Tropospheric ozone, a secondary pollutant formed by photochemical reactions under strong solar radiation, has reached worrying levels in Catalonia during the summer. July, the hottest month since 1950, concentrated most episodes, especially in the Plana de Vic and the Barcelona Area. The increased frequency of heatwaves, linked to climate change, makes ozone one of the priority environmental and public health challenges.
Between May 15 and September 15, the XVPCA recorded 115 exceedances of the LLI threshold (180 µg/m³) through 51 automatic stations. This figure breaks the downward trend of recent years and represents the highest value since the 2019 campaign.
The triggering meteorological conditions include the extraordinary persistence of heat and atmospheric stagnation. July 2026 was the hottest and driest month recorded in Catalonia since 1950. During the second heatwave, the Fabra Observatory in Barcelona reached its absolute historical temperature record (40.9 °C on July 8), coinciding with the peak of ozone exceedances on the central coast.
These data align with the Atmosphere Watch study by the Copernicus Climate Change Service, which indicates that over a third of the world's population was exposed to harmful levels of tropospheric ozone in 2026. In Europe, the increase in heatwaves has driven up ozone concentration, neutralizing the effect of reducing its precursor pollutants.
The report from the Department of Territory, Housing, and Ecological Transition concludes that, although general air quality has remained within ordinary legal frameworks, the increase in heatwaves makes ozone a priority challenge.
The Government is implementing actions through the Air Quality Plan, horizon 2027 to reduce ozone precursor emissions in sectors such as transport, industry, energy, agriculture, and maritime transport. It also promotes low-emission zones, sustainable mobility, and vehicle electrification.
The plan includes a specific strategy for ozone in Catalonia, strengthens air quality monitoring, and promotes studies to improve knowledge about this pollutant.
Key data from the campaign indicate 113 exceedances of the LLI threshold and 2 exceedances of the alert threshold (LLA, 240 µg/m³), spread over 29 different days. The maximum value was reached in Badalona on July 9 (269 µg/m³). 41% of stations recorded exceedance episodes, affecting 10 out of 14 air quality zones. The Plana de Vic was the most affected zone (51 exceedances), followed by the Barcelona Area (19).
July was the critical period (65 exceedances), with an intense episode between July 6 and 10 (42 exceedances). The time slot with the most incidents was between 4 PM and 5 PM.
