How much dry ice per passenger is allowed to be airlifted without certification?

None. Dry ice is considered a hazardous material for air shipments for two reasons: when it sublimates, the carbon dioxide displaces air and can suffocate the people in the plane, including the crew; and an improperly ventilated container of dry ice can explode. The certification isn't hard to do, but it must be done for any size shipment of dry ice. Additionally, the International Air Transport Association does not allow dry ice shipments larger than 200 kilograms per parcel, and the airline must be informed ahead of time that you're shipping dry ice so they can be sure the vents on the airplane work.