Nearly a third of Europe's urban population is exposed to air particles that breach European Union limits, an official report said Monday.

The figure more than triples if a UN health benchmark is used.

In 2010, 21 percent of residents of European towns and cities breathed air with concentrations of so-called PM10 fine particles that breached the most stringent daily EU limits, the European Environment Agency (EEA) said.

PM10 are particles that are 10 micrometres, or 10 millionths of a metre (0.0004 of an inch) across.

But more dangerous are PM2.5 particles, which are four times smaller and able to lodge deep into the lungs and even cross into the bloodstream.

On this score, around 30 percent of urban dwellers were exposed to PM2.5 levels that were above EU levels, which are based on an annual measure rather than a daily one, the EAA said.

By the yardstick of the higher air-quality standards set by the UN's World Health Organisation (WHO), 81 percent of urban residents were exposed to excessive levels of PM10 particles and 95 percent to excessive levels of PM 2.5, the EEA.

The particles are contained chiefly in vehicle exhaust gases in towns and cities, and industrialised regions of central and eastern Europe had the highest readings.

The good news is that emissions of "primary" PM10 and PM2.5 -- particles released directly into the air, as opposed to indirectly -- decreased by 15 percent between 2001 and 2010.

"European Union policy has reduced emissions of many pollutants over the last decade, but we can go further," said the EEA's executive director, Jacqueline McGlade.

"In many countries, air pollutant concentrations are still above the legal and recommended limits that are set to protect the health of European citizens. In fact, air pollution reduces human life expectancy by around two years in the most polluted cities and regions."