Under the Air Pollution Prevention and Control Action Plan (APPCAP) implemented, China has witnessed an air quality change during the past five years, yet the main influence factors remain relatively unexplored. Taking the Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) regions as typical cluster cities, the Weather Research Forecasting (WRF) and Comprehensive Air Quality Model with Extension (CAMx) were introduced to demonstrate the meteorological and emission contribution and PM_2.5 flux distribution. The results showed that the PM_2.5 concentration in BTH and YRD significantly declined with a descend ratio of −39.6% and −28.1%, respectively. For the meteorological contribution, those regions had a similar tendency with unfavorable conditions in 2013–2015 (contribution concentration 1.6–3.8 μg/m³ and 1.1–3.6 μg/m³) and favorable in 2016 (contribution concentration −1.5 μg/m³ and −0.2 μg/m³). Further, the absolute value of the net flux’s intensity was positively correlated with the degree of the favorable/unfavorable weather conditions. When it came to emission intensity, the total net inflow flux increased, and the outflow flux decreased significantly across the border with the emission increasing. In short: the aforementioned results confirmed the effectiveness of the regional joint emission control and provided scientific support for the proposed effective joint control measures.

Following the relaxation of coronavirus disease 2019 restrictions and the subsequent full economic recovery, Shandong Province, China experienced a 4.3% re

In eastern China, heatwaves increasingly co‐occur with extreme ozone pollution, posing substantial public health risks. However, the spatiotemporal heterogeneity of heatwave levels and their nonlinear modulation of photochemical mechanisms remain insufficiently resolved. Integrating explainable machine learning with WRF–CAMx simulations, this study quantifies key drivers of ozone variability, characterizes nationwide heatwave evolution, and evaluates how heatwave levels affect surface ozone formation and precursor control efficiency in the Yangtze River Delta (YRD). Machine learning results show that meteorological factors explain over 70% of daytime ozone variability, with temperature, solar radiation, and relative humidity exerting dominant influences. A threshold‐like temperature–ozone response is identified in the YRD, with ozone growth weakening above approximately 38°C. A decadal analysis (2014–2023) shows heterogeneous heatwave patterns across China. Driven by background warming, mild heatwaves prevail in coastal regions, whereas stronger events are concentrated in inland basins and northwestern China. Further analysis shows that the heatwave level critically reshapes atmospheric chemical sensitivity. Extreme heat accelerates radical cycling and NO _x oxidation, weakens NO titration, and shifts ozone formation from VOC‐limited conditions during non‐heatwaves to transitional regimes during heatwaves, reducing the rebound associated with only‐NO _x reductions. Results indicate that NO _x ‐oriented strategies become markedly more effective under severe heatwaves than under climatological mean conditions. Overall, the results indicate that air quality management should shift from static, climatology‐based mitigation frameworks to dynamic, climate‐adaptive strategies that adjust precursor reduction ratios according to heatwave level, achieving synergistic air quality and climate benefits.

To explore the impact of temporary control measures on photochemical pollution, a comprehensive observation of peroxyacetyl nitrate (PAN) and other pollutants as well as meteorological conditions was conducted during the Chengdu 2023 Summer World University Games. Based on the measurement results and box model simulations, the temporary control measures achieved a good effect in reducing air pollution. Most pollutants included SO ₂ , NO ₂ , TVOCs, O ₃ and HONO have been significantly reduced by 22%–38% compared to the pre‐control period. Nevertheless, the PAN reduction was only about 2% during the control measures period. Methylglyoxal and acetaldehyde were the two largest precursors for PA radicals, which accounted for more than 50% of PA radical formation. As a reservoir molecule, temporary control measures result in lower reductions in PAN concentration than in the case of other pollutants. Therefore, it is inappropriate to evaluate the effectiveness of temporary emission reduction measures on photochemical pollution solely through PAN concentration assessments. PAN concentrations are significantly influenced by the volatile organic compound (VOC)/NO ₂ ratio, and reducing NO _x emissions alone could have an adverse effect on controlling PAN pollution. Therefore, reducing VOC emissions is the preferred measure for controlling PAN pollution.