ESSDD

Earth System Science Data Discussions

ESSDD

Earth Syst. Sci. Data Discuss.

1866-3591

Göttingen, Germany

10.5194/essd-2025-480

Deriving regional and point source nitrogen oxides emissions in China from TROPOMI using the directional derivative approach with nonlinear chemical lifetime fitting

Chen

Ling

¹ ² ³ Cai

Zhaonan

⁴ ⁵ ¹ Sun

Kang

https://orcid.org/0000-0002-9930-7509

⁶ ⁷ Liu

https://orcid.org/0000-0001-9305-5358

¹ ² ⁴ Yang

Dongxu

¹ Li

Mingming

³ Zhu

Lingyun

Carbon Neutrality Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

University of Chinese Academy of Sciences, Beijing 100049, China

Shanxi Center of Technology Innovation for Environmental Meteorology Forecast and Evaluation, Shanxi Institute of Meteorological Science, Taiyuan 030002, China

State Key labrotory of Atmospheric Enviroment and Extreme Meterology, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China

Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, NY, USA

Research and Education in Energy, Environment and Water Institute, University at Buffalo, Buffalo, NY, USA

03 11 2025

2025 1 28

2025

This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/

This article is available from https://essd.copernicus.org/preprints/essd-2025-480/

The full text article is available as a PDF file from https://essd.copernicus.org/preprints/essd-2025-480/essd-2025-480.pdf

An appropriate representation of the NOx/NO2 ratio and NOx lifetime is essential for estimating NOx emissions from satellite NO2 observations. We introduce a satellite-based, data-driven approach that applies variable NOx/NO2 ratio and derives a nonlinear chemical lifetime using a piecewise fitting method based on the directional derivative approach (DDA). This method enables the estimation of both regional and point-source NOx emissions across China, representing the first application of a lightweight, satellite-driven method to directly capture nonlinear NOx lifetime for emission estimation over large, topographically complex region. The incorporation of a variable NOx/NO2 ratio enhances the accuracy of source divergence and emission estimates and the improved fitting scheme captures the nonlinear behavior of NOx chemistry. Anthropogenic contributions are isolated by subtracting natural sources from satellite-derived total emissions, with natural NOx identified using a seasonal criterion and further constrained by Nighttime Light (NTL) data. Estimated anthropogenic NOx emissions in China from 2019 to 2024 are 20.2 Tg, 18.5 Tg, 19.4 Tg, 18.9 Tg, 20.7 Tg and 18.8 Tg, respectively, with annual uncertainties of 27 %–30 %. These values show good agreement with both bottom-up inventories and top-down inversions, with national scale discrepancies ranging from −11.8 % to 0.8 %. The DDA captures key spatial and temporal emission patterns, including consistent decline in NOx emissions in megacities and provincial disparities linked to urbanization and economic development. The DDA estimates are consistent with previous studies on coal-fired power plant emissions, and emissions from 124 plants vary between 0.02–2.13 kg s−1 for 2019–2024, with uncertainties spanning 4 %–78 %, averaging 16 %. This satellite-based, lightweight method enables low-latency, timely long-term monitoring of NOx emissions and offers a promising alternative to bottom-up inventories and resource-intensive top-down models. The data are publicly available at <a href="https://zenodo.org/records/16787342" target="_blank" rel="noopener">https://zenodo.org/records/16787342</a> (Chen et al., 2025).