Here’s Why India’s Air Quality Is Worse During the Winter

India winter high unsafe PM2.5 pollution levels compared with summer

Every winter, India’s PM2.5 pollution levels reach more than 10 times the World Health Organization’s annual limit. Hazy skies and high pollution alerts have become the norm during India’s winters. But just why is this?

Analyzing India’s Summer & Winter Pollution Levels

Data analyzed by Smart Air showed that India’s winter PM2.5 air pollution levels are three times higher than summer levels in some cities. That’s a huge increase, in PM2.5 levels.

A graph of Delhi’s pollution levels shows these winter peaks in pollution levels. PM2.5 typically begins to  rise from October, and remains high until March of the next year.

Delhi's Annual PM2.5

The winter peaks and summer troughs in PM2.5 levels are clear, but just why is this?

Why Is Air Quality Worse in the Winter in India?

Air quality worsens in the winter because of how the air mixes. In the winter, the surface of the earth gets cooler, and the air near the surface is also cooled. This dense layer of cool often gets trapped below a layer of warm air, which is called a “temperature inversion.” With less air mixing, pollutants are trapped near the ground, leaving cities to choke on their own pollution.


Temperature Inversion
Source: The Weather Network

Diwali, typically taking place around October and November is India’s new year festival. Firecrackers are often let off which create huge rises in air pollution during Diwali. This is another reason for an increase in PM2.5 levels during India’s winters.

India Diwali air pollution due to burning firecrackers

The winter also brings pollution from farmers burning their crop stubble, as well as people burning fires for warmth.

crop stubble burning in India creating air pollution

Bottom Line: Air quality data shows that PM2.5 air pollution is 59% higher in winter than in summer across five major cities in India. This air quality exceeds the WHO annual limit regardless of the season.

How I Protect Myself From India’s Winter PM2.5

Breathing clean air doesn’t need to cost an arm and a leg. Here’s how I protect myself from high pollution levels during India’s polluted winters

  1. Wear a pollution mask outdoors when PM2.5 is above 10 micrograms. Learn more: How wearing masks can benefit health ».
  2. Use an air purifier when at home. Studies of air purifiers have found that reducing particulate indoors prevents harm to blood pressure, inflammation, and immune response—even among young, healthy twenty-year-olds.
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