Humidity effects on the detection of soluble and insoluble nanoparticles in butanol operated condensation particle counters

Abstract

Abstract. In this study the impact of humidity on heterogeneous nucleation of n-butanol onto hygroscopic and nonabsorbent particles was investigated using a fast expansion chamber and commercial continuous flow type condensation particle counters (CPCs). More specifically, we measured the activation probability of sodium chloride (NaCl) and silver (Ag) nano-particles by using n-butanol as condensing liquid with the size analyzing nuclei counter (SANC). In addition, the cut-off diameter of regular butanol based CPCs for both seed materials was measured and compared to SANC results. Our findings reveal a strong humidity dependence of NaCl particles in the sub-10 nm size range since the activation of sodium chloride seeds is enhanced with increasing relative humidity. For Ag seeds this humidity dependence was not observed, underlining the importance of molecular interactions between seed and vapor molecules. Consequently, the cut-off diameter of a butanol based CPC can be reduced significantly by increasing the relative humidity. This finding suggests that cut-off diameters of butanol CPCs under ambient conditions are likely smaller than corresponding cut-off diameters measured under clean (dry) laboratory conditions. At the same time, we caution that the humidity dependence may lead to wrong interpretations if the aerosol composition is not known.

New Particle Formation and Sub-10 nm Size Distribution Measurements during the A-LIFE field experiment in Paphos, Cyprus

“…In the third and fourth channels, two TSI UCPC Model 3776 with an inlet flow rate of 1.5 L/min were implemented and operated at modified temperature settings, i.e. the saturator temperature was set to 30.1°C and the condenser temperature set at 0.1°C for enhanced 120 particle activation (Barmpounis et al, 2018;Tauber et al, 2019). A water-based TSI CPC Model 3788 was employed in the https://doi.org/10.5194/acp-2019-1123 Preprint.…”

“…Previous studies have shown that the RH and the seed solubility with respect to the working fluid have an influence on the CPC detection efficiency (Kangasluoma et al, 2013;Tauber et al, 2019). To appropriately account for the seed variability present in the atmosphere, we used the mean counting efficiency at the classified diameter using results of the counting efficiency for silver and sodium chloride particles exposed to 0% or 10% RH as a best estimate.…”