Long-range taransport of air pollution studied by Bark Pocket Method

来自亚洲大陆的空气污染的远程运输是目前日本环境的一个重要问题，特别是在由于缓冲能力低而容易酸化的地区，如位于日本中部西海岸的新泻县村上。通过对84个存档降水过滤器的铅和铅同位素分析，获得了铅远距离迁移的证据，显示了1999年5月至2002年5月铅沉积的季节性变化。每年冬季和春季（11月至5月）铅沉降量最高，夏季最低。计算的72小时后向轨迹显示，冬季气团主要来自西北，经过中国北部和俄罗斯东部，而夏季气团主要来自东南，经过日本。铅同位素分析结果显示，冬季铅的来源不同，Pb <208> / Pb <206>较高。在^<207>Pb/^<206>Pb vs.^<208>Pb/^<206>Pb剖面上发现了一个造铅成分，与标准铅生长剖面相比，该成分的铅含量高于^<208>Pb，表明亚洲大陆存在某些铅矿石和煤。这些数据提供了铅从亚洲大陆长途运输到日本的证据。1972年至1982年间，在村上附近收获的两棵日本雪松树干上的树皮袋显示出铅同位素比率，表明铅来自日本。相比之下，当前（2003年）树皮显示出胸源性比率，与日本来源的相对下降和大陆酸铅的增加相一致。这一结果与来自日本的铅排放减少，而来自亚洲大陆的污染长距离运输增加的情况相一致，表明跨界空气污染对该区域的威胁。在该地区高海拔地区采集的树皮中也测量了致胸铅同位素定量。

Long-range transport of air pollution from the continental Asia is currently an important issue concerning the Japanese environment, especially in regions susceptible to acidification due to low buffering capacity, such as Murakami, Niigata prefecture located in on the west coast of central Japan. Evidence for long range transport was obtained through lead and lead isotopic analysis of 84 archived precipitation filters, showing seasonal changes in lead deposition from May 1999 to May 2002. Lead deposition was highest in winter and spring (November through May) each year and lowest in summer. Computed 72-hour back trajectories showed that in winter air masses were predominantly transported from the northwest, passing over northern China and eastern Russia, whilst in summer air masses predominantly originated from the southeast passing over Japan. Lead isotopie analysis showed higher ^<208>Pb/^<206>Pb during winter, indicating that lead originated from a different source. A plot of ^<207>Pb/^<206>Pb vs.^<208>Pb/^<206>Pb identified a thorogenic component, which is excess ^<208>Pb compared to a standard lead growth carve, indicative of certain lead ores and coals in continental Asia. The data provided evidence of long-range transport of lead from continental Asia to Japan. Bark pockets included within the trunks of two Japanese cedar trees harvested near Murakami, dating between 1972 and 1982,exhibited lead isotope ratios indicative of Japanese sourced lead. In contrast, current (2003) bark showed thorogenic ratios, consistent with a relative decline in Japanese sourced and increase in continental soureed lead. The result is consistent with the scenario of decreasing Japanese sourced lead emission and increasing long range transport of pollution from continental Asia, signifying the threat of transboundary air pollution to the region. Thorogenic lead isotope rations were also measured in tree bark collected at high altitude in the area.