Prevalence of the nano- and microplastics detected in the ecosystem is an emerging problem worldwide. Nanoplastics have been shown to not only have adverse implications on human health and the ecosystem, but also contribute to climate forcing by efficiently scattering shortwave radiation and absorbing longwave radiation. Despite being increasingly important, there is no real-time online detection of atmospheric nanoplastic particles (NPP). Herein, we provide the first study to quantify real-time nanoplastics concentrations in the atmosphere and their chemical reaction process. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is employed to detect submicron polystyrene (PS) particles, one of the most abundant microplastics produced. Tracer ions, including m/z 74 and 104, are shown to be unique to PS particles. TAmbient particles are also collected and analyzed by a constrained PMF (multilinear engine, ME-2) method to determine the temporal distribution of microplastic particles. A distinct factor that is highly correlated to the pure PS profile is separated. The mass concentration of PS nanoplastic particles is estimated to be 10-50 ng/m³ with a detection limit of 3 ng/m³during our sampling in Houston. In addition, the aging and lifetime of PS particles reacting with hydroxyl radicals (OH●), ozone, and UV light are characterized using a Potential Aersosol Mass (PAM) oxidation flow reactor. The pseudo first order rate constant of PS particles against OH● radicals, k_PS, is calculated to be, 9.21 × 10^-14 cm³ molecule^-1 s^-1. Assuming an ambient OH● concentration of 1×10⁶ cm^-3, the half-life time of microplastic in the atmosphere is estimated to be 126 days, significantly longer when compared with an average 2-week-lifetime of particulate matter in the atmosphere but shorter than their marine lifetime. The hygroscopicity of the nanoplastic particles was also enhanced upon aging. Characterizing atmospheric NPP and their lifetime may bridge important gaps in understanding their long range transportat, environmental persistence, health implications, and potential contribution to climate forcing.

Qian Zhao

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