In addition, we performed aging experiments using a commercial UV-ozone cleaning device (ProCleaner™, Bioforce Nanosciences). We put a thin layer of each microplastic sample onto the sample stage within the oxidation chamber. The cleaning device generates UVC light (185 nm and 254 nm) using a mercury lamp. Figure in the Supplement Information depicts the irradiance spectrum of the mercury lamp used in the chamber. Also, 185 nm light generates O atoms and O3 by reactions ( ) and ( ) :