I flew ONT-PDX round trip at the height of the fires in both places. The fires aren't near enough to either airport to have any real effect on turbulence. On top of that, the smoke in PDX is finally getting cleared out by a wind change and is finally down from "beyond hazardous" (monday) to "unhealthy for sensitive groups" (today, and typical of a hot los angeles summer day). Big fires can produce pyrocumulus clouds that probably have a lot of turbulence, but they tend to be very localized and easy to fly around.

You will get a very strong smoke smell while flying in the smoke - planes change out half the air every ~3 minutes or so, and smoke is extremely difficult to filter out. Places that run cleanrooms for things like semiconductor fab will shut them down during smoke events. Once you're above the smoke it will clear out quickly.

Alaska cancelled all of their flights out of PDX for one day (monday) this past week. Not because it's not safe for the planes, but because it's not safe for people. The air in PDX was over 400 (and sometimes over 500) AQI, which is hazardous for ground crews working outside. The airport also isn't filtered all that well - it's better than outside, but not by a lot. The air can also be worse up high if the smoke is thicker - it was particularly bad from about 10K feet to about 5K feet on my way into PDX last thursday, but wasn't quite as bad on the way out this past tuesday.

As far as the effect on engines- they fly firefighting aircraft at very low altitudes in smoky environments all the time. I've been watching, both live and on adsbexchange, as they send bunches of aircraft to put water and retardant on the Bobcat fire in the Angeles National Forest. If smoke were hazardous to the engines there's no way they could fly safely the way they do. The helicopters are all turbine powered and fly in the worst conditions. They're also flying a variety of fixed wings: a couple DC-10s, a couple DC-9s, a bunch of RJ-85/BAe-146, a couple C-130s, at least one P3, and some S2Ps, all as air tankers. Plus a variety of twin turboprops for lead planes, IR survey, and local air traffic management in the drop zones. At times the fixed wings are only a few hundred feet above the local ground level and can't avoid ingesting some amount of smoke. There's a list of most of the aircraft that get used in California forest fires here: CalFire Aircraft ID

Unfortunately the PDX fires weren't creating any unstable weather - that might have helped clear out the smoke. Instead, the smoke just hung over Portland (and most of the rest of western Oregon) for a week with horrifically bad air quality. There's finally a breeze and some humidity coming in off the ocean to clean some of it out and also help suppress what's left of the western bits of the fires.