Q: Can I use the same ticket fo travel from Barcelona Airport to Barcelona Nord Bus station? My final destination is Tossa del Mar and I need to catch a bus from Nord station to get there.
A: Yes you can use the same ticket but you need to know which ticket and you also need to know which means of transport to use.
If you intend to only make one journey from the airport to the bus station then the cheapest ticket would be the T Dia which cost €6.95 and is valid for only 1 day of travel. With this ticket you can take either the RENFE airport train to Clot in the city centre and then change for the red line metro to go to Arc de Triumf which is right next door to the Nord train station.
Alternatively if you intend to return to Barcelona airport from Nord station is would be best to purchase the T10 Zone 1 travel card. This card is valid until 31 January of each year and you can take 10 journeys on the metro / bus or airport RENFE train during this time. A journey will last 1 hour and 15 minutes. Therefore you could use the T10 for both your outward and inward journey to Barcelona airport. The price of the of the T10 is €9.80. The journey from the airport should be well within the 1 hour and 15 minutes maximum journey time of the T10 so you will still have 8 other journeys around Barcelona on the metro or buses if you need them.