Chemical characterization, source identification and health risk assessment of polycyclic aromatic hydrocarbons in ambient particulate matter over central Indo-Gangetic Plain

Polycyclic aromatic hydrocarbons (PAHs) are the carcinogenic component of carbonaceous aerosols and the toxicity of PAHs depends on their molecular structure. PM2.5-bound PAHs concentration, their isomeric ratios and health impacts during wintertime (fog and non-fog episodes) are assessed at two heavily polluted sites (Allahabad and Kanpur) in central IGP (IndoGangetic plains) to better understand the spatial-temporal variability of PAHs as well as identification of their major sources. The highest contribution to PAH loading is reported from indeno (1,2,3-c,d) pyrene, benzo(g,h,i) perylene, benzo (b,j) fluoranthene and benzo (a) pyrene at the two sites during studied winter campaigns. Significantly higher contribution from 6-ring PAHs to total PAH concentration at Allahabad has been observed as compared to Kanpur. Moreover, lower PAHs concentration observed during dense fog episodes can be attributed to wet scavenging of aerosols by fog droplets. Isomeric ratios of PAHs indicated significant contribution from diesel engine exhaust at Allahabad and gasoline combustion at Kanpur. Substantial contribution from coal combustion and biomass burning emissions during wintertime over these sites was also observed. Estimation of health risk due to PAHs indicate potential health hazard to adults as well as children at both the sites. Furthermore, health risk observed due to carcinogenic metals (Cr (VI), Cd, Ni, As) and PAHs is nearly twice at Allahabad as compared to Kanpur. Diesel exhaust emissions (a dominant source of Cd and PAHs) appeared to be responsible for increased cancer risk at Allahabad. Whereas, higher Cr(VI) and PAHs concentration in the ambient aerosol is aggravating cancer risk at Kanpur.