[Hourly variations in the dispersion of Japanese cedar (Cryptomeria japonica) pollens in the Yamagata basin and the effect of cold and warm fronts on the pollen counts].

Airborne pollen counts of Cryptomeria japonica (CJ) were investigated at three points in the Yamagata Basin: 1. the central part of Yamagata City (point A), 2. at the foot of a mountain with a CJ grove (point B), 3. within the CJ grove (point C). At the beginning of the CJ pollen season, the airborne pollen counts at point B showed higher values than those at point A, whereas the relation of the count values was reversed later at the major pollen dispersion period. Numerous airborne pollens were detected at point C during the daytime, but few at night. On the other hand, many airborne pollens were found at point A during both the day and night. These results suggest that the pollens which come to rest on the roofs of houses and the pavement surfaces may be blown up into the air again. It was found that many pollens could be counted before a warm front passed through point A but that few pollens could be counted at the passage of a cold front.