Abstract. We present a method to infer CO2 emissions from
individual power plants based on satellite observations of co-emitted
nitrogen dioxide (NO2), which could serve as complementary verification
of bottom-up inventories or be used to supplement these inventories. We
demonstrate its utility on eight large and isolated US power plants, where
accurate stack emission estimates of both gases are available for
comparison. In the first step of our methodology, we infer nitrogen oxides
(NOx) emissions from US power plants using Ozone Monitoring Instrument
(OMI) NO2 tropospheric vertical column densities (VCDs) averaged over
the ozone season (May–September) and a “top-down” approach that we
previously developed. Second, we determine the relationship between NOx
and CO2 emissions based on the direct stack emissions measurements
reported by continuous emissions monitoring system (CEMS) programs,
accounting for coal quality, boiler firing technology, NOx emission
control device type, and any change in operating conditions. Third, we
estimate CO2 emissions for power plants using the OMI-estimated
NOx emissions and the CEMS NOx∕CO2 emission ratio. We find
that the CO2 emissions estimated by our satellite-based method during
2005–2017 are in reasonable agreement with the US CEMS measurements, with a
relative difference of 8 %±41 % (mean ± standard
deviation). The broader implication of our methodology is that it has the
potential to provide an additional constraint on CO2 emissions from
power plants in regions of the world without reliable emissions accounting.
We explore the feasibility by comparing the derived NOx∕CO2
emission ratios for the US with those from a bottom-up emission inventory
for other countries and applying our methodology to a power plant in South
Africa, where the satellite-based emission estimates show reasonable
consistency with other independent estimates. Though our analysis is limited
to a few power plants, we expect to be able to apply our method to more US
(and world) power plants when multi-year data records become available from
new OMI-like sensors with improved capabilities, such as the TROPOspheric
Monitoring Instrument (TROPOMI), and upcoming geostationary satellites, such
as the Tropospheric Emissions: Monitoring Pollution (TEMPO) instrument.