Our clients sometimes appear to be slightly befuddled as to why we recommend an air sample from the outside, which is perfectly understandable! Why would one be concerned with getting an air sample from the outside, when, what we're concerned with is the interior air quality!
Our environment naturally harbors myriad types of mold, such as Cladosporium, but at levels which aren't concerning. If we take 3 air samples from within a property, and we review the results, the outside air serves as a useful barometer to extrapolate a reliable interpretation of the interior results.
For example, if, upon initiating an air sample in a bathroom, the results display 459 spores m/3 of Aspergillus, we may have reason for concern. Conversely, if, in our outdoor air sample, Aspergillus is registered at 569 spores m/3, then we don't have any reason for concern due to the exchanging of air between the exterior and interior of the property. This, ultimately, can save the homeowner or tenant a lot of issues, and money, in determining the presence, or extent, of a mold issue.
Then, there's the question of, 'why can't just a standard outside air sample be used time and time again, indefinitely? Why take an outside air sample at each new property and each new inspection?'
This is a very pertinent question. The concentration and overall distribution of mold spores can sway in its variation due to various factors such as the season and the time of day due to variations in meteorological conditions. According to data collated via the Environmental Analysis Associates (EAA), the range in the quality of outside air can vary in parts greater than a hundredfold. An excerpt from the EAA Journal of Occupational and Environmental Hygiene states,
"For example, total mold spore concentrations at EAA’s outdoor monitoring station in San Diego have ranged from 200 spores/m3 during calm wind conditions to 80,000 spores/m3 during high Santa Ana wind conditions (wind speeds greater than 20 miles per hour). The most predominant fungal groups found outdoors include ascospore/basidiospore and Cladosporium species. Occasionally, elevated concentrations of other fungal groups, including Aspergillus/Penicillium, Alternaria, and smuts/myxomycetes, can also be found."
Due to the amount of variables involved in air quality testing, this is why it is highly recommended that people who are interested in discovering what is in their homes, have an outside air sample completed.
MOLD HEALTH EFFECTS BLOG AND RESEARCH