Research on Comprehensive Evaluation of Air Quality in Underground Stations of Urban Rail Transit Systems

Research purposes: This paper proposes an entropy-weighted-linear weighting integrated evaluation approach combining numerical simulation with field measurements. Using a specific island-type station in Beijing Metro as a case study, the research first employed Revit to construct a full-scale 3D model and utilized Autodesk Simulation CFD software to simulate indoor airflow fields and air concentration distributions under three typical scenarios: train absence, train arrival, and train departure, thereby identifying ventilation weak zones and optimizing measurement point placement. Subsequently, handheld high-precision instruments were deployed to monitor pollutant concentrations at key locations in the concourse and platforms during morning and evening peak hours. Finally, a multi-index comprehensive evaluation model centered on CO2, PM2.5, PM10, and TVOC was developed to quantitatively characterize spatial variations in indoor air quality. Research conclusions: (1) The CFD-based measurement point optimization method effectively identifies air retention zones, providing a theoretical basis for actual measurement site selection; (2) Under low-frequency operation modes of the environmental control system, air retention zones tend to form in the central areas of platforms and station halls, resulting in poor air quality; although train piston ventilation improves indoor air circulation, it may carry tunnel pollutants into public areas; (3) Overall ventilation effectiveness during train departure is less noticeable than during arrival; (4) CO2 concentration exhibits a clear positive trend with passenger flow density, with potential exceedance risks in poorly ventilated areas such as escalator entrances; particulate matter concentrations are largely influenced by outdoor environmental inputs, while internal sources may also contribute to local levels, suggesting a moderate control effect of the environmental control system on internal particulate pollution; TVOC concentrations remain consistently at low levels; (5) Comprehensive evaluation reveals that escalator entrances and central platform areas constitute weak air quality zones, with overall air quality in station halls during evening peak hours being superior to that during morning peak hours; (6) This study provides theoretical foundations and data support for optimizing operational strategies of subway station environmental control systems and enhancing indoor air quality.