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

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 Pb-208/Pb-204, Pb-207/Pb-204, Pb-206/Pb-204, and Nd-143/Nd-144 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.

Automated summary

This study demonstrates a seasonal pattern of anthropogenic lead transport from the Indo-Gangetic Plain to the Himalayas, with enhanced transport coinciding with higher summer temperatures. Over 50% of lead in Himalayan aerosols originates from the resuspension of historic lead derived from phased out leaded gasoline, underscoring the importance of legacy lead stored in the Indo-Gangetic Plains.