German satellite measures CO₂ and NO₂ simultaneously from power plant emissions for the first time

A research team from the Max Planck Institute for Chemistry in Mainz and Heidelberg University has, for the first time, used the German environmental satellite EnMAP (Environmental Mapping and Analysis Program) to simultaneously detect the two key air pollutants carbon dioxide (CO₂) and nitrogen dioxide (NO₂) in emission plumes from power plants—with an unprecedented spatial resolution of just 30 meters.

The newly developed method allows for tracking of industrial emissions from space with great precision and enables atmospheric processes to be analyzed in detail. The results were published in the journal Environmental Research Letters.

Carbon dioxide (CO₂) and nitrogen oxides (NO_x) are among the most significant anthropogenic air pollutants—with consequences for climate, health, and air quality. Satellite measurements are considered a key tool for independent emission monitoring. Previously, however, they were subject to significant limitations: Many sensors have spatial resolutions that are too coarse to detect isolated emissions sources such as power plants reliably.

Atmospheric processes—such as clouds, or the chemical reaction of nitrogen oxides—also complicate data interpretation. In the case of CO₂, the high background values often mask the relatively weak emission signals.

As NO₂ and CO₂ are emitted together, NO₂ measurements are often used to estimate CO₂ emissions based on known emission ratios. Until now, however, there has been no instrument that can detect both gases simultaneously with a high spatial resolution.

The method now presented closes this gap: for the first time, both gases can be measured simultaneously and with high resolution directly above the emission sources—and their ratio precisely determined. This opens the door to more transparent and independent satellite-based emissions monitoring.

EnMAP: High-resolution perspectives

Atmospheric trace gases such as CO_₂ and NO_₂ leave characteristic absorption patterns in sunlight, which can be detected using spectrometers. Instruments with very high spectral resolution are typically used for satellite-based measurements. They can analyze the fine absorption structures of the gases in the reflected sunlight, but usually only achieve a spatial resolution of 3 to 5 kilometers.

By contrast, the German Earth observation satellite EnMAP was originally designed for remote sensing of land surfaces. It provides imagery with an exceptionally high level of spatial detail of 30 x 30 meters, but has a comparatively low spectral resolution.

The new study now demonstrates that—contrary to previous assumptions—reliable measurements of trace gases are possible even with an instrument not specifically designed for atmospheric observation.

“Using the EnMAP data, we were able to determine the distribution of CO₂ and NO₂ in emission plumes from individual power plants—for example, from plants in Saudi Arabia and in the South African Highveld region, one of the world’s largest emission hotspots,” explains Christian Borger, first author of the study and, until recently, a postdoctoral researcher in the Satellite Remote Sensing Group at the Max Planck Institute for Chemistry. He now works at the European Center for Medium-Range Weather Forecasts (ECMWF) in Bonn.

From measurement to application

This means that the EnMAP satellite can be used to determine CO₂ and NO_x emissions from individual power plants simultaneously and at high resolution. Additionally, NO_x/CO₂ ratios can be derived from this, which allows conclusions to be drawn about the technology, efficiency, and operating mode of the systems. In the future, such ratios could be used to estimate CO₂ emissions solely on the basis of NO₂ data.

The data also offers new insights into the chemical conversion of NO to NO₂ within emission plumes. Until now, this central process in atmospheric chemistry could only be studied through complex aircraft measurement campaigns. The use of satellite data has major advantages in this context as it enables the worldwide, consistent, and comparable detection of industrial pollutant emissions.

“Our study shows how satellites with high spatial resolution can contribute to the targeted monitoring of industrial emissions in the future—in addition to large-scale missions such as the European CO₂M satellite,” summarizes group leader Thomas Wagner. The EnMAP environmental satellite opens new perspectives for a global, satellite-based monitoring system for air pollutants and greenhouse gases.