Delhi's air is a daily conversation — and for good reason. The city consistently ranks among the most polluted capitals in the world, with air quality data showing dangerous pollution levels for much of the year. Whether you're a Delhi resident planning a morning run, a parent worried about your child's school commute, or a traveller arriving for the first time, understanding the AQI in Delhi is not optional — it's essential.
This guide covers everything: what the air quality index (AQI) actually means, real-time pollution levels, the difference between PM2.5 and PM10, who is most at risk, and a practical outdoor activity guide based on the day's AQI reading.
What Is AQI? (Air Quality Index Explained)
The Air Quality Index (AQI) is a standardised scale used by governments and environmental agencies — including the World Health Organization (WHO) — to communicate how clean or polluted the air is on any given day. In India, the AQI is published by the Central Pollution Control Board (CPCB) and runs from 0 to 500.
The higher the AQI number, the worse the air quality — and the greater the potential health effects.
AQI Scale: What the Numbers Mean
| AQI Range | Category | Health Implication |
|---|---|---|
| 0 – 50 | Good | Air quality is satisfactory. Outdoor activity is safe for all. |
| 51 – 100 | Satisfactory | Acceptable air quality. Minor discomfort for sensitive groups. |
| 101 – 200 | Moderate | Sensitive groups may experience breathing discomfort. |
| 201 – 300 | Poor | Breathing discomfort for most people on prolonged exposure. |
| 301 – 400 | Very Poor | Respiratory illness likely on prolonged exposure. Limit outdoor time. |
| 401 – 500 | Severe | Affects healthy people. Serious risk for sensitive groups. |
The AQI is calculated based on eight pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, and Pb. For Delhi, PM2.5 is typically the driving pollutant — the one that pushes the AQI into dangerous territory.
Current AQI in Delhi — Real-Time Air Quality Data
Delhi's AQI fluctuates significantly across the day and across the year. Mornings and evenings tend to see higher pollution levels due to temperature inversions that trap pollutants near the ground. Midday readings often drop as wind and heat disperse particles.
For the most accurate real-time data, always check:
- CPCB Sameer App (official Indian government source)
- IQAir Delhi (global air quality data platform)
- AQI India (aqicn.org/city/delhi)
Monitoring stations across Delhi — including Anand Vihar, ITO, Lodhi Road, and Dwarka — report varying readings. The city-wide AQI is an average, so your neighbourhood reading may differ.
PM2.5 and PM10 in Delhi: What the Numbers Mean
When you see headlines about Delhi's pollution, the terms PM2.5 and PM10 come up constantly. Here's what they actually mean.
PM2.5 — The More Dangerous Particle
PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometres or less — about 30 times smaller than a human hair. These particles are small enough to penetrate deep into the lungs and even enter the bloodstream.
The World Health Organization's safe annual limit for PM2.5 is 5 µg/m³. Delhi's annual average routinely exceeds 90–100 µg/m³ — more than 20 times the WHO guideline.
PM10 — Coarser, but Still Harmful
PM10 particles (up to 10 micrometres) are larger and get trapped in the nose and throat. They cause irritation, coughing, and aggravate respiratory conditions. Delhi's PM10 levels frequently exceed 200–300 µg/m³ during peak pollution season, against a WHO annual guideline of 15 µg/m³.
Seasonal Spikes
Delhi's pollution levels follow a predictable annual pattern:
- October–January: Worst months. Cold temperatures create temperature inversions. Stubble burning in Punjab and Haryana adds a thick layer of smoke. Diwali firecrackers cause single-day AQI spikes above 400.
- February–April: Gradual improvement as temperatures rise and winds pick up.
- May–June: Dust storms from Rajasthan spike PM10 levels.
- July–September: Best months. Monsoon rains wash pollutants from the air. AQI frequently falls below 100.
Health Effects of Delhi's Air Pollution
Air pollution does not affect everyone equally. The health effects depend on the pollution level, duration of exposure, and individual vulnerability.
Short-Term Effects (Days of High AQI)
On days when Delhi's AQI crosses 200–300, even healthy adults can experience:
- Coughing, throat irritation, and congestion
- Eye irritation and watering
- Shortness of breath during physical activity
- Headaches and fatigue
Long-Term Effects (Chronic Exposure)
Research published in medical journals and endorsed by the World Health Organization links long-term exposure to high PM2.5 levels with:
- Reduced lung function and chronic obstructive pulmonary disease (COPD)
- Increased risk of heart disease and stroke
- Higher rates of lung cancer
- Cognitive decline in older adults
- Developmental issues in children
Sensitive Groups: Who Is Most at Risk?
