Distribution, Sources, and Association of Polycyclic Aromatic Hydrocarbons, Black Carbon, and Total Organic Carbon in Size-Segregated Soil Samples Along a Background-Urban-Rural Transect

Soil samples were collected over a year-long period along a background-urban-rural transect in Delhi, India for the analysis of polycyclic aromatic hydrocarbons (PAHs), black carbon (BC), and total organic carbon (TOC) in five grain size fractions, x, in mu m of 0 <= x < 53 (I), 53 <= x < 250 (II), 250 <= x < 500 (III), 500 <= x < 2000 (IV), and their sum (total: T). Maximum concentrations of PAH, BC, and TOC were observed in the smallest fraction (I) comprising silt and clay, irrespective of site or season. Results of the molecular diagnostic ratios and principal component analysis (PCA) identified coal, wood, biomass burning, and vehicular emissions as major sources of PAHs at all the three sites, while BC/TOC ratios pointed toward biomass combustion as the chief source of carbonaceous species. This work presents the first such rural-urban transect study considering PAH, BC, and TOC in soil.