Date: 202011
Local time of day: 1801-2400
Location: ZZZ1.ARTCC, US
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ1
ATC / advisory: Center ZZZ1
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Just prior to level off at FL370 FO and I decided we should go back to FL 350 for wider margin. As we were about to descend from FL357 back to FL350 we heard a squealing noise which turned to a vibration followed by smell of acrid smoke. Donned O2 masks and advised ATC and new destination of ZZZ. FO was flying Pilot and remained so. I ran checklists and accomplished communications with Dispatch and company.[Captain theorized possible cause] a blower motor failed.


Second narrative: Passing through FL355 on the way to FL370 (cruising altitude); we were talking about the bad ride and the tight allowance on the speed tape and decided to request and make FL350 our final. We received clearance and started down when we heard an unusual and loud noise. It seemed to be coming from underneath my oxygen mask area. A heavy and acrid smell of electrical burning hit us at the same time and we immediately went on oxygen and established communication. The Captain went to the Quick Reference Card and started running the checklist. I was looking at our close proximity to ZZZ and I heard 'LAND ASAP' and asked him if he was alright diverting to ZZZ (about 70-80 NM away). It was my aircraft and radios; so I advised ATC (ZZZ1 Center) and asked for immediate vectors to ZZZ with the intent to divert and land. We were given direct and cleared to FL240; then 11;000. By the time the Captain completed all of his tasks; I had us on a modified downwind and briefed him on our situation and asked him to brief ILS 33 for me. He mentioned my airspeed (308 knots below 10;000) and I told him I was using that airspeed to expedite our descent. The approach was stabilized and landing was uneventful; otherwise. We had CFR meet the aircraft immediately after landing and they cleared us with no signs of smoke and/or fire. We taxied to the gate with a CFR escort to ensure maximum safety. ZZZ ops and personal were fantastic and very professional. In my opinion; we immediately went to our training for a successful outcome and I believe we got everything done in a relatively short amount of time and stayed safe throughout the event.We can't necessarily prevent this type of event in the future and I believe it will be an unpopular opinion; but more training using the oxygen masks would benefit the pilot group. They are uncomfortable the captain running the checklist while inhaling with a hot mic was so loud I couldn't hear ATC at times. Movement of hot mic off while breathing greatly improved our communication.


Synopsis: A321 Captain reported noticing a 'smell of acrid smoke' during cruise resulting in a diversion.