Air pollution linked to breathing difficulties, including asthma flare-ups, is close to breaching EU safety limits in areas where homes are close to the M50 motorway, new tests show.
On certain days, the amount of nitrogen dioxide (NO2) in the air exceeds the safety threshold, but results are averaged over a year, which keeps the overall result within permissible levels.
High levels of NO2 were detected in parts of Castleknock, Cherry Orchard, Tallaght and Palmerstown - all residential areas with homes bordered by the M50.
Nitrogen dioxide is produced by burning fuel and is prevalent in areas of heavy traffic.
At high levels it can cause a range of throat and lung problems, contribute to the development of asthma and aggravate existing asthma. Children and the elderly are particularly vulnerable.
Green Party councillor Roderic O'Gorman, who obtained the test results, said it was a concern that many residents were living in areas with poor air quality, particularly as traffic levels on the M50 were increasing.
"It's one thing if you're passing through a polluted area but these people are living, working and playing here so they can't escape it," he said.
"The Environmental Protection Agency (EPA) estimates that 1,200 people die prematurely due to air pollution every single year.
"That's a huge number of people but we don't have campaigns to draw attention to it like we do with other causes of premature death."
Under EU regulations, NO2 should not exceed 40 micrograms per cubic metre, averaged over a year, or 200 micrograms per cubic metre in an hour on 18 or more occasions during a year.
Testing by the EPA earlier this year revealed that heavily congested areas within Dublin city centre showed indications of being in breach of the limits and, based on that data, the EPA said it suspected there may be problems along the M50 too.
Transport Infrastructure Ireland (TII) has begun testing at 34 points along the M50.
It is putting the results online and will continually update the findings. Records for the June-December 2018 period and from January to May this year are currently available.
They show that on numerous occasions in at least six locations, N02 levels have breached the 40 microgram limit, reaching almost 60 micrograms at times. Winter months are the most problematic.
If breaches persist and EU regulations are broken, local authorities must devise action plans and come up with interventions to improve air quality which could mean having to restrict traffic.
TII said testing would be continued. It added eight more NO2 monitoring stations had recently been installed around the northern and southern entrances to the Dublin Tunnel, including two in residential areas, and results from those would be added to the website.
TII spokesman Sean O'Neill said better traffic flow would help ease NO2 emissions.
"One of the problems is congestion, with engines idling and emissions building up, so if we can improve that, we can improve air quality," he said.