Is it permissible for me to combine the Dhuhr and Asr prayers by performing them earlier (jama' taqdeem) when traveling, knowing that there will be time to perform the Asr prayer at the airport, but with some difficulty due to the lack of a prayer room?

A traveler is not permitted to combine prayers until after they have embarked on their journey, based on the Almighty's saying: "And when you travel throughout the land, there is no blame upon you for shortening the prayer." If prayer time overtakes them before that, they should pray it at its appointed time. They are permitted to pray it at the airport or any clean place, according to the Prophet's (peace be upon him) saying: "The earth has been made for me a place of prayer and purification, so wherever a man from my Ummah is overtaken by prayer, let him pray."