Regional Variation in Airborne Alternaria Spore Concentrations in Denmark Through 2012-2015 Seasons: The Influence of Meteorology and Grain Harvesting

High airborne Alternaria spore concentrations measured in eastern Denmark have been associated with local agricultural sources. However, the density of agricultural areas is highest in western Denmark. This is the first report of airborne Alternaria spore concentrations obtained with Burkard volumetric spore sampler in western Denmark, Viborg. We compared the concentrations of airborne Alternaria spores and the patterns of air mass transport using HYSPLIT model between Copenhagen and Viborg for the seasons 2012-2015, with the main focus on the days with daily average Alternaria spore concentrations ≥ 100 s m-3 (high concentration days). Except for 2012, Annual Spore Integrals (ASIns) were on average 3,335 s day m-3 higher in Viborg than in Copenhagen. The high concentration days during 2012-2015 occurred more frequently and with higher values in Viborg (96 days; mean=381 s m-3) than in Copenhagen (79 days; mean=270 s m-3). We found increased shares of trajectories coming from South-East on the high concentration days and increased shares of trajectories coming from the West and North-West on the days with concentrations below 100 s m-3 for both stations. July and August had the highest spore integrals matching the periods of grain harvesting in Denmark. The absence of the concurrent grain harvesting in Denmark was associated with the lowest ASIns in 2012. The results of this study support the hypothesis that local sources cause the main load of airborne Alternaria spore concentrations in Denmark, however, the contribution from the remote source areas in northern Germany, Poland and southern Sweden remains unquantified