Pollution source tracing and health impact of PM elements using DN-PMF in sub-urban sites of the Indian Himalayan Region.

Air pollution, once considered a problem of urban and industrial centers, is now increasingly impacting remote and ecologically fragile regions like the Indian Himalayas, threatening both environmental stability and public health. This study presents a comprehensive assessment of PM-bound elements across the Indian Himalayan Region, covering western (Mohal-Kullu), central (Almora and Nainital), and eastern (Darjeeling) Himalayas. Extensive sampling from January 2019 to December 2020 revealed a complex mixture of natural and anthropogenic emissions. Morphological characterization using field emission-scanning electron microscopy identified diverse particle types-spherical, irregular, and flocculent-indicating sources such as crustal dust, combustion, and vehicular emissions. Elemental analysis via WD-XRF quantified 23 major and trace elements (e.g., Al, Fe, Ca, Cr, Zn, Cu) consistently across all sites. Source apportionment using dispersion-normalized positive matrix factorization identified 9  major pollution sources, including road dust, industrial activities, biomass burning, and vehicular emissions. Conditional bivariate probability function and concentration weighted trajectory analyses further highlighted dominant local sources and significant regional and transboundary pollution transport. A multi-pathway health risk assessment revealed that toxic elements like Cr(VI), Mn, and As pose both carcinogenic and non-carcinogenic risks, particularly to children. Seasonal variations in PM levels reflected region-specific emission characteristics. This study is the first of its kind to integrate source apportionment and health risk assessment across the entire IHR, providing critical insights necessary for targeted mitigation and sustainable environmental management in this under-studied but highly sensitive region.