Towards a sector-specific CO/CO2 emission ratio: Satellite-based observation of CO release from steel production in Germany.

Global crude steel production is expected to continue to increase in the coming decades to meet the demands of the growing world population. Currently, the dominant steelmaking technology worldwide is the conventional highly CO₂-intensive Blast Furnace – Basic Oxygen Furnace production route (also known as the Linz-Donawitz process) using iron ore as raw material and coke as a reducing agent. As a result, large quantities of special gases that are rich in carbon monoxide (CO) are by-products of the various stages of the steelmaking process. Given the challenges associated with satellite-based estimates of carbon dioxide (CO₂) emissions at the scale of emitting installations due to significant background levels, co-emitted CO may serve as a valuable indicator of the carbon footprint of steel plants. We show that regional CO release from steel production sites can be monitored from space using 5 years of measurements (2018–2022) from the TROPOspheric monitoring instrument (TROPOMI) on board the Sentinel-5 Precursor satellite benefiting from its relatively high spatial resolution and daily global coverage. We analyse all German steel plants with blast furnaces and basic oxygen furnaces and obtain associated CO emissions in the range of 50–400 kt yr^-1 per site. A comparison with the respective CO₂ emissions on the level of emitting installations available from emissions trading data of the European Union Emissions Trading System yields a linear relationship with a sector-specific CO/CO₂ emission ratio for the analysed steelworks of 3.24 % [2.73–3.89; 1 σ ] suggesting the feasibility of using CO as a proxy for CO₂ emissions from comparable steel production sites. [ABSTRACT FROM AUTHOR]