08 Jun 2022
08 Jun 2022

Interactions between the terrestrial biosphere and atmosphere during droughts and heatwaves: impact on surface ozone over Southwestern Europe

Antoine Guion1,a, Solène Turquety1,b, Arineh Cholakian2, Jan Polcher2, Antoine Ehret1, and Juliette Lathière3 Antoine Guion et al.
  • 1LMD/IPSL, Sorbonne Université, ENS, PSL Université, École polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France
  • 2LMD/IPSL, École polytechnique, Institut Polytechnique de Paris, ENS, PSL Université, Sorbonne Université, CNRS, Palaiseau, France
  • 3LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France
  • anow at: INERIS, Verneuil-en-Halatte, France
  • bnow at: LATMOS/IPSL, Sorbonne Université, UVSQ, CNRS, Paris, France

Abstract. At high concentration, tropospheric O3 deteriorates air quality, inducing adverse effects on human and ecosystem health. Meteorological conditions are key to understand the variability of O3 concentration, especially during extreme weather events. They modify the photochemistry activity and the vegetation state. An important source of uncertainties and inaccuracy in simulating surface O3 during droughts and heatwaves is the lack of interactions between the biosphere and the troposphere. Based on the biogenic emission model MEGAN v2.1 and the chemistry-transport model CHIMERE v2020r1, the first objective of this study is to assess the sensitivity of biogenic emissions, O3 dry deposition and surface O3 to biomass decrease and soil dryness effect (using several configurations) during the extremely dry summer 2012. Secondly, this research aims at quantifying the variation of observed (EEA’s air quality database, 2000–2016) and simulated (CHIMERE, 2012–2014) surface O3 during summer heatwaves and agricultural droughts that have been identified using the Percentile Limit Anomalies (PLA) method. Our sensitivity analysis shows that soil dryness is a key factor during drought events, decreasing considerably the C5H8 emissions and O3 dry deposition velocity. This effect has a larger impact than the biomass decrease. However, the resulting effect on surface O3 remains limited.

Based on a cluster approach using the PLA indicator, we show that observed O3 concentration is on average significantly higher during heatwaves (+18 μg/m3 in daily maximum) and droughts (+9 μg/m3) compared to normal conditions. Despite a difference of several μg/m3, CHIMERE correctly simulates the variations of O3 concentration between the clusters of extreme events. The overall increase of surface O3 during both heatwaves and droughts would be explained by O3 precursor emission enhancement (in agreement with HCHO satellite observations), O3 dry deposition decrease and favourable weather conditions. However, we simulated a decrease of C5H8 emissions (in agreement with HCHO observations) during droughts not accompanied by a heatwave, resulting in a non-significant difference of surface O3 compared to normal conditions (from both observations and simulations).

Finally, we stress that considerable uncertainties characterize our simulated surface-troposphere interactions. Multi-year flux measurements would contribute to better assess the model performance. Nevertheless, we emphasize the need for a more dynamical representation of interactions between vegetation, hydrology, meteorology and atmospheric chemistry in models in order to improve the simulation of summer O3.

Antoine Guion et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee Comment', Anonymous Referee #1, 21 Jun 2022
    • AC1: 'Reply on RC1 & RC3', Antoine Guion, 17 Oct 2022
  • RC2: 'Comment on egusphere-2022-222', Anonymous Referee #3, 26 Jun 2022
    • AC2: 'Reply on RC1-3', Antoine Guion, 17 Oct 2022

Antoine Guion et al.


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Short summary
At high concentrations, ozone (O3) deteriorates air quality. Meteorological conditions are a key driver for O3 concentration. In this paper, we show that droughts and especially heatwaves, are associated with an overall increase in O3 concentration including pollution peaks. This is partly explained by an increase in precursor emissions from the canopy and a decrease in dry deposition within the canopy. Moreover, soil dryness appears to induce a critical effect on such interactions.