Photochemistry of tropospheric CS2, a new chemical pathway
Authors: Li Yuanzhe , Kamezaki Kazuki , Danielache Sebastian 
Published: March 2021

&lt;p&gt;&lt;strong&gt;Photochemistry of tropospheric CS&lt;sub&gt;2&lt;/sub&gt;, a new chemical pathway&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Yuanzhe Li&lt;sup&gt;1&lt;/sup&gt;, Kazuki Kamezaki&lt;sup&gt;1&lt;/sup&gt; and Sebastian Danielache&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; Faculty of Science and Technology, Sophia University&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Abstract&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Carbon disulfide (CS&lt;sub&gt;2&lt;/sub&gt;) is an atmospheric trace gas and is mainly produced by anthropogenic emissions. Its oxidation end-products in the atmosphere are carbonyl sulfide (OCS) and sulfur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;). Therefore, CS&lt;sub&gt;2&lt;/sub&gt; indirectly contributes to the production of sulfate aerosol, which influences atmospheric radiative properties and stratospheric ozone depletion.&lt;/p&gt;&lt;p&gt;Current understanding suggests that the main sink of CS&lt;sub&gt;2&lt;/sub&gt; is the reaction with the OH radical which shares of 75-88% CS&lt;sub&gt;2&lt;/sub&gt; global removal (Khan et al., 2017). This reaction pathway generates an adduct SCSOH, followed by oxidation with O&lt;sub&gt;2&lt;/sub&gt; to form OCS and SO&lt;sub&gt;2&lt;/sub&gt;. UV induced processes are usually considered irrelevant in the troposphere. Tropospheric CS&lt;sub&gt;2&lt;/sub&gt; photo-oxidation mechanism was first suggested by Wine et al. (1981). The CS&lt;sub&gt;2&lt;/sub&gt; UV-absorption spectrum has a strong absorption band (280-360 nm), which generates a photo-excited (CS&lt;sub&gt;2&lt;/sub&gt;(&lt;sup&gt;3&lt;/sup&gt;A&lt;sub&gt;2&lt;/sub&gt;) often presented as CS&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;* &lt;/sup&gt;state) fragment, which gets further oxidized by O&lt;sub&gt;2&lt;/sub&gt; to produce OCS and SO&lt;sub&gt;2&lt;/sub&gt;. The solar flux spectrum in the troposphere satisfies conditions for a CS&lt;sub&gt;2&lt;/sub&gt; photo-excitation, enabling a potential CS&lt;sub&gt;2&lt;/sub&gt; photo-oxidation pathway in the troposphere.&lt;/p&gt;&lt;p&gt;In this study, CS&lt;sub&gt;2&lt;/sub&gt; photochemistry is revised and studied by a 1-D atmospheric model (PATMO) capable of handling photochemistry with a high-resolution spectrum. Simulated main reduced sulfur species (CS&lt;sub&gt;2&lt;/sub&gt;, OCS and SO&lt;sub&gt;2&lt;/sub&gt;) reproduce field measurements. Under strong light conditions, the CS&lt;sub&gt;2&lt;/sub&gt; photo-excitation reaction is followed by two CS&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;*&lt;/sup&gt; excited state quenching reactions. The reaction rate &lt;em&gt;r&lt;/em&gt; for the net CS&lt;sub&gt;2&lt;/sub&gt; photo-induced oxidation and CS&lt;sub&gt;2 &lt;/sub&gt;+ OH reactions at 1 km are 71 and 26 molecule cm&lt;sup&gt;-3&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; respectively. These results indicate that, under favorable light conditions photochemistry is a relevant tropospheric sink of CS&lt;sub&gt;2&lt;/sub&gt;.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Khan, A., Razis, B., Gillespie, S., Percival, C., Shallcross, D., Global analysis of carbon disulfide (CS&lt;sub&gt;2&lt;/sub&gt;) using the 3-D chemistry transport model STOCHEM, &lt;em&gt;Aims Environ. Sci.&lt;/em&gt; &lt;strong&gt;2017&lt;/strong&gt;, &lt;em&gt;4&lt;/em&gt;, 484&amp;#8211;501.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Wine, P. H., Chameides, W. L., Ravishankara, A. R., Potential role of CS&lt;sub&gt;2&lt;/sub&gt; photooxidation in tropospheric sulfur chemistry, &lt;em&gt;Geophys. Res. Lett.&lt;/em&gt; &lt;strong&gt;1981&lt;/strong&gt;, &lt;em&gt;8&lt;/em&gt;, 543-546.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;div&gt;
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