Critical Issues of Aerobiological Monitoring: The Long-Distance Transport of Ambrosia Pollen into Rome

Pollen data obtained from aerobiological monitoring are utilized in various fields of application but require statistical processing. In this study, airborne pollen data from the Rome aerobiological monitoring stations (San Pietro Hospital and Tor Vergata), covering the period 1997–2025, were analyzed, with a specific focus on an Ambrosia pollen episode occurring on 11–12 September 2009. Many studies have employed descriptive statistical methods or predictive models. Among these, the HYSPLIT model was employed in a case study to verify whether the elevated levels of ragweed pollen recorded on 11–12 September 2009 in Rome were attributed to long-distance transport, and to determine the possible source areas through back-trajectories. The relationships between pollen concentrations, distribution maps of Ambrosia spp. individuals, transport conditions, and meteorological conditions were examined. The combination of these tools appears to confirm that the presence of Ambrosia pollen is the result of long-distance transport. To complement the modeling analysis, backward trajectories were computed using the HYSPLIT model with a 48 h duration at three altitudes (0, 100, and 1500 m above sea level) to evaluate the influence of planetary boundary layer dynamics on the transport pathways. Despite being an excellent tool, the use of HYSPLIT in Italy could present some critical issues due to the terrain topography, which affects the calculation of altitude levels and introduces uncertainties in trajectory reconstruction. New techniques are emerging daily, leading to increasingly precise forecasts. Nevertheless, an increase in aerobiological sampling sites with adequate regulation would represent a sound starting point for standardizing intervention strategies.