Aerobiological data as a tool to monitor allergenic urban weeds (Urticaceae) in the city of Granada over 32 years

The Urticaceae family includes the genera Urtica and Parietaria, some of the most common urban weeds, whose pollen is a significant cause of allergies, particularly in Mediterranean areas. This study analyzes the airborne dynamics of Urticaceae pollen over a 32-year period and its relationship with environmental changes and their management in recent decades in Granada (Southern Spain). Aerobiological analysis has shown that Urticaceae pollen is detected in the city's atmosphere an average of 255 days per year, with peak concentrations between February and June, and a peak that can exceed 100 pollen grains/day in early April, generally. The Annual Pollen Integral (APIn) has shown a downward trend throughout the period, especially since 2010, due to environmental factors, including prolonged periods of drought, but also due to intensive urban weed management techniques that involve the removal of plants throughout the city. Exploratory field trips conducted in the city to identify the main sources of Urticaceae pollen have found the largest number of populations in the historic Albayzín district. This district, in addition to having the highest number of preferred substrates for species like Parietaria—cracks in old stone walls, churches, and historic buildings—its designation as a UNESCO World Heritage Site entails specific cleaning and management requirements. It can be concluded that the analysis of a long series of aerobiological data can be used as a tool to analyze the environmental and anthropogenic impacts on one of the main allergenic weeds in Mediterranean cities.