Questions & Answers about Soğuk havada kalınca çok hapşırıyorum.
Because Turkish uses the locative case here.
- hava = weather / air
- havada = in the weather / in the air
The sentence is describing the situation or environment where the sneezing happens, so Turkish marks that with -da / -de.
This is very common:
- evde = at home
- okulda = at school
- soğuk havada = in cold weather