Quantifying South Eastern Europe NOx and SO2 emissions using S5P/TROPOMI; from the urban to the regional scale.

<p>Even though the actual levels of anthropogenic pollution around South Eastern Europe do not reach the ones experienced in numerous Central and Western locations such as the Po Valley, the Benelux regions, the English Channel, etc., both nitrogen and sulphur oxides remain a cause for concern for air quality issues in the area. S5P/TROPOMI offers a high enough spatial resolution of 3.5x7km<sup>2</sup> (x5.5km<sup>2</sup> since August 2019) coupled with a high signal-to-noise to allow the monitoring of air quality levels, as well as the calculation of emissions, around the overpass time of the satellite. In that respect, LOTOS-EUROS Chemical Transport Model (CTM) simulations for year 2018 will be used in conjunction to the S5P/TROPOMI NO<sub>2</sub> v01.03.02 and SO<sub>2</sub> v01.01.07 columns to update the current emission inventory used in CAMS, provided recently by TNO for year 2015.</p><p>The process is validated at every step; the CTM surface concentrations are being compared to the European Environmental Agency E1a & E2a in situ air quality station data while the satellite vertical columns are compared to MAX-DOAS ground-based measurements. The diurnal variability of the NO<sub>2</sub> depicted by the in situ and the CTM is examined, as a source of understanding the effect of the apriori emission fields, the OH radical chemistry, the planetary boundary layer definition, etc., within the model structure. The seasonal variability of the SO<sub>2</sub> columns observed by the satellite and ground-based instruments reveals the amount of insufficiently filtered power plants and smelting activities in the area, including transboundary transport around the Balkan Peninsula.</p><p>Area sources, such as cities and industrial regions, as well as shipping plumes around the Aegean Sea, the Bosporus Strait and the Eastern Mediterranean, will be characterized vis-à-vis their updated emissions and discussed.</p><p><em>Acknowledgements:</em></p><p>We acknowledge support of this work by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). This work was co-funded by ESA within the Contract No. 4000117151/16/l-LG “Preparation and Operations of the Mission Performance Centre (MPC) for the Copernicus Sentinel-5 Precursor Satellite”.</p>