Submitted as: model evaluation paper 10 Dec 2021

Submitted as: model evaluation paper | 10 Dec 2021

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

Effects of point source emission heights in WRF–STILT: a step towards exploiting nocturnal observations in models

Fabian Maier1,2, Christoph Gerbig3, Ingeborg Levin1, Ingrid Super4, Julia Marshall5, and Samuel Hammer1,2 Fabian Maier et al.
  • 1Institut für Umweltphysik, Heidelberg University, INF 229, 69120 Heidelberg, Germany
  • 2ICOS Central Radiocarbon Laboratory, Heidelberg University, Berliner Straße 53, 69120 Heidelberg, Germany
  • 3Department Biogeochemical Systems, Max Planck Institute for Biogeochemistry, Hans-Knöll-Straße 10, 07745 Jena, Germany
  • 4Department of Climate, Air and Sustainability, TNO, P.O. Box 80015, 3508 TA Utrecht, the Netherlands
  • 5Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. An appropriate representation of point source emissions in atmospheric transport models is very challenging. In the Stochastic Time Inverted Lagrangian Transport model (STILT), all point source emissions are typically released from the surface, meaning that the actual emission stack height plus subsequent plume rise is not considered. This can lead to erroneous predictions of trace gas concentrations, especially during nighttime when vertical atmospheric mixing is minimal. In this study we use two WRF–STILT model approaches to simulate fossil fuel CO2 (ffCO2) concentrations: (1) the standard “surface source influence (SSI)” approach, and (2) an alternative “volume source influence (VSI)” approach, where nearby point sources release CO2 according to their effective emission height profiles. The comparison with 14C-based measured ffCO2 data from two-week integrated afternoon and nighttime samples collected at Heidelberg, 30 m above ground level, shows that the root-mean-square deviation (RMSD) between modelled and measured ffCO2 is indeed almost twice as high during night (RMSD = 6.3 ppm) compared to the afternoon (RMSD = 3.7 ppm) when using the standard SSI approach. In contrast, the VSI approach leads to a much better performance at nighttime (RMSD = 3.4 ppm), which is similar to its performance during afternoon (RMSD = 3.7 ppm). Representing nearby point source emissions with the VSI approach could, thus, be a first step towards exploiting nocturnal observations in STILT. To further investigate the differences between these two approaches, we conducted a model experiment in which we simulated the ffCO2 contributions from 12 artificial power plants with typical annual emissions of one million tons of CO2 and with distances between 5 and 200 km from the Heidelberg observation site. We find that such a power plant must be more than 50 km away from the observation site in order for the mean modelled ffCO2 concentration difference between the SSI and VSI approach to fall below 0.1 ppm.

Fabian Maier et al.

Status: open (until 23 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on gmd-2021-386', Juan Antonio Añel, 30 Dec 2021 reply
    • AC1: 'Reply on CEC1', Fabian Maier, 07 Jan 2022 reply
      • CEC2: 'Reply on AC1', Juan Antonio Añel, 09 Jan 2022 reply
        • AC2: 'Reply on CEC2', Fabian Maier, 11 Jan 2022 reply
          • CEC3: 'Reply on AC2', Juan Antonio Añel, 18 Jan 2022 reply
            • AC3: 'Reply on CEC3', Fabian Maier, 20 Jan 2022 reply
              • CEC4: 'Reply on AC3', Juan Antonio Añel, 20 Jan 2022 reply
                • AC4: 'Reply on CEC4', Fabian Maier, 28 Jan 2022 reply

Fabian Maier et al.

Data sets

Heidelberg integrated samples 2018-2020 and pseudo power plant experiment results [Data] Maier, Fabian; Gerbig, Christoph; Levin, Ingeborg; Super, Ingrid; Marshall, Julia; Hammer, Samuel

Fabian Maier et al.


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Short summary
We show that the default representation of point source emissions in WRF-STILT leads to large overestimations when modelling fossil fuel CO2 concentrations for a 30 m high observation site during stable atmospheric conditions. We therefore introduce a novel point source modelling approach in WRF-STILT, which takes into account their effective emission heights and results in a much better agreement with observations.