What Does Indoor Air Quality Testing Actually Measure?

Derrick Fredendall

Licensed Environmental Inspector • Army Veteran • RN

The Comprehensive Blood Panel for Your House

Air quality is invisible. You can't look at a room and know if the air is healthy the same way you can't look at someone and know their cholesterol level. But with the right instruments, you can measure exactly what's in the air you're breathing — and whether it's causing the headaches, the fatigue, the persistent cough, or the general "I just don't feel great in this house" sensation you can't quite explain.

When people hear "air quality testing," they typically picture someone waving a device around and getting a simple green-light/red-light answer. Good air. Bad air. The reality is more like a comprehensive blood panel at your doctor's office — multiple measurements, each telling you something different about the overall health of your indoor environment.

Let me break down what each measurement actually tells you, in clinical terms that don't require an environmental science degree to understand.

What You're Getting: Air quality testing measures multiple factors — mold spores, VOCs (volatile organic compounds), particulate matter, humidity, CO2, and sometimes carbon monoxide and radon. Together, these give a complete picture of your indoor environment. Individually, each number tells a specific story. The interpretation is where the value lives.

Mold Spores and Biological Contaminants

This is usually what brings people to air quality testing in the first place. Something smells wrong, someone is coughing, and the question is whether mold is responsible.

What it measures: Types of mold spores present, concentrations (measured in spores per cubic meter of air), and — critically — comparison to outdoor baseline levels.

Why the outdoor comparison matters: Mold spores exist naturally in all outdoor air. Your indoor air always contains some mold spores because air moves in and out of your home. The diagnostic question isn't "are there mold spores?" — there always are. The question is "are indoor levels significantly higher than outdoor levels, suggesting an indoor source?" That's the difference between normal background and a problem.

What elevated counts mean clinically: Elevated indoor mold spores can trigger allergic responses, worsen asthma, cause respiratory irritation, and in people with compromised immune systems, cause more serious infections. Certain species — Stachybotrys, Chaetomium — specifically indicate water damage that needs addressing, because they only grow with sustained moisture. Their presence tells you something about the building, not just the air.

For detailed guidance on reading mold results, see Understanding Mold Testing Results.

Volatile Organic Compounds (VOCs)

VOCs are chemicals that evaporate at room temperature — and they're quietly present in every modern home. They're the "new car smell" of buildings, except the smell isn't charm; it's off-gassing chemicals.

Where they come from (more sources than you'd expect):

Paints, stains, and finishes — even "low-VOC" paints have some off-gassing, particularly when fresh
Cleaning products and air fresheners — the irony of air fresheners contributing to poor air quality is not lost on me
New furniture and carpets — that "new carpet" smell is formaldehyde and other VOCs releasing from adhesives and synthetic fibers
Building materials — plywood, particle board, adhesives, caulks, sealants
Personal care products — hairspray, perfume, nail polish
Hobby supplies — art materials, model glues, craft adhesives

What it measures: Total VOCs (TVOCs) in parts per billion or micrograms per cubic meter. Some advanced testing can identify specific compounds.

Why it matters: VOCs cause eye irritation, headaches, dizziness, nausea, and with chronic exposure, potentially more serious health effects. They're a major contributor to "sick building syndrome" — that phenomenon where people feel fine everywhere except inside one particular building. The building isn't haunted. It's off-gassing.

Important Oklahoma note: VOCs off-gas significantly more at higher temperatures. A newly renovated home during an Oklahoma July will have substantially higher VOC levels than the same space in January. If you're testing after renovation, summer Testing captures worst-case conditions — which is actually what you want.

Particulate Matter (PM2.5 and PM10)

Particulate matter is the stuff floating in air that you can sometimes see when sunlight streams through a window — except the most dangerous particles are far too small to see.

The numbers indicate size:

PM10: Particles under 10 micrometers — includes dust, pollen, some mold spores, animal dander. Visible in strong light. Typically caught by your body's upper respiratory defenses (nose, throat)
PM2.5: Particles under 2.5 micrometers — includes smoke, combustion particles, some bacteria, fine dust. These are the concerning ones. They're small enough to bypass your body's filtration and penetrate deep into your lungs, reaching the alveoli where gas exchange happens. Some particles this size can cross into your bloodstream

Common indoor sources: Cooking (especially frying and grilling), candles, fireplaces, smoking, incense, outdoor pollution entering through windows and HVAC, dust disturbance during cleaning or renovation.

The clinical perspective: PM2.5 is linked to both respiratory and cardiovascular problems. This is one of those areas where my nursing background connects directly to environmental inspection — understanding how particles interact with lung tissue helps me explain to clients why their asthma gets worse in certain rooms but not others. Sometimes the answer is in the particle count, not the mold count.

Humidity Levels

Humidity isn't technically a "pollutant," but it's the puppet master of indoor air quality. It influences everything else.

Ideal range: 30-50% relative humidity

Too high (above 60%):

Promotes mold growth — most species need sustained humidity above 60% to colonize
Dust mites thrive and reproduce aggressively
Building materials absorb moisture and deteriorate
Musty odors develop as microbial activity increases
Condensation on windows and cold surfaces creates water damage

Too low (below 30%):

Dry skin and respiratory irritation — winter complaint #1 in Oklahoma
Static electricity increases (annoying at best, equipment-damaging at worst)
Wood furniture and flooring can crack as moisture content drops
Mucous membranes dry out, reducing your body's first-line defense against pathogens

Oklahoma's challenge: This state has a split personality when it comes to humidity. Summer brings sustained 70-80% outdoor humidity — your HVAC system is the only thing keeping indoor levels manageable. Winter brings dry 20-30% conditions that turn every doorknob into a static shock delivery system. Managing humidity in Oklahoma means fighting a different battle every six months.

