A method for estimating localized CO2 emissions from co-located satellite XCO2 and NO2 images

CO₂ emissions need to be rapidly reduced in order to peak greenhouse gas emissions and limit global warming to well below 2ºC. Most of these anthropogenic CO₂ emissions result from the combustion of fossil fuels from localized sources. Therefore, it is essential to monitor these emissions to corroborate the compliance with the objectives of the Paris Agreement. Under this agreement, the parties report their national greenhouse gas inventories, usually computed using bottom-up methods based on statistical activity data and emission factors. Top-down approaches, based on atmospheric observations, can complement and verify these inventories. Satellite-based observations have the advantage of potential global coverage and the feasibility of providing independent emission estimates from localized sources, like cities and power plants.

In this study we present a top-down method to quantify the CO₂ emissions from localized sources by using XCO₂ (the column-averaged dry-air mole fraction of CO₂) retrievals from the Orbiting Carbon Observatory 3 (OCO-3) in its snapshot area mode. It is a cross-sectional flux method, so that our estimate of the source rate is obtained from the flux through a number of cross-sections downwind of the source.

The detection of CO₂ emission plumes is challenging due to the small enhancements resulting from anthropogenic emissions from individual source points compared to the background concentrations and the satellite’s instrument noise. NO₂ is co-emitted with CO₂ in the combustion of fossil fuels and its vertical column densities can exceed background values and sensor noise by orders of magnitude in emission plumes, what makes it a suitable tracer for recently emitted CO₂. Therefore, our plume detection method uses TROPOMI NO₂ data which is co-located with the XCO₂ snapshot.

We expose the CO₂ emissions estimates for 7 overpasses over the Bełchatów power plant, in Poland, together with bottom-up emission estimates for comparison, showing that we can repeatedly monitor power plant CO₂ emissions.