Constraining Microplastic Particle Emission Flux from the Ocean

Sea spray aerosols (SSA) are believed to be a significant source of atmospheric microplastic particles (MP). However, only a few receptor calculations, with considerable uncertainties, have quantified the oceanic contribution to atmospheric MP. Here we conducted laboratory studies of the transfer of MP via SSA and found that MP were highly enriched in SSA relative to seawater, with experimentally determined enrichment factors reaching similar to 24 000 depending on the size of MP. These results were utilized to obtain bottom-up emission estimates of oceanic MP. For MP with diameters of 0.3-70 mu m, the annual global flux was estimated to be 24 (similar to 1-47) quintillion pieces or 773 (similar to 30-1515) tons. For MP with diameters of <10 mu m that are capable of long-range atmospheric transport, it was 23 (similar to 1-45) quintillion pieces or 39 (similar to 2-76) tons. Our study strongly suggests that the oceans are unlikely to be a significant source of atmospheric MP relative to other anthropogenic sources of MP.