A global atmospheric microplastics dataset and model-assisted insights into their atmospheric emissions

Microplastics, defined as synthetic polymers from 1 μm to 5 mm, are manufactured for specific purposes or created from the fragmentation and degradation of larger plastic items in the environment. Microplastics are transported by wind and water, can traverse long distances in the atmosphere, and pose ecological and potential human-health risks by acting as vectors for additives and pollutants. Despite increasing attention, their atmospheric distribution remains poorly understood. Although observations are becoming more abundant, estimates of their emissions to the atmosphere differ by orders of magnitude. In this work, we compile a global dataset of atmospheric microplastic measurements and compare it with size-aligned simulations based on the Lagrangian particle dispersion model FLEXPART. The simulations overestimate measured global median concentrations up to four orders of magnitude. Median concentrations above land are 27 times higher than over the ocean (0.08 versus 0.003 particles m-3). Using a simple scaling approach, we infer that the oceanic source emits fewer particles than terrestrial sources. We estimate annual emissions of 6.1×1017 (1.3×1017-1.1×1018) particles yr-1 from land and 2.6×1016 (2.7×1015-5.0×1016) particles yr-1 from the ocean. Land sources dominate particle counts but not mass, highlighting the need to better constrain the emission size distributions.