The effect of long-term exposure to air pollution is associated with increased mortality even when the pollution is below European Union limits, research conducted under the lead of the Utrecht University showed on Monday.

The researchers, led by Utrecht professor Rob Beelen, used data from the European Study of Cohorts for Air Pollution Effects (ESCAPE), which included data from 13 European countries and a total of 367,251 people.

With each increase of 5 micrograms per cubic meter of particulate matter, the risk that someone dies increases by 7 per cent, the study showed.

"This is the difference between a busy street in the city and a place without the influence of traffic," Rob Beelen said in a statement.

The European air quality norm is 25 micrograms per cubic meter but the research showed the risks are still significant under 15 micrograms.

"Our findings show that there are significant health benefits to be gained when the concentrations of particulate matter will be further reduced," Beelen said.

Particulate matter is the collective name for airborne particles that are so small that they penetrate deep into the lungs. The traffic is a major source, but factory plants and heating plants contribute to affect human health.