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Check out the time tables for the 16 group of busses and 41 group of busses - these go to the airport. They will give you an idea of where they go by.
Just be aware that the 16 is an extremely long route that starts in Rathfarnham and travels across the City Centre to get to the Airport. Even though there are bus corridors for part of the way, it can still be a very long journey. I would avoid any areas on its route that are South of the Liffey and just concentrate on the North side. Unless you want to spend half your life commuting.