Depositions of airborne microplastics during the wet and dry seasons in Pathum Thani, Thailand

In this study, microplastics were monitored separately in the wet and dry deposition in the peri-urban area of Thailand. Over eighteen weeks from September 2021 to January 2022, rainwater (wet deposition) and settled microplastics (dry deposition) were systematically collected. Subsequent analyses involved the extraction, quantification, and identification of microplastics through wet peroxide oxidation, density separation, stereomicroscopic visual inspection and Fourier-transform infrared (FTIR) analysis. The results show that the wet deposition flux of microplastics was averaged at 285 numbers/m²/day while the dry deposition flux of microplastics was averaged at 199 numbers/m²/day, contributing to a total deposition flux (dry + wet) of 325 numbers/m²/day. Comparative assessments with prior studies from different locations demonstrated similarities in microplastic numbers, color and polymer types. Notably, this study found a higher microplastic deposition flux during the period when wet deposition existed than the flux during the period with only dry deposition, underscoring the important role of rainfall in adding more removal of microplastics from the atmosphere. These findings provide crucial insights into the dynamics of microplastic deposition in outdoor settings, significantly contributing to understanding the microplastic pollution cycle in the environment.