The arrival of an intense heat wave has caused tropospheric ozone levels to spike in various parts of Spain. During the first days of August, several monitoring stations recorded exceedances of the established thresholds for informing the public, and in some cases, the alert level was even activated.
Ozone, which forms in the lower layers of the atmosphere, is a secondary pollutant that appears when other gases react under strong solar radiation. The high temperatures and lack of wind in recent days have created perfect conditions for its accumulation in urban and rural areas, prompting authorities to activate specific protocols.
Episodes in Seville, Valladolid and Puertollano
The most striking episode occurred in Seville, where the Sierra Norte station recorded 202 micrograms per cubic meter on August 10th between 19:00 and 20:00 PM. This figure exceeds the reporting threshold of 180 µg/m³, although it remains far from the alert level of 240 µg/m³, which requires a sustained level for three consecutive hours. The Andalusian Regional Government, through its Environmental Quality Data Center, confirmed the data and urged caution in the face of possible further exceedances.
In Valladolid, the City Council activated 'Preventive Situation 1' after air quality levels exceeded 100 µg/m³ at several monitoring stations for three consecutive days (August 9, 10, and 11), and surpassed 120 µg/m³ on the second day. Although these levels are lower than those in Andalusia, local regulations are stricter. The City Council recommended limiting car travel and using public transportation, especially during the middle of the day.
Puertollano, in Castilla-La Mancha, experienced a more severe situation. On Wednesday, August 12, three of its four monitoring stations exceeded the alert threshold of 180 µg/m³ for one hour, and then remained above the information threshold of 120 for several hours. Health authorities advised at-risk groups, such as the elderly and people with respiratory problems, to stay indoors and avoid strenuous outdoor activity.
What is tropospheric ozone and how is it formed?
Tropospheric ozone is not emitted directly from a specific source, but rather is generated from chemical reactions between precursor pollutants such as nitrogen oxides and volatile organic compounds. For these reactions to occur, intense solar radiation over several hours is essential, something that happens frequently during the summer months. Therefore, episodes of air pollution often coincide with heat waves and clear skies.
The main sources of these precursors include road traffic, thermal power plants, domestic gas boilers, certain industries, and incinerators . The storage and distribution of fossil fuels also contribute. The combination of all these activities, along with adverse weather conditions, explains the spike in levels in urban and peri-urban areas.
It's important not to confuse this ozone with the ozone found in the stratosphere, which acts as a protective shield against ultraviolet radiation. Ground-level ozone, on the other hand, is a pollutant that can irritate the respiratory system and worsen air quality in Spain , especially for sensitive individuals.
Recommendations for the population
In response to these events, health and environmental authorities agree on a series of practical tips. The first is to reduce strenuous outdoor physical activity , especially during the hottest hours, between 12:00 and 19:00. If you exercise, it's best to do so early in the morning or at dusk, when temperatures are generally lower.
For the most vulnerable groups, such as children, the elderly, or people with respiratory or cardiovascular conditions, it is recommended to limit outdoor exposure as much as possible and strictly follow prescribed medical treatments. If you experience symptoms such as a cough, difficulty breathing, or a sore throat, it is best to take refuge in a closed, well-ventilated space.
Furthermore, citizens are being asked to opt for public transport or shared mobility to reduce precursor emissions. In Valladolid, for example, the City Council warned that if these measures are not followed, stricter restrictions could be implemented, such as speed limits or restrictions on the use of private vehicles.
Monitoring and regulations
These episodes are monitored by surveillance networks such as the Andalusian Environmental Quality Data Center and the municipal monitoring stations in Valladolid. These systems operate 24/7 and provide real-time data on pollutant levels. The information is constantly updated and communicated through official channels, such as websites and mobile applications.
Regarding regulations, each autonomous community has its own action plan, but all are based on the limit values ​​established by European and Spanish legislation. For ozone, the threshold for informing the public is set at 180 µg/m³ as an hourly average, while the alert threshold is 240 µg/m³ for three consecutive hours. These values ​​are key to deciding whether to issue a warning or declare an emergency.
Authorities are maintaining active surveillance as long as high temperatures and intense solar radiation persist. The evolution of pollution levels will depend largely on the weather, but also on public cooperation in reducing emissions. The combination of extreme heat and pollution has put several cities on alert, and although the episodes have been subsiding, prevention remains the best tool for protecting everyone's health.
