Abstract
To understand the characteristics of diurnal changes in hourly counts for the pollen of Cryptomeriaceae dispersed in the atmosphere of Kobe, we investigated the relationship between hourly pollen counts and wind direction in 2002, 2003 and 2005. Stratified by four wind directions and four time periods (thus divided into 16 sections), the pollen count was statistically analyzed by the Kruskal-Wallis rank sum test and multiple comparison. When the wind direction was from the north to northwesterly from the Tanba and Chugoku mountains (the major sources of the pollens), their counts were characterized by the follow: they tended to increase between 13:00 and 18:00 hours in comparison with other wind directions and other time periods and decrease between 01:00 and 06:00 hours, in contrast to other wind directions. According to Bonferroni correction, a significantly decrease (p<0.05) was found with the northeast to east wind in 2003 and 2005. In some instances, however, the intra-day counts reached the highest from 01:00 to 06:00 hours when the approach of a low atmospheric pressure caused the wind to shift from the northeast to east direction. These findings indicate that the pollen count in the winds coming from the direction of the main source of pollen was affected differently during different time periods. It was also found that the pollen count could increase after midnight as a result of specific meteorological conditions.
