Grain harvesting as a local source of Cladosporium spp. in Denmark

Cladosporium spp. are omnipresent moulds that grow on multiple substrates. Their spores possess a high allergenic potential. Currently, little is known about the incidence and the sources of airborne Cladosporium spores in Denmark. Air samples were collected between 31 May and 22 September 2015 in Viborg (Jutland, western Denmark). Eighteen out of 21 days with daily average concentrations exceeding the health-relevant threshold of 3000 Spores m −3 , including the day with peak daily (13,553 Spores m −3 ) and 3-h concentrations (35,662 Spores m −3 ), occurred in August. The air masses that approached Viborg during the longest episode of elevated spore concentrations originated from northern Poland, the Baltics, passing over southern Sweden and the eastern Danish island of Zealand. The Cladosporium spore concentrations from Viborg were compared with the Cladosporium spore concentrations from the operational monitoring station in Copenhagen (Zealand, eastern Denmark). During the episode, concentrations in Viborg were on average 2268 spores m −3 higher than in Copenhagen. On the peak day between 8:00 and 15:00, concentrations in Viborg were 4–7 times higher than in Copenhagen, which we associated with grain crop harvesting in eastern Jutland. Elevated day time concentrations in Viborg on the days with daily average concentrations exceeding the threshold also indicate the local character of the sources.