Establishing site specific reference levels for fungi in outdoor air for building evaluation

Culturable airborne fungal spore sampling at five building sites during 2002-2003 provided a bank of outdoor data (102 samples total) to evaluate differences in levels of individual species of airborne fungi during the morning and afternoon hours. A minimum of 15 (outdoor) air samples was collected at each site, and data were segregated into morning (before noon) and afternoon subsets. Significant differences in airborne levels for all detected fungal types between the morning and afternoon subsets were determined for each site, using a direct calculation of probability. Significance was defined by differences in frequency of detection above the combined median (p=0.90 or greater) for the respective fungal type. The levels of various species of fungi in the outdoor air varied significantly between morning and afternoon data sets at all five sites, with no pattern by species, time of day, or location. Levels of Penicillium, Aspergillus, or other fungal species associated with problematic buildings if detected outdoors, can be significantly greater in the morning or afternoon (or exhibit no significant difference) on any given day. The data does not indicate laboratory analysis as a major contributor to the variability exhibited in bioaerosols, and underscores the necessity of collecting sufficient number of samples in the outdoor air in both the morning and afternoon to prevent bias when comparing a suspect indoor environment to outdoor conditions.