Natural Aerosol Particles Research Articles

Absorption by airborne and deposited particles in the 8-13 micrometer range

The absorption of radiation by natural aerosol particles was measured in the 8–13 micrometer wavelength interval. A comparison was made between an in situ method and measurements of particles of deposited form. The results are in agreement to about 30 percent. The main feature of aerosol absorption within the infrared window is a strong absorption peak near 9 micrometers caused by sulfate or quartz particles present in all continental aerosol types. Consequences for the atmospheric heat balance are clear sky cooling rates growing from about 2 per cent in the tropics to about 20 per cent of the total cooling in arctic regions under normal conditions, additionally increasing with increasing relative humidity. DOI: 10.1111/j.2153-3490.1975.tb01706.x

Extraneous particles shed from large soil particles

Abstract Large soil particles (predominantly montmorillonite) shed small (submicron- and micron-sized) particles when collected in water or on membrane filters or upon collision with an obstacle. Small particles present in large numbers in the interstices of a large soil particle are released into air or water and form an independent aerosol or hydrosol colloidal suspension leaving the parent particles practically unchanged. The shed particles did not originally belong to the aerosol or hydrosol population but are released in the sampling apparatus; consequently the determined concentration of aerosol particles is not representative of the aerosol concentration in air. Da- and h-μm aerosol particles act as accretion centers for cloud droplets when ingested by a cloud; they form large drops which shatter and form numerous fragments. The shed hydrosol particles in water drops formed on those fragments provide additional freezing nuclei that freeze these water drops. Studies of natural aerosol particles must include not only their size, surface structure and chemical composition, but also the function those aerosol particles perform in nature as condensation and ice-forming nuclei.

Turnover times of137Cs and HTO in the troposphere and removal rates of natural aerosol particles and water vapor

Turnover times of¹³⁷Cs and HTO in the troposphere and removal rates of natural aerosol particles and water vapor

Water-affected fraction of natural 1.5–9 μ diameter aerosol particles

The water-affected fraction of a given size class of an aerosol population reflects the change in particle concentration when that population becomes hydrosolized. The water-affected fraction was determined for natural aerosol particles in the 1.5–9 μ diameter size range. The largest change was observed in the 1.5–3 μ size group in a polluted atmosphere, especially in the presence of scattered rain and overcast sky. The aggregates formed through evaporation of cloud droplets seem to be the principal source of smaller hydrosol particles. Parallel determination of changes in air concentration of chloride particles and water-affected fraction of aerosol particles, coupled with analysis of air parcel trajectories, showed excellent agreement in identification of the movement of maritime air parcels over the central part of the continent (Colorado).

Radioactive Fallout Particles Collected by an Electrostatic Precipitator

A Gerdien type of ion chamber was used as an electrostatic precipitator to collect radioactive fallout. Aerosol particles were collected on different parts of the central electrode according to their ionic mobilities. The dust samples thus collected were investigated by γ ray spectrometry and microautoradiography. The experimental results indicate that aerosol particles which are attached by primary fallout particles of higher activity are charged multiply resulting in higher ionic mobilities presumably because they get a positive unit charge when they emit a β ray. This is in contrast with the fact that natural aerosol particles become mostly to be charged singly through attaching ions produced by natural radiation and radioactivity.

Investigation of radon daughters

A Goetz aerosol spectrometer and low-level counting techniques were used in studying the size distribution of natural radioactive aerosol particles. A number of values down to radii of 3×10−6 cm were obtained. These are compared with computed distribution curves and with estimates from experimental work of a different kind.

Recent Investigations in Air Chemistry

New results of chemical analyses of natural aerosol particles in Florida and in the Boston area are presented. These data are compared with the results obtained earlier at various other locations. The continental and maritime components of NH4, Na2, Cl, SO4, and NO3 can be separated for two different size ranges, viz. large particles (radius 0.08 μ to 0.8 μ) and giant particles (radius 0.8 μ to 8 μ). It is found that the continental influence on aerosols extends far into the ocean. The nitrate content of the particles presents an especially interesting problem, since it appears that the major part of NO3 stems neither from a continental nor from a maritime source, but from a certain area along the coast. A comparison is made of the total amounts of material found in the large and the giant particles of the various locations. Information gained from this comparison provides the basis for conclusions regarding the size distribution of aerosols. A pronounced difference between maritime and continental distributions becomes evident in this case. The concentration of the corresponding gas traces of NH3, SO2, nitrogen oxides and chlorine components were measured in Florida and at other locations simultaneously with the chemical analysis of the aerosols. For most components the concentration of these gas traces is considerably higher than that for the corresponding substances in the aerosols. The importance of these findings for air chemistry is discussed.

THE SIZE DISTRIBUTION AND AGING OF NATURAL AEROSOLS AS DETERMINED FROM ELECTRICAL AND OPTICAL DATA ON THE ATMOSPHERE

A first attempt at surveying the complete size distribution of natural aerosol particles is made. The size range covers more than three orders of magnitude in radius, with approximate limits of 2 × 10−3 and 5 × 10−7 cm. Previously only parts of this spectrum had been carefully investigated, due to the size limits of the various experimental methods used. Particle spectra down to radii below 10&-4 cm are well known, having been obtained by direct count under the microscope. Particles of radius less than 10−5 cm are counted in the Aitken counter, but their size distribution can only be determined from mobility measurements on those particles which are charged. However, to deduce nuclei spectra from ion spectra, the fraction of charged particles must be known. Previous determinations of this fraction are examined and are shown to contain inaccuracies or errors. The expression derived here theoretically, is used to convert some of the ion-spectra data into nuclei spectra. The particle-size range between radii of 10×5 and 10−4 cm has hardly been investigated by direct measurements, because of the experimental difficulties encountered. Valuable information can be gained here from the dependence of haze scattering on wavelength. The available data seem to indicate that the maximum number concentration is located in the size region between 10−5 and 10−6 cm radius, and that the number concentration drops to zero between 10−6cm and 10−7 cm radius. The size range greater than 10&-5 cm can be well represented by a power law which seems to hold for large parts of the world. It can be shown further, where ion and nuclei counts or other electrical data are available from a large number of places all over the world, that the average radius of all particles increases when the total number decreases. This can be explained by coagulation processes. It should be emphasized that the results obtained in this article are to be considered as a rough first approach, valid only for average conditions in time and space, and that more detailed information is needed to improve our knowledge of this field.