Work

Estimating the variability in NO x emissions from Wuhan with TROPOMI NO 2 data during 2018 to 2023

Year: 2025

Type: article

Abstract: . Accurate NOx emission estimates are required to better understand air pollution, investigate the effectiveness of emission restrictions, and develop effective emission control strategies. This study investigates and demonstrates the ability of the superposition column model in combination with TROPOMI tropospheric NO2 column data to estimate city-scale NOx emissions and lifetimes and their variabilities. Using the recently improved TROPOMI tropospheric NO2 column product (v2.4–2.6), we derive daily NOx emissions and lifetimes over the city of Wuhan for 335 clear sky days between May 2018 and December 2023. We find a slight weekend reduction in NOx emission with a weekend-to-weekday ratio of 0.95 and a small seasonal variation of NOx emissions over Wuhan with a summer-to-winter emission ratio of 0.87. We calculate a steady decline of NOx emissions from 2019 to 2023, and the emission in 2023 is ~15 % below the 2019 level, indicating the success of the emission control strategy. The estimated NOx lifetimes range from 0.8 h (summer) to 5.3 h (winter), with an average of 2.6 h. Meanwhile, our method shows ~30 % lower NOx lifetimes for fast wind (> 7 m s−1) speed. The superposition model method results in ~10 % lower estimation of NOx emissions when the wind direction is from distinct upwind NO2 hotspots compared to other wind directions, indicating the need to improve the approach for cities that are not relatively isolated pollution hotspots. The results of this work nevertheless confirm the strength of the superposition column model in estimating urban NOx emissions with reasonable accuracy.

Source: Atmospheric chemistry and physics

DOI: 10.5194/acp-25-3313-2025