Concentration uncertainties in atmospheric aerosol measurement with Condensation Particle Counters

Condensation Particle Counters (CPCs) are the best-known and most frequently used tools for determining airborne particle number concentrations in the laboratory and a variety of real-life situations. While being a very established technique, current generations of CPCs have enhanced capabilities in terms of lower cut-off diameters, upper concentration limit as well as measurement quality features (e.g. pulse height monitoring). Knowledge of instrument accuracy is a primary matter in order to retrieve high quality data. In recent years, there has been an effort from measurement networks and within the EU’s standardization committee (CEN-TS 16976) to make ambient ultrafine particle number concentration data comparable. Long-term ambient monitoring requires frequent validation of instrument performance.

Inter-comparisons of multiple instruments against a reference instrument are important measures in order to secure long-term data quality. During inter-comparisons in the laboratory typically an aerosol of a certain type is generated and eventually classified in order to retrieve a monodisperse aerosol population. The aerosol needs to be equally distributed between the different instruments without being biased by sampling line losses.

This presentation will focus on inter-comparisons of CPCs being challenged with different types of aerosol. This includes lab-generated, highly monodisperse aerosol as well as ambient polydisperse aerosol. The accuracy of 10 units of a recently-introduced CPC (Model 3750, TSI Inc.) will be shown for ambient aerosol at data rates up to 50 Hz. All CPCs characterized agreed within 10% during the test, with concentrations of the ambient aerosol ranging from a few thousands up to 100,000 Particles/cm³.

In addition, results from inter-comparison studies using different butanol- and water-based CPC models that have been used for multiple years in different laboratories will be shown. Despite the different schedules for all instrument services and calibrations related to owners metrology requirement, these different CPC models demonstrated similar responses for the tested aerosols taking into account 10% uncertainties and are suitable candidates for reliable long-term operation in ambient ultrafine particle monitoring.