Characteristics of Atmospheric Particle-bound Polycyclic Aromatic Compounds over the Himalayan Middle Hills: Implications for Sources and Health Risk Assessment

This study was conducted in the Central Himalayan middle hills to understand the nature of polycyclic aromatic hydrocarbons (PAHs) embedded in aerosol particles, their sources and human health risk assessments. The level of sum of 15 particle-phase PAHs was between 9 and 335 ng/m³, with an average concentration of 73±66 ng/m³. There were strong seasonal differences in total suspended particles (TSP) and particle-bound PAH concentrations with higher concentrations in winter, followed by pre-monsoon and lowest in monsoon. The main contributor to the suspended particles was 5-ring PAHs (32%), followed by 4-ring (29%), 6-ring (28%), and 3-ring PAHs (11%). Conversely, the gas-phase PAHs showed that 3-ring PAHs contributed utmost to the total particles. The molecular ratios and principal component analysis indicated that both petrogenic and pyrogenic sources, particularly fossil fuel combustion, biomass combustion, and car exhausts, were the major sources of PAHs. The overall average Benzo (a)pyrene equivalent concentration of particulate PAHs was 11.71 ng/m³, which substantially exceeded the WHO guideline (1 ng/m³), and indicated the potential health risks for local residents. The average lifetime inhalation cancer risk (ILCR) estimates associated with carcinogenic PAHs was 8.78×10⁻⁶ for adults, suggesting the possible cancer risk and 2.47×10⁻⁵ for children, signifying extreme carcinogenic effects of PAHs on children’s health. Therefore, strict measures should be taken to reduce PAHs emissions in the region.