The chaining of intense and prolonged heat waves has pushed tropospheric ozone to unusually high levels in Spain. This summer, described by analyses as the warmest on record, has acted as a chemical accelerator that, in the presence of solar radiation, multiplies the formation of the so-called “bad” ozone.
Data collected by organizations and public bodies indicate that Concentrations have reached ten-year highs in numerous areas. With current standards already exceeded in multiple stations, the implementation of the new European Union limits for 2030 would further expand the map of non-compliance, while under the WHO guidelines, virtually the entire territory has exceeded the recommended threshold.
What is happening and why is ozone rising?
Tropospheric ozone does not come from a specific chimney or a car exhaust pipe; It forms in the lower atmosphere when sunlight hits precursor pollutants. These include nitrogen dioxide (NO2)—mostly associated with road traffic—and volatile organic compounds from various activities.
Added to this mix is a growing role of methane (CH4), associated in Spain mainly with intensive livestock farms, and episodes with carbon monoxide increased by large forest fires. It is a typically seasonal phenomenon: where there is more radiation (spring and summer), there is more reaction and, therefore, more ozone peaks, especially in suburban and rural areas affected by urban and industrial pollution.
Where the largest increases have been detected
Records show that the warmer summer has pushed the seasonal average above the legal limit in force in the entire Community of Madrid, much of Extremadura, southwest Castilla-La Mancha, inland areas of Catalonia, the Region of Murcia, and various parts of Andalusia. With the new EU legal maximum value for 2030, practically all of Andalusia and a large area of Castilla-La Mancha would be incorporated into the areas with overruns.
If the analysis is made using the WHO's health criteria, the picture is even more severe: almost the entire population would have been exposed to levels above those recommended during the summer. Regarding hourly peaks, legal limits have been exceeded at stations in Madrid, the western half of Castilla-La Mancha, Extremadura, Andalusia, areas of Catalonia and Mallorca.
In the three-year period 2023-2025, more than twelve million people breathed air with ozone above the new European limits for 2030, according to Ecologists in Action. With the legal target still in place, the figure would be around eight million. In parallel, 2025 accumulated, as of September 30, 320 exceedances of the information threshold to the population, concentrated mainly in Madrid and Catalonia.
The Community of Madrid stands out for an unprecedented deterioration: the reference report describes the highest levels since the 1990s, with a notable increase compared to the 2012-2019 period, and a large number of overruns in June, July and August. In the Mediterranean arc, episodes and warnings were reported in Castellón and the interior of Valencia —with several activations of the information threshold—; In 2025, the source consulted did not identify an exposed population above the annual legal target in the Community, although specific episodes with very high concentrations below the WHO threshold were recorded.
Health risks and health response
Exposure to ozone is associated with inflammation and oxidative stress in the respiratory system, worsening of cardiac and respiratory pathologies, neurological affectation and, according to various studies, effects on mental health. The Carlos III Health Institute estimates around 23.000 urgent admissions annual ozone-related emissions in Spain; only NO2 causes more, with about 28.000 per year.
In 2025, the same body attributes 3.840 deaths to excessive temperatures and greater exposure to pollutants such as ozone. In the Community of Madrid, the figures were hundreds of deaths associated with heat and ozone during the summer, which supports that we are facing a public health problem de first orderIn people over 65, ozone accounts for more than half of admissions for upper respiratory tract infections.
In addition, health services warn that episodes do not affect everyone equally: they are especially vulnerable children, older people, pregnant women, and those with cardiorespiratory diseases. Therefore, the Carlos III Health Institute recommends addressing the source: reduce urban traffic, key due to its link with NO2 and other precursors.
Impact on the field and ecosystems
Ozone not only harms people: when absorbed by leaves, damages plant tissues, slows growth and reproduction and reduces agricultural and forestry yields, with impact on biodiversity, according to the European Environment Agency.
A study by the European Topic Center found significant losses associated with ozone peaks in 2022: more than three million tons of wheat and around 1.300 millones de euros in value, in addition to about 680 million in potatoes. Southern European countries, with longer and more intense radiation seasons, such as Spain and Italy are especially vulnerable. In Spain, environmentalists denounce lack of official evaluation sufficient impact on vegetation and ecosystems.
Public information and plans in progress
The network of alerts and warnings to citizens showed some light and shadows during the episodes of 2025. There was hundreds of exceedances of the information threshold, but deficiencies were detected: in Aragon, Asturias, Extremadura and Euskadi the ozone levels were not warned as required, and in other communities the warnings were routine and ineffective to reach the whole population.
Ecologists in Action denounce that seven autonomous communities still lack specific plans against ozone, and calls for the urgent approval of a National Ozone PlanIn Madrid, the group is taking legal action for administrative inaction and is asking for the activation of protocols during episodes of high pollution, in line with other European capitals.
What measures are proposed
The priority, according to experts and organizations, is to cut emissions of precursors. Among the most cited measures are reduce urban motorized traffic (including effective Low Emission Zones), promote public transport, and technologically and tax-disincentivize diesel vehicles and aviation.
It is also proposed to replace organic solvents by water in industrial processes, improve efficiency and energy savings, plan the renewable deployment in an orderly manner, and advance in the Emission Control Areas of the Mediterranean Sea and Northeast Atlantic. For background ozone, the need to act on the methane: compost bio-waste and establish a moratorium on new macro-farms that increase these emissions.
However, health authorities insist on daily prevention: check the levels Before exercising outdoors on days of intense radiation, avoid peak hours and protect vulnerable groups during episodes.
With an exceptionally warm summer as a catalyst, the rebound in tropospheric ozone has left more of the population exposed, more episodes and greater pressure on health and the countryside. Stopping its precursors—especially the NO2 from traffic and methane—, improving information for citizens and deploying effective plans at the state and regional levels seems crucial to ensure that the next hot season does not result in another surge in this pollutant.
