Decomposing Health Co-benefits and Climate Penalties of Net-Zero Mitigation: PM2.5 and O3 Evidence from Taiwan

Net-zero mitigation is expected to improve human health through air-quality co-benefits, but these benefits may be constrained by climate-driven warming, particularly in small greenhouse gas-emitting economies. Using Taiwan as a case study, this study applied an integrated LEAP-CMAQ-CRF framework to link net-zero energy pathways, air-quality responses, and mortality impact assessment. A 2×2 scenario design was used to separate mitigation co-benefits from climate penalties under present-day and +2°C warming conditions. Under present-day meteorology, net-zero mitigation reduced population-weighted PM2.5 (-35.7%) but increased MDA8 O3 (+18.8%). Under the combined warming and net-zero scenario relative to the baseline, PM2.5 remained substantially reduced (-35.0%), while O3 increased (+21.6%). Mortality decomposition further showed that +2°C warming added 97 PM2.5-related deaths (+0.3%) and 220 O3-related deaths (+0.6%), whereas net-zero mitigation reduced PM2.5-related deaths by 2,626 (-7.0%) but added 2,062 O3-related deaths (+5.5%). The final combined scenario reached 37,047 premature deaths, equivalent to 99.3% of the baseline level. Spatially, PM2.5 reductions were widespread, while O3 increases were concentrated mainly along western Taiwan and overlapped with several medium-high and high-SVI counties. These findings indicate that net-zero mitigation can reduce aggregate mortality risks, but its benefits are not pollutant-neutral or spatially uniform. Health-oriented integrated assessment should therefore evaluate both total risk reduction and residual burden redistribution across pollutants, climate conditions, and vulnerable regions.