Abstract:

This article investigated diurnal variations of pollen dispersal and the relationship with microclimate factors during the flowering period of Pinus tabulaeformis, Pinus bungeana and Ailanthus altissima. Pollen concentrations of the three species were monitored at 10 m away from trunk of the sampling tree and 1.5 m high above ground of hard ground surfaces. Results showed that: 1) Diurnal variations of pollen dispersal among three species had similar double-peak curves which presented at 14:00 and 20:00 on hard ground surface. 2) There was a significant relationship between pollen concentration and air temperature, air relative humidity, ground temperature，light intensity. 3) The ground temperature played a crucial role in the diurnal variations of pollen concentration and might be a decisive factor for the emergence of the second peak of pollen concentration. The heat stored in hard ground during the day would be slowly released at night, which could promote the air convection and hence be the main reason for the second peak of pollen concentration at 20:00. Compared with the soft ground, the airborne allergenic pollen showed much more harmful in the air near hard ground. In addition, tree species selection, urban surface condition, and timing for outdoor sports and activities were suggested.

Key words: pollen concentration, diurnal variation, microclimate factors, hard ground surface