Modelling the seasonal cycle of atmospheric &#948;13C-CH4 using source specific &#948;13C-CH4 values
Authors: Kangasaho Vilma , Tsuruta Aki , Aalto Tuula , Backman Leif , Houweling Sander , Krol Maarten , Peters Wouter , Luijkx Ingrid , Lienert Sebastian , Joos Fortunat , Dlugokencky Edward , Michael Sylvia , White James , Fisher Rebecca 
Published: March 2020

&lt;p&gt;&lt;span&gt;The atmospheric burden of methane (CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;) has more than doubled since the 18&lt;/span&gt;&lt;sup&gt;&lt;span&gt;th&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Century. Currently the abundance of CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; in the atmosphere is well known, but emission rates from different source sectors are uncertain. CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4 &lt;/span&gt;&lt;/sub&gt;&lt;span&gt;is emitted to the atmosphere from various sources. To better understand the changes in atmospheric CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; abundance before and after 2006, it is &lt;/span&gt;&lt;span&gt;important &lt;/span&gt;&lt;span&gt;to study the contribution from these different sources separately. &lt;/span&gt;&lt;span&gt;Most&lt;/span&gt;&lt;span&gt; CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; source ha&lt;/span&gt;&lt;span&gt;ve&lt;/span&gt;&lt;span&gt; process specific &lt;/span&gt;&lt;span&gt; &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt; values, which can be used to broadly identify source sectors. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;This study &lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;xamines &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;seasonal cycle of atmospheric &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt;&lt;/span&gt; &lt;span&gt;in recent decades &lt;/span&gt;&lt;span&gt;using the &lt;/span&gt;&lt;span&gt;TM5 atmospheric transport. TM5 is &lt;/span&gt;&lt;span&gt;driven&lt;/span&gt;&lt;span&gt; by &lt;/span&gt;&lt;span&gt;ECMWF &lt;/span&gt;&lt;span&gt;ERA-Interim meteorological fields, and uses &lt;/span&gt;&lt;span&gt;pre-calculated OH-fields and reaction rates with Cl&lt;/span&gt;&lt;span&gt; and O&lt;/span&gt;&lt;span&gt;(&lt;/span&gt;&lt;sup&gt;&lt;span&gt;1&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;D&lt;/span&gt;&lt;span&gt;) &lt;/span&gt;&lt;span&gt;to account for the &lt;/span&gt;&lt;span&gt;CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; sink processes in the atmosphere. &lt;/span&gt;&lt;span&gt;TM5 is run &lt;/span&gt;&lt;span&gt;at&lt;/span&gt; &lt;span&gt;a &lt;/span&gt;&lt;span&gt;1&lt;/span&gt;&lt;sup&gt;&lt;span&gt;o&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;x1&lt;/span&gt;&lt;sup&gt;&lt;span&gt;o&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; resolution over Europe and globally &lt;/span&gt;&lt;span&gt;at&lt;/span&gt; &lt;span&gt;6&lt;/span&gt;&lt;sup&gt;&lt;span&gt;o&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;x4&lt;/span&gt;&lt;sup&gt;&lt;span&gt;o&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;E&lt;/span&gt;&lt;span&gt;missions for enteric fermentation and manure management, landfills and waste water treatment, rice cultivation, coal industry, oil and gas industry, and residential are taken from the EDGAR inventory. &lt;/span&gt;&lt;span&gt;N&lt;/span&gt;&lt;span&gt;atural emission for wetlands, peatlands and mineral soils, &lt;/span&gt;&lt;span&gt;and soil sinks&lt;/span&gt;&lt;span&gt; are taken from the LPX-Bern DYPTOP ecosystem model. &lt;/span&gt;&lt;span&gt;E&lt;/span&gt;&lt;span&gt;missions for geological seeps including onshore hydrocarbon macro-seeps (including mud volcanoes), submarine (offshore) seeps, diffuse microseepage and geothermal manifestations are included. Emissions for fire&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; (GFED v4), termites, &lt;/span&gt;&lt;span&gt;wild &lt;/span&gt;&lt;span&gt;animals&lt;/span&gt;&lt;span&gt; and &lt;/span&gt;&lt;span&gt;from the &lt;/span&gt;&lt;span&gt;ocean are &lt;/span&gt;&lt;span&gt;also &lt;/span&gt;&lt;span&gt;included. &lt;/span&gt;&lt;span&gt;Several&lt;/span&gt;&lt;span&gt; sensitivity analys&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;s &lt;/span&gt;&lt;span&gt;are carried out&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;The sensitivity analyses include &lt;/span&gt;&lt;span&gt;simulations &lt;/span&gt;&lt;span&gt;with and without seasonal cycles &lt;/span&gt;&lt;span&gt;in the anthropogenic emission fields &lt;/span&gt;&lt;span&gt;(EDGAR v4.2 FT2010 vs EDGAR v4.3.2)&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;and with &lt;/span&gt;&lt;span&gt;and without &lt;/span&gt;&lt;span&gt;spatial variations &lt;/span&gt;&lt;span&gt;in &lt;/span&gt;&lt;span&gt;source specific&amp;#160;&lt;/span&gt;&lt;span&gt; &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4 &lt;/sub&gt;&lt;/span&gt;&lt;span&gt;values, &lt;/span&gt;&lt;span&gt;which are&lt;/span&gt; &lt;span&gt;used to calculate &lt;/span&gt;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;4&lt;/sub&gt;/CH&lt;sub&gt;4 &lt;/sub&gt;&lt;span&gt;emission ratios&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;The effect of including the seasonal cycle in the anthropogenic emissions were not significant, which means natural sources probably play more important role in determining the seasonal cycle of &lt;/span&gt;&lt;span&gt;&amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt;&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;he &lt;/span&gt;&lt;span&gt;global &lt;/span&gt;&lt;span&gt;observations of &lt;/span&gt;&lt;span&gt;atmospheric &lt;/span&gt;&lt;span&gt;CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt;&lt;/span&gt;&lt;span&gt;, provided by NOAA&amp;#8217;&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; G&lt;/span&gt;&lt;span&gt;MD&lt;/span&gt;&lt;span&gt;, the &lt;/span&gt;&lt;span&gt;INSTAAR&lt;/span&gt;&lt;span&gt; and Royal Holloway, &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;University of London, &lt;/span&gt;&lt;span&gt;are used for evaluation&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;We present&lt;/span&gt; &lt;span&gt;the &lt;/span&gt;&lt;span&gt;importance of having &lt;/span&gt;&lt;span&gt;reasonable initial fields of &lt;/span&gt;&lt;span&gt;atmospheric&lt;/span&gt; &lt;span&gt;13CH&lt;sub&gt;4&lt;/sub&gt;&lt;/span&gt;&lt;span&gt;, which &lt;/span&gt;&lt;span&gt;will&lt;/span&gt;&lt;span&gt; be &lt;/span&gt;&lt;span&gt;later &lt;/span&gt;&lt;span&gt;used as input&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; for &lt;/span&gt;&lt;span&gt;CarbonTracker Europe-&amp;#948;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;4&lt;/sub&gt; (CTE-&amp;#948;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;4&lt;/sub&gt;) &lt;/span&gt;&lt;span&gt;data assimilation system&lt;/span&gt;&lt;span&gt; to optimise&lt;/span&gt;&lt;span&gt; CH&lt;sub&gt;4&lt;/sub&gt;&lt;/span&gt;&lt;span&gt; emissions &lt;/span&gt;&lt;span&gt;by source category.&lt;/span&gt;&lt;/p&gt;