Coordinated effects of energy transition on air pollution mitigation and CO2 emission control in China

China has made progress in energy transition to improve air quality, but still confronts challenges including further ambient PM2.5 reduction, O3 pollution mitigation, and CO2 emission control. To explore the coordinated effects of energy transition on air quality and carbon emission in the near term in China, we designed 4 scenarios in 2025 based on different projections of energy transition progress with varying end-of-pipe control level, in each of which we calculated emissions of major air pollutants and CO2, and simulated ambient PM2.5 and O3 concentrations. Results show that energy transition has disparate effects on emission reduction of different air pollutants and sectors, which largely depends on their current end-of-pipe control levels. The different effects on emission reduction may result in opposite variation tendencies of ambient PM2.5 and O3 concentration in a future scenario with aggressive energy transition policies and end-of-pipe control level in 2018. With the end-of-pipe control level strengthened in 2025, PM2.5 and O3 concentration could both reduce on the national scale, but the reduction of ambient O3 lags behind PM2.5, indicating the difficulty of O3 pollution control. As to CO2, national emission would go up in 2025 either implementing current or aggressive energy transition policies due to growing needs of electricity and on-road transportation, but emissions in most provinces could decline to below the 2018 level with aggressive energy transition policies because of substitution of clean energy in industrial, residential and off-road transportation sectors. The study results suggest strictly implementing restrictive end-of-pipe control measures along with energy transition to simultaneously reduce ambient PM2.5 and O3 concentration, and accelerating substitution of renewable energy in power sectors where electricity generation grows rapidly to synergistically control air pollution and CO2 emissions. Furthermore, the projection of CO2 emissions could provide references for short-term emission control targets from the perspective of air quality improvement.