The heat wave triggers ozone pollution in much of Spain

Roasted and oxidized. The heat wave that crosses Spain, in addition to maintaining high rigor temperatures day after dayhas triggered the levels of contamination by tropospheric ozone (O3), a powerful "cellular oxidant", as defined by the Ministry of Ecological Transition.

During this exceptionally warm episode, the air over the Iberian Peninsula, loaded with gases emitted, for example, by exhaust pipes, is receiving a large amount of solar radiation over many hours. That is the perfect scenario to generate bad ozone.

The "high insolation", as described by the Aemet, which has been heating the air above normal since last Sunday, transforms nitrogen oxides – whose most famous representative is the NO2 expelled by vehicles – and other harmful compounds into ozone . All these rays cause, finally, high levels of this gas to accumulate in the part of the atmosphere closest to living beings: the troposphere. Right where it is harmful.

"It is being a very relevant episode", analyzes Miguel Ángel Ceballos, from Ecologists in Action. Ceballos calculates that "a third of the 500 stations that measure tropospheric ozone in Spain have exceeded the levels of health protection established by the regulations."

That threshold is 120 micrograms per cubic meter of air measured over an eight-hour period that should not be reached more than 25 times a year. In addition, if the hourly average reaches 180 micrograms, an information device must be activated for the population.

According to data offered by the Ministry of Ecological Transition, the worst records to date have been concentrated on Wednesday, July 13, in the city of Madrid. There, in one day, the limits by which the public must be informed were exceeded 11 times. Five of the 13 stations exceeded that level, as compiled by the environmental group. In all of 2021 it had never happened.

In addition, Catalonia, the Community of Madrid, Extremadura, Andalusia and Castilla-La Mancha accumulate a week with rates beyond the legal limit. They stand out, apart from the capital of Madrid, Algete, Coslada, San Martín de Valdeiglesias and Torrejón de Ardoz in that community; the Tona and Vic stations in Barcelona as well as Medina de Pomar (Burgos) and Valderejo (Álava). All of them are affected by the pollution generated in the large nearby cities: Madrid, Barcelona and Bilbao.

"Levels are higher on the outskirts of large cities and rural areas because the photochemical reaction that generates it requires a certain distance," explains the Ministry of Ecological Transition. That is why much lower concentrations appear in urban areas with a lot of traffic. The transport of air from the sources where nitrogen dioxides are emitted causes very high levels of ozone in more remote areas.

This gas in the stratosphere (the layer of the atmosphere between 15 km and 60 km above the surface) is crucial for life on Earth. It acts as a shield against the ultraviolet rays of the Sun. the importance of plugging the hole that opens seasonally in Antarctica. But, when the ozone forms further down, he goes from hero to villain.

In the troposphere, this gas is oxidative for living beings: it attacks cells. In this way, scientists have found that, in the short term, it reduces lung function, causes headaches, fatigue and vascular effects. In the long term, it causes negative effects on the development of the lungs and asthma and induces cognitive alterations. It also increases mortality in chronic patients with diabetes, obstructive pulmonary disease and heart failure. The European Environment Agency attributes between 1,500 and 1,800 annual premature deaths to ozone pollution in Spain.

Ozone thus forms a first-order pollutant, although it goes unnoticed since, despite having a bluish hue, it is not as obvious to the senses as the smoke from a diesel truck. It smells like a storm.

The extreme heat gives no respite. The Spanish Meteorological Agency has warned that the temperatures, day and night, will continue to be very high until next Monday, in a sharp warm wave that has been activated a month after another that was also especially intense: both illustrate the new climate panorama caused from human emissions of greenhouse gases.

"It is an advance in the climate that awaits us as a result of the unstoppable increase in the concentrations of these gases", analyzes in SMC Spain the senior meteorologist of the State Ernesto Rodríguez Camino. Rodríguez Camino maintains that, when the data for this wave is reviewed, "they will tell us that, with the current disturbed climate, the probability of this event occurring has increased with respect to the probability in a hypothetical undisturbed climate."

Climate crisis, heat waves and ozone pollution form a vicious circle. Global warming, as Rodríguez Camino indicated, is multiplying heat waves. These waves bring more solar radiation which, at the same time, generates more ozone in the troposphere. The ozone in that layer is considered the third most powerful greenhouse gas. Add 16% of that effect, according to the European Environment Agency. And the circle is closed.

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