The climate crisis will alter sea breezes and threatens more pollution in Barcelona

Climate change will profoundly alter the dynamics of sea breezes in the metropolitan area of Barcelona. This will cause more pollutant gases such as ozone to be retained over coastal areas and increase the health risk for millions of people. This is according to a study by the Institute of Environmental Science and Technology of the Autonomous University of Barcelona (ICTA-UAB), which has projected the evolution of sea breezes and air quality according to the climate change scenarios predicted for 2050 and 2100.

Sea breezes play a crucial role during the summer months: they act as a natural thermal regulator that slows down extreme heat on the coast and, at the same time, function as a ventilation mechanism that helps disperse and move urban pollutant gases from the coastline towards the interior of the territory. This process alleviates pollution in coastal areas, although it also transfers part of the impact to inland areas.

However, simulations from this new study also reveal an unprecedented change in pattern by the year 2100: the wind will tend to move more parallel to the coastline instead of penetrating inland. The study concludes that this will reduce the capacity to transport inland the pollutants emitted in coastal urban areas and will delay their arrival by one to two hours. Therefore, polluted air masses will remain for longer over the most populated areas of the Catalan coast.

According to Gara Villalba, an ICREA researcher at ICTA-UAB and in the department of chemical, biological, and environmental engineering at UAB, polluted air masses will be retained over coastal areas – the most densely populated in Catalonia – which will prolong the population's exposure to dangerous levels of ozone. The main pollutant affected is tropospheric ozone (O₃), an invisible pollutant gas that is not emitted directly, but is formed in the atmosphere from other pollutants – such as nitrogen oxides from traffic and industry – under conditions of high solar radiation and elevated temperatures.

According to the study, the generalized increase in temperatures will modify the structure of the lowest layer of the atmosphere – the boundary layer – and will accelerate the chemical production of tropospheric ozone – a pollutant that is generated from other gases under conditions of high solar radiation and heat–. "The study points to increases of between 5 and 7 parts per billion in ozone concentrations in the central coastal, littoral, and pre-littoral strip during the strongest heat episodes," indicates Sergi Ventura, principal investigator of the study.

Consequences for the public health of the population

Therefore, air pollution is a public health problem, as sea breezes act as a natural thermal regulator and help displace some of the pollutants accumulated on the coast inland. This generates a new public health concern, mainly in urban coastal areas, where prolonged exposure to ozone can cause acute respiratory and cardiovascular problems, especially in vulnerable groups during heatwaves. These results also imply a change in the pollution risk maps for the Barcelona area.

Researchers point out that, when designing future mobility plans and air quality policies, it is no longer enough to reduce the volume of emissions from cars and factories. It is also necessary to "urgently" integrate how global warming modifies the dynamics of our own winds and local microclimatic phenomena.