"Prolonged exposure to tiny particles of soot or dust found in traffic fumes and industrial emissions may be more deadly below current EU air quality limits than previously thought," the authors of the study published in The Lancet say.
The research based on health information from people in 13 countries in Western Europe labels so-called PM2.5 particles the worst offenders.
PM2.5 — a tiny particle under 2.5 microns, or 2.5 millionths of a metre across — is so small that it can lodge deep in the lungs, potentially causing lung and heart problems.
The risk of early death rises by seven percent with every increase of five micrograms of PM2.5 per cubic metre, the Lancet study found.
This was true even after taking into account other factors such as whether people smoked or were overweight.
And while levels of PM2.5 for Spain are not recorded in the Lancet study, the finding is significant for people living in built-up or industrial areas of Spain.
"The level of pollution in Spain depends very much on where you are," Lancet study author Mark Nieuwenhuijsen told The Local.
"Barcelona and Madrid have very high pollution rates because they are very dense, compact cities," said the researcher, who is the Director of Air Pollution Studies at Spain's Centre for Research in Environmental Epidemiology (CREAL).
"In Barcelona this pollution is partly from industry and partly from traffic, whereas in Madrid, traffic is the main problem."
Other areas with pollution problems include the Basque Country and Huelva in southern Spain, both of which have higher rates of industry, Nieuwenhuijsen explained.
European Union guidelines currently set maximum exposure to PM2.5 of 25 micrograms per cubic metre.
But the Lancet study found even in locations where the pollution levels were well below this, there were still higher-than-normal cases of early death.
The study's authors therefore recommend bringing down Europe's PM2.5 standards from 25 per cubic metre to the 10 per cubic metre recommended by the World Health Organization.
"The way to bring down these levels is to look at things from the city-level and encourage policies which promote cleaner energy usage," Nieuwenhuijsen told The Local.
But he admitted it may be difficult to reduce these levels in the current economic climate.
Industry would have to invest in cleaner technology and "that's expensive", he said.
The other key strategy is to put more of an emphasis on clean cars, and encourage people to use public transport or to walk or cycle.
"Don't use face masks," Nieuwenhuijsen added. "They are a waste of time."