Characteristics, source analysis, and health risk of PM2.5 in the urban tunnel environment associated with E10 petrol usage.

The increase in the number of motor vehicles has intensified the impact of traffic sources on air quality. Our aim was to illustrate the characteristics of PM_2.5 emissions from vehicles fueled with E10 (a blend of 10% ethanol and 90% gasoline). A 21-day PM_2.5 sampling in a fully enclosed urban tunnel and the component analysis were completed, and the characteristics, sources, and health risks of tunnel PM_2.5 were studied. Moreover, the PM_2.5 pH and its sensitivity were investigated by the thermodynamic model (ISORROPIA-II). In addition, exposure models were used to assess the health risks of different heavy metals in PM_2.5 to humans through respiratory pathways. The two-point Cu/Sb ratio (entrance: 4.0 ± 1.4; exit: 4.4 ± 1.7) was close to the diagnostic criteria indicating a significant impact from brake wear. NO₃⁻, NH₄⁺, and SO₄²⁻ constituted the main components of water-soluble ions in PM_2.5 of the tunnel, accounting for 83.0–84.6% of the total concentration of inorganic ions. The organic carbon/elemental carbon ratio of the tunnel was greater than 2, indicating that the contribution of gasoline vehicle exhaust was significant. The average emission factors of PM_2.5 in the fleet was 31.4 ± 16.6 mg/(veh·km). The pH value of PM_2.5 in a tunnel environment (4.6 ± 0.3) was more acidic than that in an urban environment (4.9 ± 0.6). The main sensitive factors of PM_2.5 pH in the urban atmosphere and tunnel environment were total ammonia (sum of gas and aerosol, NH₃) and temperature, respectively. The results of the health risk assessment showed that Pb posed a potential carcinogenic risk, while As and Cd presented unacceptable risks for tunnel workers. The non-carcinogenic risk index of heavy metals of PM_2.5 in the tunnel environment exceeded the safety threshold. [ABSTRACT FROM AUTHOR]