Preprints
https://doi.org/10.5194/acp-2021-369
https://doi.org/10.5194/acp-2021-369

  04 May 2021

04 May 2021

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

Response of atmospheric composition to COVID-19 lockdown measures during Spring in the Paris region (France)

Jean-Eudes Petit1, Jean-Charles Dupont2, Olivier Favez3, Valérie Gros1, Yunjiang Zhang1,3, Jean Sciare1,a, Leïla Simon1,3, François Truong1, Nicolas Bonnaire1, Tanguy Amodeo3, Robert Vautard1, and Martial Haeffelin4 Jean-Eudes Petit et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, CEA/Orme des Merisiers, Gif-sur-Yvette, France
  • 2Institut Pierre Simon Laplace, Ecole Polytechnique, UVSQ, Université Paris-Saclay, Palaiseau, France
  • 3Institut National de l’Environnement Industriel et des Risques, Parc Technologique ALATA, Verneuil en Halatte, France
  • 4Institut Pierre Simon Laplace, Ecole Polytechnique, CNRS, Université Paris-Saclay, Palaiseau, France
  • anow at: Cyprus Institute, Nicosia, Cyprus

Abstract. Since early 2020, the COVID-19 pandemic has led to lockdowns at national scales. These lockdowns resulted in large cuts of atmospheric pollutant emissions, notably related to the vehicular traffic source where daily commuting of light-duty vehicles was almost completely stopped in numerous urban areas worldwide, especially during Spring 2020. As a result, air quality changed in manners that are still currently under investigation. Long-term in-situ monitoring of atmospheric composition provides, to this perspective, essential information. However, a robust quantitative assessment of the impact of lockdown measures on ambient concentrations is hindered by weather variability. Basic comparisons with previous years may thus be flawed, especially regarding secondary pollutants, whose concentrations strongly depends on meteorological conditions. In order to circumvent this difficulty, an innovative methodology has been developed. The Analog Application for Air Quality (A3Q) method is based on the comparison of each day of lockdown to a group of analog days having similar meteorological conditions. The A3Q method has been successfully evaluated and applied to a comprehensive in-situ dataset of primary and secondary pollutants obtained at the SIRTA observatory, a suburban background site of the Paris megacity (France). The overall slight decrease of PM1 concentrations (−14 %) compared to business-as-usual conditions conceals contrasting behaviours. Primary traffic tracers (NOx and traffic-related carbonaceous aerosols) dropped by 42–66 % during the lockdown period. Further, the A3Q method enabled us to characterize of changes triggered by NOx decreases. Particulate nitrate and secondary organic aerosols (SOA), two of the main springtime aerosol components in North-Western Europe, decreased by −45 % and −25 %, respectively. A NOx-relationship emphasizes the interest of NOx mitigation policies at the regional (i.e. city) scale, although long-range pollution advection sporadically overcompensated regional decreases. Variations of the oxidation state of SOA suggests discrepancies in SOA formation processes. At the same time, the expected ozone increase (+20 %) underlines the negative feedback of NO titration. These results provide a quasi-comprehensive observation-based insight on mitigation policies regarding air quality in future low-carbon urban areas.

Jean-Eudes Petit et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-369', Martine Collaud Coen, 05 May 2021
  • CC2: 'Comment on acp-2021-369', Thomas Karl, 05 Jul 2021
  • RC1: 'Comment on acp-2021-369', Anonymous Referee #1, 17 Aug 2021
  • RC2: 'Comment on acp-2021-369', Anonymous Referee #2, 23 Sep 2021

Jean-Eudes Petit et al.

Jean-Eudes Petit et al.

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Short summary
The COVID-19 outbreak led to lockdowns at national scales in Spring 2020. Large cuts in emissions occurred, but the quantitative assessment of their role from observations is hindered by weather and interannual variability. That is why we developed an innovative methodology in order to best characterize the impact of lockdown on atmospheric chemistry. We find that a local decrease in traffic-related pollutants triggered a decrease of secondary aerosols, and an increase in ozone.
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