Physical Properties Of Coarse Aerosol Particles And Haze Elements In Polluted Urban-marine Environment

Measurements of coarse particles (with r ≥ 1.0 μm) with the aid of a cascade impactor and of particle (droplet) identification in sensitized gelatine layers reveal their mean concentration of about 1.5 cm-3 during the months of May and June 20 km west from Napoli in Italy. Haze particles (droplets) are usually featured by insoluble core and many small particles deposited on their surface. Sea salt aerosol does not play a dominant role in the haze element formation at this site of measurement. © 1990

Potential Use Of Chemical Spot Test Method For Submicron Aerosol Sizing

A submicron particle, which is too small to be observed in an optical microscope, may form an observable spot on a chemically prepared substrate of the collector. The size of the spot or Liesegang circle is related to the aerodynamic diameter of the particle through a magnification factor. This paper presents the experimental results of the study of this factor using sodium chloride aerosol in the size range of 0.5 to 2 pm which has not previously been studied. We calibrated a cylindrical centrifuge with known sized latex particles. A relationship between the aerodynamic diameter and the deposition length is established. From this calibration one can obtain the aerodynamic diameter of particles of the same geometrical size but of different densities. This provides the needed parameter for calculating the magnification factor. © 1980, American Chemical Society. All rights reserved

A Note On The Use Of A Photoelectric Counter For Total Particle Counting

The ability of the Nolan-Pollak counter to function as a total particle counter was investigated. Comparison with the UMR Absolute Aitken Nuclei Counter operated at an expansion pressure ratio of 1.33 revealed that in mean, the N-P counter measurements (at an expansion pressure ratio of 1.21) were 30% less. This correction, however, depends on particle nature, concentration and size distribution and assumes that particle losses in the central part of the UMRAAN counter are negligible. © 1982

Hot-wire Anemometer Behaviour In Low Velocity Air Flow

The behavior characteristics of a commercially available hot-wire anemometer have been examined in the presence of low velocities, lwss than 0.1 m/s for the most part, and in both horizontal and vertical air flows. The orientation of the probe in a horizontal flow has been found to have a definite effect on velocity measurements, and a lower limit to the reliable application of hot-wire anemometry has been evaluated for a particular type of probe. Vertical flow measurements have resulted in the discovery of the magnitude of natural convective velocity, and a possible method for determining the dimensions of the temperature jump distance has been developed indirectly from the description of the shape of the calibration curve

The Magnification Factor For Sodium Chloride Liesegang Circles Established With An Aerosol Centrifuge

Sodium chloride particles deposited on a gelatin film containing silver nitrate form in a humid environment clearly visible dark brown reaction spots (Liesegang circles) after development in u.v.-light. The size of these reaction spots depends on the mass of NaCl in the particles. To establish the spot size vs particle size relation, particles produced by nebulising NaCl-solutions and sea water were sampled in an aerosol centrifuge. The location of deposition yields the aerodynamic diameter of the particle, and the spot size is measured microscopically. In this way the spot size vs aerodynamic diameter relation is established experimentally in the so far unexplored aerodynamic diameter range between 0.5 and 2.0 μm. © 1976

General Features Of The Aerosol Observed In The Guinean Savannah At The Level Of The ITCZ Influence Of The Drought

The stagnation and mixing of various air masses at the level of the ITCZ in the dry season, together with the absence of rain, favor, in the Guinean savannah, the formation of a well-aged and homogeneous aerosol made up of very active mixed nuclei. When the drought increases, the aerosol always remains an aged one, i.e. absence of particles with radius r \u3c 0.02 μm, no nucleation mode. However, different properties show a younger and less homogeneous aerosol, i.e. very high counts in all the categories of particles (the concentration of nuclei activated at the supersaturation S {reversed tilde equals} 0.32% reaches 9960 cm-3), poor correlations between the concentrations of various groups of particles and no fog. When the fires are frequent and spread all over the savannah, a permanent addition of new particles to the local background aerosol (due to a complicated circulation) prevents the ageing of the aerosol that is observed during the usual drought with a moderate extension of bushfires. © 1986

A Continental Well-aged Aerosol In The Guinean Savannah At The Level Of A Trough Along The ITCZ

Simultaneous measurements of Aitken nuclei, cloud condensation nuclei and aerosol particles sizes larger than 0.3 μm in the Guinean savannah during the dry season show an aerosol of very exceptional physical properties: numerous cloud condensation nuclei (2000-3000 per cm3) active at low supersaturation (or slight \u27undersaturation\u27), absence of very small Aitken nuclei active at 180% of supersaturation and concentrations of large aerosol particles (D \u3e 0.3 μm) between 30 and 60 per cm3. The analysis of the aerosol behavior during a \u27typical\u27 24-hr period of the dry season and during a fog situation indicates that (1) the aerosol is a very homogeneous and aged one; (2) the active nuclei might be of a mixed nature or nuclei on the surface of which the capillary condensation plays an important role. © 1985

Upper-Tropospheric Aerosol Sampled During Project Fire IFO II

Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropospause, and there was a tendency toward depletion of the ambient aerosol at both ends of the condensation nuclei (CN) size distribution

Comparison Of Several Aitken Nuclei Counters

The basic thermodynamical processes leading to the formation of droplets in the central part of the Nolan-Pollak counter are analyzed in some detail. The comparison of the UMR-Absolute Aitken Nuclei counter with Nolan-Pollak, General Electric and Gardner counters showed consistently higher counts of the UMR-AAN counter. The mean deviations varied between 20% and 50% depending on the type of the counter, nuclei concentration and nature. Several observations are made on ultrafine particle counting. © 1981

The University Of Missouri-rolla, Absolute Aitken Nucleus Counter

The authors discuss the expansion cloud chamber system known as the University of Missouri-Rolla-absolute Aitken nucleus counter. A review of the properties of an expansion chamber and how it creates a supersaturation are given and a critical examination is made of the assumptions in its operation, e.g. adiabaticity of the expansion. The design of the chamber is described in detail and an analysis of the propagation of errors is given for quantities measured and calculated. A short review of the performance of the chamber and some general comments relative to comparisons with other Aitken nucleus counting instruments are given. The chamber is capable of making measurements on aerosols of number concentration up to 106 nuclei/cm3 to an accuracy of about 10-15% at any desired supersaturation ratio up to the ion limit. Finally mention is made of other expansion chambers developed in this laboratory for measurements of homogeneous nucleation rates. © 1982