Understanding NOx emission changes from 2019 to 2021 in the EMME region through variational inversions and satellite data

The Eastern Mediterranean and Middle East (EMME) is one of the most vulnerable regions to climate change globally and is becoming one of the world leading emitters of green-house gas (GHG) and air pollutants. Among these, nitrogen oxides NO_x (=NO+NO₂) are crucial to tropospheric chemistry, due to their role in the formation of tropospheric ozone O₃ and Particulate Matter (PM); both of which are harmful to human health and the ecosystem. NO_x are primarily emitted from the combustion of fossil fuels, which occurs in several sectors including transportation, energy production, industrial activities, residential heating, and agriculture. In spite of the direct and indirect threats of NO_x emissions, Saudi Arabia and the United Arab Emirates (UAE) continue expanding their fossil fuel production, with Saudi Arabia aiming to boost oil capacity to 13 million barrels per day by 2027, undermining its own 2060 net-zero pledge under the Saudi Green Initiative. The EMME region remains under studied regarding anthropogenic emissions, which highlights the need for accurate emission estimates to inform policy decisions.

In this work, we estimate NO_x emissions in the EMME region at a horizontal resolution of 0.5°, for the period 2019 to 2021. We employ the Community Inversion Framework (CIF) model, coupled to the CHIMERE chemistry transport model (CTM) and its adjoint, using a variational inversion method to construct NO_x emissions. We assimilate nitrogen dioxide (NO₂) observations from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Copernicus Sentinel-5 Precursor (S-5P) satellite, and both anthropogenic and biogenic NO_x estimates from the Copernicus Atmosphere Monitoring Service (CAMS). Our emission data are close to those provided by other inventories. We examine key emitters in the EMME region, including countries that are affected by economic changes and/or political instabilities; such as Palestine, Israel, Lebanon, Iraq, Iran, Qatar, the UAE, and Saudi Arabia, among others. Our results show that, from 2019 to 2021, NO_x emissions exhibit a positive trend in most of the studied regions, except in Tehran (Iran) and Jeddah (Saudi Arabia), where we observe a decrease of NO_x emissions by -27% and -12% respectively. In the UAE, however, emissions increased by +17%, and in Yanbu (Saudi Arabia) by +24%, in 2021 compared to 2019. In Lebanon, a rise in NO_x emissions can be attributed to the country's economic crisis and shortages in national electricity supply, which led to a rapid increase in privately operated diesel-fueled energy producers. Our NO_x emissions data are expected to help policy makers monitor emissions in the EMME, at regional and national scales, to better tackle challenges specific to this region.