Spatio-temporal variation of in-cabin PM 2.5 levels in Metro Rolling Stock Saloons, Kochi Metro, South India

Abstract

Increasing particulate matter (PM) especially PM2.5 (particles less than 2.5µm in aerodynamic diameter), pollution in the air-conditioned indoor microenvironment can spread infectious diseases such as Covid-19 on occupants in addition to respiratory and cardiovascular diseases. Given the importance of this subject in the contemporary social context, this study seeks to assess the spatiotemporal variation of PM2.5 concentration in Metro Rolling Stock (MRS) saloons of Kochi Metro Rail Limited (KMRL), Kerala, India. During the in-transit survey data was collected according to the four different plans depending on the time and direction of the metro service using a real-time Indoor Air Quality (IAQ) monitor. The spatial variation in PM2.5 content en-route 22 stations (Aluva to Petta) shows, Kalamassery Town station recorded the maximum value of 40.33µg/m3 and station Maharajas Ground recorded the lowest value of 23.95µg/m3 respectively. Comparing the median concentration of PM2.5 of the four plans implied that plan-1 (Aluva-Petta during morning peak hours) record the highest concentration than other plans (p-value < 0.05). Principal Component Analysis biplots, did not display strong positive associations among PM2.5 and the other in-transit variables such as temperature, relative humidity, carbon dioxide concentration, and the number of occupants. Therefore, the study infers that the infiltration of outdoor air when the doors are opened at each station could be the influencing factor of PM2.5 level in MRS saloons of KMRL. Moreover, the proximity to traffic signals, industrial establishments, and muncipal waste dumping sites increase the probability of PM2.5 level which was evident at Kalamassery Town station.