As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING THE ENG FOR A SCENE FLIGHT, THE NURSE & MEDIC DETECTED AN UNIDENTIFIED ODOR. ATTEMPTS TO LOCALIZE & IDENTIFY THE ODOR WERE UNSUCCESSFUL & WE ELECTED TO SHUT DOWN WITH NO FURTHER INCIDENT. AFTER ADDITIONAL GND RUN, THE ODOR WAS DETERMINED TO BE DUST & POLLEN IN THE HEATER DUCT. THE ACFT WAS RETURNED TO SERVICE.