Distinct properties of plastic-derived submicrometer particles from smoldering burning.

Widespread plastic use and mismanaged disposal release substantial amounts of particles into the atmosphere during waste burning. We define these thermally generated particles as plastic-derived submicrometer particles (PDSPs), a poorly characterized class of contaminants. We provide direct evidence that PDSPs are distinct from conventional micro- and nanoplastic particles that are formed mainly by mechanical processes. We show that PDSPs contain mixtures of altered polymeric substances and oxygenated compounds produced by extensive thermal decomposition and chemical transformations during smoldering. Volatility distributions suggest that PDSPs exist in semisolid phase states with lower viscosities than their original polymers. Upon exposure to hydroxyl radicals, the principal oxidant in the atmosphere, PDSPs exhibit higher reactivity than the original polymer particles, forming highly oxidized aerosol species at reaction rates comparable to typical atmospheric organic aerosols. These findings demonstrate that plastic smoldering introduces a previously unrecognized class of atmospherically active particles, with implications for their contribution to global plastic budgets, persistence in the atmosphere, and potential effects on human health and climate-relevant processes.