Zinc Isotopes Reveal Cross‐Border Transport of Coal Combustion Pollutants Across the Himalayas During the Summer Monsoon

Abstract The Himalayas form a major atmospheric barrier between South Asia and Tibetan Plateau, yet cross‐barrier transport of anthropogenic metals remains poorly constrained. We use moss δ 66 Zn along a 750–4,100 m a.s.l. south‐north transect in Motuo to trace pollution sources and transport processes. On the southern slope, trace metals (Zn, Pb, As, Ni, Co) display pronounced altitudinal gradients, with low elevations showing high concentrations and light δ 66 Zn (−0.41‰ to −0.32‰) dominated by smelting (42%–50%). With increasing elevation, concentrations decrease and δ 66 Zn becomes heavier (0.20‰ to 0.29‰), reflecting greater coal combustion inputs (35%–50%). North of the crest, overall metal loads are lower, but high elevations (>3,500 m) show heavy δ 66 Zn (0.30‰ to 0.44‰) and strong coal contributions (43%–54%). Our results show that topography, anthropogenic emissions, and vegetation coverage regulate vertical pollutant distribution patterns, providing direct Zn isotopic evidence for transboundary transport of coal combustion emissions from South Asia to the Tibetan Plateau.