Measurement report: Sources and meteorology influencing highly-time resolved PM2.5 trace elements at 3 urban sites in extremely polluted Indo Gangetic Plain in India

Abstract. High time-resolution aerosol measurements across various regions of the Indo-Gangetic Plain (IGP) are essential due to its dense population, intense industry, pollution episodes, agriculture, health impacts, and climate implications. However, absence of studies in Central IGP (C-IGP) limits the comprehensive understanding, as research has been primarily concentrated in Upper IGP (U-IGP) with limited spatial coverage. To address this gap, the study aimed to provide insights into elemental concentrations, sources, regional comparisons, seasonal variations, meteorological influences, and health risks using Xact at three urban sites in U-IGP and C-IGP regions. During cold, S, Cl, and K were major contributors to elemental-PM2.5, while warm periods exhibited significant variations in Al, Si, Sr, and Ba concentrations, indicating seasonal influences on pollution levels. Average concentrations of carcinogenic elements (Pb, Ni, As, and Cr) typically stayed below recommended levels, but individual exceedances of Pb was 40–50 % during both periods in U-IGP, linked to coal combustion and lead smelting. Positive Matrix Factorization (PMF) using ME-2 (Multilinear engine 2) solver was performed, resolving Cl-rich, coal combustion, Cu-rich, dust, SFC1 (Solid fuel combustion 1), SFC2, and S-rich. Cl-rich, S-rich, and SFC1 in both regions, with differences observed in their relative contributions, indicating the influence of regional emissions. Role of meteorology in variation of elemental-PM2.5 during clean and polluted episodes in IGP regions were observed. During pollution episodes, when PM2.5 concentrations showed sharp increase as compared to clean periods especially during cold, the relative contribution of Cl-rich increased which is due to the condensation of Chloride during low temperature, indicating the role of steel industries as well as trash (plastic and PVC (Polyvinyl chloride) mixed) in the pollution episode as well as haze formations. However, the clean periods during warm were dominated by Dust and S-rich. Overall, the study highlights the variation of elemental pollution across IGP regions, its health impact and factors driving the pollution episodes. These findings aid in understanding spatial and temporal dynamics of elemental pollution, informing mitigation strategies and policies for public health protection in the region.