Microplastics in total atmospheric fallout: from lockdown to business-as-usual

International audienceSince the earliest studies on microplastic (MP) pollution in the atmospheric compartment in 2015, a few dozen studies have been published on the subject. Over that period, analytical methods and targeted MPs have evolved. Several factors are suspected by authors to affect MP atmospheric deposition, human activity and precipitation being the leading ones. In this work, total atmospheric fallout from an urban campus (site A) and an agricultural site (site B) was sampled over three continuous monitoring campaigns of 4 to 6 months each. Campaigns in site A occurred during the French national lockdown of spring 2020 as human activity was drastically reduced there, and in spring 2021. The monitoring campaign in site B occurred in spring 2021, simultaneously to site A. In all campaigns, precipitations were followed to adjust sampling accordingly. All samples underwent a density separation followed by a chemical treatment, before they were analysed using an automated µFTIR mapping analysis using a Nicolet iN10 by Thermo Scientific. MPs were identified down to a size of 25 µm, cutoff point determined by the µFTIR detectors. When pooling all results together, overall median deposition rates of 18.3 MP/m²/d were found. The lowest deposition rates were recorded during the national lockdown monitoring campaign in site A, with a median of 5.3 MP/m²/d compared to 26 MP/m²/d in the same site during normal periods of activity. Based on the rain events and precipitation rates, no clear effect of rain events or accumulated rainfall on microplastic deposition was measured, suggesting the dominant effect observed here was local human activity