The following groups face significantly higher health risks in polluted air. On days with AQI above 150, these individuals should limit outdoor activity as much as possible:
- Children under 14 — lungs are still developing; more air breathed per body weight
- Elderly adults (65+) — reduced lung capacity and immune response
- People with asthma, bronchitis, or COPD — pollutants trigger attacks
- Pregnant women — PM2.5 linked to low birth weight and preterm births
- People with heart disease — PM2.5 enters the bloodstream and stresses the cardiovascular system
- Outdoor workers — prolonged daily exposure with no option to stay indoors
Outdoor Activity Guide: When to Go Out (and When to Stay In)
This is the practical question most Delhi residents ask every morning. Here's a clear guide based on the day's AQI reading:
AQI-Based Outdoor Activity Table
| AQI Level | Category | Safe for Everyone? | Recommendation |
|---|---|---|---|
| 0–50 | Good | ✅ Yes | Ideal for all outdoor activity including running, cycling. |
| 51–100 | Satisfactory | ✅ Yes | Safe for most. Sensitive groups should monitor symptoms. |
| 101–200 | Moderate | ⚠️ Mostly | Sensitive groups should limit strenuous outdoor activity. |
| 201–300 | Poor | ⚠️ No | Reduce prolonged outdoor exertion. Wear N95 if outdoors. |
| 301–400 | Very Poor | ❌ No | Avoid outdoor activity. Sensitive groups must stay indoors. |
| 401–500 | Severe | ❌ No | Stay indoors. Keep windows closed. Use air purifier. |
Practical Tips for Going Outside on Polluted Days
When AQI is between 150–300 and you must go outside:
- Wear an N95 or N99 mask — surgical masks do not filter PM2.5
- Avoid peak pollution hours — early morning (6–9am) and evening (6–9pm) tend to be worst
- Avoid high-traffic routes — roadside pollution levels are 2–3x higher than ambient AQI
- Limit exercise intensity — heavy breathing increases particle inhalation
- Shower after returning — removes particles from hair and skin
Indoor Protection
On severe AQI days, staying indoors is only safe if your indoor air is filtered:
- Use an air purifier with a HEPA filter rated for PM2.5 (look for CADR rating matching your room size)
- Keep windows and doors closed
- Avoid cooking on a gas stove without ventilation — it adds to indoor PM2.5
Why Is Delhi So Polluted? Causes Behind the Numbers
Understanding why Delhi's air quality data is so alarming requires looking at multiple overlapping sources.
1. Stubble Burning (October–November)
Each year, farmers in Punjab and Haryana burn rice stubble to clear fields before the next crop. Satellite imagery shows thousands of fire hotspots. Winds carry smoke directly into Delhi, causing AQI to spike above 400 within hours.
2. Vehicle Emissions
Delhi has one of the highest vehicle densities in the world. Diesel trucks, two-wheelers, and older petrol vehicles emit significant NOₓ and PM2.5 directly at ground level where people breathe.
3. Construction Dust
Ongoing infrastructure development — roads, metro lines, buildings — generates massive amounts of PM10. Delhi's construction dust is a year-round contributor.
4. Diwali Firecrackers
Despite restrictions, Diwali night routinely produces the worst single-night AQI spike of the year. Some monitoring stations record AQI above 500 (beyond scale) in the hours following fireworks.
5. Geographic Factors
Delhi sits in the Indo-Gangetic Plain, surrounded by hills to the north and east. This geography, combined with winter temperature inversions, traps pollutants close to the surface with no wind to disperse them.
Frequently Asked Questions About AQI in Delhi
Q: What is a safe AQI level for outdoor activity in Delhi?
An AQI below 100 is generally considered safe for most people, including moderate exercise. Sensitive groups should be cautious above 50. For intense physical activity like running, an AQI under 50 is ideal.
Q: Is AQI 150 dangerous in Delhi?
At AQI 150 (Moderate category), healthy adults can typically handle light outdoor activity without significant short-term effects. However, sensitive groups — including children, elderly people, and those with respiratory conditions — should limit time outside and avoid strenuous activity.
Q: What does PM2.5 mean on an AQI app?
PM2.5 is fine particulate matter smaller than 2.5 micrometres. It is the most harmful air pollutant because it bypasses the nose and throat and penetrates deep into the lungs. On most Indian AQI apps, the displayed AQI is dominated by the PM2.5 reading.
Q: When is Delhi's air quality the worst?
Delhi's pollution peaks between October and January, driven by winter temperature inversions, stubble burning in neighbouring states, and cold, stagnant air. Diwali (typically October or November) consistently produces the worst single-day AQI readings.
Q: How does the World Health Organization define safe air quality?
The WHO's 2021 Air Quality Guidelines recommend an annual mean PM2.5 concentration of no more than 5 µg/m³, and a 24-hour mean of no more than 15 µg/m³. Delhi's actual levels routinely exceed these limits by 10–20 times.
Q: Does wearing a mask help against Delhi's pollution?
Yes — but only the right type of mask. An N95 mask (or better, N99) filters fine particulate matter effectively. Standard surgical masks and cloth masks do not filter PM2.5-sized particles and provide minimal protection against air pollution.
Q: Should children go to school when AQI is above 300?
Most health authorities recommend keeping children indoors when AQI exceeds 300. At this level (Very Poor category), prolonged exposure causes measurable respiratory stress even in healthy children. Delhi schools are often directed to shut or move classes indoors based on CPCB advisories.
Conclusion
Delhi's air quality challenge is real, persistent, and complex — but it's also measurable and manageable at the individual level. Knowing how to read the air quality index AQI, understanding what PM2.5 and PM10 actually do to your body, and using a simple outdoor activity framework can meaningfully reduce your exposure and protect your health.
Check real-time AQI data daily before heading out. Prioritise N95 masks when pollution levels are poor or worse. And if you're part of a sensitive group — or live with someone who is — treat an AQI above 200 as a serious health signal, not just a number on an app.
The air may not always be within your control, but your response to it is.
Sources: Central Pollution Control Board (CPCB) India, World Health Organization Air Quality Guidelines (2021), Ministry of Earth Sciences — SAFAR Delhi, The Lancet Planetary Health.
