• • Urban PM2.5 concentrations were significantly higher than suburban, with peak levels at Changsha New Railway Station and Mapoling, indicating localized emission hotspots that require targeted mitigation.
• • Source apportionment identified secondary nitrate, vehicle emissions, and secondary sulfate as major contributors, with distinct spatial patterns: secondary nitrate lower in central but higher in west/southeast; secondary sulfate higher in southeast; vehicle emissions higher in southeast and lower in west.
• • Aerosol liquid water content was found to promote secondary formation of nitrate and sulfate, exacerbating PM2.5 pollution, highlighting the role of aqueous-phase chemistry in pollution episodes.
• • Secondary organic carbon was elevated in high pedestrian traffic areas, suggesting that human activity enhances secondary organic aerosol formation, which has implications for urban planning and emission controls.