantitatively confirmed that use of larger grid cells leads to greater uncertainty in emissions distribution. Problems with data collection are clarified and measures to improve the accuracy of future estimation are proposed.汞等重金属排放进入环境后会长期留存，对生态环境与人类健康构成长期威胁。元素汞（elemental mercury）易挥发且以气态形式存在，加之其在环境中的停留时间较长，可实现长距离传输。因此，汞排放的综合防控仍是重要的国际议题。设计高效汞排放防控方案的关键步骤包括对各类排放源的汞排放量进行量化，以及明确排放的地理特征。本研究构建了2005年日本汞排放的详细高分辨率排放清单（emissions inventory），以提升对其地理分布特征的认知。本研究以基于源类别的国家排放清单为基础，结合地理信息资源统计数据，通过逐步提升空间分辨率的方式完成排放量的空间分配，最终得到各都道府县、各市町村以及约1×1千米网格单元（grid cell）的汞排放量数据。排放量最高的五个都道府县依次为福冈县、山口县、兵库县、大分县与北海道，其排放量合计占总排放量的35.2%。在每个都道府县内，仅少量市町村贡献了绝大部分的汞排放量。网格单元尺度的排放分布特征表现为：本研究覆盖的255954个网格单元中，仅32个单元即集中了总排放量的50%。本研究还定量证实，使用更大尺度的网格单元会导致排放分布估算的不确定性升高。本研究明确了当前数据收集环节存在的问题，并提出了提升未来排放量估算精度的改进措施。