Characterization of a Non-Thermal Plasma Source for the Use as a Mass Spec Calibration Tool and Non-Radioactive Aerosol Charger

Abstract. In this study the charging efficiency of a radioactive and a non-radioactive plasma neutralizer (Gilbert Mark I plasma charger) have been investigated at various aerosol flow rates. The results were compared to classic theoretical approaches. In addition, the chemical composition and electrical mobilities of the charger ions have been examined using an atmospheric pressure interface – time-of-flight mass spectrometer (APi-TOF MS). A comparison of the different neutralization methods revealed an increased charging efficiency for negatively charged particles using the non-radioactive plasma charger with nitrogen as working gas. The mobility and mass spectrometric measurements show that the generated neutralizer ions are of the same mobilities and composition independent of the charging mechanism. It was the first time that the Gilbert Mark I plasma charger was characterized in comparison to the standard TSI X-Ray (TSI Inc, Model 3088) and a radioactive americium neutralizer. We observed that the plasma charger with nitrogen as working gas can enhance the charging probability for sub-10 nm particles. Consequently, the limit of detection of differential or scanning mobility particle sizers can be increased down towards to smaller sizes with the Gilbert Mark I plasma charger.