Effectiveness of pyrolysis coupled with thermal desorption for the analysis of micro- and nanoplastics in Asian urban outdoor atmosphere using pyrolysis-GC/MS

Pyrolysis-gas chromatography-mass spectrometry is one of the most promising techniques for investigating plastic particles ranging from micro to nano-sizes (less than 1 µm). However, most studies on the occurrence of micro- and nanoplastics in the air applied single-shot analysis (only pyrolysis), whereas double-shot analysis (thermal desorption followed by pyrolysis) has not been fully investigated. This paper compares single-shot and double-shot methods to investigate the pyrolysis conditions for the detection and quantification of urban outdoor airborne plastics. The findings are applied to the outdoor air in Tokyo (Japan), Bangkok (Thailand), and Kathmandu (Nepal). Relative to single-shot, the double-shot analysis detected the indicator substances of polymethylmethacrylate, polyamide 66, and polypropylene in the aerosol collected in Kyoto city, Japan, and separated some volatile compounds, such as those produced by the pyrolysis of the polymer. In addition, the result indicates that the double-shot analysis may affect the quantification of polyethylene terephthalate (PET) because the pyrolysis of this polymer can be initiated at a thermal desorption temperature of 320°C. Therefore, we optimized the double-shot method to a maximum final temperature of 300°C for thermal desorption and achieved good PET quantification. The total airborne plastic concentration sized between 0.43 and 11 µm was 325 ng/m3 in Tokyo, 141 ng/m3 in Bangkok, and 434 ng/m3 in Kathmandu. The size distribution of each polymer varied; for polyethylene and PET, the concentrations of the nano-sized fractions tended to be similar or higher than those of the micro-sized fractions, whereas styrene-butadiene rubber was not detected at the size fractions under 3.3 µm in Tokyo and 2.1 µm in Bangkok and Kathmandu.