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

Abstract

High-time-resolution aerosol measurements across various Indo-Gangetic Plain (IGP) regions are critical due to these regions' dense populations, intense industrial activities, recurring pollution episodes, and agricultural practices, as well as the associated health impacts and broader climate implications of aerosol. However, studies (mostly offline) have been predominantly concentrated in the upper IGP (U-IGP), with limited spatial coverage across the central IGP (C-IGP). This study aims to bridge the gap by examining both U-IGP and C-IGP regions, offering an in-depth analysis of elemental concentrations, source apportionment, inter-regional comparisons, seasonal variations, meteorological influences, and health risks through high-resolution Xact measurements conducted at three urban locations. During the colder seasons, elements such as sulfur (S), chlorine (Cl), and potassium (K) were found to dominate elemental PM2.5 concentrations, while the warm seasons showed notable changes in aluminum (Al), silica (Si), strontium (Sr), and barium (Ba) concentrations. These variations underscore the influence of meteorological conditions and different emission sources on pollution levels. From a health perspective, average levels of carcinogenic elements (lead (Pb), nickel (Ni), arsenic (As), and chromium (Cr)) were usually kept below reference levels. However, Pb concentrations exceeded these thresholds by 40 %-50 % during both periods in the U-IGP, largely attributed to coal combustion and lead smelting activities. Using the Multilinear Engine 2 (ME-2) solver, positive matrix factorization (PMF) deconvolved Cl-rich, coal combustion, Cu-rich, dust, solid fuel combustion 1 (SFC1), SFC2, and S-rich components. In both IGP regions, Cl-rich sources, S-rich sources, and SFC1 dominated the elemental sources, with differences observed in their relative contributions, indicating the influence of regional emissions. The role of meteorology in elemental PM2.5 variations during both clean and polluted episodes in the IGP regions was observed. During pollution episodes, the relative contribution of Cl-rich sources increased when PM2.5 concentrations showed a sharp increase as compared to clean periods, especially during cold periods, indicating the role of emissions from trash burning (plastic and PVC) and steel industries along with favorable meteorological conditions in the formation and accumulation of pollutants. During the warm period, the relative contribution of Cl-rich sources in the C-IGP is less, but during the cold period, both the U-IGP and the C-IGP have significant Cl-rich source contributions (44 %), indicating the role of chlorine in extreme haze air pollution in the whole IGP region. During warm periods, high-pollution events occurred across the IGP with major contributions from SFC1 (crop residue burning), indicating that severe pollution events also depend on seasonal emission sources despite less favorable meteorological conditions. These findings provide valuable insights into the spatial and temporal dynamics of elemental pollution across the IGP, offering a robust foundation for devising targeted mitigation strategies and regulatory policies to safeguard public health in this densely populated region.