Clean Air Glossary
New to air-purifier jargon? Here's every key term in plain English. Each links to a fuller explanation on our independent reference site, Air Purifier Directory.
The essentials
- Air purifier — a device that draws room air through filters to remove pollutants and returns cleaner air.
- How an air purifier works — fan → pre-filter → particle filter → (carbon) → clean air, repeated many times an hour.
- Do air purifiers work — what the evidence actually shows.
- CADR — clean-air delivery rate: how much clean air a unit delivers per hour. The key spec.
- CFM (airflow) — the airflow figure behind CADR.
- ACH — air changes per hour: how many times it replaces a room's air each hour.
- ACH vs CADR — how the two relate, and which to use when.
Particles & pollutants
- PM2.5 — fine particle pollution under 2.5 microns; the main health concern.
- PM10 — coarser particles such as dust and pollen.
- VOCs — gases from paint, cleaning products and furnishings; need carbon, not a particle filter.
- TVOC — total volatile organic compounds, as one reading.
- Formaldehyde — a common indoor VOC and how to reduce it.
- Off-gassing — why new furniture and paint smell.
- Nitrogen dioxide (NO₂) — traffic and gas-hob pollution.
- Ozone — why it's a pollutant, not a cleaner.
- Radon — the radioactive gas, and what actually helps.
- Dust mites — the allergen and how filtration helps.
- AQI — air quality index: pollution levels as a single number and colour.
- Air quality monitor — measures PM2.5, CO2 and VOCs so you can see and act on problems.
- Sick building syndrome — symptoms linked to poor indoor air.
Filters
- MERV rating — the HVAC filter scale explained.
- HEPA vs MERV-13 — two ways to capture fine particles, and why airflow often matters more than grade.
- HEPA (H13/H14) — what the true-HEPA grades capture.
- True HEPA vs “HEPA-type” — why the qualifier matters.
- ULPA vs HEPA — the even-finer grade, and when it's overkill.
- Activated carbon filter — removes gases and odours a particle filter can't.
- HEPA vs carbon — particles vs gases: which you actually need.
- Pre-filter — the coarse first layer that protects the main filter.
- Washable & permanent filters — do they really last forever?
Designs & technologies
- Corsi-Rosenthal box — the high-airflow, low-cost MERV-13 design. Build one at corsirosenthalbox.com.
- Smart air purifier — app control and auto modes.
- Ionisers & ozone — how they differ from filters, and the ozone caveat.
- Negative ions — what they are and whether ionic purifiers clean air.
- UV-C — do UV-C purifiers work, and are they safe?
- PCO — photocatalytic oxidation explained.
Air purifier vs…
Choosing & sizing
- What size do I need — match CADR to your room.
- Sq ft ↔ m² — convert coverage areas.
- How many do I need — one big unit or several.
- Where to place it — the best position for airflow.
- Are they worth it — an honest look.
- Running cost — how much electricity purifiers use.
By room & situation
- Bedroom
- Living room
- Whole house
- Office
- Baby nursery
- Allergies
- Hay fever — see also HayFeverUK.
- Asthma
- Pets — see also Pet Air Purifier.
- Mould — see also Mould Purifier.
- Smoke — see also Smoke Allergy.
- Cigarette smoke
- Wood smoke / log burner
- Vaping
- Kitchen & cooking smells
- Flat / rental
Browse the full reference at airpurifierdirectory.com.
Topic guides in our network: Corsi-Rosenthal Box · Air Purifier Kits · Best Air Purifier UK · Hay Fever UK · Smoke Allergy · Mould & Damp · Pet Air Purifier.