Objective To evaluate the environmental quality in Wuhan subway, reveal the temporal and spatial distribution characteristics of the main air pollutants and their influencing factors, and provide scientific basis for taking targeted prevention and control measures.

Methods Eighteen subway stations were selected as monitoring sites from Wuhan Metro Line 2, Line 3 and Line 7 in light of the impact factors of the subway air quality, such as the opening time of the subway line, and the station functions of the subway line (commercial network and transit). The four-season measures were performed for temperature, relative humidity, wind speed, illumination, noise, CO, CO₂, PM₁₀, PM_2.5 and total bacterial count from December 2018 to October 2019. The monitoring lasted for 7 consecutive days each quarter.

Results The median values of temperature at the platforms (24.8 ℃, 13.1 ℃) and the station halls (25.1 ℃, 11.4 ℃) were lower than the standard limit in Hygienic Indicators and Limits for Public Places (GB 37488-2019) in summer and winter. In four seasons, the illuminance values at the station halls and platforms were all highest at Line 7 and lowest at Line 2 (P<0.05). Only in autumn and winter, the differences in the illuminance values outside the stations presented statistically significant differences among the three lines (P<0.05). In four seasons, the median values of ambient noise in the stations were all higher than the standard limit 70 dB (A) in GB 37488-2019, and the values were all highest in platforms and lowest outdoor (P<0.05). The CO concentrations at the platforms, station halls and outside the stations were all highest in winter. In spring, summer and autumn, the CO₂ concentrations were all highest in platforms and lowest outdoor (P<0.01). The PM₁₀ and PM_2.5 concentrations at the platforms, the station halls and outside the stations were highest in winter (P<0.01). The median values of PM_2.5 concentrations at the platforms and the station halls were higher than the standard limit in the amendment sheet of the Ambient Air Quality Standards (GB 3095-2012), were 115 μg/m³ and 126 μg/m³, respectively. In spring, summer, and winter, the differences in the PM₁₀ and PM_2.5 concentrations at the platforms, station halls and outside the stations presented statistically significant differences among the three lines (P<0.01).In the four seasons, no significant differences in total bacterial counts were seen between platforms and halls (P>0.05).

Conclusion More attention should be payed to the indoor temperature problem, PM_2.5 concentration and noise pollution in Wuhan subways. The environment outside the station, passenger flow, centralized ventilation and air conditioning system, subway lighting system, and air purification equipment in the subway station affects the environmental quality inside the subway stations in Wuhan.