thousands of people will be exposed to dangerous levels of air pollution in Scotland's towns and cities for years to come because of the Scottish Government's failure to cut traffic fumes, ministers have been told.

The Scottish Environment Protection Agency (Sepa) has warned that revised targets to reduce air pollution – already postponed for up to a decade – will be breached because not enough is being done to curb vehicle exhaust emissions.

As a result, people in Glasgow, Edinburgh, Aberdeen, Dundee and other urban areas will keep breathing in toxic gases, which can damage their lungs, blood and immune systems. According to the Institute of Occupational Medicine, air pollution kills more than 600 people a year in the central belt.

An analysis by the Sunday Herald has revealed that European Union (EU) safety limits for nitrogen dioxide, one of the main vehicle exhaust fumes, were breached at 12 sites in urban areas across Scotland in 2011. As well as the four big cities, they included Perth, Paisley, Kirkintilloch, East Kilbride and Broxburn.

The safety limits were first agreed in 2001 and were meant to have been met by 2010. But new official figures show that, averaged out over all of last year, concentrations of nitrogen dioxide in the air near busy roads were often well above the limit of 40 micrograms per cubic metre.

By far the worst pollution was measured in the centre of Glasgow on Hope Street, followed by Corstorphine in Edinburgh and Atholl Street in Perth (see table above). Only a limited number of sites are monitored, so there are likely to be other places just as polluted.

Scottish ministers have applied to the EU for permission to delay complying with the safety limits, suggesting that they can be met in Aberdeen and Dundee by 2013, Edinburgh by 2015 and Glasgow by 2020.

But in a submission to ministers, Sepa has described these targets as "very ambitious". It pointed out that in recent years pollution in some areas had been getting worse, and was spreading.

There had been "little or no demonstrable improvement in air quality" over the last 10 years in areas targeted for action by local and national government, Sepa said.

In Glasgow, monitoring at new locations was uncovering "new exceedances" and there were problems with emissions from old buses and taxis which were "largely unregulated". According to Sepa, "it is unclear how Glasgow will comply with the limit values by 2020".

Sepa made its submission last August in response to a Government consultation, but it has only just come to light. Environmental groups have praised the agency for its tough stance.

Dr Dan Barlow, head of policy at WWF Scotland, sad: "It is shocking that the Government is seeking EU approval to delay meeting these targets until as late as 2020.

"It is even more alarming that the government's own environment watchdog doesn't have confidence that the plans proposed will be sufficient to meet such extended deadlines."

The Scottish Government accepted that there were "localised" areas of poorer air quality, though overall pollution had been reduced significantly in the last 20 years.

A spokesman said: "We are committed to achieving continued improvements in air quality and are working with Sepa and local authorities to see this happen."

The Government is expecting to hear later this year whether the EU would permit the postponement of its pollution targets.

The Convention of Scottish Local Authorities declined to comment.

Figures show the hourly mean for 2011. The pollution limit is 40 micrograms per cubic metre (annual hourly mean) Source: