Mechanism of pollutant diffusion in subway environment with central air conditioning ventilation system under mixed air supply mode

  Objective  To explore the mechanism of pollutant diffusion under mixed air supply by central air conditioning ventilation system and the influence of central air conditioning ventilation on indoor air quality in subway environment.

  Methods  Totally 4 subway lines′ 24 subway stations (6 for each line) with central air conditioning ventilation system in a city were randomly selected for detections on particulate matter ≤ 2.5/10 μm in aerodynamic diameter (PM_2.5/PM₁₀), total bacteria and total fungi in air samplings collected at various sites of ventilation system and subway environment.

  Results  There were significant differences among concentrations of detected pollutants in fresh air, return air, mixed air and supply air (P < 0.05 for all); the concentrations of the pollutants in supply air were all lower than those in fresh, return, and mixed air and significantly lower than those in indoor air samples collected at station hall and platform floor (all P < 0.05). The concentration of PM_2.5 and PM₁₀ in air samples collected at platforms were higher than those in samples collected in station halls (P < 0.05 for all); but there were no significant differences in colony forming units (CFU) of total bacteria and fungi (P > 0.05 for all). There were significant positive correlations among PM_2.5 concentration of supply, fresh, and mixed air and between PM_2.5 concentrations of supply air with those of air samples collected at station halls and platforms (P < 0.05 for all). There were also significant positive correlations among CFU of total bacteria for supply, fresh, and mixed air and between CFU of total bacteria for supply air and that for air samples collected at station halls (P < 0.05 for all); while, no significant correlation was observed between the CFU of total bacteria for supply air and that for air samples collected at station platform.

  Conclusion  The central air conditioning ventilation system can effectively reduce concentrations of pollutants in subway environment and the pollutant reduction for indoor air in station halls is more obvious than that for indoor air at station platforms.