Do Air Purifiers Really Work?

The Short Answer

Yes, air purifiers with True HEPA filters significantly reduce indoor particulate matter. Multiple studies, including research published in the Indian Journal of Medical Research, show that HEPA air purifiers can reduce indoor PM2.5 concentrations by 50–85% within hours of operation.

How Air Purifiers Work

Air purifiers draw room air through a series of filters, trap pollutants, and recirculate clean air. Most use a combination of:

• Pre-filter: Captures large particles like dust, hair, and pet dander
• HEPA filter: Captures 99.97% of particles as small as 0.3 microns (PM2.5, pollen, mould spores, bacteria)
• Activated carbon filter: Absorbs gases, odours, and VOCs (smoke, cooking smells, chemical fumes)

Some units add UV-C light or ionizers, but these are supplemental — the HEPA filter does the heavy lifting.

What Air Purifiers Are Good At

• PM2.5 and PM10 reduction: Excellent. A good purifier can reduce indoor PM2.5 from 250 µg/m³ to under 50 µg/m³ within 30–60 minutes
• Allergen removal: Very effective for pollen, dust mites, pet dander
• Mould spores: Captures airborne spores (does not address the mould source)
• Smoke: Highly effective for tobacco smoke, cooking smoke, and wildfire smoke
• Odour reduction: Carbon filter helps with cooking, pet, and chemical odours

What Air Purifiers Cannot Do

• Remove gases: Basic purifiers with small carbon filters cannot remove NO2, SO2, or high levels of VOCs effectively. You need a purifier with a thick carbon filter (at least 1 kg of activated carbon) for gas removal
• Generate oxygen: Air purifiers do not produce oxygen. They only filter existing air
• Stop outdoor pollution from entering: Without sealing the room, outdoor air will continuously infiltrate
• Eliminate mould sources: They capture airborne spores but do not treat mould growing on surfaces
• Remove CO2: No consumer air purifier removes carbon dioxide. You need ventilation for that

Understanding CADR Ratings

CADR (Clean Air Delivery Rate) measures how quickly a purifier cleans a room. It is expressed in cubic feet per minute (CFM) for three pollutants: smoke, dust, and pollen.

What CADR numbers mean:

• For a 150 sq ft room, you need CADR of at least 120 CFM for smoke
• For a 300 sq ft room, you need CADR of at least 240 CFM for smoke
• Higher CADR = faster cleaning = quieter operation at lower fan speeds

Always look at the smoke CADR rating, as it is the most relevant for PM2.5 removal in Indian conditions.

Real-World Performance in India

Testing by Dyson, IQAir, and independent reviewers shows:

• In Delhi winter (AQI 350+), a properly sized purifier can bring indoor PM2.5 from 300+ µg/m³ to under 50 µg/m³ within 1 hour
• In Mumbai (AQI 150–200), the same purifier maintains indoor levels under 25 µg/m³ continuously
• Effectiveness drops dramatically if doors/windows are opened or the purifier is undersized

When an Air Purifier Is Worth It

• You live in a city where AQI regularly exceeds 150
• You or family members have asthma, allergies, or respiratory conditions
• Your home has poor sealing (high infiltration)
• You are sensitive to seasonal pollen or mould

Key Takeaways

• True HEPA air purifiers reduce indoor PM2.5 by 50–85% in properly sized rooms
• They are highly effective for particles but limited for gases and VOCs
• CADR rating matters more than brand — match it to your room size
• They cannot replace ventilation; they filter air but do not add oxygen or remove CO2
• In polluted Indian cities, a good air purifier is one of the most effective investments for health