EGU22-9271, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Impact of droughts and heatwaves on surface ozone over Southwestern Europe

Antoine Guion1, Solène Turquety1, Arineh Cholakian2, Jan Polcher2, Antoine Ehret1, and Juliette Lathière3
Antoine Guion et al.
  • 1LMD/IPSL, Sorbonne Université, ENS, PSL Université, Ecole Polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France
  • 2LMD/IPSL, Ecole Polytechnique, Institut Polytechnique de Paris, ENS, PSL Université, Sorbonne Université, CNRS, Palaiseau, France
  • 3LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France

Tropospheric ozone (O3) plays a critical role in maintaining the oxidative capacity of the troposphere. However, as a high oxidant, it also deteriorates air quality at high concentration, inducing adverse effects on human and ecosystem health. Meteorological conditions are key to understand the variability of many surface atmospheric pollutants and of the vegetation state. The variability of O3 concentration is generally well represented in chemistry-transport models (CTM) compared to observations, but the amplitude of the variations are more difficult to simulate (peaks and minima). One factor that has been identified as a possible cause of these uncertainties is the lack of interactions between the biosphere and the atmosphere.

The aim of this study is to quantify the variation of surface O3 over the Southwestern Europe during agricultural droughts, combined or not with heatwaves. Therefore, we analyze both emissions of biogenic volatile organic compounds (BVOCs) and O3 dry deposition velocity during these extreme events, based on the available observations (O3 from the EEA surface network and formaldehyde (HCHO) from OMI satellite instrument) and regional CTM simulations (CHIMERE model), which have been clustered depending on the underlying meteorological conditions. To better understand the observed variations, sensitivity studies are performed implementing the effect of soil dryness and biomass decrease in CHIMERE CTM simulations using online calculation of BVOC emissions from the MEGAN model, during three selected summers: 2012, 2013 and 2014.

Our results show that observed O3 concentration is on average significantly higher during heatwaves (+10µg/m3 in daily mean and +18µg/m3 in daily maximum) and droughts (+5µg/m3 and +9µg/m3), due to an overall O3 precursor emissions enhancement (in agreement with HCHO observations) and O3 dry deposition decrease. However, isolated droughts are characterized by reduced O3 precursor emissions (in agreement with HCHO observations) and reduced O3 dry deposition, compared to normal conditions. Both effects compensate each other with a slight dominance of the latter one, leading to a small but significant increase of observed O3 concentration for the daily maximum only (+4 μg/m3). However, important uncertainties appear to be related to BVOC concentrations, especially about the land cover classification, and to NOX concentrations for which CHIMERE presents limited performance scores of validation. Nevertheless, we emphasize the need for a more dynamical interaction between surface vegetation and hydrology, meteorology and atmospheric chemistry for the simulation of O3 during summers in Southwestern Europe.

Finally, almost half of summer days exceeding the EU standard of O3 for air quality in Southwestern Europe occurred during droughts or heatwaves, on average for the time period 2000-2016. However, this percentage can increase (up to 80%) for exceptionally dry and hot summers, like in 2012. Only 14% of the exceedance days occurred during isolated droughts (summers 2000-2016).

How to cite: Guion, A., Turquety, S., Cholakian, A., Polcher, J., Ehret, A., and Lathière, J.: Impact of droughts and heatwaves on surface ozone over Southwestern Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9271,, 2022.

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