Precision characterization of three ultrafine condensation particle counters using singly charged salt clusters in the 1–4 nm size range generated by a bipolar electrospray source

Abstract

Molecular singly charged clusters generated by electrospray sources are commonly used for calibration measurements of ultrafine Condensation Particle Counters (CPCs) in the sub-2 nm size range. This technique has been limited to the smallest singly charged clusters. In this study, we used a bipolar electrospray source combining two electrosprays of opposite polarities to generate singly charged clusters of ammonium salts dissolved in acetonitrile, i.e., tetra-heptyl ammonium bromide (THABr) and tetra-butyl ammonium iodide (TBAI) clusters. A high-resolution UDMA acts as a classifier for positively and negatively charged clusters which are used as mobility standards for the measurement of the complete ascent of the detection efficiency curve of three ultrafine CPCs. The CPCs characterized in this work are two laminar flow-type CPCs using n-butanol (TSI UCPC Model 3776, TSI Inc., Minneapolis, MN USA) and diethylene glycol (DEG) (TSI UCPC Model 3777, TSI Inc.) as working fluid and the turbulent mixing-type DEG-based Particle Size Magnifier (Airmodus A10 PSM). The clusters generated by the bipolar electrospray source are analyzed for their elemental composition using the Atmospheric Pressure interface Time-Of-Flight mass spectrometer (ioniAPi-TOF, Ionicon Analytik GmbH, Austria) in positive and negative ion mode. We present mobility-dependent mass spectra from experiments using the UDMA and the ioniAPi-TOF in series for the analysis of positively charged clusters when operating the electrospray source in unipolar and in bipolar mode to demonstrate the charge reduction and purity of the sample.

Counting on Chemistry: Laboratory Evaluation of Seed Material-Dependent Detection Efficiencies of Ultrafine Condensation Particle Counters

“…Our results for Ag and NaCl are in perfect agreement with the results for a dry aerosol flow ofTauber et al (2019a). AsBrilke et al (2020) highlight, there is no composition dependence of the detection efficiencies of the TSI 3776*. The 50 % cut-off diam-5 eters for negatively-charged Ag seeds presented by the authors are also confirmed by our measurements.…”

“…the TSI 3772, 15 the TSI 3776 and the Airmodus A20, show the expected activation pattern: BCYO x and Ag seeds are activated at smaller diameters compared to (NH 4 ) 2 SO 4 and NaCl seeds. The Airmodus A20 reaches its plateau, located at detection efficiency values of about 0.9 at 20 nm.Astoundingly, the TSI 3776* shows barely no composition dependence of the 50 % cut-off diameters, thereby confirming the results for ofBrilke et al (2020) for Ag seeds. There is no significant difference between the smallest and the largest 50 % 20 cut-off diameter, which are centered around 2.1 nm.…”

“…In order to assess the suitability of the used nano DMA for seed particles with diameters smaller than 2 nm, previous measurements of negatively charged Ag and NaCl seeds using a tuned TSI 3776, the TSI 3777 and a high resolution UDMA (Steiner, 2011) were used. Parts of the results and the used experimental setup were published by Brilke et al (2020). The 5 results of the comparison are displayed in the SI.…”

“…In case of the tuned TSI 3776 (denoted as TSI 3776*), the internal flows were also adjusted. The valve regulating the sheath air flow is adjusted such, that the sample flow rate of the CPC increases to 2.5 lpm (Barmpounis et al, 2017; Brilke et al, 2020).…”

“…Used Instrumentation: The table shows the used particle counters, including their model numbers, the used working fluids as well as the 50 % cut-off diameter as stated by the manufacturers.Table 2. Temperature Settings: The table summarizes the standard temperature settings according to the user manuals of the particle counters as well as empirically derived tuned temperature settings (s. alsoBrilke et al (2020)). …”