Fig. 5: Onset of water uptake and freezing of water on microplastics (MPs) of varying chemistry.

a, b scanning electron microscopy (SEM) images of a milled polyethylene (PE) MP. The scale bars in (a), and (b) are 50 µm and 5 µm, respectively. c X-ray photoelectron spectroscopy (XPS) spectra in the O 1 s region of the milled MPs. The solid lines are the XPS spectra of each unweathered milled MP, and the dashed lines are the XPS spectra of the weathered (1 day) milled MPs. d Box plot representation of the relative humidity (RH) and temperature at which water uptake was observed for unweathered (D0) and weathered (D1) PE, polypropene (PP), polystyrene (PS) and polyethylene terephthalate (PET) MPs immobilized on a hydrophobic substrate. The water condensation on the hydrophobic substrate (Sub.) was observed at RH ~ 95%. e The temperature of ice nucleation of the water condensed onto unweathered (D0) and weathered (D1) PE, PP, PS or PET MPs and the hydrophobic substrate (Sub.). The data in (d) and (e) represent an average of at least 5 experimental runs represented by individual points. The box represents the interquartile range, error bars represent one standard deviation, and the line represents the mean. Source data are provided as a Source Data file.