Land-use-specific soil NO_x emissions in eastern China derived from TROPOMI observations

Abstract. Quantifying soil nitrogen oxide (NO_x) emissions is essential for constraining the nitrogen cycle and understanding its impacts on atmospheric chemistry and regional air quality. This study presents the first land-use-specific estimate of soil NO_x emissions across eastern China derived from TROPOMI satellite observations at a spatial resolution of 0.2° × 0.2°, covering forest, cropland, grassland/shrubland and bare land. We derive the emission intensity factor β for these land use types as functions of soil temperature (T_s) and soil volumetric water content (θ_v). Total soil NO_x emissions from eastern China in 2019 are estimated to be 1305 ± 368 Gg N, with largest contributions from cropland (623 ± 267 Gg N, ~ 48 %) and forest (486 ± 124 Gg N, ~ 37 %). High-emission areas (> 4 kg N ha^-1 yr^-1) are concentrated in the North China Plain, and all land use types show summer-peak seasonal patterns. Soil NO_x emissions exhibit land-use-specific responses to temperature and moisture. Most land use types show a clear optimum temperature and high-temperature inhibition effect, which are captured by a Gaussian response function. We find that existing global emission inventories may underestimate soil NO_x emissions from forests in China. The comparison with other emission inventories and soil emission observations demonstrates that the proposed method provides a reliable basis for estimating soil NO_x emissions by capturing land-use-specific responses to environmental drivers. This satellite-based approach can provide input to the formulation of emission reduction strategies and support ecosystem management under climate change.