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“op 2 June 1960 ARS-33-58 
UNITED STATES DEPARTMENT OF AGRICULTURE 
Agricultural Research Service 
( |BRARY 
{' he OORD 
DIRECTIONS FOR INDUSTRIAL USE OF hoe | pe | 
Pe Jub 21960 4 
By A. H. Yeomans 
Entomology Research Division 
Aerosols are used in many industrial structures to control insects 
by direct contact or by applying a light deposit of insecticide on the 
top of exposed horizontal surfaces. 
An aerosol is composed of a number of fine liquid particles suspended 
in the air. It is considered that in an insecticidal aerosol all the 
particles should be smaller than 50 microns in diameter and 80 percent 
(by weight) of them should be less than 30 microns. Vapors or smokes 
composed of particles less than 0.1 micron in diameter are not classed 
as insecticidal aerosols because they exhibit slightly different 
characteristics. 
Aerosols may be produced by liquefied-gas formulations released 
through capillary or expansion-chamber nozzles, by stream or air atomiza- 
tion of liquid, by spinning disks and rotors, by forcing liquid under 
high pressure through atomizing nozzles, by heat vaporization, or by a 
combination of these methods. 
A wide range of particle sizes can be produced, and the size of the 
particles has a greater influence on the effectiveness of the aerosol. 
The particle size determines the time the aerosol remains suspended in 
the air and therefore the amount of dispersion by air currents through- 
out the enclosure. The particle size is a critical factor influencing 
the amount that collects on an insect as it flies through the aerosol. 
If the particles are too small, they are deflected from the flying insect 
as smoke is from a moving automobile, but they will settle out on the 
insect while it is at rest if the exposure time is adequate. If they 
are too large, they settle rapidly and their dispersion is poor; there- 
fore their chance of contacting the insect is also poor. When an insect 
does collide with an oversized droplet, the excess insecticide is wasted. 
aly/ This is a revision of E-835, issued by the former Bureau of 
Entomology and Plant Quarantiné in October 1953. 
