Tanjun Knowledge Library

Air Sampling — Indoor vs. Outdoor Control Baselines

Mold is naturally present in the outdoor air. When performing air sampling, an outdoor control sample is taken to establish a baseline. An indoor environment is often considered normal when the types and amounts of mold inside are below or similar to the outdoor sample. If a lab report shows elevated mold counts indoors — as compared to the outdoor sample — or detects certain types of molds that are absent outside, it can indicate a potential mold growth and moisture issues that may require further investigation.

Air Sampling vs. ERMI and HERTSMI

Property and homeowners researching advanced mold testing options often encounter the terms ERMI (Environmental Relative Moldiness Index) or HERTSMI-2 (Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens). Both rely on DNA-based testing to analyze mold species found in settled dust samples — an approach originally developed by the EPA as a research tool for ERMI.

However, the EPA and leading industrial hygiene and indoor air quality organizations — such as the AIHA — do not recommend ERMI testing for routine home inspections. Because mold DNA can persist indoors for years, an ERMI test may report historical mold signatures from an old leak that was resolved long ago. As a result, the test results can reflect past dust accumulation rather than what occupants are actively breathing.

It should be noted that some specialty medical practices do recommend ERMI and HERTSMI-2 to their patients. Physicians treating individuals with severe mold sensitivities or Chronic Inflammatory Response Syndrome (CIRS) sometimes request these tests to evaluate a home's overall fungal load against specific medical recovery thresholds.

For most home environments and general inspections, air sampling via spore traps remains the standard industry method. Spore traps collect a point-in-time sample of ambient air, which an accredited laboratory analyzes under a microscope. While a single air sample is only a brief snapshot of current conditions, combining those results with an outdoor control sample, a professional visual assessment, and moisture content (MC) testing — can provide a reliable picture of whether an active indoor mold issue is present.

Test-Only

No Remediation. No Conflicts of Interest.

Since we do not perform mold removal or remediations, we avoid conflicts of interests. This allows us to focus on an objective, evidence based report and unbiased recommendations.