Preprints
https://doi.org/10.5194/acp-2021-739
https://doi.org/10.5194/acp-2021-739

  13 Sep 2021

13 Sep 2021

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

Are cities responsible for their air pollution?

Philippe Thunis1, Alain Clappier2, Alexander de Meij3, Enrico Pisoni1, Bertrand Bessagnet1, and Leonor Tarrason4 Philippe Thunis et al.
  • 1European Commission, Joint Research Centre, Ispra, Italy
  • 2Université de Strasbourg, Laboratoire Image Ville Environnement, Strasbourg, France
  • 3MetClim, Varese, Italy
  • 4NILU, Norway

Abstract. While the burden caused by air pollution in urban areas is well documented, the origin of this pollution and therefore the responsibility of the urban areas in generating this pollution is still a subject of scientific discussion. Source Apportionment represents a useful technique to quantify the city responsibility but the approaches and applications are not harmonized, therefore not comparable, resulting in confusing and sometimes contradicting interpretations. In this work, we analyze how different source apportionment approaches apply to the urban scale and how their building elements and parameters are defined and set. We discuss in particular the options available in terms of indicator, receptor, source and methodology. We show that different choices for these options lead to very large differences in terms of outcome. In average over the 150 EU large cities selected in our study, the choices made for the indicator, the receptor and the source each lead to an average factor 2 difference. We also show that temporal and spatial averaging processes applied to the air quality indicator, especially when diverging source apportionments are aggregated into a single number lead to favor strategies that target background sources while occulting actions that would be efficient at the city center. We stress that methodological choices and assumptions most often lead to a systematic and important underestimation of the city responsibility, with important implications. Indeed, if cities are seen as a minor actor, plans will target in priority the background at the expense of potentially effective local actions.

Philippe Thunis et al.

Status: open (until 25 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Philippe Thunis et al.

Philippe Thunis et al.

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Short summary
The origin of air pollution in cities is yet a point of discussion and the approaches to assess the city responsibility on its pollution are not harmonized, therefore not comparable, resulting in sometimes contradicting interpretations. From our 150 EU cities dataset, we show that methodological choices can easily lead to factor 2 differences. We stress that methodological choices and assumptions most often lead to a systematic and important underestimation of the city responsibility.
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