Vertical Profile Corrections Explain Satellite–Inventory Ammonia Discrepancies and Reveal Concentrated Agricultural Sources in China

Persistent discrepancies exist between bottom-up inventories and satellite-based ammonia (NH₃) emission estimates, with satellites typically reporting values one-third higher. These discrepancies prevent accurate targeting of NH₃ control policies for reducing air pollution and ecosystem nitrogen deposition. Here, we demonstrate that systematic biases in satellite vertical profile assumptions substantially explain these long-standing discrepancies. By replacing default vertical profile in satellite retrievals with spatially and temporally resolved atmospheric profiles, we reduced satellite-model discrepancies from 71 to 18%. Our hybrid inversion analysis across China reveals that baseline satellite retrievals overestimated growing season emissions by up to 44% due to systematic overestimation of near-surface NH₃ concentrations, while our corrected estimates show close agreement with bottom-up inventories (7.9% difference). Critically, our analysis reveals that China's NH₃ emissions are more spatially concentrated than what the <i>a priori</i> inventory indicates, with the top 10% of high-emitting areas contributing 54-56% of national emissions. This concentration reflects agricultural intensification patterns inadequately captured by bottom-up inventories. Independent validation confirms improved accuracy with 1-27% error reductions across all months. These findings provide essential insights for targeted emission control policies in the most concentrated agricultural regions while resolving methodological uncertainties that have long complicated NH₃ management strategies.