Urban expansion, seasonal climate and fine particulate matter in Lahore, Pakistan: a spatiotemporal analysis of regional environmental change (2015–2024)

Background Rapid urban expansion and land-use change in the Indo-Gangetic Plain interact with seasonal climate to shape regional air quality, yet how associations of fine particulate matter (PM₂.₅) with climatic and urban-growth factors vary jointly across space and time within one urban region is poorly understood. This study examined these associations across Lahore, Pakistan. Methods Satellite-derived PM₂.₅ (2015–2024) was analysed using two geographically and temporally weighted regression (GTWR) models: a climatic model (temperature, relative humidity, rainfall and wind speed; 1,400 point-seasons) and a socioeconomic model (built-up area, road density and population; 5,710 point-years). Local coefficients significant at the 5% level (|t| ≥ 1.96) were mapped. Results Annual mean PM₂.₅ ranged from 62.9 to 74.5 µg/m³, increased modestly (about 4.7% over the decade), spread from the centre toward the periphery and peaked in winter. In the climatic model (R² = 0.894), relative humidity was positively and rainfall negatively associated with PM₂.₅, temperature was predominantly negative, and wind speed changed sign: dispersive in the open north-east but positive in the western fringe, consistent with transport of regional crop-burning smoke. In the socioeconomic model (R² = 0.562), built-up area, road density and population were predominantly positive drivers, strongest on the rapidly urbanizing south-western periphery and in the congested Youhanabad/Model Town corridor. Conclusions PM₂.₅ in Lahore reflects a structural urban baseline overlaid by a strongly seasonal climatic signal. Converging climatic and structural hotspots on the south-western fringe call for spatially and seasonally differentiated interventions.