Why are outdoor mold counts important?
In most instances, indoor mold levels will closely parallel outdoor levels, both in type and amount. In naturally ventilated buildings such as many homes, air from the outside enters the building whenever the windows or doors are open. Mold is present outdoors and can enter buildings in many ways, such as when windows and doors are open and people are entering and leaving. Depending on the effectiveness of the building air cleaning devices, outdoor fungi can be removed somewhat from the airstream. The extent to which such a reduction occurs depends on the efficiency of the filtration system and how "open" the building is to the outdoors. Outdoor counts will vary greatly and may in turn cause similar variation in indoor levels. Because of this variability, it can be difficult to differentiate true difference between outdoor and indoor samples without taking a large number of samples. Soil and plant materials are major sources of airborne mold. Studies indicate that outdoor fungal levels vary greatly by region, season, weather conditions, and air movement.