Condensation accelerates polyvinyl chloride microplastics aging via hydrogen radical generation

Polyvinyl chloride (PVC) microplastics (MPs) are widely distributed in the environment, and their impacts and associated risks intensify as they undergo aging. In addition to well-recognized processes such as photochemical reactions, thermo-oxidation, mechanical abrasion, and microbial colonization, unknown pathways of PVC MPs aging may also occur under natural conditions. Here, we demonstrate that the natural condensation process leads to a decrease in C Cl bonds from 40.61% to 36.73%, highlighting its overlooked importance in accelerating the aging of PVC MPs. Our results show that microdroplets formed on PVC MPs during condensation induce cleavage of C H and C Cl bonds, leading to the formation of conjugated C C bonds. Simulated condensation experiments reveal that particle size, condensation duration, humidity, and temperature strongly affect this process. Free radical detection and quenching tests confirm that hydrogen radicals generated at the microplastic–microdroplet interface drive the observed chemical transformations. Notably, comparison with light-induced aging indicates that condensation represents a crucial pathway for PVC MPs aging in the absence of light. Overall, this study provides new mechanistic insights into the natural aging of MPs and highlights the critical role of condensation in shaping their environmental fate and potential risks. • The natural condensation process can induce the aging of microplastics. • The condensation process can induce the cleavage of chemical bonds in microplastics. • The condensation process generates reactive species such as •OH, •H, and O₂• − . • PVC microplastic aging during condensation is primarily driven by •H. • Condensation serves as an important complementary pathway for PVC microplastics aging under dark conditions.