Dunno about nosebleeds caused by dry air, but when I was a kid I used to have frequent and random nosebleeds. At the time it was caused by a lack of iron (anemia) and I took iron pills for a few years and it went away. When I was an older teen they came back but I immediately went for the iron pills for a couple months and have never had a problem since, nor do I have to take iron pills now.