G.P. Reischl

A new electromobility spectrometer for the measurement of aerosol size distributions in the size range from 1 to 1000 nm

Abstract The Electromobility Spectrometer is an automated measurement system for the size analysis of fine and ultrafine aerosols using Differential Mobility Analysers (DMA) for the classification of particles and an electrical sensor for their detection. To cover a particle size range from 1 to 1000 nm, new DMAs with different geometries have been designed to optimize performance for small and large particles. Key problems in the size characterization of particles smaller than 20 nm have been addressed. A Faraday cup electrometer with a sensitivity of 10 −16 A is used as a particle sensor to avoid the deficiency of condensation nucleus counters with counting efficiencies decreasing with particle size. A new flow control technique allows the generation of stable air flows to further improve system performance. Additional improvements include the use of a multi-stage cascade impactor at the aerosol inlet, an instrument background correction mechanism and a refined data reduction algorithm. The computer controlled measurement program allows for variable size resolution, parallel operation of two DMAs and a time resolution for the measurement of size distributions of the order of 1 min.

Bipolar charging of ultrafine particles in the size range below 10 nm

Bipolar diffusion charging of aerosol particles in the size range of 2.3–10 nm was studied experimentally. Charging probability for WOx nanoparticles as a function of particle size was measured using an 241Am aerosol neutralizer for aerosol charging and a tandem DMA (Reischl type) with a VIE-06 Faraday cup electrometer for aerosol measurement. In spite of small deviations in the predictions from the theory of N. Fuchs on bipolar aerosol charging at 2–4 nm range, the theory was seen to be valid. Correction of the deviations may be performed by adjusting the free parameters in the theory (ion mass and mobility). As a rule of thumb, the charging probability of 2 nm particles was seen to be around 0.6% for negative and around 0.4% for positive particles.

Measurement of Ambient Aerosols by the Differential Mobility Analyzer Method: Concepts and Realization Criteria for the Size Range Between 2 and 500 nm

Requirements for aerosol spectrometer based on the differential electrical mobility method are deduced from the principles of aerosol classification and concentration determination. Data reduction and method-inherent sources of errors are discussed in detail. Criteria for the components of the arrangement to be used for ambient aerosol size distribution measurements are given with respect to size range, concentration range and time resolution.

CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter

Abstract The cloud droplet activation of monodisperse laboratory aerosols consisting of single organic and inorganic substances as well as a mixture of several substances was investigated using the University of Vienna cloud condensation nuclei counter (CCNC). The CCNC operates on the principle of a static thermal diffusion chamber. Water vapour supersaturations can be set in the range from 0.1% to 2%. Aqueous solutions of oxalic acid and malonic acid as well as solutions of inorganic compounds (NaCl and (NH4)2SO4) were nebulized in a Collison atomizer and then passed through a closed-loop differential mobility particle spectrometer to produce monodispersed particles. An internally mixed aerosol consisting of ammonium sulphate, oxalic acid and malonic acid with relative concentrations resembling those found in cloud water at a mountain station [Loflund, Kasper-Giebl, Schuster, Giebl, Hitzenberger, Reischl et al. (2002) Atmos. Environ. 36, 1553] was also investigated for cloud condensation nuclei (CCN) activation. All these particles were activated at supersaturations expected from Kohler theory. Oxalic and malonic acid particles are therefore expected to be good atmospheric CCN both as pure particles and as internally mixed particles containing other chemical compounds.

Performance of Vienna Type Differential Mobility Analyzer at 1.2–20 Nanometer

ABSTRACT The transfer functions of the so called “Vienna type” differential mobility analyzer (DMA) were studied experimentally at the size range of 1.2–20 nm following the procedure suggested by Stolzenburg (1988) Ph.D. Thesis. For the study, two identical DMAs were used as a tandem DMA (TDMA) arrangement to measure nanoparticles from a hot wire WOx generator. The approximate analytical formulae by Stolzenburg describing diffusion broadening of the DMA transfer function were observed to be valid with high accuracy from 20 nm down to ∼ 2 nm. In the size range of 1.2–2 nm nominal mobility equivalent diameter small deviations of the shape of the TDMA output signal predicted by Stolzenburg were found.

