What is PM2.5, AQI, and CADR Explained Simply (for Indian Buyers)

Introduction: 

If you’re thinking about buying an air purifier, the first thing you’ll notice is how often terms like PM2.5, AQI, and CADR appear on product pages and reviews. Yet most people in India don’t know what these numbers actually mean. Understanding what is PM2.5 AQI and CADR helps you judge real purification performance instead of falling for marketing terms. It also helps you compare purifiers more accurately—something we covered in-depth in Which Is the Best Air Purifier in India? (2025 Comparison Guide).

When you know what these three terms represent, choosing the right purifier becomes simple, logical, and fully aligned with the pollution levels in your city. In this guide, we explain everything in plain words, with Indian household examples and practical tips.

What Is PM2.5? (Explained for Indian Homes)

PM2.5 refers to tiny airborne particles that are 2.5 microns or smaller. They are invisible to the naked eye and come from:

• Vehicle exhaust
  
• Construction dust
  
• Industrial smoke
  
• Burning garbage
  
• Cooking oil fumes
  
• Smog trapped during winter
  
• Firecrackers
  
• Dust on roads and open plots
  

Because these particles are extremely small, they enter deep into the lungs and even the bloodstream.

Why PM2.5 Is Dangerous in India

India has some of the highest PM2.5 levels in the world. The WHO Air Quality Guidelines state that long-term exposure increases risk of:

• Asthma
  
• Lung infections
  
• Heart disease
  
• Reduced lung function
  
• Chronic cough
  
• Throat and eye irritation
  

Even “clean-looking” homes in India often have PM2.5 levels above 80–150 µg/m³ indoors. The safe limit recommended by WHO is 5 µg/m³, and the Indian CPCB standard allows up to 40 µg/m³ for 24-hour exposure.

How to Reduce PM2.5 Indoors

• Keep windows closed during high AQI hours
  
• Use wet dusting instead of dry sweeping
  
• Run a HEPA air purifier
  
• Seal gaps in balconies
  
• Use kitchen chimneys during cooking
  

If you want to understand how HEPA removes PM2.5, our article How Air Purifiers Work: The Science Behind Cleaner Indoor Air explains the science in simple terms.

What Is AQI? (Air Quality Index Explained Simply)

AQI (Air Quality Index) measures how polluted the air around you is. It gives a single number that represents overall air quality.

AQI Scale Used in India (CPCB Standard)

AQI Range	Air Quality	Meaning
0–50	Good	Healthy
51–100	Satisfactory	Acceptable
101–200	Moderate	Sensitive groups affected
201–300	Poor	Breathing discomfort
301–400	Very Poor	Respiratory issues
401–500	Severe	Serious health effects

Indian metro cities frequently cross AQI 250–400 during winter, especially Delhi-NCR. Even cities like Mumbai, Kolkata, and Bengaluru see spikes above 150 during festivals, traffic peaks, and construction periods.

Why AQI Matters for Indian Buyers

When choosing a purifier, AQI helps you understand:

• How polluted your city actually is
  
• How strong your purifier needs to be
  
• When to keep windows closed
  
• When to increase purifier speed
  

Air purifiers with good sensors respond automatically when AQI rises indoors.

What Is CADR? (Clean Air Delivery Rate Explained)

CADR tells you how fast and how much clean air a purifier can produce in one hour. It is measured in m³/hr (cubic meters per hour).

In simple words:
Higher CADR = Faster and more effective cleaning.

Why CADR Is Important

CADR determines:

• Room size coverage
  
• Cleaning speed
  
• Air circulation rate
  
• Purifier efficiency in polluted cities
  

For example:

• CADR 200–250 → small rooms (100–150 sq ft)
  
• CADR 250–330 → medium rooms (150–250 sq ft)
  
• CADR 330–450+ → living rooms (250–500 sq ft)
  

You’ll find these ratings explained further in our pillar article Best Air Purifier for Home in India (2025 Buyer’s Guide).

Quick Summary Table: PM2.5, AQI, and CADR

Term	Meaning	Why It Matters
PM2.5	Fine particles from pollution	Most harmful to health
AQI	Overall air pollution score	Helps track air quality
CADR	Cleaning speed of purifier	Helps choose right purifier

Together, these numbers tell you how polluted your air is and how powerful your purifier needs to be.

Why PM2.5, AQI, and CADR Matter for Indian Homes

India’s air pollution levels fluctuate through the year due to:

• Winter smog
  
• Post-Diwali smoke
  
• Construction dust
  
• Vehicle emissions
  
• Crop burning
  
• Coastal humidity trapping pollutants
  

Because of this, PM2.5 and VOCs build up quickly indoors. AQI spikes often push indoor pollution higher, and only a purifier with the right CADR can clean the room effectively.

Example: Delhi NCR Winter

• Outdoor AQI: 350+
  
• Indoor PM2.5: 200+
  
• A CADR 250 purifier will struggle
  
• A CADR 350+ purifier will clean efficiently
  

Example: Mumbai Monsoon

• Humidity increases mold spores
  
• Construction dust remains trapped indoors
  
• AQI fluctuates between 80–150
  
• A HEPA purifier helps maintain healthy levels indoors
  

This is why trusted brands like Coway, Philips, and Blueair focus heavily on CADR performance in their best-selling models.

How Air Purifiers Use These Metrics

HEPA Filters → Remove PM2.5 & PM10

They trap solid particles, allergens, dust mites, pollen, and smoke. If PM2.5 is your main concern, HEPA is mandatory.

Carbon Filters → Help When AQI Has Odours or VOCs

These absorb gases from cooking, cleaning liquids, paint, and traffic.

CADR → Determines Overall Performance

A purifier with high CADR will refresh indoor air faster and handle pollution spikes better.

For a full explanation of HEPA vs carbon systems, refer to our deep-dive post HEPA vs Activated Carbon Filters: What’s Better for Indian Homes?

How Much CADR Do You Need? (Simple Calculation)

To choose the right purifier, multiply your room size by 2 or 3, depending on pollution level.

Step-by-step:

1. Measure room in sq ft
   
2. Convert to sq meters (divide by 10)
   
3. Multiply by 2
   
4. Multiply by 3 (for polluted cities)
   

Example: 150 sq ft room

• 150 sq ft ≈ 15 sq m
  
• CADR needed: 15 × 2 = 300 m³/hr
  

This is why models like Philips AC2887/20 and Coway AirMega 150 are popular—they offer ideal CADR for Indian bedrooms.

How to Interpret AQI Indoors

A good purifier reduces indoor AQI significantly:

Indoor AQI	Meaning
0–30	Excellent
30–70	Clean
70–100	Acceptable
100–150	Slight pollution
150–250	Polluted
250+	Highly polluted

Many premium purifiers display real-time indoor AQI through LEDs or screens. For example, the Philips 3000i shows exact PM2.5 levels digitally.

Why Indian Buyers Should Understand CADR Before Purchasing

Most Indian homes have:

• Open kitchens
  
• Small bedrooms
  
• Medium living rooms
  
• Poor ventilation
  
• Traffic exposure
  
• High dust levels
  

CADR ensures the purifier can handle these realities. Without enough CADR, a purifier may clean too slowly or only partially.

Conclusion: Now You Know What PM2.5, AQI, and CADR Mean

Understanding what is PM2.5 AQI and CADR gives you complete clarity on how air quality works in Indian conditions and how to choose the right purifier. PM2.5 affects your lungs, AQI shows the overall pollution level, and CADR tells you how fast your purifier can clean the air. Together, these three numbers determine indoor air safety for your family.

When you use this knowledge, choosing a purifier becomes simple, factual, and effective.

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