Fig. 5: The Pb isotopic compositions of the PM_2.5 aerosols and relevant end members illustrated in three-isotope space (²⁰⁸Pb/²⁰⁶Pb vs ²⁰⁶Pb/²⁰⁷Pb).

Two distinct mixing lines are observed in the tree-isotope plot, each with crust at one end: one extends to Neyveli lignite (blue dotted line), while the other extends to Indian ore (black dotted lines). The Pb isotopic compositions of the PMs lie along the mixing line between Indian ore and crust, rather than local lignite and fly ashes. The aerosols lie close to vehicular exhaust emissions (traffic) and seawater, with less radiogenic local crust also plotting close to the aerosols compared to UCC. There is a considerable overlap between the aerosols and Indian fuelwood, local solid waste & biomass burning signatures. Isotopic signatures of previously sampled aerosols from Delhi’s Okhla landfill, overlap with the Neyveli aerosols. The enclosure formed by the red dotted line signifies the mixing envelope formed using the relevant end members. The data for Indian fuelwood and OWB aerosols have been adopted from Mitra et al.¹⁰⁸ and Kumar et al.³⁴ respectively. Data for traffic emissions, Indian ore, crust, seawater, and local crust have been compiled from Ray and Das¹¹³, Deb et al.³⁷, Lee et al.¹⁰⁹ and Chakraborty et al.¹¹⁰ respectively.