Chennai Air Quality — April 2025 CPCB Analysis

indoorair.guide — Air Purifier Guide

Independent guidance on air pollution, purifiers, ventilation and health for Indian homes, offices and cars

Understanding AQI (Air Quality Index)

India uses the CPCB National Air Quality Index with six categories:

Good (0–50) — Minimal health impact. No precautions needed.
Satisfactory (51–100) — Minor breathing discomfort for sensitive people.
Moderate (101–200) — Breathing discomfort for people with lung/heart disease. Consider an air purifier.
Poor (201–300) — Breathing discomfort for most people on prolonged exposure. Air purifier recommended.
Very Poor (301–400) — Respiratory illness on prolonged exposure. Air purifier strongly recommended.
Severe (401–500) — Health impact even on light activity. Air purifier essential indoors.

Key Factors When Choosing an Air Purifier

CADR (Clean Air Delivery Rate) — Measures how quickly a purifier cleans air in cubic meters per hour. Higher CADR = faster cleaning. Match CADR to your room size for effective purification.
HEPA Filter Grade — H13 HEPA filters capture 99.95% of particles ≥0.3μm, including PM2.5. H14 captures 99.995%. Avoid purifiers that don't specify the HEPA grade.
Room Size Coverage — A purifier rated for 300 sq ft won't be effective in a 500 sq ft room. Always check the manufacturer's recommended room size and verify with CADR.
Annual Filter Cost — Replacement filters are a recurring expense. Factor in ₹2,000–₹6,000/year for filter replacements when comparing total cost of ownership.
Noise Level — Purifiers range from 20 dB (whisper-quiet) to 65 dB (conversation level). Check noise at both low and high fan speeds, especially for bedroom use.

Air Quality in India

Indian cities frequently experience AQI levels above 200 (Poor), especially during winter months (October–February). Delhi NCR, parts of UP, Bihar, and other northern regions regularly see AQI above 300. Even southern cities like Bengaluru and Chennai can have moderate pollution (AQI 100–200). An air purifier with adequate CADR and true HEPA filtration is essential for healthy indoor air in most Indian cities.

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Frequently Asked Questions

Understanding Air Quality

What's in the air you breathe?

This short video explores the invisible particles floating in the air around us — from dust and pollen to PM2.5 and volatile organic compounds. Understanding what's in your air is the first step to breathing cleaner.

How does indoor air quality impact your lungs?

This video explains how poor indoor air quality affects your respiratory system and lung health.

Does AQI tell me how clean my indoor air is?

No. AQI reflects outdoor air at monitoring stations, not the air inside your home. Indoor air quality depends on outdoor pollution entering the home, ventilation, indoor sources (cooking, dust, incense, smoking), and use of air purifiers or filters.

What are the key pollutants in indoor air?

The main indoor air pollutants are: PM2.5 and PM10, VOCs (from paints, cleaning products, new furniture), CO₂ (indicates poor ventilation), NO₂ (from gas stoves), and biological pollutants (mould, pet dander, dust mites, pollen). In Indian homes, cooking emissions and outdoor pollution infiltration are often the biggest contributors.

Which VOC items should be avoided in homes?

Common VOC sources to minimise: synthetic air fresheners, oil-based paints, strong cleaning products with bleach or ammonia, new furniture, nail polish, mosquito coils, and scented candles. Look for 'low-VOC' or 'zero-VOC' labels.

Air Purifier Basics

Do air purifiers actually work?

Yes — when correctly sized and used in a closed room. True HEPA filters reduce PM2.5, dust, pollen, and smoke. CADR and room size matter.

What problems can air purifiers solve?

They reduce particles like PM2.5, dust, allergens, and smoke. They cannot fix CO₂ buildup, humidity, or poor ventilation.

Can air purifiers reduce CO₂ or increase oxygen?

No. Air purifiers do not add oxygen or remove CO₂. Ventilation is required for that.

Can air purifiers remove viruses or bacteria?

HEPA filters can capture airborne particles that carry viruses and bacteria, but they don't kill them. Air purifiers are not a substitute for ventilation, masks, or hygiene practices during illness.

Common Myths

Do air purifiers make the air dry?

No. Air purifiers filter particles, not moisture. The sensation of dryness in winter comes from heaters reducing humidity, not from the purifier.

Are air purifiers and humidifiers the same?

No. Air purifiers clean air by removing particles using filters. Humidifiers add moisture. They serve completely different purposes.

Do air purifiers stop the body from building immunity to pollution?

No. The human body does not build 'immunity' to air pollution. Pollution causes damage, not immunity.

Do air purifiers make people "too sensitive" to pollution?

No. Moving from clean air to polluted air makes irritation more noticeable. That's awareness, not reduced immunity.

Do indoor plants purify the air?

Not meaningfully. The NASA study was done in sealed chambers, not real rooms. You would need hundreds of plants to see any effect in a typical home.

