In situ chemical characterization of airborne nanoplastic particles by aerosol mass spectrometry

Abstract

Extensive use of plastic products has introduced a large amount of plastic pollutants in urban areas and even in remote environments. Nanoplastic particles, in particular, can remain airborne for weeks and transported across greater distances. Characterization of atmospheric nanoplastic particles has been limited. Sampling methods used for larger microplastic particles, such as deposition sampling, and characterization methods, such as spectroscopy, are not applicable to nanoplastic particles. Furthermore, offline sampling methods involve extensive sample preparation procedures which can alter physical and chemical properties of the particles.In this work, we investigate the use of aerosol mass spectrometry (AMS) as an in situ technique to characterize nanoplastic particle size and composition. We generate plastic particles via three different techniques: thermal decomposition of PET plastic bottles, 3D printing (using PET, ABS, and PLA filaments) and mechanical abrasion. Particle size was characterized using a Scanning Mobility Particle Sizer (SMPS). Particles were also sampled into a high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS) and onto quartz filters for offline characterization using pyrolysis gas chromatography mass spectrometry (Py-GC/MS).We found that the AMS produced real-time particle mass spectra that were very similar to those measured by Py-GC/MS analysis of particles collected on filters. The consistency between the two techniques demonstrate that AMS can provide similar information about polymeric content as Py-GC/MS, which is a widely used technique for plastic materials, but at a substantially lower detection limit and higher time resolution. On the other hand, the use chromatographic separation in Py-GC/MS provides more comprehensive evaluation of polymeric composition. For example, we were able to detect changes in ratios between monomers and dimers of PET using Py-GC/MS. Py-GC/MS was also able to provide simultaneous measurement of rubber polymers and additives in tire wear particles, an important source of particles in the near road atmosphere.Since AMS is a commonly used technique for non-refractory components in atmospheric aerosol, optimizing the AMS for nanoplastic particle detection will help understand the sources, dynamics, mixing state and fate of nanoplastic particles in the atmosphere.