A New Approach for Polymers Analysis in Atmospheric Aerosol by Direct Inlet Pyrolysis Gas Chromatography-Mass Spectrometry (Py-GC/MS)

Nowadays microplastics are widely dispersed throughout the environment. Although microplastics have been researched in sediments, soil, and freshwaters, the atmosphere has received less attention, even though it can be considered one of the major transport pathways from mid to high latitudes. Due to its effectiveness in chemical characterisation, pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) has been proposed as a promising technique for the analysis of macromolecules, but it has almost never been used for analysing microplastics in atmospheric aerosol yet. In this work, we investigated the potential application of direct inlet Py-GC/MS for detecting polymers in atmospheric aerosol. Evaluating the matrix interference is crucial when a pre-treatment step is missing. For this purpose, we developed the "organic the aerosol baseline" (OAB), which is our initial attempt to calculate the organic aerosol's contribution to the polymer tracer areas. Being aware it does not represent the whole organic aerosol, humic acid was chosen as the representative organic substance for this assessment, as done before in the literature. OAB was estimated for tracers of the most common polymers, using the following equation: OAB = An ∙ OM ∙ PM ∙ V ∙ frsample; where An is the average tracer normalised areas in the humic acid pyrograms; OM is the typical organic matter fraction in the aerosol in the area and period of sampling; PM is the aerosol concentration; V is the sample volume; frsample is the fraction of sampling filter introduced in the sample tube. Pyrogram peaks were considered plastic tracers only if their area was over the OAB level. The novel methodology was applied to total particulate matter (TSP) samples, collected using a AirFlowPUF (Analitica Strumenti, 0.3 m3 min-1; 48- and 72-samples) and to commercial dust (House SRM2585). Even considering the interference of the matrix, polyethylene, polypropylene, and polystyrene were successfully detected in TSP samples and confirmed by Micro-FTIR analysis. The support analysis by Micro-FTIR also indicated the presence of more polymers that Py-GC/MS had missed. The difference in the results of the two approaches is reduced when the analysis is conducted on pure commercial dust. These first findings suggest that the issue of the matrix presence can be successfully overcome by the evaluation of its baseline and that the crucial point can be represented by the small portion of the filter practically analysable. Plastics are challenging to extract and usually need specialised equipment. For this reason, the direct analysis represents the ideal screening method for saving time, costs, and waste. This work proposed a quick and simple solution for the identification of plastics in atmospheric aerosol samples, to be applied before other time-consuming techniques for obtaining more detailed information (i.e., quantification). More research is needed to improve this approach for getting the greatest possible efficiency from the analysis. This work was supported by the EU - Next Generation EU, PNRR under grant IR0000032 (ITINERIS, Italian Integrated Environmental Research Infrastructures System)