Particle phase PAHs in the atmosphere of Delhi-NCR: With spatial distribution, source characterization and risk approximation

This study was undertaken to investigate the spatial and temporal variation of sixteen priority Polycyclic Aromatic Hydrocarbons (PAHs) as per the classification of the United States Environmental Protection Agency (US EPA); bound to size-fractionated particles along with their sources and probabilistic risks in urban environments of Delhi-National Capital Region (NCR) of India, where quantification of PAHs was carried out through Gas Chromatography-Mass Spectrometry (GC-MS) for the samples collected during the period 2015–16. PAHs were observed to be highly concentrated in the smaller size ranges of particles throughout the analyses. Benzo[a]pyrene (12%) contributed the highest mean concentration, whereas Acenaphthene (2%) contributed least among the PAHs in size fractionated particles. Relative abundances of PAHs revealed that higher amount were associated with fine particles (<2.5 μm). Pyrene dominated in the particles of fine fraction with highest proportions than the corresponding particles of coarse fraction (> 2.5 μm) among the priority PAHs. Winter registered considerably maximum concentration of PAHs, whereas it was minimum during the rainy season. Spatial distribution of PAHs was interpolated by applying the spatial analyst extension Arc Geographic Information System (GIS) software (version 10.1). Molecular Diagnostic Ratio (MDR) and Principal Component Analysis (PCA) were performed for source apportionment of PAHs; where pyrogenic and petrogenic emissions were found to be the major contributors in the monitored sites. Incremental Lifetime Cancer Risks (ILCR; in terms of inhalation exposure) and Benzo[a]pyrene equivalent concentrations were investigated for toxicity assessment of PAHs. The priority PAHs having inhalation unit risk [(μg/m3)−1] were used for the investigation of ILCR associated with children and adults, where Benzo[a]pyrene possessed the maximum ILCR of all the PAHs.