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Why is Delhi's Air so Polluted? Understanding AQI in National Capital Region

12:05 PM
22 November 2025

Understanding AQI
Why is Delhi's Air so Polluted?

It’s mid-October, and Delhi's air quality has already deteriorated into the 'poor' category. But why does air pollution become such a menace in Delhi and other northern Indian cities at this time of year?

The Air Quality Index (AQI) is a tool used to communicate the pollution level in the air. In India, AQI is divided into six categories, each represented by a specific color to indicate the severity:

Air Quality IndexCategory & ColorWhat does it mean?
0 - 50Good (green)Safe to breathe. People not exposed to any health risk.
51 - 100Satisfactory(light green)Air quality safe for healthy adults.
101 - 200Moderately Polluted (yellow)Can cause difficulty breathing for people with respiratory conditions.
201 - 300Poor (orange)Unsafe for children, pregnant women and the elderly
301 - 400Very Poor (red)Prolonged exposure can cause chronic breathing problems.
401 - 500Hazardous/Severe (maroon)Prolonged exposure can lead to serious health problems and impairment.

Unfortunately, during October and November, cities like Delhi often experience air quality in the 'poor' to 'severe' range. But what exactly causes this drastic decline?

There are several factors that lead to the sharp rise in air pollution during this time: industrial emissions from factories and construction sites around the NCR, stubble (crop residue) burning in Punjab and Haryana, dip in temperature, low wind speed and vehicular emissions.

Delhi-NCR is India's largest airshed

Airshed is a common geographical area where pollution gets trapped.

What Pollutants Contribute to Poor AQI?

The following key pollutants are measured to calculate AQI, and they are the main culprits behind poor air quality:

  • Particulate Matter: PM2.5 and PM10 are the smallest particles found in smoke and dust
  • Nitrogen Dioxide: NO2 emits from combustion
  • Ozone: O3 develops in the atmosphere after contact with sunlight from gases that come out of smokestacks and factories
  • Carbon Monoxide and Sulphur Monoxide: CO and SO2 are produced from incomplete combustion of fossil fuels mostly from polluting vehicles
  • Lead: Pb comes from contaminated dust of paint, batteries, vehicles

How can you use AQI to protect your health?

Once you've checked the AQI for your city, here are some steps you can take to protect yourself and contribute to reducing air pollution:

  • Limit Outdoor Activities: Avoid strenuous outdoor activities, especially for children, the elderly, and those with respiratory issues.
  • Wear Masks: Use N95 masks to filter out harmful PM2.5 particles.
  • Use Air Purifiers: Invest in air purifiers with good filters for indoor spaces.
  • Plant More Trees: Trees help absorb pollutants and improve air quality.
  • Close Windows: Keep windows closed on poor AQI days to block polluted air.
  • Stay Hydrated: Drink plenty of water and eat antioxidant-rich foods to detoxify.
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