The Science of Indoor Air Quality Testing — What Particle Counters and Mold Sampling Actually Measure

Air quality testing produces numbers. Understanding what those numbers represent — and what they don't represent — allows homeowners to use the information meaningfully rather than treating it as either alarming or reassuring without basis.

Particle Counting: What It Measures and How

Electronic particle counters measure the number of particles in a given volume of air, categorized by size. Common measurement categories include:

• PM1.0: Particles 1 micron or smaller
• PM2.5: Particles 2.5 microns or smaller
• PM10: Particles 10 microns or smaller

Particle counters work by drawing air through a laser beam and detecting light scattered by particles passing through. The count and size of scattering events translates to a concentration measurement (typically particles per cubic centimeter or micrograms per cubic meter).

What particle counting tells you: The total concentration of particles in various size ranges. High particle counts at PM2.5 suggest elevated fine particulate from some source — biological particles, combustion, or other fine material.

What particle counting doesn't tell you: The identity of the particles. A particle counter measuring elevated PM2.5 cannot distinguish between mold spore fragments, skin cells, combustion byproducts, or other sources of fine particulate. It tells you there are particles; it doesn't tell you specifically what they are.

Mold Spore Sampling: How Identification Works

For specific mold identification and counting, air samples are collected and analyzed by a laboratory:

Air-O-Cell or similar cassettes: A calibrated pump draws a measured volume of air (typically 75 liters over 5 minutes) through a cassette containing a sticky collection medium. Mold spores in the sampled air adhere to the medium.

Laboratory analysis: The cassette is sent to an accredited laboratory where a microscopist examines the collection medium, identifying and counting mold spores. Results are reported as spore counts per cubic meter for each identified genus or species.

Outdoor comparison samples: Professional mold sampling includes outdoor baseline samples taken concurrently with indoor samples. The comparison between indoor and outdoor spore counts for each species is the most meaningful interpretation frame — indoor mold spore counts higher than outdoor levels indicate an indoor mold source.

VOC Measurement

Volatile organic compounds are measured using various methods:

PID (Photoionization detector) meters: Measure total VOC concentration in ppb (parts per billion), providing a real-time total VOC reading. Useful for identifying elevated VOC conditions but doesn't identify specific compounds.

Sorbent tube sampling: Active samples drawn through tubes containing absorbent material, analyzed by laboratory gas chromatography/mass spectrometry (GC/MS) for specific VOC identification and concentration. The most detailed analysis but more expensive and time-consuming.

Understanding Result Interpretation

For particle counts: Compare to established guidelines (EPA, ASHRAE) for indoor PM2.5. Compare before-treatment to after-treatment measurements to assess whether an intervention changed concentrations.

For mold spore counts: Compare indoor to concurrent outdoor samples. Equal or lower indoor counts suggest no significant indoor mold source. Indoor counts substantially higher than outdoor — particularly for specific species — indicate an indoor source. Compare species identified indoors vs. outdoors: species present indoors but not outdoors (or present at much higher concentrations indoors) point toward an indoor growth location.

For VOCs: Compare to ASHRAE guidelines for acceptable TVOC levels in residential spaces. Identify specific compounds if GC/MS analysis was performed.

The Before-and-After Standard

The most meaningful use of air quality testing for HVAC decontamination assessment is paired sampling: measurements taken in the same locations under comparable conditions before and after the decontamination service. Changes in particle counts, mold spore concentrations, and VOC levels document what the service actually changed in the breathing air — not what was claimed.

Every Respira Florida service includes professional before-and-after air quality testing — giving you the science, not the salesmanship. We're accepting founding clients for our 2026 Orlando launch.

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