Resuspension of microplastic particles from arid regions and global impacts on atmospheric concentrations and deposition

Microplastic particles (MP), i.e., plastic particles with a size between 1 µm and 1 mm, have been detected in all compartments of the Earth system. While we are beginning to develop a quantitative understanding of the primary emissions of MPs such as tire wear, secondary sources from polluted environmental compartments such as the oceans and arid land surfaces, are currently not understood at all.

In this study, we use reported MP concentrations in soils across the world combined with MP enrichment ratios (ER) in wind eroded sediments with respect to the soils (Bullard et al., 2021; Rezaei et al., 2019; Tian et al., 2022) and a population density map to estimate MP resuspension factors (RF) from arid regions.  We then use global, 3-hourly dust emissions at  0.5^o x 0.5^o resolution from FLEXDUST (Groot Zwaaftink et al., 2016, 2017), as a proxy for the spatial and temporal variation of MPs emitted by arid regions. Scaled with the resuspension factors, we estimate the global MP resuspensions. To calculate the uncertainty of our emission model, we conduct a one-thousand-member Monte Carlo simulation with 14 different RF scenarios for each population category, perturbing the MP concentration in soils, the ER and the spatial scale used for the population density.

We define, as a reference case, the emissions derived from the average ER, average soil concentrations and 50 km radius population categorization. These MP resuspension emissions are used as input to the Lagrangian atmospheric dispersion model FLEXPART (Pisso et al., 2019; Stohl et al., 2005) to simulate the global atmospheric cycle of resuspended MPs from arid regions. The simulations are driven by ERA5 meteorological fields at 0.5° horizontal resolution and 1-hour temporal resolution.  We simulate the global atmospheric concentration and the deposition of resuspended MPs for different size distributions as well as shapes (spheres, fibers) of MPs. Lastly, we quantify the impact and compare it with observations, to estimate the importance of resuspension from arid regions for global MP abundance.