09 Feb 2023
 | 09 Feb 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Remotely Sensed and Surface Measurement Derived Mass-Conserving Inversion of Daily High-Resolution NOx Emissions and Inferred Combustion Technologies in Energy Rich Northern China

Xiaolu Li, Jason Blake Cohen, Kai Qin, Hong Geng, Liling Wu, Xiaohui Wu, Chengli Yang, Rui Zhang, and Liqin Zhang

Abstract. This work presents a new model free inversion estimation framework using daily TROPOMI NO2 columns and observed fluxes from the continuous emissions monitoring systems (CEMS) to quantify three years of daily-scale emissions of NOx at 0.05°×0.05° over Shanxi Province, a major world-wide energy producing and consuming region. The NOx emissions, day-to-day variability, and uncertainty on a climatological basis are computed to be 1.83, 1.01, and 1.06 Tg per year respectively. The highest emissions are concentrated in the lower Fen River valley, which accounts for 25 % of the area, 52 % of the NOx emissions, and 72 % of CEMS sources. Two major forcing factors (10th to 90th percentile) are horizontal transport distance per day (66–666 km) and lifetime of NOx (6.7–18.4 h). Both of these values are consistent with NOx emissions to both the surface layer and the free troposphere. The third forcing factor, the ratio of NOx / NO2, on a pixel-by-pixel basis is demonstrated to have a significant correlation with the combustion temperature and energy efficiency of large energy consuming sources. Specifically, thermal power plants, cement, and iron and steel companies have a relatively high NOx / NO2 ratio, while coking, industrial boilers, and aluminium oxide show relatively low ratio. Variance maximization is applied to daily TROPOMI NO2 columns identifies three significant modes, and successfully attributes them both spatially and temporally to (a) this work’s computed emissions, (b) remotely sensed TROPOMI UVAI, and (c) computed transport based on TROPOMI NO2.

Xiaolu Li et al.

Status: open (until 23 Mar 2023)

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  • RC1: 'Comment on egusphere-2023-2', Anonymous Referee #2, 15 Feb 2023 reply

Xiaolu Li et al.

Xiaolu Li et al.


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Short summary
Remotely sensed NO2 and surface NOx are combined with a mathematical method to estimate daily NOx emissions. The results identify new sources and improve existing estimates. The estimation is driven by three flexible factors: thermodynamics of combustion, chemical loss, and atmospheric transport. The thermodynamic term separates power, iron, and cement from coking, boilers, and aluminum. This work attributes three causes of extremes: emissions, UV radiation, and transport.