Monitoring greenhouse gas (GHG) emissions is crucial for developing effective mitigation strategies. Recent advances in satellite remote-sensing measurements allow us to ack greenhouse gas emissions globally. This study assesses CO2 emissions from various point/local sources, particularly power plants in India, using eight years of concurrent high-resolution OCO-2 satellite measurements. Gaussian plume (GP) model was used to evaluate the power plant emissions reported in the Carbon Brief (CB) database. In total (39 cases), 42 different power plant CO2 emissions were assessed, with 26 of them being assessed more than once. The estimated power plant CO2 emissions were within ± 25% of the emissions reported in the CB database in 11 out of 39 cases and within ± 50% in 18 cases. To evaluate the EDGAR and ODIAC CO2 emission inventories in terms of missing or highly underestimated sources, we estimated the cross-sectional (CS) CO2 emission flux for 47 cases. We identified the possible omission of power plant emissions in three cases for both inventories. Furthermore, we also showed 21 cases in which CO2 emissions from unknown (non-power plant) sources were highly underestimated in the EDGAR and ODIAC CO2 emission inventories. Due to the simplicity of the employed approaches and their lower computational requirements compared to other methods, they can be applied to large datasets over extended time periods. This enables the acquisition of initial emission estimates for various sources, including those that are unknown or underestimated.

This study estimates the influence of anthropogenic emission reductions on nitrogen dioxide (NO_2) and ozone (O_3) concentration changes during the COVID-19 pandemic period using in-situ surface and Sentinel-5p (TROPOMI) satellite column measurements and GEOS-Chem model simulations. We show that, as a result of reductions in anthropogenic emission in eight German metropolitan cities, meteorology corrected mean in-situ (\& column) NO_2(2020,corr) concentrations decreased by 23 ± 4.7 % (& 16.4 ± 7.2 %) between March 21 and June 30, 2020, whereas meteorology corrected mean in-situ O_3(2020,corr) concentration increased by 4 ± 8.8 % between March 21 and May 31, 2020, and decreased by 3 ± 8.7 % in June 2020, compared to 2019 (uncertainty represents the 1 σ of mean changes of eight metropolitan cities). The impacts of meteorology on in-situ and TROPOMI NO_2 concentration changes during the lockdown compared to 2019 are relatively small (+0.4 % and -0.6 %, respectively), while those on in-situ O_3 concentration changes are more significant (+3.6 % and -13.5 % for March 21 to May 31, 2020 and June 2020, respectively). A NO_X saturated ozone production regime in German metropolitan cities in March to May explains the increased O_3(2020,corr) concentration in response to the decreased NO_2(2020,corr) concentration. This implies that future reductions in NO_X emissions are likely to increase ozone pollution in these cities if appropriate mitigation measures are not implemented. TROPOMI NO_2(2020,corr) concentrations decreased nationwide during the stricter lockdown period, except for North-West Germany, which can be attributed to enhanced NO_X emissions from agricultural soils.