Interpretation – Weather Conditions
Rain washes the air clean of many spore types while it assists in the dispersion of others. Sampling on rainy, foggy, or very humid days may result in outdoor counts which are low or have a significantly different distribution of spore types. Generally, rainy day microflora differs from dry, sunny microflora in that levels of ascospores and basidiospores may be increased (sometimes greatly increased). Non-viable methods will reflect this directly with increased counts of ascospores and basidiospores. Culturable (Andersen) sampling may result in increased counts of "non-sporulating" colonies since many ascospores and basidiospores will not sporulate in culture.
Sampling on days when there are strong winds also creates problems. Outside counts may be significantly higher than on non-windy days. High outdoor counts may mask small to moderate indoor mold problems since the interpretation is made on the basis of a ratio of indoor/outdoor spore counts.