Do the threats of alder and birch allergenic pollen differ within an urban area?

Currently, the increasing frequency of inhalant allergy is often linked to the urbanization effect. The pollen forecasts for a given city are most often prepared using data from one aerobiological station. However, there is evidence that the pollen concentrations in the air might differ depending on the city area and the height of the pollen trap. This study evaluated the spatial differences in the daily concentrations of alder and birch pollen grains in an urban area in relation to the proximity of the pollen sources and meteorological parameters. Pollen grains were sampled in Rzeszow in 2014-2016 by three volumetric traps located at the roof and nose levels in two city areas that differed in the numbers of alder and birch trees. The daily pollen concentrations were categorized into three allergy symptom thresholds. The relationship between the daily pollen concentrations and meteorological variables was examined using a redundancy analysis and circular statistics. There were spatial differences in the pollen season intensity and, to a lesser extent, the variability in its course. Generally, higher concentrations were registered at the roof level and in the city suburbs than at the nose level and in the downtown area where alder and birch trees were less numerous. Despite the spatial variability of the pollen concentrations and the differences in the proximity and abundance of pollen sources, the risks for allergy sufferers were similar throughout the city. It was concluded that the main cause of this phenomenon is the high dispersal abilities of Alnus and Betula pollen grains. Although temperature seems to be a crucial factor that influences the airborne pollen of both taxa, several weather variables were found to have complex impacts on the daily concentrations.