Air pollution is estimated to have killed nearly 10,000 people in Tehran over a one-year period, including 3,600 in a month, Iranian officials say.
Tehran is one of the world's most polluted cities
Most of the deaths were caused by heart attacks and respiratory illnesses brought on by smog, they said.
The scale of the problem led one senior official to say living in the Iranian capital was like "collective suicide".
Cheap fuel encourages car use in Iran, correspondents say, and many vehicles do not meet global emissions standards.
"It is a very serious and lethal crisis, a collective suicide," the director of Tehran's clean air committee, Mohammad Hadi Heydarzadeh, told an Iranian newspaper.
"A real revolution is needed to resolve this problem."
He said air quality had worsened and was linked to some 3,600 deaths in October. Many of the deaths were caused by heart attacks brought on by the air pollution.
New figures showed a sharp rise in pollution-related deaths in Iran, where 9,900 people died of pollution in the previous Iranian year (March 2005 to March 2006).
The latest assessments were based on World Bank figures which extrapolate mortality rates according to certain levels of pollution.