NOx emissions quantified from space reveal technological differences in Cypriot power plants

The production of nitrogen oxides (NOx = NO + NO2) is substantial in urban areas and from fossil fuel-fired power plants, causing both local and regional pollution and presenting severe consequences for human health. To estimate their emissions and implement air-quality policies, authorities often rely on reported emission inventories. The island of Cyprus is de facto divided into two different political entities, and as a result, emissions inventories are not systematically available for the whole island. We map NOx emissions in Cyprus for two six-month periods in 2021 and 2022 with a flux-divergence scheme, using spaceborne retrievals of nitrogen dioxide (NO2) columns at high spatial resolution from the TROPOMI instrument, as well as horizontal wind data to derive advection and concentrations of OH, NO and NO2 to derive chemical processes. Emissions are estimated under three different settings using ECMWF data and WRF-Chem simulations. These settings are chosen for their differences in spatial resolution and representation of wind and air composition. Exploiting the low emissions in Cyprus, we show that the flux-divergence method is limited by the resolution of wind and hydroxyl radical, the signal-to-noise ratio of the observed tropospheric column densities, and the NOx:NO2 ratio above the main pollution sources. We also provide an estimation of NOx emissions for the five power plants of the island. The estimated emissions for the three power plants in the south are in the range of reported emissions and global/regional inventories, and present differences in seasonal cycles. For the two power plants in the north, which are not included in all emission inventories, we estimate mean daytime emissions higher than for the power plants in the south combined, despite a much lower production capacity, illustrating the application of different environmental norms and the use of different technologies and fuels in the two parts of Cyprus.