PNNL

Abstract

Nanoplastic particles (NPPs) are emerging anthropogenic pollutants identified in urban, suburban, and remote areas. Characterizing the lifetime, fate, and cloud-forming potential of NPPs improves the understanding of their environmental persistence, health implications, and potential contribution to climate forcing. This study provides the first measurement of the heterogeneous oxidation reaction rate and lifetimes of atmospherically suspended polystyrene (PS) NPPs against common atmospheric oxidants. The atomized PS NPPs were introduced to a Potential Aerosol Mass (PAM) oxidation flow reactor with ·OH exposure of 0 to ~2.3 × 10^12 molecule cm-3 s, equivalent to atmospheric exposure from 0 to 27 days, assuming ambient ·OH concentration of 1 × 10^6 cm-3. The decay of the PS mass concentration was quantified by monitoring two known tracer ions, C6H6+ (m/z 78) and C8H8+ (m/z 104), using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The pseudo-first-order rate constant of PS particles reacting with ·OH, kOH, was determined to be (9.21 ± 2.26) × 10^-14 cm3 molecule-1 s-1, equivalent to a half-lifetime of 2-126 days in the atmosphere, depending on particle sizes and hydroxyl radical concentrations, while oxidation by photolysis and ozonolysis are negligible. The hygroscopicity of PS NPPs at different OH exposure levels were quantified using a cloud condensation nuclei counter (CCNC) and Environmental Scanning Electron Microscopy (ESEM), showing a two-fold increase of hygroscopicity parameter upon ~27 days of atmospheric exposure. The above results demonstrate that atmospheric aging could be a potentially important process in the environmental cycle of nanoplastic particles, altering their physicochemical properties and contributing to potential climate impacts.