Carbon Dioxide (CO2)

CO2 isn't toxic at normal indoor levels. But it's an excellent proxy for ventilation — it tells you whether your building is exchanging enough air with the outdoors.

What it measures: CO2 concentration in parts per million (PPM)

CO2 Level (PPM)	What It Means
400-600	Good ventilation. Close to outdoor levels (~420 PPM current outdoor average)
600-1,000	Acceptable for occupied spaces. Normal for houses with people breathing in them
1,000-2,000	Ventilation needs improvement. You'll start feeling drowsy and having difficulty concentrating
2,000+	Poor ventilation. Action needed. Headaches, significant cognitive impairment reported in studies

If you've ever felt sluggish in a crowded conference room or couldn't focus in a packed classroom, elevated CO2 is likely the reason. The same thing happens in homes — especially modern, energy-efficient homes built so tight that they don't exchange air with the outdoors sufficiently. Older, drafty Oklahoma homes rarely have CO2 problems. Newer, well-sealed ones sometimes do.

Carbon Monoxide (CO)

Carbon monoxide is in a different category entirely. It's not a quality-of-life issue — it's a safety issue. CO is produced by incomplete combustion and it's colorless, odorless, and potentially fatal.

Sources: Gas stoves, furnaces, water heaters, attached garages (car exhaust migrating into living spaces), fireplaces, generators

Why it's measured: CO poisoning kills people. Even low-level chronic exposure causes headaches, confusion, and fatigue that looks like a dozen other conditions. I've had clients who thought they had chronic fatigue or depression who actually had a slow CO leak from a cracked heat exchanger in their furnace. This is one of those measurements where "boring normal result" genuinely matters.

Your CO detectors at home: Dedicated CO detectors are standard in homes with gas appliances, and they save lives. But they alarm at relatively high levels — they're designed to prevent acute poisoning, not detect chronic low-level exposure. Air quality testing can identify low-level CO that falls below your detector's alarm threshold but above what's healthy for sustained exposure.

Temperature

Temperature seems simple — it's either comfortable or it's not. But in air quality assessment, temperature data serves a diagnostic purpose:

Higher temperatures increase VOC off-gassing — those new cabinets release more formaldehyde at 82°F than at 68°F
Temperature affects humidity readings — relative humidity is relative to temperature. The same amount of moisture in the air reads differently at 65°F vs 80°F
Temperature differentials indicate HVAC issues — a room that's consistently 10° warmer or cooler than adjacent rooms suggests airflow problems that also affect air quality
Thermal bridging creates condensation — cold spots on walls (often around window frames or where insulation is missing) cause moisture to condense, creating exactly the conditions mold needs to grow

What About Radon?

Radon is a radioactive gas that seeps from the ground into buildings through foundation cracks, sump pits, and construction joints. It's the second leading cause of lung cancer after smoking, and you can't see it, smell it, or taste it.

Radon testing is typically done separately from general air quality testing because it requires specialized equipment and longer sampling periods — usually 48+ hours minimum for short-term screening, and ideally 90+ days for a long-term average. It's a different instrument, a different protocol, and a different report than what's included in a standard air quality assessment.

If radon is a concern — and in Oklahoma, certain counties have naturally elevated radon levels due to the underlying geology — we discuss that as a separate service when you schedule.

How Professional Testing Works (Not What You'd Expect)

Professional air quality testing isn't someone walking through your house with a handheld device for ten minutes and emailing you a PDF. Here's what's actually involved:

Baseline assessment: Understanding your home, HVAC system, recent renovation history, and specific concerns. Why you're testing shapes how I test
Strategic sampling locations: Not random. I sample in areas where you spend time (bedrooms, living areas), areas of concern (the room that smells different), and control locations (outdoor air, unaffected rooms). The comparison between locations is where the diagnostic information lives
Indoor/outdoor baseline: Every indoor sample gets an outdoor control. Without knowing what's normal outside, indoor numbers are meaningless. A mold count of 500 spores per cubic meter could be concerning or perfectly normal — it depends entirely on what's happening outside
Laboratory analysis: Air and surface samples go to an AIHA-accredited lab with chain-of-custody documentation. The lab identifies species, quantifies concentrations, and provides data I can interpret in context
Data interpretation with context: This is where a nursing background actually helps. Raw numbers from a lab mean nothing without interpretation. "Aspergillus/Penicillium at 1,200 spores/m³" is data. "Your indoor levels are 3x outdoor baseline, concentrated in the master bedroom area, consistent with a hidden moisture source in the shared wall with the bathroom" is information you can act on

Timing Matters: Air quality varies throughout the day and across seasons. Testing captures a snapshot. If you're troubleshooting ongoing symptoms, consider testing during conditions when symptoms are worst — not when conditions are mildest. An air quality test on a breezy November day when windows have been open may tell a very different story than testing on a sealed-up August afternoon when humid outdoor air is trying to enter every crack.

When Air Quality Testing Makes Sense

You don't need air quality testing for every situation. It makes sense when:

Unexplained symptoms — respiratory issues, headaches, or fatigue that improve when you leave the house and return when you come home
Persistent odors — musty smell, chemical smell, or "something's off" that you can't identify
After renovation — new paint, carpet, cabinets, or flooring introduces VOCs and may have disturbed hidden materials
Moving into a new-to-you home — especially older construction where you don't know the building's environmental history
Following water damage or flooding — even after "drying out," air quality assessment confirms whether mold has established
Vulnerable occupants — household members with asthma, allergies, chemical sensitivities, or immune compromise where air quality directly affects health outcomes

For guidance on whether your specific situation calls for mold-specific testing or broader air quality assessment, see Mold Inspection vs. Air Quality Testing: Which Do You Need?

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