Airborne microplastics in a suburban location in the desert southwest: Occurrence and identification challenges

Abstract

Microplastics are rapidly emerging anthropogenic stressors that pose a potential threat to ecosystems and human health. While the ubiquitous nature of microplastics in water has been well documented, studies on their distribution in the air are limited. Measuring microplastics, as a component of atmospheric particulate matter, is important in assessing air pollution impacts within a breathing zone. Here we investigate and present results for the occurrence of microplastics in suspended particulate matter in Tempe, a suburban location in Arizona. Samples were collected from Oct 28th, 2020, to Nov 1st, 2021, on quartz fiber filters using a high-volume air sampler, and processed with microplastics counted under an optical microscope to obtain quantitative information of their presence and distribution in the atmosphere. Microplastics were present in all collected suspended particulate samples ranging from between 0.02 and 1.1 microplastics/m3 (average concentration of 0.2 microplastics/m3) with the size range of (5–5000) μm. Fibrous microplastics were the most prevalent accounting for a large majority (≥82%) of the microplastics suspended in air in all samples. To characterize the type of microplastics present, micro-Raman spectroscopy was used to identify the chemical composition of microplastics. Chemical characterization results revealed an array of polymers for the airborne microplastics. The most abundant identified polymer was polyvinyl chloride (19%). However, many micro-Raman spectra lacked characteristic peaks, making the chemical identification process more challenging. Laboratory experiments simulating weathering of microplastics were performed to understand how microplastics change under weathering processes; these experiments revealed that Raman spectra of microplastics change over time due to weathering processes.