Long-range transport model analysis on seasonal and spatial variations of ²¹⁰Pb deposition across Asia

This study analyzed the transport and deposition of ²¹⁰Pb across Asia, particularly focused on Japan, from 2012 to 2015, used an atmospheric transport model that combines WRF and HIRAT. Results indicated that modeled deposition fluxes aligned well with observation data. The average deposition flux in Asia is 17.2 Bq m⁻² month⁻¹, showed significant seasonal variation. Along the Sea of Japan, the four-year average was 27.0 Bq m⁻² month⁻¹, with winter peaks in Hokkaido and Tohoku-Hokuriku and summer peaks in Kyushu. The calculation results showed distinct seasonal transport routes. During summer in Kyushu, southerly and westerly winds from southern China (e.g., Guangdong and Fujian) transported ²¹⁰Pb-enriched air masses. Stationary fronts carried these air masses from the southwestern Chinese basin, leading to intensified deposition. In winter, along the northern Japan Sea coast, high ²¹⁰Pb deposition events were closely associated with the East Asian winter monsoon, characterized by East Asian troughs and Siberian highs. Strong northwesterly winds from Siberia transported ²¹⁰Pb-enriched air masses to the Hokkaido and Tohoku-Hokuriku coastal regions, resulting in significant deposition. Approximately 47% of the high winter ²¹⁰Pb deposition events originated from the Kazakhstan-Xinjiang border, while the remaining 53% came from eastern Siberia.