The reading means all members of the society are exposed to risks from air pollution and sensitive groups such as people with heart and lung diseases as well as children and pregnant women should avoid severe physical activity or any physical activity for a long period of time outside the house.
Air quality assessment shows suspended particles are creating the problem.
Pollution in Iranian cities is also worsened by drought and dust particles that officials say mainly enter the country from Afghanistan in the east and Iraq in the west.
The issue has been at its worst over the past days in the southern and southwestern provinces where schools and government were office were shut down.
