PART X — ENVIRONMENTAL CONTAMINANTS 



Figure X-10 — EFFICIENCY OF CYLINDRICAL COLLECTORS 

 FOR RAGWEED POLLEN 



100 



80 

 70 

 60 



Ml 



40 

 30 

 20 

 10 



One mm, diameter cylinder 



One mm. middle section of one-fourth inch diameter cylinder 



> One-fourth inch diameter cylinder 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 



WIND SPEED IN METERS PER SECOND 



The graph shows a plot of impaction efficiency in percent versus wind speed in 

 meters per second for three different-sized cylinders. The smaller the diameter of 

 the collecting cylinder, the higher the impaction efficiency because the stagnation 

 region in front of the cylinder is physically smaller and the particles need less 

 inertia to penetrate it. To overcome the variability in wind speed and wind direction 

 in nature and to operate the samplers at optimum impaction efficiency, samplers 

 are rotated to simulate wind speeds of 10 meters or more per second. 



spores requires highly trained ex- 

 perts. At times, concentrations, not 

 only of the species of interest but 

 also of other materials, may be so 

 high that counting becomes difficult 

 and time-consuming. This problem 

 is multiplied when samples are 

 counted for many or all species pres- 

 ent. Visual counting is a tedious 

 chore at best, but automatic counting 

 devices have not yet proved their 

 ability to differentiate and count 

 aeroallergens. 



Representativeness — Aeroaller- 

 gens are commonly sampled at a 

 single point over some pre-selected 

 time period, often twenty-four hours. 

 The spatial representativeness of 

 single-station sampling has been little 

 investigated, but it is known that 

 proximity to sources, elevation above 

 the ground, and presence of obstacles 

 to airflow can produce wide differ- 



ences in catch over short distances. 

 Even two identical samplers operated 

 side by side may often differ by 10 

 to 20 percent and sometimes by 50 

 percent. If concentrations are meas- 

 ured over some time period, they may 

 not represent concentrations over ei- 

 ther a longer or a shorter time period. 

 Thus, even a perfect sampler could 

 only measure the mean concentration 

 over some time period at a specific 

 location; extension of the measure- 

 ment to other locations or periods 

 would be accompanied by some un- 

 certainty. 



Requirements for Scientific Study 



Sampling of aeroallergens, study 

 of their behavior in the atmosphere, 

 correlation of their presence and 

 abundance with other pertinent vari- 

 ables, and application of the knowl- 



edge gained to the pollinosis problem 

 would be greatly facilitated by the 

 development and use of better sam- 

 pling devices. An ideal sampler 

 would sample the atmosphere non- 

 selectively, capturing particles of all 

 sizes and shapes with equal and 

 known, although not necessarily per- 

 fect, efficiency. The samples should 

 also be collected in such condition 

 that identification, counting, and 

 analysis would not be more difficult 

 than with present samplers. Ob- 

 viously, such a sampler would have 

 wide application in sampling air pol- 

 lutants of all types. Attempts to de- 

 velop two samplers having these 

 characteristics are in progress at 

 Brookhaven National Laboratory but 

 neither is yet operational. Further 

 research and development on sam- 

 pling methods are needed. 



Until improved samplers are de- 

 veloped, rotating impactor samplers 

 will remain the most quantitative 

 method of sampling aeroallergens. 

 Only one of these, the rotoslide, has 

 been tested under controlled condi- 

 tions for collecting efficiency for rag- 

 weed pollen. Efficiency determina- 

 tions for the rotoslide and the other 

 rotating impactor samplers should be 

 made for a wide range of pollen and 

 spore types and sizes. More research 

 is also needed to determine the best 

 available adhesive for these samplers 

 and to develop better methods of 

 application. 



Since the efficiency of impaction 

 samplers is a function of particle 

 characteristics, these should be de- 

 termined for at least the more com- 

 mon aeroallergens. Most needed are 

 measurements of pollen and spore 

 density, but changes in size, density, 

 and the state of conifer pollen blad- 

 ders with age and humidity also need 

 investigation. 



Studies are also needed to assess 

 the temporal and spatial representa- 

 tiveness of single-station samples as 

 a function of surroundings (terrain, 

 vegetation, and man-made structures), 

 distance from sources, meteorological 



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