Q: Is the price of the Barcelona Card the same on line as it is at the airport? I am concerned about not being able to use it if I buy it on line for the shuttle upon my arrival?
A: Generally speaking the price of the Barcelona Card is the same online as when you buy it in the city. Occassionally there is a small discounted price online depending with who you purchase it with. You should have no problems using your Barcelona Card on the shuttle bus if you purchase your card before you arrive. You just need to make sure that the tourist information office will be open when you flight arrives. If you arrive during office hours for the airport tourist office you will be able to pick up your card from there as it would have been reserved for you. All you need to pick up your Barcelona Card is the purchase coupon you would have printed out when you bought it online and photographic identification.
I would like to clarify something you mentioned. When you say the "Airport Shuttle" do you mean the Express Airport bus to the city centre which is called the Aerobus?. If so, the Barcelona card gives you a 20% discount on the ticket for this service from Terminal 2 and no discount from Terminal 1. However if you take the RENFE train from the airport the entire fare is free to the city centre with the Barcelona Card. The travel times are about the same so if you intend to use the Barcelona card I recommend you take the RENFE train instead.
Here are our information pages on both services follow the links to find out about times of travel, where to catch these services and ticket prices.
Barcelona Airport Shuttle Bus (Aerobus)
Barcelona Airport RENFE train transfer
Barcelona Card Information Page

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