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<p>Atmospheric transport has been shown to effectively disperse microplastic<br>particulate matter to virtually every environment on the planet. Despite this<br>efficient long-range transport, only few studies have examined the fundamental<br>mechanisms of the atmospheric transport of microplastics. Here, we present the<br>results of wind tunnel experiments, examining the detachment behavior of plastic<br>particles ranging from 38 to 125 µm in diameter from flat substrates.<br>Detachment was achieved solely by aerodynamic forces of the turbulent airflow.<br>The detachment behavior of spheric microplastic particles (Polyethylene) and<br>spheric glass microparticles (Borosilicate) of nominally the same diameter<br>(63-75 µm) are contrasted across substrates with hydrophilic to hydrophobic<br>surface coatings. We further examine the effect of particle-particle collisions on<br>the detachment behavior of both Polyethylene and glass spheres. The critical<br>friction velocity (u<sub>*,th</sub>), which is defined as the value at which 50% of all<br>microparticles detach, ranged from 0.1 to 0.3 ms <sup>−1</sup>. Particle-particle collisions<br>reduced the u<sub>*,th</sub> of glass, but not that for PE. Results were compared with<br>predictions of a Jonhson-Kendall-Roberts model. The relation of diameter to<br>u<sub>*,th</sub> compared well between results and prediction for Polyethylene spheres.<br>Glass spheres were predicted to detach at smaller u<sub>*,th</sub> than polyethylene<br>spheres, but detached at higher u<sub>*,th.</sub> Here, we argue that capillary forces<br>increased the adhesion, which is not covered by the model. The combination of<br>particle and substrate hydrophobicity influenced the relative humidity, at which<br>capillary forces increased u<sub>*,th</sub>.</p>

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<p><span>Microplastics </span><span>are ubiquitous in the environment and have also been observed </span><span>in the atmosphere</span><span>. N</span><span>evertheless</span><span>, very little work </span><span>has focused on </span><span>atmospheric </span><span>transport of microplastic particles</span><span>. </span><span>Th</span><span>is</span><span> ga</span><span>p</span><span> m</span><span>ust</span><span> be filled to gain a comprehensive overview o</span><span>f</span><span> microplastics in the environment.</span></p><p><span> This work focusses on short-distance transport of airborne microplastic particles investigated in a wind tunnel with a cross-section of 270</span><span> mm x </span><span>54</span><span>0</span><span> mm</span><span> as an idealized and controllable environment. In a set of experiments, </span><span>polystyrene (PS) m</span><span>icrospheres</span> <span>with a diameter </span><span>0.</span><span>5 µm</span> <span>a</span><span>re</span> <span>introduced </span><span>in</span><span>to</span><span> the wind tunnel </span><span>in </span><span>various</span><span> heights</span> <span>under </span><span>d</span><span>istinct</span> <span>f</span><span>low conditions</span><span>. </span><span>T</span><span>wo</span> <span>different </span><span>optical particle counter</span><span>s</span> <span>(GRIMM Mini-LAS 11-R, </span><span>Alphasense OPC-N3</span><span>) </span><span>measure particle concentrations in </span><span>t</span><span>hree</span><span> heights (</span><span>27</span><span> -15</span><span>7</span><span>mm), which results in a </span><span>p</span><span>rofile</span><span> that gives an estimate </span><span>o</span><span>f particle </span><span>deposition and </span><span>emission</span><span>.</span></p><p><span>T</span><span>he </span><span>experiments </span><span>s</span><span>how that low wind speeds generate higher concentrations in the bottom layers, while high wind speeds l</span><span>ead to</span><span> increasing concentration</span><span>s</span> <span>upwards.</span><span> Furthermore, the formation of </span><span>a </span><span>boundary </span><span>layer causes opposite gradients above and w</span><span>ithin</span><span>.</span></p><p><span>T</span><span>he</span><span> insights </span><span>gained</span> <span>on short-distance </span><span>and vertical </span><span>transport </span><span>o</span><span>f microplastic particles</span> <span>will </span><span>be the bas</span><span>is</span><span> for further wind tunnel experiments </span><span>w</span><span>ith varying</span><span> surface roughness</span><span>es</span><span>.</span></p><p><span> Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number 391977956 – SFB1357 / B0</span><span>5.</span></p>