Understanding the Influence of Open-waste Burning on Urban Aerosols using Metal Tracers and Lead Isotopic Composition

Abstract

Open-waste burning (OWB) is one of the primary sources of urban aerosols in several developing countries. To better understand the influence of OWB emissions on urban aerosols, total suspended particles (TSP) and size-segregated samples were collected at an open-waste burning site (the Okhla landfill) and two urban sites in New Delhi. The TSP samples were analysed for selected metals (As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, Se, Sn, Sr, V and Zn) using ICP-MS. In general, among the metals, Fe and Zn were mostly dominant, and As, Cd and Se were found in trace concentrations in the majority of the samples. Additionally, Pb concentrations were ~5–8 fold higher in urban wintertime samples than other samples. Tin, a tracer for waste-burning aerosols, ranged between 0.055 and 0.675 µg m–3 in OWB aerosols. Interestingly, the concentration of Sn was significantly high in the urban wintertime aerosols, specifically, 0.082–0.284 µg m–3. Tin also showed a high enrichment factor in the urban wintertime aerosols, suggesting its anthropogenic origin, possibly because of enhanced OWB practices in winter. Waste burning was also found to be one of the primary sources of chromium, which ranged between 0.102 and 0.606 µg m–3 in OWB aerosols and between 0.114 and 0.574 µg m–3 in urban aerosols. Since Cr(VI) is of interest due to its impact on health, the soluble Cr(VI) concentration was determined and found to be 6.12–10.2 ng m–3 (~1–6% of the total Cr in OWB aerosols compared to 0.33–0.65 ng m–3 [< 1% of the total Cr]) in urban aerosols. The lead isotopic signatures of OWB aerosols, viz., the 208Pb/206Pb and 206Pb/207Pb ratios, were determined to be 2.1309 ± 0.0029 and 1.1316 ± 0.0035, whereas those of the urban aerosols were 2.1369 ± 0.0026 and 1.1243 ± 0.0024, respectively. However, the ranges of these values among the different aerosol types were not very distinct and showed discreet overlaps. This Pb isotopic study, along with metal fingerprints, suggests the increased influence of OWB emissions in winter on New Delhi aerosols.