High Ambrosia pollen concentrations in Poland rather rarely come from the local sources. The aim of this study
was to define the temporal and spatial differences of the high Ambrosia pollen concentrations by creating models
for the pollen transport from the distant sources. This study was thought to determine the direction of the air
masses inflow into Poland, carrying Ambrosia pollen, from areas of the bordering countries with the pollen concentrations
higher than iSTOTEN_n Poland. Pollen and meteorological datasets at 8 monitoring sites in Poland,
and daily pollen concentrations at 11 sites in the Czech Republic, 5 sites in Slovakia and 3 sites in Ukraine were
analysed recently. Days with concentrations ≥10 Pollen/m3 and concurrent meteorological situations were
analysed in great deal. The HYSPLIT modelwas applied to compute backward trajectories up to 4 days backward
(96 h) and at three altitudes: 20, 500 and 1000 m above ground level (a.g.l.). High pollen concentrations occur
most frequently when the air masses inflow into Poland from southerly (S, SE, SW, 44%) and easterly (E, 6%) directions
and in no advection situations (25%). In years with the highest frequency of days over 10 Pollen/m3, the
prevailing directions of the pollen influx into Poland were from the South (2004–2006, 2008, 2011) but in one
year (2014) from the East. Trajectories for the studied period show that air masses come most frequently from
Slovakia and the Czech Republic. Sometimes, the Ambrosia pollen transport happens from Ukraine.