There is exactly one (usable) non-flying city in Irallith: the plateau citadel of Irmoth, which contains the gate to the Nexus. A few solitary goatherders occupy some of the higher mountain peaks, but aside from these few places, the land is covered in a poisonous black cloud, and the inhabitants of Irallith stay in the sky.
The most common airship design in use features large sections of transparent canvas along the sides of its envelope, effectively turning the interior areas between the void cells* into a giant greenhouse. A "closed" flier, without such an internal garden, was generally expected to be a pirate or other ne'er-do-well - so there is considerable resistance to adopting more efficient airship designs, even now that imported food from Astaria has made such things possible.
Heavier than air flight designs are mostly limited the gyrocopters used by the mad junk divers; short take off and landings, as well as very low flight speeds, are a requirement for navigating the wreckage, and airship designs are generally too susceptible to wind or simply too large to properly navigate city ruins. A typical junk diver wears a full suit of the same cloth as is used in an airship's void cells, and a backpack bottled air supply. While this is adequate to protect against immediate fatality, it's not a perfect defense against the mist, and junk divers are notorious for going... a bit loopy. Like a spark, but without the genius - just the mad. For this reason, the profession is not a popular one, and junk divers are increasingly rare now that raw materials can be acquired via the Nexus.
Irallith's main export is manufactured goods - while a motor made by Irallith engineers may not put out quite as much force as one from, say, Stygia, it weighs much less, and will run for decades given even the most minimal of maintenance.
* Irallith engineers abandoned gas filled bags as a lift source some centuries ago - the equipment to process and replace lost gas for an inert gas cell proved to be far too heavy and failure-prone, while lighter than air gases that were easy to refine and replace proved to be far too much of a fire hazard. Fortunately, there was an alternative: The famous spark Debby Algworth invented the void cell - a lifting system that operates by evacuating the air from a bag, held within a rigid framework to maintain volume. Of course, this requires that you use a nearly indestructible material to make the bag - but Debby had *that* on hand already. (She'd gotten tired of repairing rips in her children's clothing.)