The environmental and health effects of alternative fuel vehicles: A tunnel study on PM_2.5 and according oxidation potential

Vehicle emissions significantly contribute to inhalable particles with an aerodynamic diameter of ≤2.5 μm (PM_2.5), posing human health risks, but their impact on reactive oxygen species (ROS) remains unclear. In this study, high-time-resolution PM_2.5 samples were collected in the longest inner-city tunnel in Xi'an, China in four time periods of the day (periods 1-4), subsequently, source apportionment of PM_2.5 and its oxidative potential (OP) was conducted using the Positive Matrix Factorization (PMF) model, and the relationship between the main chemical components of PM_2.5 and ROS was analyzed. PM_2.5 concentrations were exceptionally high (108.2–223.5 μg m⁻³), with ROS levels reaching 1.3–1.7 μM H₂O₂ m⁻³. PM_2.5 peaked during rush hours (periods 1 and 3), while ROS peaked at noon (period 2). Alternative Fuel Vehicles (AFVs), including compressed natural gas [CNG] and methanol M100-powered light-duty vehicles [M100 LDVs], consistently contributed elevated ROS, peaking at 43.0% in period 1, suggesting these innovated fuels (methanol and natural gas) pose even higher environmental and health risks than gasoline ones. Source apportionment revealed AFVs as the largest contributor to PM_2.5 mass (35.4%), while fugitive dust, AFVs and combustion sources contributed comparably to OP (26.0% - 27.7%). The multiple linear regression (MLR) model identified key ROS contributing species as Cl, K⁺, Organic Carbon (OC), NO₂⁻, Cr, and Mn, highlighting their health hazards in pollution control. This study provides insights into PM_2.5 emissions and health effects under evolving vehicle compositions, challenging the AFVs as a clean option in vehicle management from the perspective of PM_2.5 and according health concerns.