Satellite-detected nitrogen oxides emission changes from power plant dynamics in North China

Emissions of nitrogen oxides (NO x) from coal-fired power plants (CFPPs) pose a significant challenge to air quality. In China, although policies like ‘Promoting the Big and Quashing the Small’ and the adoption of ultra-low emission (ULE) technologies have been implemented in power plants, accurately quantifying their impacts on NO x emissions remains difficult due to lack of facility-specific information. This study investigates the influence of CFPP changes on NO x emissions from 2018 to 2024 in North China, by integrating a self-compiled, high-accuracy power plant database (with 517 plants in North China, including 109 retired or newly built) with satellitederived NOx emission data at a high spatial resolution (0.05 ◦ × 0.05◦). W e find that among the locations with no industrial sources, emissions show substantial reductions ( −1.97 kg km−2 h−1 on average; Wilcoxon test p < 0.001; t-test p < 0.001) where CFPPs were retired during this period, compared with the increases ( +0.76 kg km−2 h−1 on average; Wilcoxon test p < 0.01; t-test p < 0.01) where CFPPs equipped with ULE technology were newly built. However, when the retired or newly built CFPPs are located in the same 0.05 ◦ × 0.05◦ grid cells with industrial sources, their emission signals are often dominated by industrial emission reductions, resulting in emission declines in both cases. These results underscore the rising relative contribution of industrial emissions in regions where power plants and heavy industry are spatially co-located, and highlight the need to strengthen emission monitoring and control efforts directed at the industrial sector. By comparison, existing emission inventories have difficulty in capturing the power plant dynamics, particularly the effect of CFPP retirement. Our results demonstrate the value of satellite remote sensing coupled with detailed facility information for assessing point-source emission dynamics.