Air quality in Europe has improved considerably over the last two decades. However, despite improvements in air quality, 86% of the European population lives in areas that exceed the annual limits recommended by the WHO for nitrogen dioxide (NO2), a pollutant caused mainly by cars. Furthermore, 98.10% of the European population suffers from excessive levels - according to the WHO - of suspended particles PM2.5 (with a diameter less than 2.5 microns), a pollutant that is produced in very diverse sources (residential uses, industry, transportation or natural origin).
The results come from a study led by the Barcelona Institute for Global Health (ISGlobal), a center promoted by the "la Caixa" Foundation, and the Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS).
The study analyzed daily air pollutant concentrations (PM2.5, PM10, NO2 and O3) in a wide range of European regions between 2003 and 2019.
The goal was to evaluate the number of days exceeding the 2021 World Health Organization (WHO) guidelines for one or more contaminants.
The research team analyzed pollution levels in more than 1,400 regions in 35 European countries, representing 543 million people.
The results, published in Nature Communications, show that global levels of suspended particulate matter (PM2.5 and PM10) and nitrogen dioxide (NO2) have decreased in most of Europe.
Specifically, PM10 levels decreased the most during the study period, followed by NO2 and PM2.5, with annual decreases of 2.72%, 2.45% and 1.72%, respectively.
On the other hand, levels of ozone (O3), a secondary pollutant that forms in the lower layers of the atmosphere, increased annually by 0.58% in southern Europe, which multiplied by almost four the number of days with poor air quality.
The study also looked at the number of days in which limits for two or more pollutants were exceeded simultaneously, a confluence known as a "composite pollution day."
Despite overall improvements, 86.3% of the European population experienced at least one day per year with composite pollution (at least two pollutants) during the study period The combinations of PM2.5-NO2 and PM2.5- O3 were the most common.
The results highlight significant improvements in air quality in Europe for PM10 and NO2, while less for PM2.5.
But above all, the situation regarding the O3 is worrying.
In any case, the high number of people exposed to levels of unclean air is of concern. "Specific efforts are needed to address PM2.5 and O3 levels and associated composite pollution days, especially in the context of rapidly increasing climate change threats in Europe," says Zhao-Yue Chen, researcher at ISGlobal and lead author of the study.
"Our estimate of population exposure to composite air pollution events provides a solid basis for future research and policy development to address air quality management and public health concerns across Europe," says Carlos. Pérez García-Pando, ICREA and AXA Research Professor at the BSC-CNS.
The analysis shows that around 98.10%, 80.15% and 86.34% of the European population lived during the study period in areas exceeding the WHO recommended annual levels of PM2.5, PM10 and NO2, respectively.
These results are largely in line with estimates by the European Environment Agency (EEA) for the 27 EU countries using only urban station data.
No country met annual ozone (O3) guidelines during the peak season of 2003 to 2019.
Regarding short-term exposure, more than 90.16% and 82.55% of the European population lived in areas with at least 4 days exceeding the WHO daily guidelines for PM2.5 and O3 in 2019, while the figures for NO2 and PM10 were 55.05% and 26.25%.
During the study period, PM2.5 and PM10 levels were highest in northern Italy and eastern Europe, while PM10 levels were highest in southern Europe.
Elevated NO2 levels were observed mainly in northern Italy and in some areas of Western Europe, such as the south of the United Kingdom, Belgium and the Netherlands.
Similarly, O3 increased by 0.58% in southern Europe, while it decreased or showed a non-significant trend in the rest of the continent.
On the other hand, the most significant reductions in PM2.5 and PM10 were observed in Central Europe, while in the case of NO2 they occurred mainly in urban areas of Western Europe.
The average exposure time and the population exposed to days with PM2.5 and O3 pollution is much greater than in the case of the other two pollutants.
According to the research team, this highlights the urgency for greater control of these pollutants, as well as the importance of addressing the growing trend and impact of O3 exposure.
"Ozone management presents a complex challenge due to its secondary formation pathway. Conventional air pollution control strategies, which focus on reducing emissions of primary pollutants, may not be sufficient to effectively mitigate high levels. of O3 and the days with associated composite pollution," says Joan Ballester Claramunt, ISGlobal researcher and senior author of the study.
However, "addressing climate change, which influences ozone formation through increased sunlight and rising temperatures, is crucial for long-term ozone management and the protection of public health," Add.
Despite improvements in air pollution, the research team reported that more than 86% of Europeans experienced at least one day with compound pollution each year between 2012 and 2019, where multiple pollutants exceeded WHO limits simultaneously.
Among these, the contribution of pollution days composed of PM2.5-O3 increased from 4.43% in 2004 to 35.23% in 2019, becoming the second most common type in Europe, indicating a worrying trend.
This phenomenon occurs mainly at lower latitudes during warm seasons and is probably related to climate change and the complex interaction between PM2.5 and O3.
