Atmospheric warming contributions from airborne microplastics and nanoplastics

Abstract

Microplastic and nanoplastic particles (MNPs) are pervasive in the atmosphere, yet their direct radiative forcing (DRF) remains poorly constrained. Using a radiative transfer model combined with experimentally derived optical properties and simulated atmospheric distributions, we show that coloured MNPs exhibit strong light absorption, with a mean refractive index of 1.49–0.22i at 550 nm and absorption coefficients 74.8 times higher than those of pristine particles. Atmospheric ageing produces minimal net optical change, as yellowing-induced absorption in white particles is largely offset by bleaching of red ones. Modelled global surface concentrations reach 4.18 MP m−3 for microplastics and 3.67 ng m−3 for nanoplastics. Resulting simulations yield mean DRF of 0.039 ± 0.019 W m−2 for MNPs, equivalent to 16.2% of black carbon forcing. Regional DRF peaks over the North Pacific Subtropical Gyre (~1.34 W m−2), exceeded located black carbon by 4.7-fold, highlighting MNPs as previously unrecognized climate forcing agents.