This study presents a long-term dataset of PM2.5 concentrations from 190 cities in China, highlighting the high levels of PM2.5 pollution and its health risks. Only 25 out of 190 cities met the National Ambient Air Quality Standards, with the population-weighted mean PM2.5 concentration at 61 μg/m³, significantly higher than the global average. PM2.5 concentrations are generally higher in northern regions due to industrial emissions and unfavorable meteorological conditions, and show seasonal variability, peaking in winter and troughing in summer. The study also reveals that PM2.5 levels are highest in the afternoon and evening, influenced by boundary layer depth and anthropogenic emissions. The diurnal distribution of the PM2.5-to-CO ratio peaks in the afternoon, indicating significant secondary PM formation. The findings underscore the need for targeted control strategies and further research to mitigate PM2.5 pollution and improve air quality.This study presents a long-term dataset of PM2.5 concentrations from 190 cities in China, highlighting the high levels of PM2.5 pollution and its health risks. Only 25 out of 190 cities met the National Ambient Air Quality Standards, with the population-weighted mean PM2.5 concentration at 61 μg/m³, significantly higher than the global average. PM2.5 concentrations are generally higher in northern regions due to industrial emissions and unfavorable meteorological conditions, and show seasonal variability, peaking in winter and troughing in summer. The study also reveals that PM2.5 levels are highest in the afternoon and evening, influenced by boundary layer depth and anthropogenic emissions. The diurnal distribution of the PM2.5-to-CO ratio peaks in the afternoon, indicating significant secondary PM formation. The findings underscore the need for targeted control strategies and further research to mitigate PM2.5 pollution and improve air quality.