Characteristics, emission factors, and health risks of vehicular polycyclic aromatic hydrocarbons

Abstract This study characterizes vehicular PAHs using roadway tunnel measurements on Mumbai-Pune Expressway, a crucial route in Western India. Dominated by four- to six-ring PAHs (75%-89%), concentrations were influenced by diesel, heavy-duty vehicles (HDVs), and super-emitters. The total PAH emission factor was 52.7(±4.5) μg veh⁻¹ km⁻¹. An inverse relationship was observed between PAH molecular weight and volatility of organic carbon (OC). Molecular weight also strongly correlated with mass absorption coefficient (MAC) of brown carbon (BrC), significantly enhancing light absorption. Methanol-soluble BrC exhibited stronger absorption correlation with higher molecular weight PAHs (ΣHMW PAH ). Carcinogenic PAHs accounted for 98.9% of total toxicity, with incremental lifetime cancer risk (ILCR) values of ~5 and ~2 per million for adults and children, respectively. These findings highlight the significant contribution of vehicular emissions to urban air quality and health risks, emphasizing the urgent need for mitigation strategies while also providing insights to improve BrC representation in climate models.