The Welsh Government says, from Monday, temporary 50 mph speed limits and other measures will be introduced at five locations on some major roads.
It says the moves are aimed at reducing levels of nitrogen dioxide where emissions exceed legal limits.
Poor air quality contributes to an estimated 2,000 deaths per year in Wales, with exposure affecting vulnerable population groups in particular.
Gases like nitrogen dioxide can increase the symptoms of people with lung diseases, while short-term exposure is associated with increased cardiovascular and respiratory morbidity.
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:
- A494 at Deeside
- A483 at Wrexham
- M4 between Junctions 41 & 42 (Port Talbot)
- M4 between junctions 25 & 26 (Newport)
- A470 between Upper Boat & Pontypridd
Officials say 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.
Evidence shows that nitrogen dioxide emissions are at their lowest when light vehicles, the main contributors to emissions, travel at speeds between 40 and 50 mph.
The speed limits are also expected to have a smoothing effect, with vehicles travelling at more constant speeds.
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.