A319
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 115; Flight Crew Total 15000; Flight Crew Type 1595
Physiological - Other
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Returned To Gate; General Maintenance Action
Aircraft
After pushback from gate in ZZZ we taxied to runway XX and were caught up in a lot of ground traffic congestion from a thunderstorm that had prevented take offs and landings. While sitting on the taxiway in line for our delayed takeoff; we noticed a smell that we had noted after engine start and initial taxi was becoming more irritating and slightly caustic to us. We called the flight attendants to see if they noticed the smell and initially they did not but later as they walked the cabin closer to the cockpit noticed the smell also. We made a write up in the logbook and broke the MRD (Maintenance Release Document). We then called Maintenance Control and talked to the Airframe Controller who said to return to the gate for further investigation by Maintenance and turn off bleeds and packs. We told the Tower that we needed to return to the gate and he began to move aircraft as able to allow us to proceed back to the gate. We donned oxygen masks as a precaution and taxied back to the gate without incident. At block in; Maintenance met us and we filled out a form for Maintenance to help identify the source of the sour smell. I also notified the Duty Manager as per the FOM. There was no ensuing discussion with the Duty Manager regarding the odor from an unknown source; only discussion regarding crew legality.
[Report narrative contained no additional information].
A319 flight crew reported a ground return to gate due to caustic odor throughout the aircraft while waiting in line for takeoff.