2. AIRBORNE BIOLOGICAL MATERIALS 



Atmospheric Dispersal of Biologically Significant Materials 



An Aerobiology Program has been 

 established within the International 

 Biological Program (IBP). The United 

 States Aerobiology Program under the 

 IBP has been in operation about two 

 years. It is the strongest national 

 aerobiology program, with the Neth- 

 erlands nearly as active. International 

 collaboration is growing steadily. 



The activities of the Aerobiology 

 Program are generating new ap- 

 proaches to studies of biologically sig- 

 nificant materials in the atmosphere, 

 such as spores, pollen, fragments of 

 algae and molds, minute insects, and 

 toxic particles and gases. Until now 

 studies of these materials in the at- 

 mosphere have been done in highly 

 individualistic ways, with almost no 

 comparison of work by different au- 

 thors and no theoretical bases for 

 guiding research and organizing the 

 resulting information. There are a 

 few notable exceptions, such as the 

 well-conceived bodies of research in 

 the 1930's and 1940's by Stakman and 

 Harrar on cereal-rust epidemiology on 

 the North American plains. But now 

 there are new pressures to guard food 

 crops against losses, to reduce human 

 disease, to curtail additions to atmos- 

 pheric turbidity, to clean air of nox- 

 ious pollutants, and many other tasks 

 involving atmospheric dispersal in 

 ecological systems, all of which are 

 objectives to which aerobiologists can 

 contribute. (See Figure X-6) 



The science of meteorology has be- 

 come "systems ordered," from the 

 research-planning to the data-han- 

 dling phases, and is fast becoming 

 coordinated on a worldwide scale with 

 respect to observations. Now is a 

 propitious time for aerobiologists to 

 link up with meteorologists for the 

 mutual benefit of their researches and 



Figure X-6 — ATMOSPHERIC PARTICULATE MATTER 

 IMPORTANT IN AEROBIOLOGY 



Diameters 

 (meters) 



10 > 



10 ' 



Commonly 



Used Units 001u 01u 



(microns, millimeters & centimeters) 



10- 



,lu 



Fall Speeds 

 (cm/sec) 



_Browman 



movement 



1(H 



lu 



.003 



io- 5 



lOu 



10-" 10- 3 io- ? 



lOOu 1 mm 1 cm 



30 



.300 



ation 



Permanent Suspension 



-• — (Gravitational 



fallout is not 

 significant) 



■ Smokes - 



Transition_ 

 Region 



Dusts 

 (fine) 



Transient Particulates 



(only strong winds can 



sustain these in the 



atmosphere) 



Dusts 

 (coarse) 



Haze particles 



■ Condensation nuclei 



Viruses *- 



-» Bacteria 



Algae 



-— Protozoa 



Fungus 

 "*" spores " 



Lichen fragments 



Moss 

 spores" 



Pollen 



Fragments of plants, 

 seeds, insects, & 

 other microfauna 



The table gives some physical properties of particulates encountered in aerobiology 

 — diameter, expressed in meters and other commonly used units, and approximate 

 terminal fall speed. From an aerobiological point of view, smokes, fine dusts, haze 

 particles, condensation nuclei, viruses, bacteria, and algae are the atmospheric 

 particulates of greatest concern. This is because gravity does not cause them to 

 fall out of the atmosphere as do most of the heavier particulates in the lower-right- 

 hand part of the table. Instead, they are deposited on surfaces by impaction or 

 are washed out by precipitation. 



339 



