Tropospheric ozone has taken a worrying leap in Spain after an unusually warm summer, with two prolonged heat waves that have favored its formation. The analysis of almost 500 official stations places 2025 with the highest levels of the last decade, a scenario that recovers pre-pandemic dynamics and puts the focus back on the public health.
Beyond the specific peaks, the health burden is significant: the European Environment Agency estimates up to 10.000 premature deaths per year in our country associated with ozone, and the Carlos III Health Institute has calculated this summer an excess of 3.840 deaths linked to the combination of extreme heat and poor air quality, with the tropospheric ozone protagonist.
Heat waves, records and key figures
The report of Ecologists in Action, based on data from January 1 to September 30, takes as a reference the new European Union target applicable in 2030. With that bar, more than 12 million people breathed air that does not comply with this guideline in the three-year period 2023-2025; with the legal value still in force, the figure drops to about 8 million. If the much stricter WHO guideline is used, exposure reaches 47 million, practically the entire population.
2025 also stands out for the recurrence of episodes: until September 30, 320 exceedances of the information threshold, the highest number since 2015, and a frequency of excesses 5% higher than the 2012-2019 average. These peaks were concentrated mainly in the Community of Madrid and Catalonia during the hottest days. ozone episodes are increasingly frequent and prolonged.
Ground-level ozone is not emitted directly: it is a secondary pollutant which arises when solar radiation acts on precursors such as nitrogen oxides from road traffic, volatile organic compounds from industrial and solvent uses, and methane linked to intensive livestock farming and waste management. Hence its peak in spring and summer, and its greatest impact on suburban and rural areas influenced by urban and industrial emissions.
By territories, the Region of Madrid Ozone pollution is at the top of the list, with almost all stations above the new European target. Also increasing were Andalusia, the Mediterranean coast (Balearic Islands, Catalonia, the Region of Murcia and Melilla), Castile and León and Extremadura; however, decreases were detected in Ebro Valley, the Cantabrian coast, Castilla-La Mancha, the Valencian Community and the Canary Islands.
In the three-year period 2023-2025, 26 zones Andalusia, the Balearic Islands, Castilla-La Mancha, Catalonia, the Valencian Community, Extremadura, the Community of Madrid and the Region of Murcia failed to meet the current legal target. If the new 2030 standard is applied, the map will expand to around thirty areas with 18 million affected.
Health impact, public management and what is proposed
Breathing ozone damages the respiratory and cardiovascular systems, and has been associated with neurological effects. The Carlos III Health Institute links O3 to around 23.000 urgent admissions annually, and among those over 65, it accounts for a large proportion of upper respiratory tract infection visits. The hottest days with the most stable atmosphere are the most critical.
The institutional response is not up to the problem, according to the NGO: insufficient warnings and a lack of effective protocols. In 2025, governments such as Aragon, Asturias, Extremadura, and the Basque Country did not issue alerts despite exceeding thresholds, while other communities limited themselves to routine communications with limited dissemination.
At the regulatory level, the urgent approval of a National Ozone Plan, after years of preparatory work, and the development of regional plans in regions that still lack them. There are also court rulings urging compliance with the air quality regulations in force since 2010, with more demanding objectives already approved for 2030 at European level.
What would work? Reducing precursors is key: less motorized traffic and low emission zones effective, electrification of public transport, replacement of organic solvents with water, energy saving, orderly deployment of renewables, emission control areas in the Mediterranean and Northeast Atlantic, and environmental taxation of diesel and aviation. Also proposed are compost biowaste and a moratorium on new macro-farms to contain methane.
Ozone also takes its toll on field and ecosystems: When it penetrates through the stomata, it damages plant tissue, reduces yields and slows forest growth. European studies have quantified losses in crops such as wheat and potatoes, and place Spain and southern Europe among the most vulnerable areas due to their high radiation and the duration of the summer episodes.
