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 (CO 2 ) and nitrogen dioxide (NO 2 ) 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.
Key points of the study
Carbon dioxide (CO 2 ) 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 CO 2 , the high background values often mask the relatively weak emission signals.
As NO 2 and CO 2 are emitted together, NO 2 measurements are often used to estimate CO 2 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 three to five 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 CO 2 and NO 2 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 Centre for Medium-Range Weather Forecasts (ECMWF) in Bonn.
From measurement to application
This means that the EnMAP satellite can be used to determine CO 2 and NO x emissions from individual power plants simultaneously and at high resolution. Additionally, NO x /CO 2 ratios can be derived from this, which allow conclusions to be drawn about the technology, efficiency, and operating mode of the systems. In the future, such ratios could be used to estimate CO 2 emissions solely on the basis of NO 2 data.
The data also offers new insights into the chemical conversion of NO to NO 2 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.
Impetus for new missions
"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.
Environmental Research Letters
Computational simulation/modeling
Not applicable
High-resolution observations of NO2 and CO2 emission plumes from EnMAP satellite measurements