VIII 

 AIR SAMPLING TECHNIQUE 



Knowledge of the air-spora has depended on developing sound tech- 

 niques for air sampHng. Smoke and many industrial dusts can be studied 

 satisfactorily with the ultra-microscope {see Green & Lane, 1957, p. 218), 

 but direct microscopic examination of spores suspended in air is scarcely 

 ever practicable. All convenient methods depend on apparatus to remove 

 the spores to a surface where they can be examined — either directly under 

 the microscope or after growth in culture. 



Early methods of air sampling were summarized by Cunningham 

 (1873). Developments during the next seventy years were reviewed by the 

 Committee on Apparatus in Aerobiology of the National Research Council, 

 Washington, D.C. (1941), and again by duBuy et al. (1945) of the United 

 States Public Health Service. Now that deposition efficiencies are better 

 understood, sampling methods can be reviewed once more. 



The various sampling techniques that are now possible have different 

 advantages and limitations. The following questions have to be answered 

 before a technique is chosen for a particular job. Is an assessment of the 

 total air-spora wanted, or is the study concerned only with a few groups or 

 a single species .f' Is a continuous day-and-night record needed, or will 

 short and regular or occasional samples suffice ? If changes in the air-spora 

 are being studied, what time-intervals are necessary: would a 24-hour 

 mean suffice, or must an accuracy of i i hour be attained, or again, is an 

 instantaneous cut-off needed to give a time-discrimination of minutes or 

 seconds ? The size of the sample must be decided upon, and the choice 

 made between the volumetric or deposition methods. Allergists are 

 normally interested in the number of particles (dead or alive) in a given 

 volume of air, whereas plant pathologists and plant breeders are more 

 interested in the deposition of viable spores or pollen grains. 



Spore trapping requires apparatus, and many questions have to be 

 asked about this. What are its capital and running costs ? (It is uneconomic 

 to use the time of a trained scientist with a good microscope on inefficient 

 sampling methods.) Does it need a power supply ? Must it be portable } 

 Is it to be operated by a skilled staff or must it be robust and foolproof.'' 

 Does its efficiency vary with wind-speed ? 



When the spore has been caught it has to be identified — but is this 

 to be done visually or by cultural methods ? Visual methods (using various 

 forms of microscopy) should give the complete picture of the air-spora 



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