Sixteen MPs from the western provinces of Khuzestan, Ilam and Kermanshah donned the masks to draw awareness to the plight of their constituents, said official news agency IRNA.
Media reports said many Khuzestan residents have been hospitalised suffering respiratory problems, while schools have been closed for the past week.
Iran is among the worst polluted countries in the world, and a 2011 report by the World Health Organisation listed Khuzestan city of Ahvaz as the most polluted in the world.
Tehran is also known for its poor air quality, because of an altitude ranging from 1,100-1,700 metres (3,600-5,600 feet) above sea level in a basin surrounded by mountains and also due to exhaust fumes from more than four million cars plying the roads of the city.
On Sunday, authorities urged children and the elderly not to venture outdoors as pollution levels peaked in Tehran.
The latest peaks come as sandstorms have lashed the region over the past week.
In 2012, pollution contributed to the premature deaths of 4,500 people in Tehran and about 80,000 across Iran, according to the health ministry.