High-resolution identification of toxic VOC emission hotspots and multi-endpoint health risk assessment in Tibet, Third Pole of Earth.

This study presented a plateau-tailored, high-resolution (3 km × 3 km) VOC species emission inventory for Tibet, integrating high-altitude-specific emission factors and source profiles. In 2023, anthropogenic VOC emissions reached 32.45 kt, dominated by residential activities (40.4%) and on-road vehicles (31.6%). Toxic VOC species accounted for 41-45% in each city, involving 11 alkylbenzenes, 6 aldehydes, 2 alkenes and 2 alkanes. Spatially, 37.2% of VOC emissions happened in urban grids, which covering 0.3% of total area yet 23.7% of total population. Urban grids of Lhasa had the highest emission (27.00 t/km2/yr), while the urban areas of other cities (1.40-3.88 t/km2/yr) were comparable to the suburban grids of Lhasa. Correspondingly, VOC in ambient air in Lhasa was measured to be 25.31 ppb (urban site) and 11.16 ppb (suburban site), also implying the substantial VOC pollution in the emission hotspots. Furthermore, health risk assessment of VOC exposure was conducted for urban residents regarding four health endpoints, by using ADMETlab-predicted toxicity equivalency. As a result, 14 high- and 18 medium-risk species were identified, including aforementioned 21 toxic species as well as C2-C4 and C8-C10 alkanes, C9-C10 aromatics, and C6-C10 aldehydes. Diesel vehicles and yak dung combustion were found as the major contributors of these risk species. Accordingly, an idealized emission reduction scenario was proposed, under which the complete phase-out of old diesel vehicles and the full replacement of yak dung by clean energy could theoretically reduce toxic VOC emissions by up to 49.1% and lower health risks by 31.9-37.0%.