The volumetric incidence of atmospheric allergens: I. Specific gravity of pollen grains

Abstract

1. 1. Adequate application of Stokes' law to the problem of volumetric pollen content of the air, even for fairly spherical pollen grains, requires reasonably accurate data on the specific gravity (density) of these granules. 2. 2. The specific gravity (density) of free-floating pollen grains varies with their moisture content and with the consequent changes in volume and surface character of the affected grains. 3. 3. While extreme moisture absorption may cause appreciable changes in the weight and volume of pollen grains, it is quite likely that freefloating pollen usually contains little, if any, more moisture than commercially dried pollen. 4. 4. Approximate specific gravity figures are herewith submitted for typical weed, grass, and tree pollens, based on various experimental approaches. 5. 5. The assumption that ragweed pollen grains have a specific gravity of 1 has led to the publication of calculated factors for rate of fall and volumetric ragweed air content which are in error nearly 100 per cent, except as that error may be exceeded or diminished under actual outdoor conditions by factors which have as yet not been recognized or evaluated.