Contrasting Long-Term Trends in Airborne Pollen: Evidence from 30 Years of Aerobiological Monitoring in Bolzano (South Tyrol)

Airborne pollen is a major public health concern due to its allergenic properties. Understanding long-term changes in pollen dynamics is essential for evaluating shifts in exposure to airborne allergens and enhancing allergy risk management. In this study we examine long-term trends in airborne pollen in the urban area of Bolzano, the capital city of the Autonomous Province of Bolzano—South Tyrol (Northern Italy), over a 30-year period (1995–2024), with a focus on changes in pollen taxa composition, abundance and the phenological descriptors of the pollen season. Pollen was collected using a Hirst-type volumetric sampler, operated as part of the continuous aerobiological monitoring program of the Agency for Environment and Climate Protection of the Autonomous Province of Bolzano—South Tyrol, and analysed following European standard protocols. Thirty-one taxa dominated the pollen spectrum and were investigated using two different statistical approaches. First, we used generalised linear models (GLMs) to calculate the relative annual change in Annual Pollen Integral (ΔAPIn), and then we analysed the overall trends of the main pollen season (MPS) descriptors: timing, duration and total amount of airborne pollen recorded over an entire year for a given taxon. Although no overall trend in Annual Pollen Integral (APIn) was detected, marked taxon-specific heterogeneity emerged. The strongest positive estimated trends occurred in allergenic taxa such as Morus (+4.56% Yr−1), Olea (+3.76% Yr−1), and Cupressaceae (+2.46% Yr−1), whereas negative estimated trends were seen in taxa such as Poaceae (−0.75%Yr−1), Urticaceae (−0.79%Yr−1), and native Artemisia taxa (−4.89%Yr−1). When taxa were grouped according to their ecological categories, arboreal and non-native pollen increased significantly by 1.44 and 2.12%Yr−1 respectively. Several taxa also exhibited earlier season onset and longer pollen seasons, notably Poaceae and Urticaceae. These findings provide evidence of taxon-specific changes in pollen seasons and airborne pollen concentrations in Bolzano, highlighting their relevance for allergy risk assessment.