Air quality: VOCs & particulate matter
Indoor air is, on average, 2-5x more polluted than outdoor air (EPA). The dominant sources are not what most people guess: cleaning products, new construction materials, gas appliances, the act of cooking, and — increasingly — wildfire smoke intruding from outside.
The two-sentence summary
VOCs (volatile organic compounds) and PM2.5 (particulate matter ≤2.5 µm) account for most of the indoor air quality story for people with respiratory or cardiovascular sensitivity. Both are testable; both have specific, defensible action levels; both have specific, addressable source-control plays.
VOCs: what they are
Volatile organic compounds are carbon-based chemicals that evaporate at room temperature. The EPA defines them by their reactivity in atmospheric photochemistry; what matters in indoor air is which specific VOC, at what concentration, for how long.
The TO-15 method we sample against analyzes 62 common indoor VOCs. The ones that most often drive symptoms:
| VOC | Common sources | Action level |
|---|---|---|
| Formaldehyde | Composite wood (MDF, particleboard), permanent-press fabrics, some insulations, smoking, off-gassing of new furniture | NIOSH REL 16 ppb 8-hr; ATSDR MRL 8 ppb chronic |
| Benzene | Attached-garage emissions, smoking, gasoline-powered tools | ATSDR MRL 3 ppb chronic |
| Toluene + Xylene | Paint thinners, adhesives, vehicle exhaust | NIOSH RELs |
| Acetaldehyde | Combustion, smoking, some plastics | OEHHA REL 140 µg/m³ |
| d-Limonene | "Citrus"-scented cleaners | Not regulated, but reacts with indoor ozone to form ultrafine particles + secondary aldehydes |
"New house smell," "new car smell," the smell of a freshly painted room — all VOC-dominated. The smell fades because the dominant VOCs (formaldehyde, benzene, toluene) off-gas exponentially. Most of the off-gassing happens in the first 6-12 months; some materials keep emitting for years.
Where the VOCs come from (in order of frequency)
- Composite-wood furniture less than 2 years old (MDF and particleboard contain urea-formaldehyde adhesives).
- Recently installed cabinets, flooring, countertops.
- Recently painted rooms (latex paints emit less than oil- based, but still emit for 30+ days).
- Attached garage with combustion equipment (gas-powered mower, gasoline storage, car). Benzene + CO can intrude through the wall.
- Gas range / oven (formaldehyde + NO2 + CO).
- Aerosol sprays + scented cleaners.
- Smoking indoors (any), including vaping.
- Permanent-press / wrinkle-free clothing + bedding fresh from packaging.
How we sample VOCs
Active-pump sampling onto a Tenax sorbent tube for 60 minutes, analyzed by GC-MS for the TO-15 standard 62-compound list at an AIHA-LAP-accredited lab. The active-pump approach is more quantitative than passive badge sampling and catches transient sources (e.g. a cleaning event 4 hours before) that a 24-hour passive badge averages out.
Inspectors record what was happening in the home during the sample (cooking, recent cleaning, weather/HVAC state) so the interpretation accounts for the conditions.
Particulate matter: what it is
PM2.5 = solid + liquid particles ≤2.5 µm in aerodynamic diameter. Small enough to bypass nasal filtration and reach the alveoli; some fractions cross into the bloodstream. The cardiopulmonary literature on PM2.5 is one of the most robust in environmental health.
PM10 = particles ≤10 µm. Includes pollen, dust, larger combustion particles. Caught more efficiently by upper-airway defenses; the clinical concern is mostly upper-airway irritation + allergic sensitization.
EPA NAAQS (2024 revision):
| Pollutant | Threshold | Averaging period |
|---|---|---|
| PM2.5 | 9 µg/m³ | Annual |
| PM2.5 | 35 µg/m³ | 24-hour |
| PM10 | 150 µg/m³ | 24-hour |
The 2024 NAAQS revision tightened the annual PM2.5 standard from 12 to 9 µg/m³ — a meaningful shift that puts more indoor and outdoor environments out of compliance and re-frames what "moderate" AQI means clinically.
Where indoor PM2.5 comes from
- Cooking, especially gas + frying / searing. A single dinner can push PM2.5 to 200 µg/m³ in a closed kitchen.
- Gas appliances without exhaust to outside (stoves, dryers).
- Wildfire smoke intrusion through windows, HVAC fresh-air intakes, and building leaks.
- Wood-burning fireplace or stove, even when not in active use (intrusion via chimney downdraft).
- Vacuuming without a HEPA filter resuspends settled particulate.
- Candles, especially scented and paraffin.
How we sample PM
1-hour averaged real-time PM2.5 + PM10 readings using a light-scattering reference-grade instrument (DustTrak or equivalent), at both the indoor location of concern AND outdoors as a baseline. Same indoor/outdoor logic as our mold sampling — the question is amplification, not absolute level.
What we report
- VOC concentrations for every compound exceeding LOD, with specific action levels cited per compound.
- Formaldehyde specifically broken out (NIOSH 8-hr REL, ATSDR chronic MRL).
- PM2.5 + PM10 indoor vs outdoor 1-hr averages.
- Inspector's plain-English interpretation: likely source, recommended source-control plays, and whether mechanical mitigation (range hood retrofit, HEPA-filter air cleaner, wildfire box-fan filter) would meaningfully change the picture.
When to test
- Recent renovation, especially with composite-wood materials.
- New furniture, cabinets, or flooring within the last 12 months.
- Attached garage with combustion equipment + symptoms in adjacent rooms.
- Gas range with no range hood OR range hood that doesn't vent outside.
- Living in a wildfire-prone region with respiratory or cardiovascular diagnosis.
- Unexplained headaches, eye irritation, or cough indoors without an obvious allergen story.
When NOT to test (yet)
- You already know the source (you can smell the recent paint, or you cooked dinner an hour ago and the kitchen still smells). Address the source + re-test in 2-4 weeks if symptoms persist.
- The reading would be worse without the conditions you want to test under (e.g. testing the kitchen mid-cooking tells you the worst case but not the typical case).
Selected references
- EPA. National Ambient Air Quality Standards (NAAQS) for Particulate Matter — Final Rule. February 2024.
- EPA. Compendium Method TO-15: Determination of Volatile Organic Compounds in Air Collected in Specially-Prepared Canisters. 1999.
- NIOSH. Pocket Guide to Chemical Hazards. Updated 2023.
- ATSDR. Minimal Risk Levels for Hazardous Substances. Updated 2023.
- WHO. Global Air Quality Guidelines: PM2.5, PM10, O3, NO2, SO2, CO. 2021.
- Pope CA III, Dockery DW. Health effects of fine particulate air pollution: lines that connect. J Air Waste Manag Assoc 2006.