Model simulations are conducted for fine particles diameter less than 2.5 microns (PM_2.5) in the Chulalongkorn University area in the central business district of Bangkok, Thailand, where PM_2.5 originating from road traffic is a recurring problem. For input to the American Meteorological Society/U.S. Environmental Protection Agency Regulatory Model (AERMOD), an hourly continuous vehicle type classified emissions inventory is developed based on local traffic observations and published emissions factors. The simulation accounts for advected-in PM_2.5 by hourly measurements from upwind stations. The result reveals a hotspot location near a nearby expressway with PM_2.5 concentration peaking at 1-h and 24-h averages of 344 and 130 μg m⁻³, respectively. Source contribution analysis of the annual average PM_2.5 at this hotspot suggests that the expressway contributes approximately 32% of the total PM_2.5. Meanwhile, at receptor points farther from the expressway, ground-level urban roads contribute only 17.5% roadside PM_2.5 concentrations, the remainder coming from outside the modeled area. A different source contribution breakdown by vehicle type suggests that heavy-duty vehicles contribute up to 21% of annual average PM_2.5 at a location near the expressway. At a roadside receptor point farther from the expressway, the top contributors are light-duty (9%) and heavy-duty vehicles (6%). Advected-in PM_2.5 dominates the overall PM_2.5 concentrations, accounting for 64%–99% depending on the receptor point. The model performance for 24-h average prediction is acceptable. A scenario study is also performed to compare the potential effectiveness of two PM_2.5 abatement measures.

Particulate matter (PM) has been associated with various health issues. However, the most hazardous constituents of fine particles remain unclear, particularly in Asia where the chemical compositions are highly diverse and understudied. This study investigated the concentration and health risks of particulate-bound polycyclic aromatic hydrocarbons (PAHs) and heavy metals in the indoor air of religious spaces in Bangkok, Thailand. Air samples were collected from four religious sites during periods of high activity using a six-stage NanoSampler to capture particle sizes ranging from 10 µm. Chemical analyses were conducted using gas chromatography-mass spectrometry (GC-MS/MS) for PAHs and inductively coupled plasma-mass spectrometry (ICP-MS) for heavy metals. The results revealed significantly elevated concentrations of PM2.5, PAHs (notably benzo[a]anthracene (BaA), chrysene (CHR), and fluoranthene (FLU)), and heavy metals (particularly Mn, Ni, and Cu). Health risk assessments indicated that both the incremental lifetime cancer risk (ILCR) and hazard quotient (HQ) values for several pollutants exceeded the U.S. EPA safety thresholds, suggesting serious cancer and non-cancer health risks for workers exposed to these environments over prolonged periods. This study highlights incense burning as a dominant source of toxic indoor air pollutants and underscores the urgent need for mitigation strategies to reduce occupational exposure in religious buildings.