Do neck-based personal air purifiers help?

No. Studies show they can increase ozone concentration in your breathing zone. Stick with room-based HEPA air purifiers.

Choosing an Air Purifier

What filters should I look for in India?

Look for true HEPA (H13 or higher). Add activated carbon if odours or chemical smells are a concern.

Is HEPA 14 better than HEPA 13?

In practice, a well-designed HEPA 13 purifier with proper airflow performs almost as well in homes.

How many air purifiers do I need?

One purifier cleans one room. Multiple rooms usually require multiple units.

Is the CADR on the box accurate for daily use?

CADR is measured at the highest fan speed, which is often too noisy for continuous use. Choose a purifier with CADR 20–30% higher than your room requirement.

What sensors should an air purifier have?

A PM2.5 sensor is essential. A TVOC sensor helps track gases from cooking and cleaning. A CO₂ sensor is a nice-to-have for ventilation monitoring.

How often should I replace HEPA filters in India?

In high-pollution cities, replace HEPA filters once a year. In less polluted areas, filters may last longer. If the filter looks grey or black, it's time to change.

About Indoor Air Guide

Is Indoor Air Guide affiliated with any brands?

No. Indoor Air Guide is an independent, educational resource.

Glossary of Air Purifier Terms

Core Pollutants and Air-Quality Terms

PM2.5: Very fine particles ≤ 2.5 micrometers, from smoke, traffic, fine dust; go deep into lungs. Tip: Prefer True HEPA / H13 HEPA.
PM10: Coarse particles ≤ 10 micrometers, like bigger dust, soil, construction and road dust. Tip: Look for pre-filter + HEPA.
Allergens: Pollen, pet dander, dust mites, mould spores — things that trigger allergies/asthma. Tip: HEPA and adequate CADR for dust and pollen.
VOCs: Volatile organic compounds from paint, cleaning chemicals, furniture, incense, cooking. Tip: Insist on a proper activated carbon filter.
Smoke: Fine particles and gases from cigarettes, mosquito coils, cooking, incense, crop burning. Tip: High CADR + HEPA + activated carbon.
AQI: Air Quality Index — a single number showing how polluted the air is. Tip: Built-in AQI display helps see air quality improve.
Construction Dust: Dust from cement, sand, plaster, tiles, cutting/grinding. Tip: Washable pre-filter + HEPA, slightly higher CADR.
Vehicular / Traffic Pollution: Very fine particles and gases from vehicles. Tip: For homes near busy roads, push True/H13 HEPA + carbon filter.

Filters and Ratings

HEPA Filter: Dense fibre filter capturing ≥ 99.95–99.97% of ~0.3 μm particles. HEPA is for particles — dust, pollen, smoke.
True HEPA: Meets the official standard (~99.97% at 0.3 μm). Prefer labels with stated efficiency.
HEPA-type / HEPA-like: Marketing terms — may not meet true HEPA standard. Push True HEPA / H13 instead.
H13 / H14: European HEPA classes: H13 ≥ 99.95%, H14 ≥ 99.995%. H13 is a strong choice for high-pollution cities.
Pre-filter: Coarse filter catching hair, lint, big dust; often washable. Protects expensive HEPA, reduces long-term cost.
Activated Carbon Filter: Adsorbs gases and odours. For odour, smoke, traffic fumes, insist on a thick, real carbon filter.

Performance and Sizing

CADR (Clean Air Delivery Rate): How much clean air a purifier delivers (airflow × filter efficiency), in CFM or m³/h. Higher is better.
ACH (Air Changes per Hour): How many times per hour all room air passes through the purifier. Target 4–6 ACH for heavy pollution.
Coverage Area / Room Size: Manufacturer's max room size at a given CADR/ACH. Slightly oversize for Delhi-type pollution.
Airflow: Raw air moved per hour (without filter efficiency). CADR is more meaningful than airflow alone.

Operation, Comfort, and Running Cost

Noise Level (dB): Higher dB = louder. For bedrooms, look for < 30 dB in sleep/low mode.
Power Consumption (W): Electricity usage in watts. For 24×7 use, prefer lower wattage + auto mode.
Filter Life / Replacement Interval: Expected life before clogging. In dusty areas, filters need replacing more often.
Filter Change Indicator: Light or app alert when filters need replacing. Reduces guesswork.
Auto Mode: Sensors detect pollution and auto-adjust fan speed. Good for set-and-forget use.

Extra Technologies and Safety

Ionizer / Negative Ion Generator: Releases negative ions to clump particles. Some designs produce ozone. For sensitive lungs, prefer ozone-free models.
Ozone: Reactive gas that irritates lungs. Home purifiers should not generate ozone.
UV-C Light: Germicidal UV inside some purifiers. HEPA already captures most germs. Ensure UV is enclosed.
PCO (Photocatalytic Oxidation): UV + catalyst to break down pollutants. Focus on HEPA + carbon + CADR as primary criteria.