Hourly Nitrogen Oxides Emissions Estimated From TEMPO and Comparison With Facility-Level Monitoring Data

We use the directional derivative approach to estimate hourly (Formula presented.) emissions from (Formula presented.) measured by the Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument. The hourly scanning capacity of TEMPO enables the inclusion of the tendency term, relaxing the steady-state assumption that limits previous satellite-based methods. The directional derivative emission estimator is calculated on the local coordinates of TEMPO Level-2 pixels and consequently oversampled to 1-km grids. These innovations enable integration of emission estimators over (Formula presented.) km elliptical footprints centered at 14 power plants in the US, resulting in over 15,500 hr of emission rates in the first 17 months of TEMPO operation. TEMPO-based emission rates are compared with measurements from stack-mounted Continuous Emissions Monitoring Systems (CEMS). Inclusion of the tendency term improves correlations in 10 out of 14 power plants and the overall correlations at hourly, daily, and monthly scales. The TEMPO-based emission rates are around four times lower than CEMS, highlighting the challenges to accurately retrieve (Formula presented.) vertical column and to quantify (Formula presented.) / (Formula presented.) ratio near strong point sources.