Ship traffic and military activity identified as emerging sources of lead in remote island air.

Atmospheric particulate matter (PM) pollution in remote, tropical island environments remains underexplored, a significant knowledge gap compared to extensive studies in polar and high-altitude regions (e.g., Arctic, Antarctic, and Tibetan Plateau). The Andaman and Nicobar (A & N) Islands provide a unique setting to study background pollution due to minimal industrial activity and coal combustion. This study addresses this gap by analyzing elemental concentrations and Pb isotopic compositions in PM₁₀ and PM_2.5 aerosols along with potential end members, collected in Port Blair during winter and monsoon 2023. Ship fuel (diesel, lubricants, and coolants), an underexplored source of atmospheric Pb was characterized for metal concentrations and Pb isotopes. The results indicate that while crustal components (up to 76% in monsoon and 53% in winter) and marine sources (up to 28% in monsoon and 15% in winter) contribute significantly to Pb in aerosols, anthropogenic sources such as vehicular and ship emissions (up to ≥10%), non-exhaust emissions, and transboundary aerosols (up to ∼10%) also play key roles. Notably, Pb isotopic signatures reveal a distinct source that cannot be explained by conventional contributors. By comparing Pb isotopic compositions with global ammunition data, we identify military activities, particularly bullet-derived Pb, as a significant and previously unrecognized source in the region (up to 23% in monsoon and 30% in winter). This study advances our understanding of atmospheric Pb sources in remote tropical archipelagos, reporting the first comprehensive Pb isotopic composition of PM from these islands.