During dry periods, fungi increase in number until noon and decrease throughout the evening. Ascospores and Basidiospores are considered wet weather spores, and are plentiful during light rainfall or in predawn hours when condensation is heavy. Many fungi have internal mechanisms which actively discharge their spores into the air. Other fungi rely on air movement for their dispersal. Pollen grains and mold spores are reported as the number of particles per cubic meter of air sampled.
Efficient equipment collects tiny particles.
The device is mounted on the roof of a centrally located, Saint Louis County Department of Health building, where it collects airborne particles of pollen and mold. Pollen grains and mold spores, ranging in size between one and 100 microns, flow through the sampling apparatus and stick to a greased flat surface. Although counts for pollen grains are comparable, counts for mold spores may typically be three to ten times higher than numbers reported in the past, which were based on the roto-rod sampler. Before a pollen sample can be identified and counted, it must be magnified at least 400 times. Many mold spores are extremely samll, and need to be magnified 1,000 times for observation.