Metrological developments for aerosol and mass measurements: Dissertation

Reliable, comparable and accurate measurement results are only achieved by having traceability to recognized primary standards. Scientific and technological progress demand for and rely on developments in already established fields of metrology, such as mass, and in new evolving fields, such as aerosol particles, where the traceability is incomplete. In this thesis, a novel device called single charged aerosol reference (SCAR) invented by Tampere University of Technology (TUT) was developed into a primary standard for particle number concentration. For this, a full metrological validation was performed for determining the uncertainty of generated particle number concentration. It was shown that the generated particles are singly charged with a standard uncertainty of only 0.16 %. As a result, SCAR is the only primary standard capable of performing calibrations in a wide size range from 10 nm to 500 nm with a relative uncertainty (k = 2) of less than 2 %. A comprehensive inter-comparison of different particle number concentration standards was performed for the first time. The particle charge concentration measurements were compared in the particle size and concentration ranges 20 nm to 200 nm and 0.16 * 10-15 C cm-3 to 2.72 * 10-15 C cm-3 (equivalent to 1000 cm-3 to 17 000 cm-3 singly charged particles), respectively. An overall agreement of ±3 % was achieve with a few exceptions at low concentrations. As a result, a solid metrological basis for particle number concentration measurements worldwide was established for the first time. A significant source of error in gravimetric measurements of vehicle particulate exhaust is the so called filter artefact, i.e. adsorption of gas phase compounds onto the sampling filter. An experimental setup based on mixing hydrocarbon vapour and soot particles was constructed for studying the effect of the filter artefact in a systematic way. Studies with teflon coated filters and pentadecane (C15H32) vapour show that both the particle concentration and the filter soot load influence the filter artefact, such that lower particle concentrations and soot loads yield more adsorption. Instability of standard weights caused by sorption effects introduces uncertainties in the realization of the unit of mass, which is the ultimate basis for traceability for most particle measurements. Atomic force microscopy (AFM) was applied for studying changes in surface contamination of stainless steel weights upon ultrasonic cleaning in ethanol and vacuum exposure. An image processing method for increasing the sensitivity of detecting changes was developed. Results show that grooves are preferential sites for adsorption of contaminants.