Evaluation of long-term trend of atmospheric lead pollution in western Japan based on lead isotope ratios and Pb/Zn ratio as indicators of long-range transport of aerosols from the Asian continent

Abstract

In this study, we evaluated the long-term trend of atmospheric lead pollution in western Japan based on lead isotope ratios and Pb/Zn ratio as indicators of long-range transport of aerosols from the Asian continent. First, recent seasonal changes (May 2013–April 2015) in atmospheric lead concentration, lead isotope ratios, and Pb/Zn ratio were investigated in Hirado City on the Asian continent side of Japan. Each parameter increased during winter and decreased during summer. The increase during winter was due to the enhanced long-range transport of lead from the Asian continent based on the back-trajectory analysis and lead isotope ratios of aerosols in major cities of China. Then, the long-term trends (approximately after 1990) of lead concentration, lead isotope ratios, and Pb/Zn ratio during winter in several sites in western Japan were evaluated using the data from this study and literature. The lead concentration and Pb/Zn ratio tended to decrease over the years, whereas the lead isotope ratios in 2013–2015 were lower than the ratios before 2001. These long-term trends were attributable to the long-term changes in atmospheric emissions and sources of lead in China. Moreover, it is likely that the rapid increase in zinc emissions in China also contributed to the decreasing trend of Pb/Zn ratio over the years. This study confirmed that atmospheric lead pollution in western Japan has improved over the years owing to the decrease in the amounts of lead transported from the Asian continent.