Vertical concentration gradients and transport of airborne microplastics in wind tunnel experiments
Authors: Georgi Christoph , Esders Eike , Thomas Christoph , Held Andreas 
Published: March 2022

&lt;p&gt;&lt;span&gt;Microplastics &lt;/span&gt;&lt;span&gt;are ubiquitous in the environment and have also been observed &lt;/span&gt;&lt;span&gt;in the atmosphere&lt;/span&gt;&lt;span&gt;. N&lt;/span&gt;&lt;span&gt;evertheless&lt;/span&gt;&lt;span&gt;, very little work &lt;/span&gt;&lt;span&gt;has focused on &lt;/span&gt;&lt;span&gt;atmospheric &lt;/span&gt;&lt;span&gt;transport of microplastic particles&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Th&lt;/span&gt;&lt;span&gt;is&lt;/span&gt;&lt;span&gt; ga&lt;/span&gt;&lt;span&gt;p&lt;/span&gt;&lt;span&gt; m&lt;/span&gt;&lt;span&gt;ust&lt;/span&gt;&lt;span&gt; be filled to gain a comprehensive overview o&lt;/span&gt;&lt;span&gt;f&lt;/span&gt;&lt;span&gt; microplastics in the environment.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt; This work focusses on short-distance transport of airborne microplastic particles investigated in a wind tunnel with a cross-section of 270&lt;/span&gt;&lt;span&gt; mm x &lt;/span&gt;&lt;span&gt;54&lt;/span&gt;&lt;span&gt;0&lt;/span&gt;&lt;span&gt; mm&lt;/span&gt;&lt;span&gt; as an idealized and controllable environment. In a set of experiments, &lt;/span&gt;&lt;span&gt;polystyrene (PS) m&lt;/span&gt;&lt;span&gt;icrospheres&lt;/span&gt; &lt;span&gt;with a diameter &lt;/span&gt;&lt;span&gt;0.&lt;/span&gt;&lt;span&gt;5 &amp;#181;m&lt;/span&gt; &lt;span&gt;a&lt;/span&gt;&lt;span&gt;re&lt;/span&gt; &lt;span&gt;introduced &lt;/span&gt;&lt;span&gt;in&lt;/span&gt;&lt;span&gt;to&lt;/span&gt;&lt;span&gt; the wind tunnel &lt;/span&gt;&lt;span&gt;in &lt;/span&gt;&lt;span&gt;various&lt;/span&gt;&lt;span&gt; heights&lt;/span&gt; &lt;span&gt;under &lt;/span&gt;&lt;span&gt;d&lt;/span&gt;&lt;span&gt;istinct&lt;/span&gt; &lt;span&gt;f&lt;/span&gt;&lt;span&gt;low conditions&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;wo&lt;/span&gt; &lt;span&gt;different &lt;/span&gt;&lt;span&gt;optical particle counter&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;(GRIMM Mini-LAS 11-R, &lt;/span&gt;&lt;span&gt;Alphasense OPC-N3&lt;/span&gt;&lt;span&gt;) &lt;/span&gt;&lt;span&gt;measure particle concentrations in &lt;/span&gt;&lt;span&gt;t&lt;/span&gt;&lt;span&gt;hree&lt;/span&gt;&lt;span&gt; heights (&lt;/span&gt;&lt;span&gt;27&lt;/span&gt;&lt;span&gt; -15&lt;/span&gt;&lt;span&gt;7&lt;/span&gt;&lt;span&gt;mm), which results in a &lt;/span&gt;&lt;span&gt;p&lt;/span&gt;&lt;span&gt;rofile&lt;/span&gt;&lt;span&gt; that gives an estimate &lt;/span&gt;&lt;span&gt;o&lt;/span&gt;&lt;span&gt;f particle &lt;/span&gt;&lt;span&gt;deposition and &lt;/span&gt;&lt;span&gt;emission&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;he &lt;/span&gt;&lt;span&gt;experiments &lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;how that low wind speeds generate higher concentrations in the bottom layers, while high wind speeds l&lt;/span&gt;&lt;span&gt;ead to&lt;/span&gt;&lt;span&gt; increasing concentration&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;upwards.&lt;/span&gt;&lt;span&gt; Furthermore, the formation of &lt;/span&gt;&lt;span&gt;a &lt;/span&gt;&lt;span&gt;boundary &lt;/span&gt;&lt;span&gt;layer causes opposite gradients above and w&lt;/span&gt;&lt;span&gt;ithin&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;he&lt;/span&gt;&lt;span&gt; insights &lt;/span&gt;&lt;span&gt;gained&lt;/span&gt; &lt;span&gt;on short-distance &lt;/span&gt;&lt;span&gt;and vertical &lt;/span&gt;&lt;span&gt;transport &lt;/span&gt;&lt;span&gt;o&lt;/span&gt;&lt;span&gt;f microplastic particles&lt;/span&gt; &lt;span&gt;will &lt;/span&gt;&lt;span&gt;be the bas&lt;/span&gt;&lt;span&gt;is&lt;/span&gt;&lt;span&gt; for further wind tunnel experiments &lt;/span&gt;&lt;span&gt;w&lt;/span&gt;&lt;span&gt;ith varying&lt;/span&gt;&lt;span&gt; surface roughness&lt;/span&gt;&lt;span&gt;es&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt; Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) &amp;#8211; project number 391977956 &amp;#8211; SFB1357 / B0&lt;/span&gt;&lt;span&gt;5.&lt;/span&gt;&lt;/p&gt;