Lead Isotope Evidence for Enhanced Anthropogenic Particle Transport to the Himalayas during Summer Months

Abstract

The Indo-Gangetic Plain (IGP) is one of the most highly polluted regions of the world, yet the temporal pattern of transport of anthropogenic aerosols from this region to the Himalayas is poorly constrained. On the basis of the seasonal variation of planetary boundary layer heights, air mass back trajectory analysis, and year-long time-series data for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, and 143Nd/144Nd from aerosols collected over a high-altitude station, we demonstrate that anthropogenic Pb transport to the glacierized catchment has a seasonal pattern. The Pb isotope data reveal that during winter, the thinned boundary layer traps up to 10 ± 7% more coal-derived Pb in the IGP. In contrast, in nonwinter months, a thicker boundary layer and enhanced subtropical westerly winds result in efficient Pb transport to the Himalayas. As Pb isotope ratios are robust conservative chemical tracers and Pb is predominantly derived from anthropogenic sources, these observations suggest that enhanced transport of anthropogenic aerosols to the glacierized catchment of the Himalayas coincides with higher near-surface temperatures in the summer, creating positive feedback that enhances melting. Our results further suggest that >50% of Pb in the Himalayan aerosols originates from the resuspension of historic Pb derived from phased out leaded gasoline, highlighting the importance of legacy Pb stored in the Indo-Gangetic Plains.

Spatial‐Temporal Variability and Sources of Lead (Pb) in the Indian Ocean and Asian Marginal Seas

“…The Pb isotope ratios of the corals in this study (Chagos, Phuket), together with regional published coral records (Vietnam, Indonesia, Singapore), show interesting geographic trends: the Pb isotope composition in open ocean corals (Chagos) show the highest fractional contribution of anthropogenic sources, while the coastal corals in this region (Thailand, Vietnam, Indonesia, and Singapore) consistently show lower fractional contributions of anthropogenic sources and higher fractional contributions of natural sources. However, this large contribution of natural Pb and low contribution of anthropogenic Pb in coastal corals cannot be explained by lower anthropogenic emissions, as the coastal regions are undoubtedly closer to the anthropogenic Pb sources compared to open oceans (Boyle et al., 2020; M. L. Chen et al., 2022), and the recent aerosol Pb concentrations do not show any significant geographical difference among southeast Asian cities close to the coral localities (Singapore: 206 Pb/ 207 Pb = 1.154, 208 Pb/ 207 Pb = 2.431 (Kayee et al., 2020); Thai cities: 206 Pb/ 207 Pb = 1.150, 208 Pb/ 207 Pb = 2.427 (Kayee et al., 2021); and Southeast Asian aerosols: 206 Pb/ 207 Pb = 1.143 ± 0.020, 208 Pb/ 207 Pb = 2.420 ± 0.021 (Bollhöfer & Rosman, 2000, 2001; Cheng et al., 2011; Chien et al., 2019; Chifflet et al., 2018; Das et al., 2018; Jung et al., 2019; Kayee et al., 2020, 2021; Kumar et al., 2016, 2018; Mitra et al., 2021; P.‐C. Wu & Huang, 2021; Sen et al., 2016; Zhu et al., 2010)).…”