Heterogeneous Nucleation of Water Vapor on Monodispersed Ag and NaCl Particles with Diameters Between 6 and 18 nm

During the 1980 workshop of the working group on ultrafine aerosols (WUFA), the heterogeneous nucleation of supersaturated water vapor on well-defined aerosols was investigated. Ultrafine Ag and NaCl aerosols were generated using a constant temperature tube furnace. By means of electrostatic classification of the polydispersed primary aerosol, monodispersed fractions with electrical mobility particle diameters of 6, 8, 12, and 18 nm were obtained. After passing through a humidifier, the vapor-saturated monodispersed aerosol entered a process-controlled expansion chamber, the size-analyzing nuclei counter (SANC)). Supersaturation was then achieved by a fast adiabatic expansion, and heterogeneous nucleation was initiated by aerosol particles acting as condensation nuclei. The number concentrations of the droplets growing in the expansion chamber were measured for stepwise increasing supersaturations. At well-defined “critical” saturation ratios, the onset of heterogeneous nucleation was observed. For the in...

Performance of a New Commercial Electrical Mobility Spectrometer

A commercial electrical mobility spectrometer (Grimm 5.4-900 DMA and Grimm 5.403 CPC) was examined with respect to size, concentration and time-dependent responses of the CPC, the transfer function of the DMA, as well as the performance of the data inversion algorithm. For comparison with previously published results, the responses were also measured for two other commercial CPCs (TSI Model 3010 and TSI Model 3022). All measurements were performed using sodium chloride aerosol produced by an atomizer, except for size-dependent counting efficiency measurements, where an evaporation and condensation method was used to produce particles down to a size of 2 nm. The concentration-dependent CPC counting efficiency was measured against a reference instrument working in the single particle count mode following dilution. The CPC time response was evaluated for monodisperse aerosol by measuring the step response using a solenoid valve technique. The transfer function of the Grimm DMA 5.4-900 was determined between 10 and 100 nm with two verified identical DMAs in series following the approach of Fissan et al. Measured tandem-DMA responses were compared to simulated responses based on the diffusion-broadened transfer function of Stolzenburg to define the factors influencing resolution. Finally the data inversion algorithm was tested by comparison with other devices.

Intercomparison of number concentration measurements by various aerosol particle counters

Abstract Total aerosol particle number concentrations, as measured by means of 16 different measurement systems, have been quantitatively compared during an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (ICCP-IUGG). The range of measuring instruments includes Pollak counters (PCO) in use already for several decades, presently available commercial particle counters, as well as laboratory prototypes. The operation of the instruments considered was based on different measurement principles: (1) adiabatic expansion condensation particle counter, (2) flow diffusion condensation particle counter, (3) turbulent mixing condensation particle counter, (4) laser optical particle counter, and (5) electrostatic particle measurement system. Well-defined test aerosols with various chemical compositions were considered: DEHS, sodium chloride, silver, hydrocarbons, and tungsten oxide. The test aerosols were nearly monodispersed with mean particle diameters between 4 and 520 nm, the particle number concentrations were varied over a range from about 4×10 1 to 7×10 6 cm −3 . A few measurements were performed with two-component aerosol mixtures. For simultaneous concentration measurements, the various instruments considered were operated under steady state conditions in a linear flow system. A series of at least 10 single concentration measurements was performed by each individual instrument at each set of test aerosol parameters. The average of the concentration data measured by the various instruments was defined as a common reference. The number concentrations obtained from the various instruments typically agreed within a factor of about two over the entire concentration range considered. The agreement of the measured concentrations is notable considering the various different measurement principles applied in this study, and particularly in view of the broad range of measurement instruments used. Significant deviations and nonlinear response were observed only in a few cases and are possibly related to calibration errors. For certain conditions, a dependence of aerosol counter response on particle composition has been found. The scatter of the number concentrations obtained from each individual instrument during measurements with constant test aerosol typically did not exceed 20% to 25%. At concentrations below 10 3 cm −3 , however, several of the instruments, including electrostatic particle measurement systems, tend to show increased experimental scatter.

Particle size dependent response of aerosol counters

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions. The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the

Measurements of Kelvin-equivalent size distributions of well-defined aerosols with particle diameters > 13 nm

During the 1979 workshop of the working group on ultrafine aerosols, different experimental techniques for measuring the number concentration and size of ultrafine aerosol particles were compared. In the present paper we report on a comparison of different particle size measuring techniques for ultrafine aerosols. Well-defined monodisperse aerosols with electrical mobility particle diameters ranging from 13 to 100 nm were generated using an electrical aerosol classifier. Kelvin-equivalent size distributions of these aerosols were determined by means of a process-controlled expansion chamber, the size-analyzing nuclei counter (SANC). To this end the considered aerosol was humidified and the number concentration of the droplets growing in the expansion chamber was measured for stepwise increase in supersaturation. At a quite well defined critical supersaturation, a significant increase in the measured droplet concentration, and thus the onset of heterogeneous nucleation, was observed. By means of the Kelvin...