The prevalence of ragweed (Ambrosia artemisiifolia) pollinosis has been increasing worldwide. This study focused on the behavior of autumn airborne pollen and the major ragweed allergen -Amb a 1 particle in urban Saitama, Japan, in 2016. Burkard sampler results showed that the airborne ragweed pollen scattering season was from September 1st to October 9th. Over 83% of sampling events had pollen counts of over 13 grains/m(3), indicating the high potential health risks of ragweed pollen in the atmosphere. The results of a surface plasmon resonance immunoassay (SPR) indicated that the average Amb a 1 count was about 16.5 pg /pollen. The airborne Amb a 1 concentration was up to 4.7 ng/m(3), of which about 45% was accumulated in ultrafine particles, such as particulate matter with a diameter <= 1.1 mu m (PM1.1). Although ragweed pollen was hardly observed during the October 14th-17th sampling campaign, the concentration of ambient Amb a 1 particles in PM1.1 was also determined to be 4.59 ng/m(3), which could be explained by the longer scattering of fine particles in the atmosphere. Pearson correlation coefficient analysis results showed that temperature (daily, r = 0.41; event, r = 0.87) could affect the behavior of the airborne pollen counts, and ambient water-soluble ions (such as Ca2+ and NO3-) could affect Amb a 1 in PM1.1. Additionally, air mass trajectories and wind rose results indicated that air masses with long-range transportation could also influence the temporary behavior of Amb a 1 and pollen counts via the wind. Mugwort and Humulus japonicus pollens were also observed to extend pollen scattering periods. Airborne pollen and allergenic particles could be considered air pollutants, as they pose health risks and are susceptible to environmental influences.