Chemical composition and oxidative potential of roadside PM2.5 with associated health implications in urban Bangkok, Thailand

Fine particulate matter (PM2.5) has emerged as a significant environmental and public health issue in various urban areas around the world, including Bangkok, Thailand. A thorough investigation was carried out to examine the chemical composition, sources, and public health implications of PM2.5 at the roadside of Lumphini Park and Thonburirom Park in Bangkok. The PM2.5 samples were collected during a 10-day sampling campaign from January 30 to February 8, 2024. The analysis focused on various chemical components, including carbonaceous species, water-soluble inorganic ions, and trace elements. The oxidative potential (OP) and hydroxyl radical (•OH) generation rate were assessed using the dithiothreitol (DTT) assay to quantify the redox activity of PM2.5 and its implications for respiratory health. Source apportionment of PM2.5 was conducted using Principal Component Analysis (PCA). The inhalation dose of •OH radicals and the oxidative burden index (OBI) were used to evaluate potential health risks in the study area. The average PM2.5 concentrations at the roadsides of Lumphini Park and Thonburirom Park were 34.5 ± 11.2 µg/m3 (21.9 to 55.4 µg/m3) and 35.9 ± 11.8 µg/m3 (26.5 to 58.7 µg/m3), respectively. Favorable meteorological conditions, such as moderate winds and atmospheric mixing following the end of a haze episode in Bangkok, combined with the absence of significant biomass burning and limited regional transport, contributed to reduced PM2.5 accumulation. Both sampling sites exhibited high concentrations of carbonaceous components. The mean OC/EC ratio at the roadside of Lumphini Park is higher than that at the roadside of Thonburirom Park, indicating a predominance of fresh combustion sources at Lumphini Park, while Thonburirom Park reflects reduced vehicular influence or aged aerosol plumes. The roadside of Lumphini Park and the roadside of Thonburirom Park both show significantly high concentrations of NO3– and NH4+, reflecting the influence of regional pollution and the formation of secondary inorganic aerosols in both sites. The correlation between DTT activity, •OH radicals, and PM2.5 components is significantly higher at the roadside of Lumphini Park compared to Thonburirom Park, indicating greater oxidative stress in the roadside of Lumphini Park. The mean OBI values for roadside of Lumphini Park and roadside of Thonburirom Park are 0.10 ± 0.01 nmol/min/µg and 0.10 ± 0.02 nmol/min/µg. The mean values of inhalation doses of •OH radicals for adults and children in Lumphini Park roadside were 11.1 µmol/day and 8.3 µmol/day, and Thonburirom Park roadside were 13.3 µmol/day and 10.0 µmol/day, respectively. These findings are consistent with the source contributions identified through principal component analysis at both sites. Encouraging the use of cleaner fuels and electric vehicles is essential for reducing the roadside PM2.5 concentrations. Additionally, regulating agricultural residue burning in the surrounding provinces is necessary to minimise aerosol and metal contamination in Thailand and particularly in Bangkok.