130 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



£ 



a. 



5 



DC 



< 

 Q 



atural aerosol 

 particles with 

 diameters > 1 Mm 

 near the surface 

 in continental air 



10 20 30 40 50 60 70 80 90 95 98 99 

 PARTICLES WITH DIAMETER < D, % 



Fig. 7 Size distribution plots for natural and collected partijles. 



the more useful expression 



dN 



ddog D) 



= (ln 10)aD" 



(4) 



is obtained, where c= b — 1 and dN/d (log D) is the number distribution. Junge (1965) 

 found c to be about 3 over the size range — 0.7 < log D < 1.5 or 0.2 < D < 32 //m. 

 Integrating the first equation between Do and D (Dq < D) gives 



^, aD-^l^° a/1 1\ 



(5) 



Instead of expressing the distribution as the number of particles per unit volume, it can 

 be expressed as a fraction, F, of the total number of particles, or 



Nt 



m 



(6) 



where Nj is the total number of particles when D = °° and Nj - a/3Do. For a reasonable 

 distribution, only those particles which could be easily seen with an optical microscope 

 were included. Thus Do was assumed to be 1 jum, and Eq. 6 can be expressed as 



i 

 D^ 



F= 1 --^ 



(7) 



