Increase in airborne allergenic pollen in Trentino (North Italy) over a 30-year period (1989-2018) is connected to temperature rise

The aim of this study is to verify if changes occurred in the seasonality and yearly amounts of airborne pollen in San Michele all’Adige - Northern Italy, and to evaluate their relation with climate change-related variables, such as air temperatures and frost days in the period 1989 - 2018. The study of airborne pollen and its spatio-temporal changes is highly important due to the allergenicity of many pollen taxa. The pollen allergy, in fact, interests 25-40% of population, globally, and displays an increasing trend. Climate change may impact pollen allergenicity and production, as well as plant distribution, with the potential spread of neophytes that produce allergenic pollen. The main hypothesis of our research is that climate change impacting our study area influences pollen dispersal in the atmosphere, and therefore on human-health related issues. Airborne pollen was collected using a volumetric Hirst-type aerobiological sampler (Lanzoni VPPS 2000), and the daily concentration of airborne pollen (P*m-3 ) was calculated for a total of 24 arboreal (AP; trees and shrubs) and non-arboreal pollen taxa (NAP; herbaceous) over a 30- year period. The sampling and analysis of airborne pollen have been performed in accordance with the UNI EN 16868:2019 European standard procedure. The main pollen season (MPS) descriptors were calculated for each taxon. The presence of a monotonic upward or downward temporal trend in pollen season descriptors was verified (non-parametric Mann-Kendall test) and changes were analyzed in relation to air temperature, precipitation, and land use; in addition, pollen data were analyzed clustered into three decadic blocks (non-parametric Kruskal-Wallis ANOVA) to minimize interannual fluctuations and maximize relevant change signals. The major change observed during the study period was the significant increase in annual pollen integral (APIn). This change is strongly emphasized when analyzing the pollen data in three decadic blocks, both for all the considered taxa (+58%) and for Arboreal Pollen (AP; +155%). When considering single taxa, APIn shows a significant positive trend for Cupressaceae/Taxaceae, Ulmus, Populus, Salix, Ostrya, Quercus, Olea, Plantago, Cannabaceae, and Ambrosia; a significantly earlier start of the MPS is proved for Rumex and Poaceae. Cumulated APIn shows a significant positive correlation with annual T min (<0.005) and T mean (<0.001), both of which showing a significant increase, and a negative correlation (<0.025) with the number of frost days. The research demonstrates an increasingly larger amount of airborne pollen connected to climate change, such as rising temperatures and milder winter conditions in the study area, leading to a major threat to people suffering of pollen allergies.