An air quality test detects pollutants that are invisible to the eye and often odorless: gases like radon and carbon monoxide, volatile organic compounds from household products, particulate matter from combustion and dust, and biological contaminants like mold spores. The exact list depends on the type of test you use, but most tests target the pollutants known to cause the greatest health risks indoors.
Volatile Organic Compounds (VOCs)
VOCs are chemicals that evaporate from everyday products and building materials at room temperature. Air quality tests that screen for VOCs can pick up compounds like formaldehyde, benzene, toluene, xylene, and methylene chloride. These chemicals come from paint, cleaning products, new furniture, flooring adhesives, air fresheners, and dry-cleaned clothing. Formaldehyde alone can off-gas from pressed wood products for years.
Some tests measure total VOC levels as a single number, giving you a general sense of chemical contamination. Professional lab-based tests can break that number down into individual compounds, which matters because the health risks vary widely. Benzene, for example, is a known carcinogen, while other VOCs primarily cause headaches, eye irritation, or dizziness at lower concentrations. VOC levels are typically reported in parts per billion (ppb) or parts per million (ppm).
Particulate Matter
Particulate matter refers to tiny solid particles and liquid droplets suspended in the air. Tests measure two main size categories. PM10 particles are 10 microns or smaller, roughly one-seventh the width of a human hair. PM2.5 particles are 2.5 microns or smaller, fine enough to pass deep into your lungs and even enter your bloodstream.
PM2.5 comes primarily from combustion: cooking on gas stoves, burning candles, wood-burning fireplaces, cigarette smoke, and vehicle exhaust that drifts indoors. PM10 includes those same sources plus dust, pollen, pet dander fragments, and construction debris. Both are measured in micrograms per cubic meter of air (μg/m³). Consumer-grade air quality monitors with laser sensors can give you real-time PM2.5 and PM10 readings, making particulate matter one of the easiest pollutants to track at home.
Radon
Radon is a radioactive gas that seeps into buildings from naturally occurring uranium in soil and rock. It’s colorless and odorless, so testing is the only way to know if it’s present. The EPA sets an action level at 4 picocuries per liter (pCi/L), but also recommends considering remediation for levels between 2 and 4 pCi/L since there is no known safe level of exposure. For reference, the average outdoor concentration is about 0.4 pCi/L.
Radon testing is usually done separately from other air quality tests. Short-term test kits sit in the lowest livable level of your home for two to seven days, then get mailed to a lab. Long-term tests run for 90 days or more and give a more accurate picture of your actual exposure. Radon is the second leading cause of lung cancer after smoking, which is why it gets its own dedicated testing category.
Carbon Monoxide and Other Gases
Carbon monoxide (CO) is produced by anything that burns fuel: gas stoves, furnaces, water heaters, fireplaces, and attached garages where cars idle. CO detectors are common in homes, but air quality tests can also measure it alongside other pollutants. Concentrations are reported in ppm, and even low levels over extended periods can cause headaches, confusion, and fatigue.
Nitrogen dioxide (NO2) is another combustion byproduct that air quality tests can detect, primarily from gas stoves and heaters. The EPA’s annual standard for outdoor NO2 is 53 ppb, but indoor levels near a gas stove can spike well above that during cooking. Sulfur dioxide and ozone are also measurable, though they’re more commonly tracked in outdoor air monitoring.
Mold Spores and Biological Contaminants
Air quality tests can capture mold spores using a pump that draws air through a collection cassette. A lab then identifies the types and quantities of spores present, reporting results as spore counts per cubic meter. Common indoor molds that show up include Aspergillus, Penicillium, Cladosporium, and the sometimes-feared Stachybotrys (black mold).
Here’s an important caveat: the CDC does not recommend routine air sampling for mold and notes that there are no health-based standards for mold levels in indoor air. Spore counts from short-term air samples can’t be reliably interpreted in relation to health risks because mold levels fluctuate constantly. A more useful approach is comparing indoor spore counts to outdoor counts taken at the same time. If indoor levels of a particular mold species are significantly higher than outdoor levels, that suggests active indoor growth. Visual inspection and moisture assessment are often more informative than air sampling alone.
Allergens
Some specialized air quality assessments test for allergen particles like dust mite proteins, pet dander, cockroach antigens, and mouse allergens. These are particularly useful if you’re experiencing unexplained respiratory symptoms at home. The particles are collected from air or settled dust samples and sent to a lab for analysis.
This is distinct from a blood allergy test, which measures your immune system’s response to allergens rather than measuring what’s actually in your air. Both can be useful, but for different reasons. An air test tells you what’s present in your environment. A blood test tells you what your body reacts to. If you’re trying to figure out why you’re sneezing every morning, the air test identifies the trigger in your space while the allergy panel confirms whether your body is sensitive to it.
Professional Tests vs. DIY Monitors
What a test detects depends heavily on what type of test you’re using. The options fall into three general categories:
- Consumer-grade monitors are plug-in or battery-powered devices that give continuous readings, typically for PM2.5, total VOCs, CO2, temperature, and humidity. They’re useful for spotting trends (cooking spikes, poor ventilation) but lack the precision to identify specific chemicals.
- DIY test kits focus on one pollutant at a time. Radon kits and mold sampling cassettes are the most common. You collect the sample at home and mail it to a lab. Results take a few days to a couple of weeks.
- Professional testing covers the broadest range. Certified inspectors use calibrated instruments and collect air samples for accredited lab analysis. They can identify individual VOC compounds, specific mold species, allergen proteins, and combustion gases simultaneously. This is the route to take if you need legally defensible results or suspect a complex problem.
How Results Are Reported
Air quality results use different units depending on the pollutant. Particulate matter is reported in micrograms per cubic meter (μg/m³). Gases like carbon monoxide and ozone are reported in parts per million (ppm), while nitrogen dioxide and sulfur dioxide use parts per billion (ppb). Radon uses picocuries per liter (pCi/L). Mold results come as spore counts or colony-forming units per cubic meter.
For outdoor air, the EPA converts pollutant concentrations into a single Air Quality Index (AQI) score on a scale from 0 to 500. Scores of 0 to 50 are rated “Good,” 51 to 100 “Moderate,” and anything above 150 is “Unhealthy.” Indoor air doesn’t have an equivalent standardized index, which is why interpreting indoor test results often requires comparing your numbers against EPA guidelines, WHO recommendations, or simply against outdoor baseline levels taken at the same time.