Non-negligible health risks from atmospheric carbonyls in Tibetan Plateau's anthropogenic hotspots: Evidence from a summertime case study in Lhasa.

Atmospheric carbonyls, particularly aldehydes and ketones, are key intermediates in tropospheric chemistry, pose escalating health threats in ecologically-fragile and climate-sensitive regions like the Tibetan Plateau (TP). However, studies characterizing the source, toxicity, and health risks of speciated carbonyls remain sparse in TP's anthropogenic hotspots, particularly during the photochemically active summer period. Here, we present the most extensive carbonyl dataset for the TP to date, quantifying 37 species (25 aldehydes and 12 ketones) during summertime in urban and rural Lhasa, the most urbanized and densely populated city in TP. Total carbonyl concentrations were comparable between sites (urban: 5.70 ± 3.43 ppbv; rural: 5.86 ± 3.80 ppbv), with meta-analysis revealed a substantial increase for urban (99.8 %) and rural (82.7 %) from 2010 to 2022, primarily driven by low-carbon aldehydes (formaldehyde and acetaldehyde). Positive Matrix Factorization identified secondary formation and biomass burning as the dominant source of aldehydes and ketones, respectively. Compound-specific toxicity evaluations revealed that aldehydes contributed 87 % to total toxicity, with formaldehyde alone accounting for >60 %. Health risk assessments indicated daytime carcinogenic risks for formaldehyde exceeded the safety threshold (1 × 10-6), reaching (2.8 ± 0.8) × 10-5 (urban) and (2.6 ± 0.9) × 10-5 (rural), respectively. Acetaldehyde's carcinogenic risk also surpassed safety thresholds. Our findings demonstrate that comprehensive speciation of carbonyls is critical to unravel pollution drivers and health impacts in fragile ecosystems, urging prioritized control of low-carbon aldehydes in TP's anthropogenic hotspots.