Air quality across Europe is slowly improving, but harmful emissions remain stubbornly high in some countries, according to a study released Monday by the European Environment Agency.
The Copenhagen-based agency calculated that air pollution caused more than half a million premature deaths across Europe in 2015 — mostly from tiny airborne particles known as PM2.5.
However, improvements in air quality mean the number of premature deaths is about half the level it was in 1990, the European Union agency said.
"Air pollution is an invisible killer and we need to step up our efforts to address the causes," said the agency's head, Hans Bruyninckx. Europe must "redouble its efforts to reduce emissions caused by transport, energy and agriculture and invest in making them cleaner and more sustainable," he added.
The European study was an updated overview and analysis of the air quality across 28 European Union countries and 11 non-EU countries from 2000 to 2016, the most recent year for which data was available.
The data, collected by over 2,500 monitoring stations across the continent, found that road traffic continues to be one of the main sources of Europe's air pollution, with nitrogen oxide from diesel cars particularly prevalent in major cities such as London and Paris and in large parts of Germany and Turkey.
Levels of nitrogen oxide, or NOx, have declined since the start of the century, due in part to better filtering of the harmful gas. European automakers are under pressure from governments and the EU to further reduce their NOx emissions in the wake of revelations that some manufacturers were cheating in tests.
The EEA study also revealed that the highest concentrations of PM2.5 are in northern Italy, Poland, the Balkans and Turkey.
The Mediterranean region, meanwhile, recorded particularly high levels of toxic ozone, which is formed from chemical reactions of NOx and sunlight.
The EEA's warning was echoed by a report also released Monday by the World Health Organization, which cited the particular danger to children from air pollution.
The U.N. health agency concluded that, worldwide, indoor and outdoor air pollution contributed to respiratory tract infections that resulted in 543,000 deaths in children under the age of 5 in 2016. Children were particularly at risk in poor countries, where indoor use of wood or coal-fired stoves is common, WHO said.
"The enormous toll of disease and death revealed by these new data should result in an urgent call to action for the global community," the Geneva-based organization said.
Frank Jordans contributed from Berlin.