Reduced particle composition dependence in condensation particle counters

Abstract

Modern condensation particle counters (CPCs) are indispensable instruments for studies of aerosols in all measurement environments. Relying on heterogeneous nucleation as the basic principle, the composition dependence of particle activation is a source of profound uncertainty for the accurate assessment of new particle formation (NPF) events. While development efforts successfully pushed down minimum detectable particle sizes in recent years, composition-dependent counting efficiencies have remained to be a persisting issue in aerosol research. Addressing this pressing problem, we present calibrations of a newly developed CPC, the Airmodus A30 (Airmodus Ltd., Helsinki, Finland), that uses non-hazardous propylene glycol as working fluid. Our results conclusively demonstrate that composition-dependent particle detection can be reduced to the brink of disappearance by choice of the working fluid and corresponding high supersaturation. Counting efficiencies were determined for a set of size-selected and chemically diverse seed particles, and the measured 50 % cutoff diameters were compared to previous studies. Using computational fluid dynamics simulations, we show that the composition dependence appears to decrease with increasing saturation ratios achieved inside the CPC. Hence, our study assists in the development of future CPCs and elucidates a potential mechanism to reduce measurement uncertainties arising from composition-dependent counting efficiencies.