Ozone Pollution Surges Due to Intense Heatwaves

Tropospheric ozone pollution surged in Spain this year due to two long and intense summer heatwaves and the high temperatures experienced between June and September, marking the hottest summer on record in the country.

This toxic substance, most closely linked to climate change, recorded the highest levels detected in the last decade in 2025 as a result of the proliferation of extreme heat days, according to a study by Ecologistas en Acción based on measurements from 500 official stations across the country between January and September.

Tropospheric ozone is the most inhaled pollutant in Spain and causes the premature death of about 10,000 Spaniards annually, according to estimates by the European Environment Agency. Its presence at toxic levels is concentrated on the hottest and driest days of spring and summer, during midday and early afternoon, affecting the elderly, children, pregnant women, outdoor athletes, and individuals with chronic respiratory and cardiovascular diseases.

This pollutant is generated in the lower layers of the atmosphere by the combined effect of strong solar radiation and the accumulation of combustion gases from coal, oil, and gas in vehicles, power plants, and boilers. Although urban areas generate most of these combustion gases, the highest ozone pollution levels are found in city outskirts and rural areas because the substance is destroyed almost as quickly as it is produced in urban environments.

The report indicates that eight million Spaniards, one in six, or 17% of the population, breathed air with higher ozone concentrations than currently permitted by the EU this year. The result is even more negative when considering the new maximum values approved by Europe for this pollutant, which will be in effect in 2030. By those standards, more than 12 million Spaniards, one in four, would have inhaled air contaminated by this toxic substance. Finally, if the rate applied is the limit recommended by the World Health Organization (WHO), stricter than the legal objective and more aligned with adequate health protection, ozone-polluted air would have affected 47 million Spaniards in 2025, practically the entire country.

There are 26 areas in Andalusia, the Balearic Islands, Castilla-La Mancha, Catalonia, the Valencian Community, Extremadura, Madrid, and the Region of Murcia where at least one station exceeded the maximum ozone limits allowed by law. These areas rise to thirty and encompass 18 million inhabitants when considering the new limits that will govern in 2030. The Community of Madrid is the Spanish territory with the highest ozone pollution, with almost all its measuring stations above the future legal objective.

The frequency of legal objective value exceedances has returned to pre-COVID-19 pandemic numbers, with a 5% increase compared to the average for the 2012-2019 period. 2025 is also the year with the most exceedances of the threshold requiring public risk information since 2015, with 320 recorded by September 30, concentrated in Madrid and Catalonia.

According to Ecologistas en Acción, public administration information to citizens is "neither adequate nor commensurate with the severity of the problem." "Very few authorities have action protocols for ozone episodes. And still in 2025, the governments of Aragon, Asturias, Extremadura, and the Basque Country have not warned the population as required, while other affected communities have limited themselves to issuing routine notices through procedures that have not allowed effective communication of information," they assert.

The main measures needed to reduce air pollution from ozone include reducing motorized traffic, replacing organic solvents with water, energy savings, organizing the current chaotic deployment of renewable energies, and fiscally penalizing diesel vehicles and aviation, in addition to agreeing on a moratorium for new mega-farms.