== 
After considering the foregoing factors, the operator can select the 
most desirable particle size to meet his need, and then the type of gen- 
erator that will produce the desired particle size and volume of aerosol. 
If the available equipment will not produce the desired particle size, 
then the time will have to be adjusted to the size that can be produced. 
It has been demonstrated that particles above certain sizes, when 
composed of some solvents and insecticides used in aerosol formulations, 
will injure plant foliage. Persons treating greenhouses with aerosols 
should keep this effect in mind when selecting the particle size. 
Some structures may be too open for the successful use of aerosols 
because of too much loss through the wall openings. In large open ware- 
houses full of tobacco hogsheads, where an aerosol could not be contained 
in the structures, it was found that a spray with particles of about 50 
microns mass median diameter, blown over the top of the hogsheads by a 
mist blower, gave a uniform deposit of insecticide and good insect control. 
Formulation and Dosages 
Formulations for aerosol applications should be made as concentrated 
as possible. Thus by reducing the oils and solvents to a minimum the 
danger of explosion will be lessened as well as the tendency of the 
deposit to soak into porous surfaces. The formulation should contain a 
relatively nonvolatile oil to maintain the particle size while the 
aerosol is suspended in the air. The dosage should be on the basis of 
insecticide per square foot of floor area. DDT or malathion is usually 
applied at 1 pound per 4,500 square feet, and lindane at about half this 
dosage. Synergized pyrethrum (10:1) should be applied at the dosage 
recommended for the particular insect. Care should be taken to determine 
the amount of pyrethrins in the formulation. Where inadequate dosage is 
used the insect parasites are sometimes killed and not the injurious 
insect, with a resulting infestation worse than that which existed 
before spraying. 
Precautionary Measures 
Aerosols that are formulated with a relatively nonvolatile oil, as 
well as those containing volatile oils and solvents, should not be 
applied at rates that provide more than 2 gallons of flammable material 
per 100,000 cubic feet, and they should not be released near an open 
flame. The operator should wear a proper respirator. 
A pyrethrum formula is recommended for use around exposed foodstuffs. 
