Finnish Air Force did "sample gathering flights" with a BAE Hawk on request by traffic safety bureau. Pilot didn't need to eject but evidently findings were worrying enough that the authorities chose to close entire aerospace soon after. Earlier the day some Air Force Hornets had accumulated dust in engine intakes. Volcanic ash was also found on Vinka L-70 basic trainers (piston powered). If the ash can be found on a basic trainer, I can imagine any GA flying at lower levels is in risk.
Ref. Article in finnish (google translate isn't entirely incorrect):
Ilmavoimien koneet hakivat nytteit - HS.fi - Kotimaa