Quantifying Meteorological and Emission-Control Contributions to PM2.5 and Ozone Changes During the 2023 G20 Summit in New Delhi

India faces severe PM2.5–O3 compound pollution, and the 2023 G20 Summit in New Delhi provided a valuable case for examining how short-term emission controls interact with unfavorable late-monsoon meteorology. In this study, the WRF-CMAQ modeling system was applied to quantify the relative contributions of meteorological variability and graded multisectoral emission controls to PM2.5 and ozone changes during the summit period. The results show that both pollutants exhibited clear stage-dependent variations, with lower concentrations during the summit and rapid rebound afterward. Relative to the 2022 meteorology sensitivity case, the 2023 meteorological background increased PM2.5 by 6.76 μg/m3 and MDA8 O3 by 4.37 ppb over New Delhi, indicating a distinct meteorological penalty during the monsoon withdrawal period. Under progressively strengthened control scenarios, PM2.5 declined from 79.01 to 66.35 μg/m3, while MDA8 O3 decreased from 81.19 to 77.67 ppb. The strongest control scenario reduced PM2.5 more than the meteorological penalty and substantially mitigated the ozone enhancement, although it did not fully offset the adverse meteorological effect on O3. These findings demonstrate that high-intensity coordinated controls can effectively alleviate PM2.5–O3 compound pollution even under unfavorable meteorological conditions.