The report advised elderly people with heart or breathing problems and young children from staying in the open air, particularly where there was heavy traffic.
The advisory cited dangerous levels of carbon monoxide in the atmosphere, adding that a high level of road traffic due to the start of the new academic year was an important factor.
Tehran is one of the most polluted cities in the world. In January, all schools in the capital and Shahre-Rey, south of Tehran, had to be closed due to extreme air pollution in the region. Earlier this year, officials announced that air pollution in the capital had increased to more than 200 PSI (Pollutant Standards Index) and would top the 233 PSI mark in certain districts. Pollution levels generally fall between 0 to 100 PSI.
Many experts blame the government of not regulating harmful gas emissions by the industrial sector.