Technical description of figure:
Figure (a) shows the strong linear relationship between NOx and CO2 emissions reported by continuous emissions monitoring system (CEMS) for the US coal-fired power plants. Figure (b) shows CO2 emissions derived from OMI observations of co-emitted NO2 based on the fact that NOx and CO2 emissions are closely correlated. The OMI-based CO2 emissions estimates can be used on its own to capture the temporal variations in CO2 emissions. It can also serve as complementary verification of bottom-up inventories or be used to supplement these inventories.
Scientific significance, societal relevance, and relationships to future missions:
The OMI NO2-based CO2 emission estimation approach is timely as it is currently not feasible to infer CO2 emissions directly from satellite observations of CO2 with current sensors, and CO2 emissions are not reliably measured (at stack) and reported for most power plants around the world. The accuracy of the method can be substantially improved in the future using observations from the recently launched TROPOspheric Monitoring Instrument (TROPOMI) on the ESA Sentinel-5 Precursor satellite, which features even higher spatial resolution than OMI. More accurate estimates for diurnally and seasonally varying emissions can be expected using upcoming geostationary satellite instruments, e.g., NASA Tropospheric Emissions: Monitoring of Pollution (TEMPO), which will enable estimations for different times of the day.
Satellite-derived emission estimates are based on NO2 measurements from the Aura Ozone Monitoring Instrument (OMI). OMI is a Dutch–Finnish contribution to the NASA Aura mission.
References: Liu, F., Duncan, B. N., Krotkov, N. A., Lamsal, L. N., Beirle, S., Griffin, D., McLinden, C. A., Goldberg, D. L., and Lu, Z.: A methodology to constrain carbon dioxide emissions from coal-fired power plants using satellite observations of co-emitted nitrogen dioxide, Atmos. Chem. Phys., 20, 99-116, 10.5194/acp-20-99-2020, 2020.