O. Preining

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...

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...

Intercomparison of different “absolute” instruments for measurement of aerosol number concentration

Abstract During the 1979 workshop of the working group on ultrafine aerosols (WUFA) an intercomparison of different instruments for measurement of aerosol number concentrations was performed. Each of these instruments (TSI-aerosol electrometer, TSI-condensation nuclei counter, Jaenicke-condensation nuclei counter, size analyzing nuclei counter SANC) can be regarded as “absolute”, because they do not depend on empirical calibration relative to external reference standards. Number concentrations were measured for monodispersed NaCl-aerosols with a mean particle diameter of 56 nm, generated by means of a collision atomizer and an electrostatic aerosol classifier. The transmission losses in the SANC-humidifier were determined quantitatively and the SANC-measurements were properly corrected. Measurements were performed over a concentration range from about 2.5 × 10 2 to 3.5 × 10 5 cm –3 . Considering the differences between the various applied measuring techniques, fair agreement of the obtained concentration data was observed. The TSI-condensation nuclei counter agrees closely with the TSI-aerosol electrometer, however, it can be regarded as an “absolute” instrument only for concentrations below 10 3 cm −3 . For low concentrations the Jaenicke-condensation nuclei counter tends to agree with the average concentration, obtained from all instruments used, above 10 4 cm −3 it agrees closely with the SANC. The readings of TSI-aerosol electrometer and SANC are quite linearly related over the whole concentration range, the SANC being low by a factor of about 0.59. Thus different measuring techniques, based on completely different principles, yield comparable aerosol number concentrations and accordingly condensation nuclei counters are truly aerosol counters.

Penetration of a multistage diffusion battery at various temperatures

Abstract A six stage miniature diffusion battery with “Collimated Hole Structure” plates is described. Its penetration is measured at temperatures between +25°C and −75°C using monodispersed sodium chloride aerosols of known size distribution with spherical particles of mean diameters between 0.2–0.6 μm and relative standard deviations of about 7%. Deposition by diffusion, impaction and interception is considered; measurements are compared to various theoretical models for the deposition mechanisms and their combinations. Agreement was found to be within about 2% at all temperatures for a model combining only diffusion and impaction as independent effects.

Diffusion of aerosols at various temperatures

Abstract The theory of diffusion of aerosols has previously been experimentally verified at room temperature using large diffusion batteries of either parallel plates or long circular tubes. In this study the diffusion of aerosols was tested at low temperatures where classical Brownian movement theory may not apply. Tests were performed with a more compact diffusion battery consisting of newly developed discs of collimated hole structures with pores of 15·5 μm mean dia. and an average length to dia. ratio of 32·7. Monodisperse NaCl aerosols of sizes in the range 0·3–0.5 μm produced in a LaMer-type furnace generator, were sampled with a particle mass monitor before and after penetration through four successive units of holes. At room temperature, the diffusion coefficient, calculated from experimentally observed penetrations, agreed with the theoretically predicted coefficients. However at -16 and -72°C, the experimentally determined coefficients were 150–500 per cent greater than the theoretically predicted values.

Global Climate Change due to Aerosols

Climate is not a well defined concept. Hantel et al.1 remark: ‘Climate is concerned with an object, the climate system, a method of analysis, proper statistics, and an effect, the impact of climate. This list is not exhaustive. More, and quite different categories have been used for defining climate.’ The climate system of the Earth—and this global climate is our subject—comprises the revelant subsystems: the atmosphere, the hydrosphere, the cryosphere, the pertinent part of the lithosphere, and the biosphere.2 The WMO definition of climate reads: ‘Climate is the synthesis of weather over the whole of a period, essentially long enough to establish its statistical ensemble properties (mean values, variances, probabilities of extrema, etc.) and is largely independent of any instantaneous state.’3 Hence, the global climate comprises the local climates of all surface elements of the Earth over all seasons.

Design theory and calibration of a field type aerosol spectrometer

Abstract A cylindrical-type aerosol spectrometer, of simple compact design has been constructed and tested. The aerosol particles are injected into a horizontal centrifugal field through two ports — a pin-hole orifice situated opposite a larger port. Aerosol moving through the larger port is removed in a cumulative size deposition on half of a foil on the outer wall, and serves as clean air for aerosol injected through the pin-hole and deposited according to discrete sizes on the other half of the foil. The instrument based on a modification of a device developed by Hochrainer and offers the advantage of confining the aerosol deposit to a narrow streak or dot in the case of monodisperse particles. The spectrometer was calibrated with monodispersed polystyrene latex particles and the results were compared with a theoretical expression developed for sedimentation distances appropriate to aerosols flowing in the plane of rotation.

Intercomparison of trace metal in atmospheric aerosols collected in Kyoto and Vienna

Abstract In Kyoto and Vienna, atmospheric aerosols were collected onto two stacked Nuclepore filters with pore-sizes of 8.0 and 0.4 μm, respectively. The elemental concentrations of the aerosol samples were determined with the PIXE technique. It was confirmed in both cities that Ca, Ti, Mn, Fe and Cl were dominant in the coarse fraction and S, Pb and Zn were dominant in the fine fraction. The sulfur, especially in fine fraction, and lead content of the Vienna aerosol was about two times higher than those of the Kyoto aerosol.