Aerosol observation data assimilation is key to atmospheric environmental prediction. The original CMA chemistry–weather (CMA-CW) 3DVar data assimilation system uses simply fine and coarse particulate matter (PM_2.5 and PM_2.5–10) as control variables, with only concentrations of PM_2.5 and PM₁₀ being assimilated. In this study, a new 3DVar assimilation framework is developed, which considers seven aerosol species (black carbon, organic carbon, soil-dust, sea salt, sulfate, nitrate, and ammonium, instead of PM_2.5 and PM_2.5–10) in refined size segments as control variables, aiming to direct assimilate more aerosol related variables such as aerosol optical depth and lidar extinction and to provide accurate chemical initial fields for the CMA-CW model. Moreover, in the new assimilation framework, a novel equal-proportion distribution and compensation for background error increment is proposed and implemented, which produces physically more reasonable background error and thereby more reliable atmospheric–chemical analysis increments. The new assimilation framework is validated by idealized and real-case assimilation experiments, with reasonable performance. Based on the CMA-CW coupled model with the new assimilation framework and a rapid update cycle configuration, five-day CMA-CW simulation experiments for a widespread heavy fog–haze event in winter 2016 are carried out. The results demonstrate that assimilation of the surface aerosol observation data significantly improves the short-time forecast of atmospheric pollutants, due to refined and more precise information on aerosol compositions brought by the new assimilation framework. Meanwhile, the surface aerosol data assimilation also makes a positive contribution to visibility forecasting, significantly improving the visibility forecast in the heavy pollution areas.

Achieving the 2 ℃ climate target requires the coordination of strategies for greenhouse gases (GHGs) and air pollutants mitigation, yet their complex interactions remain insufficiently explored. BCC-ESM1 Earth system model is employed to compare global climate responses under the novel SSP2-com scenario, in which both GHGs and aerosols undergo reduction, with that under the SSP2-4.5 scenario. Moreover, the relative contributions of carbon dioxide (CO₂), sulfur dioxide (SO₂), and black carbon (BC) to future temperature increases are analyzed. Results reveal that compared with the SSP2-4.5 scenario, the SSP2-com scenario can stabilize the end-21st-century temperature rise well below 2 ℃, primarily driven by the reduction of anthropogenic CO₂ emissions. A mid-term warming rebound between 2061 and 2080 is observed due to reduced aerosol cooling. SO₂ reductions result in a weakening aerosol-induced radiative forcing, driving regional warming asymmetries―particularly in northern high latitudes (up to +1.5 ℃ in winter). Compared to CO₂-only mitigation, experiments involving SO₂ reductions also exhibit stronger global precipitation increases, suggesting an acceleration of the hydrological cycle under lower aerosol loading. Energy budget analysis further indicates that SO₂ mitigation results in an increase in net shortwave radiation at the top of the atmosphere by approximately 0.23 W/m² during the mid-term (2061―2080), and consequently leads to an accumulated surface energy gain of about 0.15 W/m². These findings highlight a key trade-off: aerosol mitigation may induce mid-term warming, but remains essential for achieving air quality and climate goals. This work underscores the necessity of balancing mid-term climate―air quality trade-offs with long-term decarbonization, offering actionable insights for policymakers to design integrated pathways align with the Paris Agreement.