The effectiveness of environmental taxes on sectoral economic and governance efficiency in a synergistic perspective of air pollution reduction and carbon mitigation.

Under China's High-Quality Development goals, growing emphasis is placed on synergistically advancing air pollution reduction, carbon mitigation, and economy growth. Environmental tax emerges as a critical instrument for harmonizing environmental stewardship with economic progress, yet gaps persist in understanding how policy objects, intensities, and scopes affect on sectoral economy and governance efficiency. Employing coupled Computable General Equilibrium (CGE) and Slacks-Based Measure (SBM) models, this study evaluates optimized environmental tax designs. The key conclusions are as follows: Compared with other policies, the more effective policy is a simultaneous application of weakened tax, such as 30 CNY/t-CO2 and 2000 CNY/t-(SO2, NOX, and PM2.5) on all sectors. Under this policy, while above one-third sectors showed a significant decrease in carbon emissions and air pollution, the losses in social welfare and GDP decrease are only 44 billion CNY and 0.20 %. Regarding sectoral efficiency, the economic efficiency of whole sectors reaches the frontier level, governance efficiencies also improve on average by 3.85 %, and the synergistic efficiency on two-third sectors fully or partially achieves a higher level of sectoral average. These findings offer actionable insights for refining environmental tax policies to bolster synergistic efficiency.