R. Rudolf

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

Experimental study of sticking probabilities for condensation of nitric acid — water vapor mixtures

Abstract In the present study condensational droplet growth rates in the binary vapor system HNO 3 –H 2 O were measured over a relatively wide range of vapor activitiesin order to investigate the mass accommodation coefficients in binary vapor mixtures. The measurements on condensational droplet growth rates were performed in an expansion chamber with a sensitive time of the order of 10 s . Droplet growth rates and the corresponding droplet number concentrations were determined by the Constant angle mie scattering (CAMS) method. In the present study the droplet radii cover a range from 0.5 to about 4 μm . The experiments were performed at constant temperature and total pressure near atmospheric conditions. The experimental growth curves determined in the binary vapor system HNO 3 –H 2 O are compared to corresponding model calculations. Thereby the mass and thermal accommodation coefficients can be determined. It can be concluded from the experiments that in binary supersaturated vapor mixtures of HNO 3 –H 2 O the sticking probability for nitric acid molecules is between 1.0 and 0.3 for the case of the sticking probability for the water molecules is set to unity. Especially at very low relative humidities below 75% very good agreement between experiment and theory can be established when the sticking probability of water as well as of nitric acid is regarded to be unity.

Kinetics of particle growthin supersaturated binary vapor mixtures

Abstract Growth rates of droplets in the unary vapor systems water and n-propanol and in the binary vapor mixture water - n-propanol have been determined experimentally. The size range of the growing droplets covers the transition as well as the continuum range. The experimental data are compared to steady state droplet growth calculations assuming a uniform droplet composition. Good agreement between experimental and theoretical values can be observed when the respective sticking probabilities and the thermal accomodation coefficient are chosen to be unity.

Experiments on binary condensational particle growth for the nearly immiscible system water - n-nonane

Abstract Investigations of binary condensational particle growth have so far been restricted to miscible systems. In this paper we report first measurements of droplet growth rates for the nearly immiscible system water - n-nonane. The experiments are performed in a new expansion chamber especially designed for low supersaturations. Particle sizes are measured using the CAMS-method. The experimental data is compared to various empirical models. The growth rates measured in the binary system seem to indicate that water is behaving analogous as in an ideal mixture whereas the surface activity of n-nonane appears to be near unity for most drop compositions. The detailed microscopic structur of the condensing particle, however, is not yet clarified.

Measurement standard for determination of aerosol number concentration

Publisher Summary Number concentration is one of the most frequently studied parameters for characterization of atmospheric aerosols and other particulate systems. Determination of aerosol number concentrations can be performed by means of various methods based on a number of different measuring principles. At comparatively low concentrations, single particle counting can be applied, however, at concentrations beyond several 10 3 cm -3 , integral methods are required, which are often based on empirical calibration. To contribute to a standardization of aerosol concentration measurements, intercomparisons of various instruments were recently performed during an international experimental workshop. For consistent standardization of concentration measuring instruments, properly defined calibration standards would be required, which allow a direct determination of the particle number concentration without empirical calibration with respect to external reference standards. This chapter describes an experimental system for determination of aerosol number concentration, which is based on the measuring principle of a condensation nuclei counter. The concentrations of the particles growing in an expansion chamber are determined from simultaneous observation of scattered and transmitted light fluxes. It is shown that this experimental method allows direct particle concentration measurements for concentrations up to more than 10 7 cm -3 , and can be considered as a primary calibration standard for particle number concentration measurement.