Skin: I imagine their scales wouldn't smell but the skin underneath would be like a sweaty pig, from all that flying Breath: Whale blubber and iron.
I remembered this commercial from way back, when I still watched TV. It was the first thing I thought of, when I saw the title to this thread!
Lol. The days of watchng TV are gone for me too! This thread just goes to show what broad depictions of dragons there are. From Clifford to Smaug and the one from Game of Thrones. (Which I have never watched either)
Since dragons are imaginary creatures, I'd say writers should use their imaginations to invent what their breath would smell like. If they breathe fire, chances are their breath would smell of whatever they ate ...but cooked. I don't imagine bacteria have a chance to form in a dragon's mouth, unless they are fire-resistant. So ordinary halitosis (as Clifford suffered from) probably wouldn't be a problem. What fuels the fire would also have an effect. If it swallowed a couple of gallons of petrol, prior to exhaling flames, it would probably smell like Grangemouth on a bad day. On the other hand, if they swallow cedar wood, it might smell really nice. And keep the moths away as well. Who knows? A dragon's breath might actually smell yummy, depending on what they ate. Cows, pigs? Like a barbeque without the sauce? Unless they eat sauce as well. Humans? Humans wearing iron suits of armor? Maybe not so much.
I'd vision it as just a black cloud. Maybe one that hangs in the air for a while. And smells inorganically fart-like. To be fanned away, if possible. Perhaps other dragons don't like their companion's farts much. Maybe a fart would scare a dragon? Or make it unlikely the farter would attract a mate?
Belches and farts both come out of the digestive system, so if a dragon's breath is flammable, one wonders... Make a great surprise attack on the adventurers who think they're being smart by sneaking up behind the dragon.
Have you ever seen a hippo poop? Now imagine a dragon starting a forest fire by doing the same thing with a spray of flaming scat.
Burn wood to hot coals and then pour water on them, that would be it. Burn sand or rock, and flick water droplets on it, that would be it. Any water-based reptile or amphibian has a fish smell. Land-based creatures would have a thin oil over their hide, it would likely varnish over time, and smell of dried oiled hide. Airbourne, hmm. Take a feather and sun-dry it. It has a unique smell, hard to describe, but once you smell it, it will be recognizable for life. Don't burn it! Blehk! Dust. Dust changes its smell when oiled, burnt, dried, or wet. A dragon sleeps, so smells like its den before it showers and shaves. Metallic, definitely. I liked the pennies.
I get sulfur, but why ozone? @Richach You might want to start figuring out what kind of chemical dragon uses to fuel the flame. Naphtha (petroleum)? Greek fire? Sulphur? White Phosphorus? Diesel?
Depends on what you want to fuel the breath. It could be something akin to lighter fluid with little to no scent. It could be a bit more chemical heavy and smell simular to burning plastic or tires. I'd also suggest googling what specific things smell like when burned. You may find your answer there as well.
It is hard to say, isn't it? I could well have just used my imagination but its really about capturing the reader's imagination in a way that they just get it, in the same way that this thread has captured our imaginations. Whatever our final notion it needs to be straight off the bat so that the reader is delighted but moves on with the story. A kind of invisible thrill. Some great little suggestions and theories going on here.
I do not think it would be powerful enough to create significant amount of ozone. At any rate, there are several ways dragon may use to ignite the chemicals, none of which require spark - chemicals may self-ignite in contact with oxygen (or something else - water, for example), or there could be two streams of chemicals which combine and ignite upon contact, or may ignite on impact.
My favorite mechanism (not science at all) is that dragons are just incredibly hot. Hot enough to have boiling blood. The fire is fueled by the ambient “power” (or mana, or whatever).