The fog has become a part of the normal life in Istanbul. Don’t get me wrong, it’s not a daily basis thing but when all the factors in the atmosphere are just right you can get the thickest fog possible. Of course our fogs are not as famous as the London ones.
So when the fog lays over the city you can consider that we all go through a chaos as everything basically stands still. The public steam ferry boats stop working along with most sea transportation. Even the traffic is affected. Of course the air traffic as well so I hope you won’t be in the plane when it happens.
But I must say when the fog lays itself on the city what you observe is exquisite, the photos you can take are priceless. As documented above you can see that the Bosphorous Bridge (opened to public in 1972) has been lost in fog and the atmosphere is just lovely. I do hope during your stay you get to experience the fog over Istanbul.