The effect ofCO2on the emission characteristics of Spindt-type molybdenum field emission cathode arrays is investigated. Exposure of active field emitters toCO2results in emission degradation. The degradation ranges from (11.8±3.8)% for 10 L to (77.2±12.6)% for 5000 LCO2exposures. The emission loss results from the formation of molybdenum oxide on tip surfaces, resulting in an increased work function. Work function changes of 0%–7.5% have been measured. The emission changes resulting fromCO2exposures are similar to the effects observed withO2exposures. The emission degradation mechanism is the interaction of oxygen with molybdenum forming surface molybdenum oxides, thus resulting in a higher surface work function and lower emission current. The emission degradation resulting fromCO2exposure is compared to the emission enhancement produced by exposure toCH4.