Outdoor Mold Assessment as a Background Control
Mold and mold spores are everywhere around us and outdoor air is the ultimate source for many fungal spores, that can eventually contaminate indoor air. Soil and plant materials are major sources of outdoor mold and the levels vary greatly by region, season, weather conditions, and air movement. These microscopic contaminants can get indoors through a number of sources including: doors, windows, structural cracks, ventilation intakes and also spores in the outside air attach themselves to people, both with the air surrounding them and on their clothes, shoes and bags making convenient vehicles for transporting indoors. When mold spores drop on places with excessive moisture, such as where leakage may have occurred in roofs, pipes, walls, or plant pots or where flooding may have occurred, molds will grow and produce thousands of new spores utilizing organic material in these sites. Many building materials provide suitable nutrients that encourage mold to grow. Wet cellulose materials, including paper products, ceiling tiles and wood materials are particularly conducive for the growth of some molds. Other materials such as dust, paints, wallpaper, wallboard, carpet, fabric and upholstery commonly support mold growth. In order to determine whether the indoor mold is different from that outdoors, one must understand the variability factor and transmission route.
Indoor environments are never entirely free of molds. As a general rule of thumb, in a “healthy building” the concentration of spores and the mix of mold species tend to be similar to outdoor environment levels.
A key component of any IAQ investigation is the outdoor air sample. It provides crucial information that helps to determine whether indoor contaminants are being generated within the structure or are from infiltration of outdoor contaminants. Because of the enormous potential for variability in the outdoor aerosol, the errors involved in comparing indoor and outdoor samples are enormous. This makes it essential that outdoor samples be collected as close as possible to the entry point of the specific indoor environment and as close as possible in time.
Read more about Exposure Standard of Mold in Air