The temporary 50 mph speed limits will be introduced at short stretches of road, between 1.4km to 5.9km in length, at the following five locations:
Poor air quality contributes to an estimated 2,000 deaths per year in Wales, with exposure affecting vulnerable population groups in particular.
Gases such as nitrogen dioxide can increase the symptoms of people with lung diseases, while short-term exposure is associated with increased cardiovascular and respiratory morbidity.
Other measures include increased signage to promote smooth traffic flow.
The measures are expected to deliver immediate improvements to air quality, with emissions estimated to potentially reduce by up to 18% at the five locations.
The temporary speed restrictions are part of a range of actions being introduced by the Welsh Government to improve air quality in Wales, including a new £20m Air Quality Fund, a Clean Air Zone Framework and a new Air Quality website providing local data on air pollution levels.
The Welsh environment minister, Hannah Blythyn, said: ‘I am committed to taking action to reduce air pollution in Wales to support a healthier future for our communities and protect our natural environment. Current levels of nitrogen dioxide exceed the legal limit at the five road locations, so we need to act as soon as possible.
‘We have been carrying out investigations into all potential measures for reducing nitrogen dioxide levels. Our initial studies tell us that 50 mph speed limits should have the greatest potential to improve air quality at each location. The actions we take to improve air quality in Wales have a key role in supporting the right conditions for better health and well-being.’