More than 20 of the busiest streets in Scotland's towns and cities are polluted in breach of safety limits, threatening the health of millions of people, the Sunday Herald can reveal.
Four streets in Aberdeen and three in each of Dundee, Edinburgh and Glasgow are contaminated by toxic concentrations of traffic fumes, according to the latest official air pollution monitoring results for 2013.
There are also dangerous pollution hotspots in Falkirk, Perthshire, Lanarkshire, West Lothian, Paisley and Irvine. In all these places average annual levels of nitrogen dioxide or tiny sooty particles in the air are above agreed levels that should have been met years ago (see table, right).
Air pollution, branded as the "silent killer" by environmentalists, is estimated by doctors to be responsible for four million deaths each year worldwide, and 166,000 deaths in western Europe. One type of particulate pollution on its own is believed to be responsible for 1600 deaths a year in Scotland.
Pollution can trigger heart attacks, aggravate lung diseases and cause infections. Last week a major new study warned that the risks of heart problems could be increased by exposure to pollution below European safety limits, and last year outdoor air pollution was formerly designated as a cause of cancer.
"Fumes from cars, lorries, buses and factories are killing off more people than car crashes," said Emilia Hanna, air pollution campaigner for Friends of the Earth Scotland. Collisions killed 174 people on Scotland's roads in 2012.
The pollution would damage Scotland's international image in the run-up to the Commonwealth Games, Hanna argued. "Potential athletes of the future need clean air, not an increased risk of developing conditions such as asthma."
Hanna called for urgent action "to make Scotland's air fit to breathe" by discouraging polluting vehicles and encouraging walking and cycling.
"Air pollution is like passive smoking," she said. "We do not choose to breathe in this poisonous air - it is inflicted upon us."
Pollution in urban Scotland is monitored by local authorities at busy road junctions and on streets used by pedestrians and residents, then posted online.
The concentration levels have been similar over the last two years, though nitrogen dioxide pollution has worsened since 2012 on Byres Road in Glasgow, Central Road in Paisley and Seagate in Dundee.
Pollution from tiny particles known as PM10s also increased between 2012 and 2013 on Market Street and Wellington Road in Aberdeen; Queensferry Road in Edinburgh; Main Street in Chapelhall, North Lanarkshire; Main Street in Rutherglen; High Street in Irvine; Atholl Street in Perth; West Bridge Street in Falkirk; and West High Street in Crieff.
Alison Galloway, who lives on Byres Road in Glasgow, is worried about the pollution in her area. "It's quite a congested area with lots of traffic queuing at lights, which must be causing the problem," she said.
"People are often enjoying a coffee out on the street - yet at the same time they're being exposed to the high levels of pollution and their health is impacted. They don't realise just how damaging air pollution is because they can't see it."
Sean Semple, an air pollution expert at the University of Aberdeen, highlighted the large amount of scientific evidence linking pollution from tiny particles to breathing problems, heart attacks and strokes. "There are many, many studies from across the globe that have shown a strong association between higher levels of particles in the air and deaths or increased illness," he said.
Breaches of the safety limits in parts of urban Scotland were "worrying" and undoubtedly caused ill health every day, he said. "People with existing heart and lung diseases, such as angina and asthma, will suffer disproportionately when they breathe in these particles."
He pointed out, however, that pollution in cities outwith Scotland was often worse. Air pollution could also be higher indoors in homes where cigarettes are smoked.
Local authorities defended their records by highlighting the measures they were taking to cut air pollution. A spokesman for Glasgow City Council said: "The air quality at all Commonwealth Games venues is expected to meet all our air quality objectives."
He accepted, however, that air quality was "unsatisfactory" in some areas. Action was being taken to reduce emissions, including testing vehicle exhausts, encouraging cycling and using electric cars.
The City of Edinburgh Council described the need to improve air quality as "a massive challenge" but pointed out it was improving in some places and would be helped by the new tram system. "These figures show that there is still much to be done," said the council's transport and environment convener, Lesley Hinds.
Aberdeen City Council recognised the "potential health effects" from pollution, and said it was trying to control traffic and reduce car use. Dundee City Council said there were "exceedances" but pollution wasn't as bad as in 2012.
The Scottish Government insisted it was committed to tackling air pollution, and pointed out that emissions had fallen significantly since 1990. Critics, however, say this is mostly due to the closure of polluting steel plants.
"Our active travel campaign aims to encourage more people to walk or cycle short journeys rather than using the car, where possible," said Environment Minister Paul Wheelhouse. "Mile for mile, it's the short car journeys that create the most carbon emissions. One in three car journeys are under two miles, where engines do not operate at optimal efficiency."
Over £78 million was being invested in cycling and walking projects, Wheelhouse said. "We recognise that more can be done," he added. "That is why we recently consulted on proposals for further action to improve air quality and expect to set out the next steps later this year."