THE MICROBIOLOGY OF THE ATMOSPHERE 



replaced the arbitrary 99 per cent of Schmidt's dispersal Kmit by the 

 concept of 'probable line of flight'. Rombakis postulated that a point P 

 at height z and time t will be a point on the probable line of flight when it 

 is statistically equally probable for a particle to occur above or below P. 

 At the 'probable flight range' (a distance about one-tenth of Schmidt's 

 'V'), 50 per cent of the particles liberated will have been deposited; 

 'probable flight height', and 'flight duration', are similarly defined. 

 Rombakis also reached the interesting conclusion that the 'probable 

 final velocity' of a particle is half its terminal velocity in still air. These 

 concepts were applied to the dispersal of fungus spores by Schrodter 

 (1954), who used Falck's (1927) calculations of terminal velocities to 

 predict probable flight ranges, altitudes, and durations for various spore- 

 sizes, wind-speeds, and values of the turbulence coefficient. Examples 

 from Schrodter's extensive calculations are given in Table XXVII. In 

 his later, valuable review of the topic Schrodter (i960) uses Rombakis's 

 method for estimating distance of dispersal, and Sutton's equations for the 

 concentration of the spore-cloud. 



TABLE XXVII 

 'probable flight range' (Schrodter, 1954) based on rombakis's 



MODIFICATION OF SCHMIDT's THEORY 



T.V. = terminal velocity. 



DEVELOPMENT OF SUTTON's THEORY 



Sutton's equations predict concentration when there is no loss by 

 deposition. To adapt them for particles which deposit appreciably during 

 travel, it is necessary to calculate Q^^? ^^he number of spores remaining in 

 suspension after the cloud has travelled a distance x, from the equation : 



A\-hn) -] 



X h (P- 77). 



Clx = CLo exp. 



2pX^ 



V(7r)C(l -hn)_ 



Expected depositions at various distances from point, line, strip and 

 area sources can then be calculated (Gregory, 1945, and unpublished). 



168 



