Synthetic fibers in atmospheric fallout may be a significant source of microplastics in the environment. This study investigated microplastic fallout in two urban and suburban sites in Paris, France. Microplastics, defined as particles smaller than 5 mm, were collected using a stainless steel funnel and observed under a stereomicroscope. Fibers accounted for almost all the microplastics collected, with atmospheric fallout ranging from 2 to 355 particles/m²/day. Urban sites showed higher fluxes than suburban ones. Chemical analysis revealed that 29% of the fibers were synthetic, while the rest were a mix of natural and synthetic materials. Extrapolation of these findings suggested that between 3 and 10 tons of synthetic fibers are deposited annually in the Parisian agglomeration. These results highlight the potential role of atmospheric fallout as a source of microplastics in both continental and marine environments. The study also found that synthetic fibers, derived from clothing or macroplastics, are a major source of microplastics in the atmosphere. These fibers can be transported by wind to aquatic environments or deposited on urban surfaces. The study underscores the need for further research to understand the sources, fate, and transport mechanisms of atmospheric microplastics. The findings suggest that atmospheric fallout should not be overlooked as a potential source of microplastics, especially given the significant proportion of synthetic fibers in the fallout. The study also highlights the importance of considering synthetic fibers in the definition of microplastics, as they may be prevalent in both marine and continental environments and could have harmful effects on organisms. The study contributes to the understanding of microplastic pollution and supports the implementation of the Marine Strategy Framework Directive, which aims to achieve good environmental status for European marine waters by 2020.Synthetic fibers in atmospheric fallout may be a significant source of microplastics in the environment. This study investigated microplastic fallout in two urban and suburban sites in Paris, France. Microplastics, defined as particles smaller than 5 mm, were collected using a stainless steel funnel and observed under a stereomicroscope. Fibers accounted for almost all the microplastics collected, with atmospheric fallout ranging from 2 to 355 particles/m²/day. Urban sites showed higher fluxes than suburban ones. Chemical analysis revealed that 29% of the fibers were synthetic, while the rest were a mix of natural and synthetic materials. Extrapolation of these findings suggested that between 3 and 10 tons of synthetic fibers are deposited annually in the Parisian agglomeration. These results highlight the potential role of atmospheric fallout as a source of microplastics in both continental and marine environments. The study also found that synthetic fibers, derived from clothing or macroplastics, are a major source of microplastics in the atmosphere. These fibers can be transported by wind to aquatic environments or deposited on urban surfaces. The study underscores the need for further research to understand the sources, fate, and transport mechanisms of atmospheric microplastics. The findings suggest that atmospheric fallout should not be overlooked as a potential source of microplastics, especially given the significant proportion of synthetic fibers in the fallout. The study also highlights the importance of considering synthetic fibers in the definition of microplastics, as they may be prevalent in both marine and continental environments and could have harmful effects on organisms. The study contributes to the understanding of microplastic pollution and supports the implementation of the Marine Strategy Framework Directive, which aims to achieve good environmental status for European marine waters by 2020.