An orange alert for heavy pollution was issued by the Tehran branch of the Iranian National Disaster Mitigation Organization (NDMO) as it recommended all citizens in the city, especially people with debilitating diseases, to stay indoors for the entire Wednesday.
The level of fine particles measuring 2.5 micrograms or PM2.5 was 173 micrograms per cubic meter of air in Tehran as of 8 p.m. local time, according to figures by Tehran Air Quality Control Company.
The figure is nearly three times above the 24 hour acceptable limit of 60 micrograms per cubic meter of air.
Plunging temperatures have exacerbated pollution in large cities in Iran in recent days. The thermometer hit 1 degree Celsius (33.8 degrees Fahrenheit) early on Tuesday in Tehran.
The PM2.5 measure reached 155 micrograms per cubic meter of air in Tabriz, an industrial city in northwestern Iran.
The NDMO has announced emergency measures to prevent a worsening of the pollution in Tehran and other cities, including curbs on construction and certain manufacturing activities as well as measures to control vehicle emissions in crowded urban areas.