Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10 % to 20 % for particles in the range of 0.9 up to 3 µm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 µm in aerodynamic diameter should only be used with caution. For particles larger than 3 µm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5–3 µm is needed.

The TSI DustTrak Aerosol Monitor is a portable real-time instrument widely used for particulate matter (PM) mass concentrations monitoring. The aim of this work is to report on issues that have arisen from the use of the latest generation models DustTrak DRX (8533 and 8534) in the BREATHE, UPTECH and IMPROVE projects that can compromise data quality. The main issue we encountered was the occurrence of sudden artefact jumps in PM concentration, which can involve an increase from a few to some hundreds of μg·m-3. These artefact jumps can sometimes be easily recognised ("obvious jump"), while others can be difficult to identify because the difference in the concentrations before and after the jump might be just few μg·m-3 ("possible jump") or because the jump is sustained over the whole monitoring period and only detectable if PM concentrations are simultaneously measured by other instruments ("hidden jump"). Moreover, in areas of relatively low PM levels, the unit reported concentration of 0μg·m-3 for ambient PM concentration or even negative concentration values which may seriously compromise the dataset. These data suggest issues with the detection of low PM concentrations, which could be due to an incorrect instrument offset or the factory calibration setting being inadequate for these PM concentrations. The upward and downward artefact jumps were not related to especially dusty or clean conditions, since they have been observed in many kinds of environments: indoor and outdoor school environments, subway stations and in ambient urban background air. Therefore, PM concentration data obtained with the TSI DustTrak DRX models should be handled with care and meticulously revised before being considered valid. To prevent these issues the use of auto zero module is recommended, so the DustTrak monitor is automatic re-zeroed without requiring the presence of any user.

This study provides insights into the performance of a new nano-water-based condensation particle counter (N-WCPC, TSI 3788) and presents a comparison to the well-established butanol-based ultrafine CPC (UCPC, TSI 3776). The suitability of the N-WCPC to measure ambient airborne nanoparticles of various compositions has been assessed with an urban background aerosol in a light industrial area and provided comparable results (within 2%) to the 3776 at various particle number concentrations. The subsequent investigation using laboratory generated nearly monodisperse positively charged sucrose, sodium chloride, proteins, emery oil, and candle-generated particles in the diameter range of 2–53 nm showed material-dependent N-WCPC cut-off sizes between 2.2 and 17.2 nm at standard operating temperatures. Copyright 2013 American Association for Aerosol Research