Health risks from PM_2.5-bound heavy metals from religious burning activities on the plateau

Long-term exposure to hypobaric hypoxia in high-altitude regions increases the cardiopulmonary burden on local populations and heightens their susceptibility to the health impacts of air pollution. Although religious burning activities, including Sang Sangsol (a traditional Tibetan religious activity) and temple incense burning, contribute a relatively small fraction of fine particulate matter (PM_2.5) emissions, they represent a distinctive and non-negligible local source on the Tibetan Plateau. However the associated health risks of this source remain poorly quantified. This study aims to characterize the chemical composition and spatial emission patterns of PM_2.5 from major religious burning activities on the Tibetan Plateau, and to quantify the associated health risks to plateau residents. Therefore PM_2.5 samples from religious burning activities were collected across seven prefecture-level cities in the Tibet Autonomous Region, and a health risk assessment model was applied to evaluate the inhalation-related health risks for populations potentially exposed to these emissions. The results revealed PM_2.5 from Sang Sangsol combustion is dominated by water-soluble ions(WSIs) (SO₄^2-, Cl^-, NO₃^-) and crustal elements (Mg, Si, Al), whereas temple incense burning is significantly enriched in organic carbon (OC), elemental carbon (EC), and tracer components (F⁻, Ca). Pollutant emissions exhibit strong spatial heterogeneity, with Lhasa showing the highest intensity of religious burning activities, where PM_2.5 and heavy metal emissions dominate the entire region. Health risks were higher than anticipated. The lifetime carcinogenic risk of Cr in all sampled cities surpassed the USEPA acceptable level (10^-6), and the non-carcinogenic risk index for the population in Lhasa was the highest. These findings demonstrate that although religious burning activities contribute relatively little to total PM_2.5 emissions on the Tibetan Plateau, they represent a distinctive local source with non-negligible health implications. Therefore, they should be more explicitly considered in regional air quality management and health protection strategies. Synopsis: This study establishes the first localized chemical fingerprint database for PM_2.5 from religious burning activities (Sang Sangsol and temple incense burning) on the Tibetan Plateau, revealing their distinct compositional signatures and demonstrating that despite their modest contribution to total PM_2.5 mass, they pose non-negligible carcinogenic and non-carcinogenic health risks-particularly from chromium (Cr)-that warrant inclusion in regional air quality management strategies.