Indoor air pollutants and microbes in mass rapid transit (MRT) trains of north-western area of Bangkok, Thailand: Impact on indoor air quality and human health

Most modern cities suffer from urban air pollution caused by human activity such as traffic and other sources. Various pollutants in the environment may pose a threat to the health of commuters. The objective of this study is to assess the indoor air quality (IAQ) in MRT purple line trains serving the north-western area of Bangkok in order to determine any potential impacts on human health. The monitored parameters include total volatile organic compounds (TVOCs), temperature, relative humidity, carbon monoxide (CO), carbon dioxide (CO₂), ozone (O₃), formaldehyde (CH₂O), and fine particulate matter (PM_2.5). The indoor air pollutant concentrations in the MRT remained within the permissible thresholds. The results of the correlation analysis reveal that relative humidity (RH) and PM_2.5 are positively correlated in both the wintertime and summertime measurement campaigns. In contrast, CO₂ correlated with temperature in the wintertime and CO in the rainy season. Bacterial and fungal loads were estimated during various measurement campaigns in MRT. Fungi and bacterial loads were higher in the MRT trains during the wintertime and rainy season campaigns. The IAQ of MRT train in Bangkok is within the satisfactory and excellent category of air quality index (AQI). The inhaled doses of PM_2.5, CO, and VOCs were also estimated to identify their health effects on commuters. The inhaled dose of PM_2.5 was comparatively higher than other pollutants. In this study, a general perspective of the IAQ in the MRT system was provided. It is recommended to conduct more research studies on various MRT lines in Bangkok to further investigate the levels of bacteria, fungi, TVOCs, O₃, and PM. Additionally, the ventilation mode in MRT needs to be investigated as it is the main factor affecting the IAQ.