Deciphering China's shifting skies: a spatial-temporal analysis of air quality across 337 cities (2015-2023)

The spatial-temporal evolution of six key air pollutants (PM_2.5, PM₁₀, CO, NO₂, SO₂, O₃) across 337 Chinese cities between 2015 and 2023 was analyzed based on the provided figure set. The period represents a critical juncture encompassing the implementation and intensification of China's ambitious national air pollution action plans. Using annual average concentration data visualized through spatial mapping, we conducted a comparative analysis of pollutant distributions for 2015, 2020, and 2023, identifying regional hotspots and temporal trends. Significant reductions were observed for most pollutants: PM_2.5 decreased by 46.3% in the Beijing-Tianjin-Hebei (BTH) region and by 24.5% in the Fenwei Plain (FWP); SO₂ declined by over 79% in BTH and FWP; CO fell by 62.9% in BTH. NO₂ showed slower reductions, particularly in urban corridors, highlighting persistent traffic-related emissions. However, O₃ increased by 14% in BTH and 12% in the Yangtze River Delta (YRD), with over 50% of BTH cities exceeding 180 μg/m³ by 2023, highlighting the complex atmospheric chemistry involved. The analysis underscores the effectiveness of targeted policy interventions for primary pollutants but emphasizes the urgent need for multi-pollutant, regionally tailored strategies to address the evolving air quality landscape, particularly the rising O₃ threat.