Decadal Variations of PM2.5 in Uttar Pradesh (2015–2024): Seasonal Insights from Rabi and Kharif

Air pollution from fine particulate matter (PM2.5)remains a critical environmental and public health challenge across the Indo-Gangetic Plain, with Uttar Pradesh experiencing some of the most severe episodes.This study investigates the seasonal, spatial, and diurnal variation of PM2.5 concentrations across 54 monitoring stations during the Rabi (April-May) and Kharif (October-November) seasons, based on nearly 700,000 hourly records.During Rabi, average concentrations were 56.6 g/m, nearly four times higher than the WHO 24-hr guideline (15 g/m) and close to the Indian NAAQS limit (60 g/m), with episodic peaks reaching 500 g/m.In contrast, the Kharif season showed substantially higher pollution, averaging 107.6 g/m, with extreme values up to 600 g/m and continuous exceedance of national standards throughout all hours of the day.Spatial heterogeneity was pronounced, with severe hotspots such as Ghaziabad, Lucknow, and Varanasi, while relatively lower levels were observed in Bareilly and IBHU Varanasi.Diurnal patterns revealed distinct morning and evening peaks, intensified during Kharif due to crop residue burning, stagnant meteorological conditions, and festival-related activities.Overall, Kharif levels were more than double those in Rabi, emphasizing the dominant role of stubble burning and adverse winter conditions.The findings confirm persistent and widespread exceedance of safe air quality limits, highlighting the urgent need for integrated mitigation strategies targeting residue management, vehicular and industrial emissions, and dust control to reduce exposure risks and improve regional air quality.