Butterflies can't take it anymore.
The Mehr news agency quoted a Professor Matin as telling a science conference, "The air pollution in Tehran has made butterflies flee to gardens and parks in the countryside."
Black crows, which are known to thrive in very dirty locales, were reported last year to be leaving the capital because of the filthy air.
The butterflies and the crows may be leaving, but 12 million Tehranis are left behind to breathe the air.
Recent research conducted by the Tehran Municipality and Iran's Environmental Protection Organization concluded that over 80 percent of Tehran's air pollution may be attributed to automobile exhaust fumes.
Winter is the season of limited air movement over the capital when pollution tends to rise to dangerous heights.