Observations of Size-Segregated Airborne Microplastics in Ho Chi Minh City, Vietnam

Microplastics (MPs), generally defined as plastic particles smaller than 5 mm in diameter, have emerged as an environmental concern owing to their persistence, mobility, and potential impacts on ecosystems and human health. Although previous studies have primarily focused on aquatic and terrestrial environments, airborne MPs (AMPs) have recently attracted increasing attention due to their potential health risks via inhalation. Nevertheless, research on AMPs remains limited. In this study, we characterized AMPs in size-segregated aerosols (PM_2.5, PM_2.5-10, and PM_10<) in HCMC, Vietnam, based on observations conducted during the rainy season in 2023. To our knowledge, this is the first size-segregated AMP investigation in this region.

Aerosol samples were collected at the top of an 11-story office building at the University of Science, Vietnam National University Ho Chi Minh City in HCMC, Vietnam. A multi-nozzle cascade impact sampler was used to continuously collect PM_2.5, PM_2.5-10, and PM_10< on Teflon-coated glass fiber filters over sampling periods of approximately 1 week at a flow rate of 20 L min^-1. Following sample collection, the filters were subjected to a series of pretreatment steps, including extraction with ultrapure water, organic removal by hydrogen peroxide solution, and density separation by sodium iodide solution. After pretreatment, AMPs on the filters were identified by attenuated total reflection imaging with micro-Fourier transform infrared spectroscopy (Spectrum3/Spotlight 400; PerkinElmer). Detailed analytical procedures are described in our previous publication (Wang et al., Environ. Chem., Lett., 21, 3055-3062, 2023).

Here, we present the results for the rainy season. AMP concentrations ranged from 0.45 to 3.51 particles m^-3 and differed significantly among samples. The polymer composition showed substantial temporal variability throughout the sampling period. Polyethylene (PE) was consistently the most abundant polymer, followed by polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), and polypropylene (PP). Other identified polymers included polyethylene/polypropylene copolymers (PE/PP), alkyd resin (alkyd), polyurethane (PU), polyester (PES), ethylene-vinyl acetate (EVA), polyvinyl chloride (PVC), and acrylic polymers. Rubber-related polymers, such as ethylene-propylene-diene monomer rubber (EPDM) and isoprene rubber, were detected in mid-July and early August. These results may suggest the presence of multiple urban sources such as packaging and textile materials, paints and coatings, and traffic-related emissions, with increasing polymer diversity toward August.

Meteorological data and backward air trajectory analyses showed predominantly southwesterly to westerly airflow during the sampling period, with a mean wind speed of 1.61 m s^-1. Air masses arriving from the southwest likely reflect the influence of marine air from coastal and ocean regions, whereas trajectories passing over the Mekong Delta may carry particles associated with agricultural activities and nearby industrial areas, including packaging and textile manufacturing. These results suggest that AMP concentrations in HCMC are influenced by both local urban emissions and regional-scale transport.