Investigation of Monthly Emission Variations using TROPOMI SO2 Retrievals for Lignite-Fired Power Plants with Temporary Shutdowns

The existing lignite reserves in Turkey are used for energy generation in coal-fired power plants (CPPs) and cause high amount of SO₂ pollution due to low calorific value and high sulfur content. Therefore, large-capacity CPPs in Turkey are the most important sources of SO₂ pollution. Shutdown and semi-shutdown periods were observed in the recent years for these CPPs with old technologies and insufficient treatment technologies. The daily electricity productions were also investigated and high variability, even in operating periods, were observed. Six major CPPs utilizing lignite were temporarily shut down on January 1, 2020 on the grounds that they did not have the necessary treatment system and exceeded the limit values, and reopened in June 2020 after requirements were partially or fully met. The impact of the temporary shutdowns for the aforementioned CPPs on SO₂ emissions, and SO₂ pollution using TROPOMI SO₂ retrievals was investigated here. 2-year period (2019-2020) covering the shutdown and reopening periods was selected and the impacts on SO₂ retrievals were examined. Although there are limited number of ground measurement stations in the region for the study period (2019-2020), ground-level SO₂ concentrations were also used for comparison with retrievals and investigation of the impact of shutdown periods.   

To estimate monthly SO₂ emissions from point sources using retrievals, a previously developed method by Fioletov et al. (2015) fitting SO₂ retrievals to a three-dimensional (3-D) parameterization were used for processing SO₂ columns and wind speed data. For emission estimations, TROPOMI Level-2 (L2) SO₂ product was processed and low quality data were removed according to quality criteria. In order to reduce noise in the data, SO₂ retrievals were averaged for 1×1 km² gridded domains around CPPs using an oversampling method and monthly averages were estimated. Different oversampling distances were applied to obtain the clearest signal, and 10 km radius was selected indicating reduced noise but sufficient spatial variability. The 3-D parameterization method was applied to SO₂ retrievals near the CPPs that were shut down. Since the uncertainty in the emission inventories can be quite high, these emission estimates using TROPOMI SO₂ retrievals give us a chance to assess the available annual estimates such as EMEP. This method aims to obtain more realistic and accurate emissions by estimating monthly SO₂ emissions for CPPs with shutdowns.