Investigating In-Cabin Air Quality in Public Utility Buses in the Philippines Using Small-Sensors

This study investigates in-cabin air quality on Philippine public utility buses (PUBs) by measuring particulate matter (PM) and carbon dioxide (CO₂) concentrations to assess potential exposure levels among daily commuters. Using compact air quality monitors with small-sensor technology, measurements were taken inside two types of PUBs: regular buses in the EDSA carousel and the smaller modern jeepneys currently being deployed across different routes in the metro. Data was collected across different routes with varying traffic and occupancy conditions to evaluate how these factors influence the variability and range of PM and CO₂ concentrations. The air quality aboard the EDSA Carousel bus was assessed along its bus rapid transit route on EDSA, extending to the Parañaque Integrated Terminal Exchange (PITX). Meanwhile, the modern jeepney route began at its terminal near EDSA-Shaw Boulevard and ended in Antipolo City. The bus route covered approximately 28 kilometers (~2 hrs), while the modern jeepney route spanned 14 kilometers (~1 hr). Elevated CO₂ levels were observed in both types of PUBs during rush hours increasing from 1039.51 ppm to 2284.03 ppm and 3806.9 ppm to 6150.44 ppm for the carousel bus and modern jeepney, respectively. This effect can be attributed to higher passenger occupancy and is more pronounced in the modern jeepney, which has a smaller cabin and often experiences passenger overloading, compared to the EDSA carousel bus, which features a larger cabin and enforces stricter passenger limits. CO₂ concentrations also read higher at the rear of the buses, farther from the bus doors. Additionally, PM2.5 levels were elevated during periods of heavier road traffic, with levels climbing from 7.12 µg/m³ to 10.39 µg/m³ and 6.66 µg/m³ to 18.79 µg/m³ for the carousel bus and modern jeepney, respectively. The observed increase suggests that traffic conditions contribute considerably to indoor particulate matter exposure within the PUBs, which is likely due to the diffusion of outdoor air pollution when the doors open during stops.