Traceable methods for calibrating condensation particle counters at concentrations down to 1 cm−3

Abstract

The concentration of nanometer-sized particles is frequently measured in terms of particle number concentration using well-established measuring instruments, such as condensation particle counters (CPCs). Traceability for these measurements can be achieved by means of calibration against a reference aerosol electrometer starting at concentrations >1000 cm−3. Here, two independent methods for extending traceability down to 1 cm−3 are described. The first method relies on a custom-made, reference optical particle counter while the second method combines electrometer measurements with a series of dilution steps. An inter-comparison of the two methods was carried out using polystyrene spheres with a nominal diameter of 100 nm in the concentration range 1 cm−3–100 cm−3. A CPC Model 3752 (TSI Inc, USA) was used as transfer standard. The obtained results showed a deviation of 1%–4% between the two methods, which was in agreement with the stated uncertainties.