Characterization of a non-thermal plasma source for use as a mass specrometric calibration tool and non-radioactive aerosol charger

Abstract

Abstract. In this study the charging efficiency of a radioactive and a non-radioactive plasma bipolar diffusion charger (Gilbert Mark I plasma charger) for sub-12 nm particles has 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 the working gas compared to a radioactive americium bipolar diffusion charger. The mobility and mass spectrometric measurements show that the generated bipolar diffusion charger ions are of the same mobilities and composition independent of the examined bipolar diffusion charger. It was the first time that the Gilbert Mark I plasma charger was characterized in comparison to a commercial TSI X-Ray (TSI Inc, Model 3088) and a radioactive americium bipolar diffusion charger. We observed that the plasma charger with nitrogen as the working gas can enhance the charging probability for sub-10 nm particles compared to a radioactive americium bipolar diffusion charger. As a result, the widely used classical charging theory disagrees for the plasma charger and for the radioactive chargers with increased aerosol flow rates. Consequently, in-depth measurements of the charging distribution are necessary for accurate measurements with differential or scanning particle sizers for laboratory and field applications.

Aerosol formation and growth rates from chamber experiments using Kalman smoothing

“…Considering the fact that inter-instrument deviations in sub-10 nm sizedistribution measurements can be as large as one order of magnitude (Kangasluoma et al, 2020), the achieved agreement is remarkable, especially as some fluctuations within the chamber can again be reconstructed in both approaches. The retrieved growth rates from the FIKS estimate and the INSIDE method agree remarkably well and both show the increasing growth rates with increasing particle size up to 4.3 nm, an indication for a strong Kelvin effect in organic condensation (Stolzenburg et al, 2018;Tröstl et al, 2016). The decreasing Kalman smoother estimate above 4.3 nm is related to the fact that the FIKS searches for a smooth esti- The FIKS estimate for the formation rate at 1.7 nm and its uncertainty, and the true formation rate.…”

“…Besides the different chemical composition of the growing particles (resulting in different assumptions for the DMAtrain transfer functions) in comparison to the experimental results used in Sect. 4.2, this experiment is characterised by a different size dependency of the growth rate, due to the increased condensation of low-and semi-volatile organics with increasing particle size (Simon et al, 2020;Tröstl et al, 2016). The formation rate, however, remains rather similar to the sulphuric acid-ammonia experiment under these specific experimental conditions, but the slower initial growth rates result in generally lower produced particle concentrations.…”

“…The other DMAs are set to classify particles of 4.3, 3.2, 2.55, 2.2, and 1.8 nm. The instrument kernels are obtained from calibration experiments, where we use the DMA transfer function and sampling loss characterisation from Stolzenburg et al (2017), the CPC activation efficiencies from Wlasits et al (2020), and the charging efficiency was tested to follow the Wiedensohler approximation in Tauber et al (2020). The kernel functions for all seven classified sizes are shown in Fig.…”

Aerosol Charging with a Piezoelectric Plasma Generator

“…Ions can be generated in different ways: of most importance for aerosol measurement are ionizing radiation [13], corona discharge [5], UV radiation (photoelectric effect) [17], and non-thermal plasma discharge [18,19], which is the method this paper focuses on. A plasma is referred to as non-thermal if the atoms are at ambient temperature while the electron temperature is in the range of a plasma discharge (a few thousand degrees Kelvin).…”