Episodes are mainly observed in winter (in February and at the end of December)

  

Episodes are mainly observed in winter (in February and at the end of December) due to a gradual accumulation, under the effect of persistent high pressure conditions, of pollutants emitted mainly by sources(road traffic, wood heating). The summer of 2019 was marked by eight episodes of ozone (O3) pollution, linked to the scorching conditions that occurred between June and August 2019. Eleven days of ozone pollution episodes were observed during the heat waves from 2018.The number of pollution episodes per year strongly depends on weather conditions. It is therefore difficult to identify an absolute trend. However, extreme weather events, such as heat waves, are more and more common with global warming. This raises fears of a potential increase in the number of pollution episodes, especially ozone. On the other hand, the intensity of the ozone episodes recorded in 2019 was rather less compared to the scorching heat of 2003, with maximum temperatures however higher and a record of 43 ° C in Paris. This situation is explained by the drop in emissions of ozone precursors (nitrogen oxides and volatile organic compounds) under the effect of French and European regulations.(All my research was found on this site https://www.airparif.asso.fr/etat-air/bilan-annuel)