Evacuation of Isfahan. What's Going On?

Yesterday, I saw a couple stories indicating that Iranian officials had ordered the evacuation of the city of Isfahan, a city of 1 and 1/2 million people. (See here and here for instance). Supposedly the evacuation was due to high levels of pollution, but rumors have circulated that it might be due to a radiation leak from a nearby uranium enrichment facility. (See here and here). However, Before Its News indicates that it is a voluntary evacuation, and similar to prior warnings in Tehran when air pollution has become particularly bad. However, I haven't seen anything further from the major media other than the very brief BBC report.