Riften - human waste, stagnant water, rotting fish
Markarth - smoke, human waste
Windhelm - horse, not much else since the snow would freeze everything. Indoors probably of human sweat though
Winterhold - might be a whiff of strange chemicals coming from the College
Solitude - a sickly mix of too many people wearing clashing perfume who may not have taken a bath recently
Morthal - rotting things, typical swamp smells
Falkreath - human sweat, freshly cut wood
Dawnstar - smoke, fish, salt water, but the cold wouldn't make those smells strong
Riverwood - cut wood, human sweat. Actually comes across as one of the cleaner places.
Crypts - rot and stagnant water
Caves - of whatever last died/lived in them
Great Outdoors - varied
It's worth keeping in mind that noses get saturated easily in addition to your brain tuning out smells. If you live with certain smells our whole life you might not notice them at all. This might nullify a lot of the disgusting people smell, except in special cases where your smell doesn't match your surroundings. Anyway, I felt like adding to the list here:
Riften - Yes, but mix in the smell of fires and moldy wood. The lower areas are also ventilated poorly, so they'd be smokey.
Markarth - Same deal with ventilation. You'd smell whatever burnt, like you said. However, some sections of the city of full of functioning dwemer technology. The keep has steam blasting everywhere, spreading the smell of the metal machinery and whatever oil they use to lubricate it.
Windhelm - I agree, but you'd still smell the fires probably more than the meat. The grey quarter might have its own scents because the dunmer live in cramped conditions and have different habits.
Winterhold - I think you'd mostly smell yourself bundled up against the cold when outdoors.
Solitude - Hehe, never thought of that. You'd probably also smell the sewer. The festival would smell cool with all the effigy burning and spiced wine being passed around. The houses have fireplaces and chimneys, so the bulk of the fire smell would be carried up there, but indoor fires always make houses smell smokey.
Morthal - My thinking too. Also, what do vampires smell like?
Falkreath - There are more coniferous trees there. When it's note extremely cold they smell awesome.
Dawnstar - Yeah, cold. The museum probably has a strange, musty smell.
Riverwood - The sawmill and smith would be very noticeable outdoors because they're big features of the place. Indoors is often lit by fires and candles. The candles probably have a unique scent that would be present in many of the buildings in the game.
Whiterun - You left it off your list, but it has unique buildings. They mostly vent smoke from the firepits and cooking food through the roofs. Since the construction is mostly wood I suspect everything would smell like fire and cooking. From Breezehome you would smell the smith next door. The market would also smell strongly of the food being sold.
Caves - Whatever died is true, but also whatever lives in there. Some of them are very lush. The ice caves would smell less of course.
Crypts - Many of them would just smell musty and dusty. In most cases everything would have been dead for too long to smell like rot. The candles of course would play a big role and special mention must be given to those explosive oil lamps.
Outdoors - Varied indeed! A lot of areas would smell less because of the cold, but the Rift with its rotting leaves and the volcanic areas would probably have very strong scents.
i read somewhere that in the medieval times the garbage was overflowing so much that it got in the way of city defenses. people drank alcohol instead of water because the water was undrinkable. stuff like that.
Here's one to think about: cars were a solution to 19th-century pollution. It's really hard to get up those hills in San Francisco with horse crap coating the streets. And yeah, beer was a solution to a lack of potable water. Just enough alcohol to keep out the bacteria and not enough to have everybody falling over drunk and dying of dehydration. Good stuff.
