Fine Particulate Matter Bound Polycyclic Aromatic Hydrocarbons and Carbonaceous Species in Delhi’s Atmosphere: Seasonal Variation, Sources, and Health Risk Assessment

This study was carried out to determine sources and health risks of fine particulate (PM2.5) bound polycyclic aromatic hydrocarbons (PAHs) and carbonaceous species in the ambient atmosphere of Delhi. Aerosol samples were collected from October 2017 to September 2018 in an institutional cum residential area of Delhi. Annual PM2.5 level was found to be 124.3 ± 107.6 µg/m3 which exceeded the Indian National Ambient Air Quality Standard (NAAQS) by over three times. Sixteen US EPA priority PAHs’ concentration exhibited a seasonal trend of winter > monsoon > summer with annual mean level of 83.6 ± 48.0 ng/m3. Winter and summer (p < 0.05), and monsoon and summer (p < 0.05) values were significantly different. Low-molecular-weight (LMW) and high-molecular-weight (HMW) PAHs contributed about 34.4% and 65.6% to Ʃ16PAHs, respectively. Annual mean organic carbon (OC) and elemental carbon (EC) levels were 21.5 ± 16.1 µg/m3 and 20.1 ± 20.5 µg/m3, respectively, with a mean OC/EC ratio of 1.8 ± 2.6. Winter OC and EC values showed significant mean difference from summer and monsoon (p < 0.01) with a seasonal trend of winter > summer ≈ monsoon. Molecular diagnostic ratios and principal component analysis identified vehicular emission as the leading source of these species followed by biomass and coal combustion, industrial emissions, and volatilization of petroleum and its products. Regional and trans-boundary incursion of pollutants was also identified with the help of back trajectories and concentration weighted trajectories. Carcinogenic PAHs contributed ̴41.4% to the aerosol PAHs load. Incremental cancer risk assessment estimated ̴ 25 additional cancer cases per million population due to lifetime inhalation exposure to PAHs at their observed concentration in Delhi.