19 Aug 2021

19 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

A new method for inferring city emissions and lifetimes of nitrogen oxides from high-resolution nitrogen dioxide observations: A model study

Fei Liu1,2, Zhining Tao1,2, Steffen Beirle3, Joanna Joiner2, Yasuko Yoshida2,4, Steven J. Smith5, K. Emma Knowland1,2, and Thomas Wagner3 Fei Liu et al.
  • 1Universities Space Research Association (USRA), Goddard Earth Sciences Technology and Research (GESTAR), Columbia, MD, 21046, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
  • 3Max-Planck-Institut für Chemie, Mainz, 55128, Germany
  • 4Science Systems and Applications Inc., Lanham, MD, 20706, USA
  • 5Joint Global Change Research Institute, Pacific Northwest National Laboratory, College Park, MD, 20740, USA

Abstract. We present a new method to infer nitrogen oxides (NOx) emissions and lifetimes based on tropospheric nitrogen dioxide (NO2) observations together with reanalysis wind fields for cities located in polluted backgrounds. Since the accuracy of the method is difficult to assess due to lack of “true values” that can be used as a benchmark, we apply the method to synthetic NO2 observations derived from the NASA-Unified Weather Research and Forecasting (NU-WRF) model at a high horizontal spatial resolution of 4 km × 4 km for cities over the continental US. We compare the inferred emissions and lifetimes with the values given by the NU-WRF model to evaluate the method. The method is applicable to 26 US cities. The derived results are generally in good agreement with the values given by the model, with the relative differences of 2 % ± 17 % (mean ± standard deviation) and 15 % ± 25 % for lifetimes and emissions, respectively. Our investigation suggests that the use of wind data prior to satellite overpass time improves the performance of the method. The correlation coefficients between inferred and NU-WRF lifetimes increase from 0.56 to 0.79 and for emissions increase from 0.88 to 0.96 when comparing results based on wind fields sampled simultaneously with satellite observations and averaged over 9 hours data prior to satellite observations, respectively. We estimate that uncertainties in NOx lifetime and emissions arising from the method are approximately 15 % and 20 %, respectively, for typical (US) cities. We expect this new method to be applicable to NO2 observations from the TROPOspheric Monitoring Instrument (TROPOMI) and geostationary satellites, such as Geostationary Environment Monitoring Spectrometer (GEMS) or the Tropospheric Emissions: Monitoring Pollution (TEMPO) instrument, to estimate urban NOx emissions and lifetimes globally.

Fei Liu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-642', Anonymous Referee #1, 10 Sep 2021
  • RC2: 'Comment on acp-2021-642', Anonymous Referee #2, 16 Sep 2021

Fei Liu et al.


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Short summary
In this work, we present a novel method to infer NOx emissions and lifetimes based on tropospheric NO2 observations together with reanalysis wind fields for cities located in polluted backgrounds. We evaluate the accuracy of the method using synthetic NO2 observations derived from a high-resolution model simulation. Our work provides an estimate for uncertainties in satellite-derived emissions inferred from chemical transport model (CTM)-independent approaches.