This glossary defines the air purifier terms shoppers encounter and organizes them into performance, filters, technologies, and user features. Each entry gives a plain-English definition, why it matters for buying decisions, how to read it on product pages, a short concrete example, related terms, and a common mistake to avoid.
Performance & ratings
CADR
Plain definition: Clean Air Delivery Rate—how quickly a purifier removes a specific particle type from a standard test room.
Why it matters: CADR is the most direct single-number way to compare cleaning speed for smoke, dust, or pollen.
How to interpret: Compare the CADR for the particle size you care about and match to room size; look for separate CADR figures for smoke/dust/pollen.
Example: A higher smoke CADR model will clear cooking fumes faster than one with lower smoke CADR.
Related terms: MPPS, particle size, AQI. Common mistake: Treating one CADR number as proof of superior all-around performance.
MPPS
Plain definition: Most Penetrating Particle Size—the particle diameter that is hardest for a filter to capture.
Why it matters: Filter efficiency is measured at MPPS, so ratings at that size show how a filter performs under its worst-case condition.
How to interpret: When manufacturers state HEPA efficiency, check whether the figure is at MPPS; better efficiency at MPPS indicates stronger real-world capture.
Example: A HEPA-rated filter listed at near-complete capture at MPPS will also remove larger particles well.
Related terms: HEPA, micron, filter efficiency. Common mistake: Confusing MPPS with average indoor particle sizes.
AQI
Plain definition: Air Quality Index—a public scale summarizing outdoor pollution levels and associated guidance.
Why it matters: AQI signals when increased indoor filtration makes more sense, for example during wildfires or heavy urban pollution.
How to interpret: Use AQI trends to decide when to run purifiers at higher speeds or add units, but match decisions to indoor volume and purifier capability.
Example: High outdoor AQI might prompt closing windows and running a purifier on higher settings until conditions improve.
Related terms: particle sensor, PM10, VOC. Common mistake: Using AQI alone to choose purifier capacity without checking CADR or room size.
Filters & particles
HEPA
Plain definition: High-Efficiency Particulate Air—a standardized class of mechanical filter media designed to capture very small particles.
Why it matters: HEPA filters are the baseline for removing airborne particles that concern most home shoppers.
How to interpret: Confirm the HEPA classification (true HEPA vs. “HEPA-type”); look for efficiency at MPPS when available.
Example: A true HEPA filter in a purifier traps fine dust and many airborne irritants carried on particles.
Related terms: MPPS, MERV, micron. Common mistake: Assuming “HEPA-like” or unverified claims equal certified HEPA performance.
MERV
Plain definition: Minimum Efficiency Reporting Value—a rating scale for HVAC filters showing particle-capture effectiveness across sizes.
Why it matters: MERV helps when comparing whole-house filters or replacement prefilters used in some purifiers.
How to interpret: Higher MERV means finer capture, but check compatibility with the purifier or HVAC system to avoid airflow restriction.
Example: A higher-MERV media filter captures more indoor dust but may need a fan designed to handle increased resistance.
Related terms: HEPA, micron. Common mistake: Choosing the highest MERV without confirming the system can maintain airflow.
Micron
Plain definition: A micron is one millionth of a meter and is the unit used to describe particle diameter.
Why it matters: Knowing particle sizes (microns) clarifies what filters will trap and what sensors can detect.
How to interpret: Compare filter specs and sensor ranges to the particle sizes of concern (e.g., fine smoke vs. coarse dust).
Example: Small combustion particles are much smaller than visible dust and require finer filtration media.
Related terms: MPPS, PM10, HEPA. Common mistake: Misreading micron talk as an absolute guarantee of indoor air quality.
PM10
Plain definition: Particulate matter 10 microns and smaller—a common outdoor/indoor particle size category used in air quality reporting.
Why it matters: PM10 captures larger inhalable particles like pollen and some dust; many purifiers report capability against PM size bands.
How to interpret: If pollen or coarse dust is your issue, ensure the purifier lists performance that includes larger particle removal.
Example: During seasonal pollen, a purifier that targets PM10 will reduce visible settling and airborne pollen counts.
Related terms: PM2.5, micron, AQI. Common mistake: Assuming PM10 performance predicts fine particle or gas removal.
Fel d 1
Plain definition: The major cat allergen commonly reported in allergy testing and purifier literature.
Why it matters: Some purifiers or filter media are tested specifically for common allergens like this; shoppers with pet allergies look for specific claims.
How to interpret: Look for verified test results for allergen reduction rather than marketing language; match the claim to your allergen source.
Example: A purifier tested for pet-allergen capture may reduce airborne proteins shed by cats and dogs.
Related terms: HEPA, particle sensor. Common mistake: Assuming allergen marketing equals clinical allergy prevention.
