Atmospheric Mineral Dust and Trace Metals over Urban Environment in Western India during Winter

Trace metal concentrations in PM2.5 and PM10 are studied from Ahmedabad, an urban location in western India. During winter, concentrations of Zn, Cd and Pb are in the range of 16.5–290, 0.1–5.4, 28–1023 ng/m3 in PM2.5 and 38–459, 0.21–8.4, 48–1223 ng/m3 in PM10, respectively. Enrichment Factor (EF) analysis with respect to Al showed significant enrichment of elements like Cd, Pb, Zn and Cu in fine mode particles, suggesting their strong anthropogenic contribution. About 43% of PM10 mass is constituted by mineral dust, and the dominant fraction (~88%) of the same exists in coarse fraction with a characteristic Fe/Al ratio of 0.53. The Ca/Al ratio is ~1.1 in PM10 and ~0.8 in PM2.5 indicating that aerosol over this region is rich in Ca minerals compared to the average upper continental crust. Positive Matrix Factorization (PMF) analysis using trace metal and major components reveals five sources for PM2.5 and six for PM10. The PMF results suggest anthropogenic sources contribute ~80% and 40–50% of the PM2.5 and PM10 mass, respectively. Incineration/industrial emission, biomass burning, vehicular emissions and re-suspended/long range transported dust are the other prominent sources identified in this work. These source contributions exhibit large temporal variations during winter, as the sampling location is influenced by air masses from different source regions.