Aluminum wire can oxidize when exposed to the atmosphere. This can especially be a problem during summer months in areas with high heat and humidity such as the gulf coast area. Alcotech also has some information for calculating the allowable amount of temperature variation between the ambient temperature,humidity and the temperature of the basemetal and electrodes to prevent condensation, which can also form hydrate oxides on the wire.

It pretty much HAS to have some oxides on it. Most of the aluminum wire I have used has been stored for several years befor I used it, but then it wasn't laying ouside in the rain either. I don't do critical work, so there seems to be enough cleaning from the argon to  allow it to work well enough for what I am doing.