Air pollution is killing more people every year than smoking, according to research published on Tuesday that called for urgent action to stop burning fossil fuels.
Researchers in Germany and Cyprus estimated that air pollution caused 8.8 million extra deaths in 2015 - almost double the previously estimated 4.5 million.
The World Health Organization (WHO) estimates smoking kills about 7 million people a year globally.
The researchers found that in Europe - the key focus of the European Society of Cardiology research - air pollution caused an estimated 790,000 deaths, between 40 and 80 percent of them from cardiovascular diseases such as heart attacks and stroke.
"Since most of the particulate matter and other air pollutants in Europe come from the burning of fossil fuels, we need to switch to other sources for generating energy urgently," said co-author Prof. Jos Lelieveld, of the Max-Plank Institute for Chemistry in Mainz and the Cyprus Institute Nicosia, Cyprus.
"When we use clean, renewable energy, we are not just fulfilling the Paris Agreement to mitigate the effects of climate change, we could also reduce air pollution-related death rates in Europe by up to 55 percent."
The study, published in the European Heart Journal, focused on ozone and the smallest pollution particles, known as PM2.5, that are particularly harmful to health as they can penetrate into the lungs and may even be able to cross into the blood.
The researchers said new data indicated the hazardous health impact of PM2.5 - the main cause of respiratory and cardiovascular disease - was much worse than previously thought.
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They urged a reduction in the upper limit for PM2.5 in the European Union, which is currently set at 25 micrograms per cubic metre, 2.5 times higher than the WHO guideline.
"In Europe the maximum permissable value ... is much too high," said Lelieveld and co-author Prof. Thomas Munzel, of the Department of Cardiology of the University Medical Centre Mainz in Germany, in a joint statement.
"In the USA, Australia and Canada the WHO guideline is taken as a basis for legislation, which is also needed in the EU."
Worldwide, air pollution caused 120 extra deaths in every 100,000 people per year, with deaths in parts of Europe at an even higher rate of up to 200 in 100,000.
"To put this into perspective, this means that air pollution causes more extra deaths a year than tobacco smoking," said Munzel.
"Smoking is avoidable but air pollution is not."