Strength of TROPOMI observations on the retrieval of SO2 emissions at high temporal resolution from space
Authors: Behera Abhinna , Boichu Marie , Thieuleux François 
Published: March 2020

&lt;p&gt;The adverse impact of volcanic gas and aerosol emission on global climate, air quality and ecosystem&amp;#160;is well recognized. A better-refined knowledge of volcanic degassing mechanism and its interaction&amp;#160;with the atmospheric environment can lead further to fill the persisting gaps in understanding well&amp;#160;the impact of volcanic activities. The key is to monitor continuously the volcanoes at a global&amp;#160;scale bearing also in mind the limitations of ground-based instruments during the ash-rich phase&amp;#160;of emission. Thus, the space-borne sensors with a high spatial and temporal as well as spectral&amp;#160;resolution are emerged but with complications in detecting low-altitude emissions, which are also&amp;#160;limited to 12 h to 24 h of data acquisition frequency. Nonetheless, recently launched TROPOMI&amp;#160;spectrometer onboard Sentinel 5P is shown to be a game-changer due to its high spatial and spectral&amp;#160;resolution albeit the data acquisition frequency of only 24 h. To make further progress in retrieving&amp;#160;high temporal SO&lt;sub&gt;2&lt;/sub&gt; emission, the contemporary inverse modelling method has already been shown to be&amp;#160;promising. The obtained modelled parameters, viz., SO&lt;sub&gt;2&lt;/sub&gt; flux and altitude of injection, are reasonably&amp;#160;compatible with the ground-based and space-borne observations [1] showing its importance in volcano&amp;#160;monitoring [2] and towards forecasting large-scale plume dispersal [3]. The current work incorporates&amp;#160;this advancing method and investigates a recent special volcanic event that occurred at Ambrym, Vanuatu&amp;#160;during December 2018. The uniqueness of this eruption is the rapid shut down of decade long SO&lt;sub&gt;2&lt;/sub&gt;&amp;#160;degassing and lava lake just after the eruption with the emplacement of a major dike [4]. Here, the&amp;#160;hourly retrieved SO&lt;sub&gt;2&lt;/sub&gt; flux and altitude of injection are aimed to put to the fore the striking features of&amp;#160;this unmonitored volcanic activity by assimilating the observations from several space-borne sensors.&lt;/p&gt;&lt;p&gt;To do so, the CHIMERE Eulerian chemistry-transport model (CTM) is used to simulate the Ambrym&amp;#160;eruption at a large-scale during 13-19 December 2018. Weather Research and Forecast (WRF) model&amp;#160;is used to force the meteorological fields in the CTM simulation, while ERA5 reanalysis data are used to&amp;#160;force the initial and boundary conditions of the WRF simulation. The modelled SO&lt;sub&gt;2&lt;/sub&gt; column amount&amp;#160;is then co-located with the TROPOMI, OMPS and GOME2 SO&lt;sub&gt;2&lt;/sub&gt; column amounts, respectively, to&amp;#160;perform the inversion to estimate the modelled flux rates and altitude of injection. The high spatial&amp;#160;and spectral resolution SO&lt;sub&gt;2&lt;/sub&gt; data from TROPOMI is shown to reshape significantly the results obtained&amp;#160;from the inverse method in comparison to OMPS and GOME2 SO&lt;sub&gt;2&lt;/sub&gt; data. Furthermore, a proxy to the&amp;#160;SO&lt;sub&gt;2&lt;/sub&gt; flux is then developed from the geostationary HIMAWARI data to validate the inversion results&amp;#160;as the time resolution of HIMAWARI data acquisition is every 20 min. This work is further intended to&amp;#160;explore more on the fate of sulphate aerosols formed during this eruption at a large-scale.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;1. Boichu et al.,&amp;#160;Atmospheric Chemistry and Physics, 15(14):8381&amp;#8211;8400, July 2015.&lt;/p&gt;&lt;p&gt;2. Boichu et al.,&amp;#160;Atmospheric Chemistry and Physics, 13(17):8569&amp;#8211;8584, September 2013.&lt;/p&gt;&lt;p&gt;3. Boichu et al.,&amp;#160;Geophysical Research Letters, 41(7):2637&amp;#8211;2643,&amp;#160;2014.&lt;/p&gt;&lt;p&gt;4. Shreve et al.,&amp;#160;Scientific reports, 9(1):1&amp;#8211;13, 2019.&lt;/p&gt;