Daylight Promotes a Transient Uptake of SO2 by Icelandic Volcanic Dust
Authors: Lasne Jerome , Urupina Darya , Maters Elena , Delmelle Pierre , Dagsson-Waldhauserova Pavla , Romanias Manolis , Thevenet Frederic 
Published: March 2022

&lt;p&gt;&lt;span&gt;Volcanic eruptions release large amounts of ash in the atmosphere, accounting for 5 - 7.5% of the total primary aerosol emission. The accompanying outgassing emits mostly water, carbon dioxide and sulfur dioxide (SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;). During the 2010 eruption of the Eyjafjallajokull volcano, an average SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; mixing ratio of 40 ppb was measured in the plume [1]. Volcanic areas such as Iceland are very active aeolian regions; as a consequence, 30 to 40 Tg of previously deposited Icelandic volcanic dust are re-suspended by winds annually [2]. In this environment, SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; can interact with volcanic dust (v-dust) in the presence of water vapour and UV light. Assessing the heterogeneous interaction of SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; with the surface of v-dust under UV-irradiation is therefore of crucial importance to understand its budget. Moreover, the quantification of SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; uptake by v-dust is necessary to understand the global SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; cycle, and to implement models with laboratory data characterizing heterogeneous processes [3]. &lt;/span&gt;&lt;/p&gt;&lt;p align=&quot;justify&quot;&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;To this aim, we have investigated the interaction of SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; with the surface of natural Icelandic v-dust samples with laboratory experiments [4,5]. A Coated-Wall Flow Tube reactor allowed determination of the steady-state uptake (&amp;#947;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;SS&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;) and of the transient number of SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; molecules taken up by v-dust (N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;S&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;) in a broad range of relative humidity (0.1%&lt;RH&lt;72%) and irradiance (J&lt;/span&gt;&lt;sub&gt;&lt;span&gt;NO2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; = 0-4.5&amp;#215;10&lt;/span&gt;&lt;sup&gt;&lt;span&gt;-3&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; s&lt;/span&gt;&lt;sup&gt;&lt;span&gt;-1&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;) values. Interestingly, &amp;#947;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;SS&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; values are the same in the dark and under UV-irradiation. N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;S&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; values however, largely increase under UV-irradiation, and with RH. Moreover, the amplification factor N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;S,UV&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;/N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;S,dark&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; increases linearly with: (i) the surface Ti concentration, (ii) the photon flux, and (iii) RH. These results reveal the importance of the heterogeneous photo-enhanced reactivity of SO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; on natural v-dust samples, and advocate for a better inclusion of these processes in atmospheric models.&lt;/span&gt;&lt;/p&gt;&lt;p align=&quot;justify&quot;&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&lt;span&gt;1&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Heue &lt;/span&gt;&lt;span&gt;&lt;em&gt;et al.&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;Atmos. Chem. Phys.&lt;/em&gt;&lt;/span&gt; &lt;span&gt;&lt;strong&gt;11&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 2973 (2011)&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Arnalds &lt;/span&gt;&lt;span&gt;&lt;em&gt;et al.&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;Aeolian Res.&lt;/em&gt;&lt;/span&gt; &lt;span&gt;&lt;strong&gt;20&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 176 (2016)&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&lt;span&gt;3&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Maters &lt;/span&gt;&lt;span&gt;&lt;em&gt;et al.&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;J. Geophys. Res. - Atmos.&lt;/em&gt;&lt;/span&gt; &lt;span&gt;&lt;strong&gt;122&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 10077 (2017)&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sup&gt; Urupina &lt;em&gt;et al.&lt;/em&gt;, &lt;em&gt;Atmos. Environ.&lt;/em&gt; &lt;strong&gt;217&lt;/strong&gt;, 116942 (2019)&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&lt;span&gt;5&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Lasne &lt;/span&gt;&lt;span&gt;&lt;em&gt;et al.&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;Env. Sci. Atm.&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, in revision&lt;/span&gt;&lt;/p&gt;