Scientists at NC State looked at a database of dust samples collected from 1000 sites in 47 states. The outdoor dust samples contained plenty of microbes, including particles of fungi. Of the nearly 40,000 types of fungi found in the samples, not too many overlapped. As the researchers mentioned in the paper, some fungi were only found on the west coast, or were closely associated with crops like grapes, so a sample containing both might have come from a wine-growing region in the West. With thousands of fungi, each with their own preferred habitat, the researchers had a lot to work with.