ERJ 145 First Officer reported smoke in the cockpit during descent which eventually dissipated. Flight continued to destination and landed safely.

Narrative

We had flown this exact plane in; the night before with no issues. Before start until climb were uneventful. Upon completion of the climb checklist we noticed a cyan Pack 2 valve closed" message on the EICAS. I turned off and on pack 2 and the message would go away for a few seconds and then flicker on and off the EICAS screen before retuning to stay on. We reset the pack twice and both times this would happen to the EICAS message. We ran the pack closed QRH and informed dispatch of the anomaly and the intent to continue to ZZZ at 24;000ft. Dispatch sent new number for the cruise altitude and confirmed our decision to continue. ICE test B was completed and passed after this troubleshooting. Cruise was standard. Shortly before TOD (Top of Descent) we were in and out of clouds at 24;000ft. We encountered light icing in these clouds and received the "Ice condition" EICAS message. All the bleeds opened as normal. We were in and out of icing conditions as we began our descent. Shortly after beginning the descent we noticed a burning smell; like a bonfire or ash; in the cockpit. A few seconds later the flight attendant called and asked if we smelt that. The captain asked the flight attendant to check the cabin and cargo peephole in the lavatory to see if we could identify the smell. While the flight attendant was checking the cockpit began to get hazy and fill with smoke. It was a slow process and there was no visible source of where the smoke was coming from. At that time the captain told me to put on my oxygen mask and that he was advising ATC. The captain requested priority handling with ZZZ center and sent a message to dispatch informing them of the situation and the intent to land in ZZZ. I grabbed my oxygen mask out of its box and when I went to put it over my head realized that the rings that go over and around my head had been installed upside down relative to the oxygen mask. I made multiple attempts to see if the mask was just twisted or if I could move the over head portion of the mask right side up but it would not move. I was able to find an angle where I could get the mask over my head however it was not a perfect seal and it made it hard for the mask microphone to pick up my voice without me holding up the mask. This took up roughly 60 seconds of my time. Once I had my headset back on we ran the smoke fire fumes QRC and began the accompanying QRH. At this point the smoke was dissipating in the cockpit and not continuing to get worse. We did not put on the smoke googles as the amount of smoke in the cockpit was not enough to justify the extra distraction of putting on the googles so close to the airport. As I was running the QRH the captain; who was still pilot flying; had spoken to ATC and began an expedited descent initially to 16000 feet. We determined it would be best to continue straight into ZZZ as we were less than 50 miles away. ATC asked if we wanted runway XXR which we accepted. Initially we were setup for XYR so at this point the captain had asked me to set up for the ILSXXR. I took a pause from completing the QRH to get the plane ready for the approach. ATC switched us from center to approach and we were cleared down to 2000ft. Due to the expedited descent by the time I was able to return back to the QRH we were already below 10000ft and maneuvering for final to runway XXR. Due to the unknown location of the fire there is a long list of QRH actions and I felt like continuing the QRH would be too much of a distraction this low and close to the runway. The captain agreed and we took this time to get on a stabilized approach; brief each other and the flight attendant on the landing/evac plan. The captain made the decision that we would evacuate the aircraft after landing. Approach switched us to tower and we were cleared to land on XXR. As we got closer to the runway we could see the configuration of the emergency equipment. Originally the plan was to stop on the runway and use all doors to evacuate. As we got closer the captain thought it would be better to exit the runway on an open taxiway and exit through the forward door. Landing was uneventful. After landing we called the flight attendant to update the evacuation instructions. We came to a stop on a taxiway parallel to the runway and ran the emergency evacuation checklist. All passengers evacuated through the forward entry door. The captain called Dispatch and I worked with ARFF (Airport Rescue and Firefighting) and the flight attendant to make sure the passengers were in a safe location and accounted for. Once ARFF and Maintenance confirmed there was no active fire we got all the passengers onto a bus and the plane connected to a tug. The captain and I rode on the plane under tow back to the gate where all the passengers retrieved their belongings and exited into the terminal."