Chemical composition and oxidative potential of roadside PM(2.5) with associated health implications in urban Bangkok, Thailand.

Zhang, Y; Ahmad, M; Chetwittayachan, T; Panyametheekul, S; Thaveevong, P; Fueangfung, A · 2026 · PubMed Central

DOI: 10.1038/s41598-026-48849-w

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Summary

This study investigates the chemical composition, sources, and oxidative potential (OP) of fine particulate matter (PM2.5) at roadside locations in Bangkok, Thailand, to assess associated health risks. Motivated by the need to understand PM2.5 toxicity beyond mass concentration, particularly in urban roadside microenvironments where exposure is high, the research focuses on two distinct sites: Lumphini Park, located in a central business district with heavy traffic, and Thonburirom Park, situated near industrial zones and secondary roads. The study aims to characterize PM2.5 components, evaluate oxidative stress markers, identify emission sources, and quantify health risks for adults and children. Researchers conducted a 10-day sampling campaign from January 30 to February 8, 2024, collecting 24-hour PM2.5 samples using low-volume air samplers. The analysis included carbonaceous species, water-soluble inorganic ions, and trace elements. Oxidative potential was assessed using the dithiothreitol (DTT) assay to measure redox activity and hydroxyl radical (•OH) generation rates. Source apportionment was performed using Principal Component Analysis (PCA). Health risks were evaluated by calculating the inhalation dose of •OH radicals and the oxidative burden index (OBI), which combines PM concentration with intrinsic OP. Statistical analyses, including Pearson correlation and Mann–Whitney U tests, were used to compare sites and identify significant relationships. The average PM2.5 concentrations were 34.5 ± 11.2 µg/m³ at Lumphini Park and 35.9 ± 11.8 µg/m³ at Thonburirom Park, both exceeding World Health Organization guidelines. Lumphini Park exhibited higher concentrations of organic carbon and elemental carbon, indicating a predominance of fresh vehicular combustion sources. Both sites showed high levels of nitrate and ammonium, reflecting secondary inorganic aerosol formation. The correlation between DTT activity, •OH radicals, and PM components was significantly higher at Lumphini Park, suggesting greater oxidative stress potential despite similar mean OBI values (0.10 ± 0.01 nmol/min/µg) at both sites. Estimated daily inhalation doses of •OH radicals were higher for adults than children, with Thonburirom Park showing slightly higher doses for both groups (13.3 µmol/day for adults, 10.0 µmol/day for children) compared to Lumphini Park (11.1 µmol/day for adults, 8.3 µmol/day for children). The findings highlight that roadside PM2.5 in Bangkok poses significant health risks due to its oxidative potential, driven largely by traffic emissions and secondary aerosols. The study concludes that traditional mass-based assessments are insufficient for capturing toxicity, advocating for the inclusion of OP metrics in air quality management. Recommendations include promoting cleaner fuels and electric vehicles to reduce traffic-related emissions and regulating agricultural residue burning in surrounding provinces to minimize regional aerosol and metal contamination. These measures are essential for mitigating oxidative stress and protecting public health in rapidly urbanizing Southeast Asian cities.

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