Diurnal emission fluxes and lifetimes of nitrogen oxide estimated from GEMS observations

Satellite observations of nitrogen dioxide (NO₂) have been widely used to estimate nitrogen oxide (NOx) emissions and lifetimes, as well as to analyze their weekday or seasonal variability. The TROPOspheric Monitoring Instrument (TROPOMI), with its high spatial resolution of 3.5 x 5.5 km², has given new opportunities to disentangle and analyze NOx sources. However, instruments in low-earth orbits usually provide only one measurement per day and location.

The Geostationary Environmental Monitoring Spectrometer (GEMS), launched in February 2020, provides hourly daytime observations of NO₂ with a spatial resolution of 3.5 x 8 km² over a large part of Asia. This opens new opportunities to quantify the diurnal variability of NOx emissions and lifetime from space.

In this study, 4 years of GEMS IUP-UB tropospheric NO₂ columns have been analyzed together with ERA5 wind, temperature, and ozone data to estimate NOx emissions and lifetime for several emission sources within the GEMS domain. The estimated emissions are compared to emission inventories and TROPOMI-based emission estimates. The high temporal resolution of GEMS with up to 10 observations per day ensures robust data availability, allowing also for the analysis of short-time variability. Using the dataset of 4 years from 2021 to 2024, hourly estimates are of good quality and are used to quantify the diurnal variability of NOx emissions and lifetime.