IT'S ALL UP IN THE AIR: COMPARING MICROPLASTIC DEPOSITION FROM PRECIPITATION AND DIRECT AIR FALL IN THE FINGER LAKES REGION OF NEW YORK

The atmosphere is an understudied conduit for environmental microplastics—synthetic polymer fragments, pellets, films, and fibers less than 5 mm in diameter. Fibers dominate the microplastic burden in terrestrial and freshwater systems. This study analyzed microplastic fiber fluxes in both direct air fall and precipitation events, and correlated flux with meteorological variables. Precipitation (rain and snow) was collected from 2021 to 2022 using a metal basin; direct air fall samples were collected in 2023 using metal trays. Microplastics were extracted using a glass vacuum filtration system onto a 0.45 µm Millipore filter. Filters were illuminated using a NightSea UV/royal blue light to induce fluorescence in many polymers and photographed for counting. Microplastic flux from both direct air fall and precipitation show large variability. Median flux for airfall is 89 fibers/m²/day; median flux for precipitation is 90 fibers/m²/day. There is no significant difference between precipitation and direct air fall, however precipitation can deliver a large number of fibers quickly. The atmospheric boundary layer (ABL) is the region of the atmosphere closest to the surface that is well mixed by daily surface heating. We found that during air fall samples air parcels tended to stay below the ABL (mean height = 1,280 m). In contrast, air parcels that produced precipitation rose to or above the ABL. On July 13, 2023, a 24-hour air fall sample was interrupted by a small convective thunderstorm. During the 20-minute storm, we retrieved the air fall sample trays and collected rainwater. The example provides the opportunity to look at both precipitation and direct air fall from the same air mass. Based on this observation, we estimate that 122,048,000,000 microplastic fibers were deposited in Seneca Lake on July 13, 2023.