Mediterranean forests emit traffic pollutant during heatwaves, study finds

Mediterranean forests release toluene, a volatile organic compound typically associated with traffic and industry, when subjected to extreme heat and drought. This emission process actively contributes to the formation of tropospheric ozone, a pollutant harmful to respiratory health. The findings stem from research conducted between 2021 and 2023 in Barcelona's Montseny Natural Park, a period marked by severe drought in Catalonia. Scientists observed recurring morning peaks of toluene approximately two days after heatwaves, which brought temperatures up to 5 degrees Celsius above average and critically low humidity levels. Researchers propose that toluene's release is a direct response from the forest ecosystem under stress. This discovery leads scientists to suggest using toluene as a bio-indicator for the physiological state and climate-induced stress of Mediterranean ecosystems. Further research is planned to compare these results with data from forests in Marseille, France, and Cyprus to confirm the hypothesis. Toluene, when reacting with nitrogen oxides from urban traffic, promotes the creation of ground-level ozone, which irritates airways and acts as a greenhouse gas. The study's authors emphasize the importance of incorporating these biogenic emissions into air quality monitoring and regulation strategies, as most such compounds are not currently specifically regulated.

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Toluene peaks appeared in the morning. This made us think that there was a response from the forest itself to these stress conditions.