Something of the behavior of clouds of small particles can be illustrated by the following field trials:

In the first trial an inert substance was disseminated from a boat travelling some ten miles off shore under appropriately selected meteorological conditions. Zinc cadmium sulfide in particles of 2 microns in size were disseminated. This material fluoresces under ultraviolet light which facilitates its sampling and assessment. Four hundred and fifty pounds was disseminated while the ship was traveling a distance of 156 miles.

Figure 1 describes the results obtained in this trial. The particles traveled a maximum detected distance of some 450 miles. From these dosage isopleths it can be seen that an area of over 34000 square miles was covered. These dosages could have been increased by increasing the source strength which was small in this case.

The behavior of a biological aerosol, on a much smaller scale, is illustrated by a specific field trial conducted with a non pathogenic organism. An aqueous suspension of the spores of B. subtilis, var. niger, generally known as Bacillus globigii, was aerosolized using commercially available nozzles. A satisfactory cloud was produced even though these nozzles were only about 5 per cent efficient in producing an initial cloud in the size range of 1 to 5 microns. In this test, 130 gallons of a suspension, having a count of ** f organisms per ml, or a total of approximately ** f spores, was aerosolized. The spraying operation was conducted from the rear deck of a small Naval vessel, cruising two miles off-shore and vertical to an on-shore breeze. Spraying continued along a two mile course.