Tracking daily NO<sub><i>x</i></sub> emissions from an urban agglomeration based on TROPOMI NO<sub>2</sub> and a local ensemble transform Kalman filter
<p>Accurate, timely, and high-resolution NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions are essential for formulating pollution control strategies and improving the accuracy of air quality modeling at fine scales. Since late 20...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/5959/2025/acp-25-5959-2025.pdf |
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| Summary: | <p>Accurate, timely, and high-resolution NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions are essential for formulating pollution control strategies and improving the accuracy of air quality modeling at fine scales. Since late 2018, the Tropospheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor (S5P) satellite has been providing daily monitoring of NO<span class="inline-formula"><sub>2</sub></span> column concentrations with global coverage and a small footprint of 5.5 km <span class="inline-formula">×</span> 3.5 km, offering great potential for tracking daily high-resolution NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions. In this study, we develop a data assimilation and emission inversion framework that couples an ensemble Kalman filter with the Community Multiscale Air Quality (CMAQ) model to estimate daily NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions at 3 km scales in Beijing and surrounding areas in 2020. By assimilating the TROPOMI NO<span class="inline-formula"><sub>2</sub></span> tropospheric vertical column densities (TVCDs) and taking the bottom-up inventory as prior emissions, we produce a posterior NO<span class="inline-formula"><sub><i>x</i></sub></span> emission dataset with a reasonable spatial distribution and daily variations at the 3 km scale. The proxy-based bottom-up emission mapping method at fine scales overestimates NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions in densely populated urban areas, whereas our posterior emissions improve this mapping by reducing the overestimation of urban emissions and increasing emissions in rural areas. The posterior NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions show considerable seasonal variations and provide a more timely insight into NO<span class="inline-formula"><sub><i>x</i></sub></span> emission fluctuations, such as those caused by the COVID-19 lockdown measures. Evaluations using the TROPOMI NO<span class="inline-formula"><sub>2</sub></span> column retrievals and ground-based observations demonstrate that the posterior emissions substantially improve the accuracy of 3 km CMAQ simulations of the NO<span class="inline-formula"><sub>2</sub></span> TVCDs as well as the daily surface NO<span class="inline-formula"><sub>2</sub></span> and O<span class="inline-formula"><sub>3</sub></span> concentrations in 2020. However, during summer, despite notable improvements in surface NO<span class="inline-formula"><sub>2</sub></span> and O<span class="inline-formula"><sub>3</sub></span> simulations, positive biases in the posterior model simulations persist, indicating weaker constraints on surface emissions from satellite NO<span class="inline-formula"><sub>2</sub></span> column retrievals in summer. The posterior daily emissions on the 3 km scale estimated by our inversion system not only provide insights into the fine-scale emission dynamic patterns but also improve air quality modeling on the kilometer scale.</p> |
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| ISSN: | 1680-7316 1680-7324 |