Technologies & safety
Ionizer
Plain definition: A device that emits charged ions to make particles clump together or stick to surfaces or collector plates.
Why it matters: Ionizers can reduce airborne particles but outcomes vary and some designs produce byproducts you should check for.
How to interpret: Verify whether the ionizer is combined with mechanical filtration and whether the unit reports ozone emissions.
Example: An ionizer can reduce haze but may leave particles on nearby surfaces instead of capturing them in a filter.
Related terms: ozone, PCO. Common mistake: Expecting ionizers to replace HEPA filtration for particle removal.
Ozone (O3)
Plain definition: A reactive gas sometimes produced as a byproduct of certain air-cleaning technologies.
Why it matters: Ozone can be harmful at elevated indoor levels, so shoppers should avoid devices that intentionally generate ozone for cleaning.
How to interpret: Choose purifiers that explicitly test and report low ozone emissions; don’t accept ozone-generating claims as a benefit.
Example: A purifier that lists “ionizing” action should also state ozone output if present, allowing you to decide on safety tradeoffs.
Related terms: ionizer, PCO. Common mistake: Believing ozone is a harmless or desirable cleaning agent indoors.
UV-C
Plain definition: Ultraviolet-C light used in some air cleaners to break down biological material on surfaces or in airflow paths.
Why it matters: UV-C can aid in reducing microbial load on internal surfaces, but it’s not a primary particle filter.
How to interpret: Look for UV-C described as an adjunct feature and check whether manufacturers provide safe enclosure and maintenance information.
Example: UV-C inside a purifier may treat the air passing through the unit but won’t remove dust without a mechanical filter.
Related terms: PCO, HEPA. Common mistake: Relying on UV-C claims as a substitute for good filtration.
PCO
Plain definition: Photocatalytic Oxidation—a technology that uses UV light and a catalyst to break down gases and odors.
Why it matters: PCO targets gases and VOCs rather than particles; effectiveness varies with design and operating conditions.
How to interpret: Treat PCO as a potential supplement for odors/VOC control and look for independent testing rather than broad performance claims.
Example: PCO might reduce cooking odors while a HEPA filter removes the smoke particles.
Related terms: VOC, UV-C, ozone. Common mistake: Expecting PCO to clean particles as effectively as HEPA filters.
Off-Gassing
Plain definition: Release of volatile chemicals from materials like furniture or paint into indoor air.
Why it matters: Off-gassing produces VOCs that purifiers may address differently than particles; some filters or adsorbents work better than others.
How to interpret: If new-products or renovations are the issue, prioritize units with active adsorbent media designed for gases rather than particle-only models.
Example: New carpeting releasing odors may need an activated-carbon stage in addition to particle filtration.
Related terms: VOC, PCO, activated carbon. Common mistake: Expecting particle-only purifiers to remove chemical odors effectively.
VOC
Plain definition: Volatile Organic Compounds—a broad class of gaseous chemicals from paints, cleaners, and other sources.
Why it matters: VOCs are gases, so removing them typically requires adsorbent media or other gas-focused technologies rather than HEPA alone.
How to interpret: Look for explicit VOC or gas-phase performance details and consider activated-carbon capacity and replacement intervals.
Example: A purifier with a substantial activated-carbon stage can reduce lingering paint or cooking odors more effectively than a particle-only unit.
Related terms: off-gassing, PCO, activated carbon. Common mistake: Assuming HEPA alone handles VOCs well.
Features & readouts
Particle Sensor
Plain definition: A sensor that detects airborne particle levels and often drives auto fan speeds or displays an air-quality readout.
Why it matters: Real-time sensing lets a purifier respond when particle levels rise, improving convenience and energy use.
How to interpret: Check whether the sensor measures the particle sizes relevant to your concerns and whether the manufacturer provides calibration details.
Example: A particle sensor that triggers higher fan speeds when indoor smoke increases helps keep air cleaner without manual control.
Related terms: AQI, PM10, MPPS. Common mistake: Trusting noisy or uncalibrated sensors as precise instruments.
Sleep Mode
Plain definition: A low-speed, low-noise operating mode intended for nighttime use.
Why it matters: Sleep mode balances quiet operation with continued filtration; its effectiveness depends on purifier airflow at reduced speed.
How to interpret: Confirm the purifier still provides adequate air changes in sleep mode for your room size rather than assuming identical performance to high speed.
Example: Running sleep mode preserves undisturbed sleep while maintaining baseline particle removal overnight.
Related terms: CADR, particle sensor. Common mistake: Assuming sleep mode equals full-performance filtration.
If you want replacement filters, test reports, or model comparisons, check the linked term pages for deeper, model-specific guidance and independent test data.
If you’re comparing models, consider CADR vs. room size first, then confirm filter type and any gas-phase media; affiliate links on product pages support our independent publishing at no extra cost to you.
