Is Paris breathing? A scrutiny of the Paris thunderstorm asthma episode of June 2023

Aim: To describe the first major epidemic thunderstorm asthma (ETSA) event detected in France in June 2023. Methods: Data on local meteorology, visits to the emergency room (ER) for asthma and hospitalization after a visit, aerobiological composition of the atmosphere (pollens and spores), phenological information on the flowering of grasses, and regional air pollution were collected, aggregated, and analyzed. Results: The ETSA was centered on the Paris region. An excess of 1,900 emergency visits for asthma was recorded over the period 10, 11, and 12 June. The people most affected were men aged 14 to 44. The hospitalization rate following a visit to the ER for asthma increased to 13%. ER visits for asthma began at around 6 pm on 10 June, just after an intense gust (15 m/s) triggering a PM10 resuspension episode, and peaked at around 10 pm on 11 June. Concentrations of mold spores (Cladosporium and Ascosporium) rose sharply during the night of 10–11 June, at the same time as the intake peak. The ETSA occurred during the grass and Urticaceae pollen season, with pollen concentrations lower (< 100 pollen grains/m3) compared to the days preceding the event (> 200 pollen grains/m3). A fraction of the pollen was observed without cytoplasm, but there was no apparent link with the ETSA. Phenological observations in the Paris pollinarium showed that the ETSA coincided with the start of the Lolium perenne (ryegrass) pollen season. Conclusions: Although the data collected did not allow the identification of a single cause for the occurrence of the ETSA, they pointed to multifactorial causes such as the occurrence of an ozone pollution episode, strong winds before the storm, an episode of resuspension of PM10 particles, the presence of broken pollen, and the significant increase in mold spores just after the stormy episode.