Dispersion and deposition of airborne Lycopodium and Ganoderma spores

Abstract

SUMMARYSpores were liberated at 0.25 and 1.0m. above grass. Airborne concentrations at twenty or more points in the spore cloud were measured with specially designed and calibrated miniature suction traps, operated off a portable vacuum system. Deposition in the downwind direction was measured on artificial surfaces on the ground. Measurements were made up to 10 m. from the source.The observed increase in horizontal cross‐wind standard deviation of the Lycopodium cloud agreed well with O. G. Sutton's theory, but was incompatible with that of W. Schmidt.The coefficient of deposition, p, calculated from mean cloud concentration per c.c. and deposition to ground per cm.2, as well as the velocity of deposition, vg, varied with distance from source. Both p and vg were larger for Lycopodium than for Ganoderma, and at the greater distances tested, vg approximated to the expected terminal velocities of the particles in still air.The total number (Q0) of Lycopodium spores liberated in each experiment was known, and tentative estimates of the proportion deposited within the sampling area indicated that, under day‐time winter conditions in England, the cloud lost not less than 13 to 24% of its load within 10 m. of the source.