Airborne Alternaria and Cladosporium spores at ground level: Influence of land use and harvesting activity

Fungal spores, a common component of biological air pollution, may negatively affect human health by triggering allergic symptoms. To assess the risk of exposure to allergens, abundant and highly allergenic Alternaria spp. and Cladosporium spp. spore concentrations are routinely measured, but almost exclusively on rooftops. In contrast, research on concentrations at ground-level, where people spend most of their time outdoors, is scarce. Although there is evidence that the main source of fungal spores is agricultural areas during harvest, it remains unclear how the proximity of crops influences ground-level spore concentrations. To address this, portable volumetric traps and meteorological stations were used to conduct three ground-level measurement campaigns (before, during, and after harvesting) throughout the main sporulation season in 2023. Nine sampling points in Poznań (Poland) represented the main land use types: agricultural, urban, and forest. The maximum concentrations were 1369 spores/m³ (Alternaria, 47% higher than the rooftop maximum) and 88 820 spores/m³ (Cladosporium, 458% higher), both recorded in agricultural areas. On average, concentrations of Cladosporium spores increased during harvest, whereas Alternaria concentrations substantially increased after harvest. The highest concentrations of Alternaria and Cladosporium spores were associated with air influxes from arable land (rho = 0.20 and 0.35, respectively) and grasslands (only Cladosporium, rho = 0.24). Overall, we successfully established an extensive, mobile, ground-level spore measurement network, which revealed differences in fungal spore concentrations across land-use types, harvest activities, and in comparison with regional-level measurements. This study represents an important step toward assessing airborne fungal spore concentrations relevant to human exposure.