D3.469 - Interaction between Meteorological Variables and Atmospheric Pollutants in the Dynamics of Alternaria Spores in Bragança, Portugal

Alternaria spores are important airborne allergens linked to respiratory diseases affecting around 4.4% of adults in Europe. Their airborne concentration is strongly influenced by vegetation and weather. This study quantified atmospheric concentration of Alternaria spores in Bragança, Portugal, and examined their associations with meteorological variables and urban air pollutants.

Daily sampling (2022 to 2024) was done using a 7-day Hirst-type volumetric sampler, and samples were analyzed by optical microscopy. The Main Spore Season and the Annual Spore Integral were computed using the AeRobiology package in R. Daily concentrations were compared with the clinical threshold of 100 spores/m³, to identify periods of potential health risk. Associations between spore concentrations with meteorological variables (average temperature, relative humidity, solar radiation and total precipitation) and atmospheric pollutants (NO₂ and O₃) were tested using Spearman's rank correlation (p < 0.05).

A total of 16,128 Alternaria spores/m³ were identified, with a 59.7% rise in annual concentrations from 2022 to 2024. The Main Spore Season showed marked seasonality with peaks in June-July and lasted from 206 days in 2022 to 238 days in 2023 and 2024, evidencing concentrations higher than those of other Iberian regions. The 100 spores/m³ threshold was exceeded on 5 days in 2022 and 2023 and on 13 days in 2024, underscoring the risk to public health in the region. Alternaria spore concentrations showed significant strong positive correlations with air temperature (from 0.65 in 2022 to 0.70 in 2024; overall 0.65) and moderate correlations with solar radiation (from 0.28 to 0.49 across the study period, overall 0.23). Relative humidity and precipitation showed significant negative correlations (overall –0.39 and –0.40, respectively). Among atmospheric pollutants, NO₂ showed a stronger and consistently significant influence on Alternaria airborne concentrations (0.54 in 2023 to 0.40 in 2024, overall 0.39), whereas O₃ exhibited only weak associations, significant only in 2022 (0.25; overall 0.092).

In Bragança, Alternaria dynamics appear to be driven by the interplay of climatic conditions and urban air quality. The rising spore load and its links with gaseous pollutants indicate increasing risk for sensitised individuals. Continuous aerobiological monitoring and integration in spore forecasts would help anticipate high-risk periods, particularly during hot periods coinciding with urban pollution episodes.