09 Nov 2023
 | 09 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Extreme ozone episodes in a major Mediterranean urban area

Jordi Massagué, Eduardo Torre-Pascual, Cristina Carnerero, Miguel Escudero, Andrés Alastuey, Marco Pandolfi, Xavier Querol, and Gotzon Gangoiti

Abstract. This study analysed three extreme ozone (O3) episodes that occurred in Barcelona (NE Spain) during the summers of 2015, 2018, and 2019. These episodes were the only instances since at least the year 2000 when the EU's hourly information threshold (180 µg·m−3) was exceeded in the city. Understanding the phenomenology of these episodes is crucial owing to Barcelona's large population. Using experimental data and diverse modelling tools, the main objective was to elucidate the underlying phenomena of recent extreme O3 episodes, identify shared patterns and improve future predictions. The results revealed a complex interplay of factors contributing to the episodes, including (i) initial regional O3 accumulation, (ii) the potential impact of Tramontana winds on O3 transport into the western Mediterranean basin, (iii) O3 accumulation via vertical recirculation and horizontal circulation of the local pollution plume in a weakened sea breeze regime, (iv) convergence of polluted air masses from multiple sources, (v) calm upper layer winds, (vi) the weekend effect, and (vii) abnormally high temperatures. Some of these factors, which may manifest in the days preceding the episodes, are readily observable or can be anticipated. Consequently, the findings of this study enhance the understanding of the mechanisms driving these extreme O3 episodes and provide valuable insights for their prediction.

Jordi Massagué et al.

Status: open (until 24 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2449', Anonymous Referee #1, 25 Nov 2023 reply
  • RC2: 'Comment on egusphere-2023-2449', Anonymous Referee #2, 30 Nov 2023 reply

Jordi Massagué et al.

Jordi Massagué et al.


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Short summary
This study analysed extreme ozone episodes in Barcelona, which have occurred only in recent years and are of particular concern due to the city's significant population. The research reveals that these episodes result from a complex interplay of factors, including the effects of pollution transport from regional to local sources and specific weather and emission patterns. These findings advance the understanding of the mechanisms behind these episodes and strengthen predictive capabilities.