Winter In-Car Microclimate and Aerosol Variability on Prague Metro Line C: Passenger Load, Tunnel Ventilation, and Surface–Environment Coupling

This study evaluates winter in-car microclimate and aerosol conditions in a Prague Metro line C M1.3 car under real operation. Five Letňany–Háje runs were divided into 19 inter-station segments. TDC, PM10, PM4, PM2.5, PM1, CO2, air temperature, relative humidity, A-weighted sound pressure level, and occupancy were recorded. Aerosol fractions were measured in separate runs and treated as operational optical estimates, not as reference-equivalent or simultaneous size-distribution data. Temperature, relative humidity, CO2, sound level, and occupancy were aggregated to one value per run and segment and analyzed by randomized-block ANOVA with run as the block. Significant segment effects were found for occupancy, CO2, relative humidity, and air temperature; LA showed no stable segment effect. Central segments showed passenger-related CO2 and heat accumulation, whereas aerosol maxima did not coincide with maximum occupancy. Larger cut-point PM runs showed greater dispersion and episodic peaks, consistent with surface–tunnel exchange, resuspension, and station/ventilation pathways. Across 19 segment means, occupancy correlated more strongly with CO2 than with air temperature (r = 0.837 vs. 0.633); after Run adjustment, the slopes were 8.494 ppm/passenger and 0.011 °C/passenger, respectively. An overnight Vltavská–Florenc transect provided qualitative evidence of local ventilation influence near Štvanice. The study is a winter, vehicle-specific segmental case study.