The Air We BreathePart 1 of 5 · The Invisible Problem
India Is Breathing Something We Cannot See
The most dangerous part of polluted air is that you don't always know you're breathing it.
Too small to see
Most people picture air pollution as smog, smoke or a dusty road. The particles that harm us most are far smaller than any of these. PM2.5 refers to particles up to 2.5 micrometres across, roughly thirty times thinner than a human hair. They come from vehicle exhaust, construction, burning of crops and waste, and industry. They are too small to see individually.
Why size matters
Their size is the problem. Larger dust is mostly caught by the nose and throat. Fine particles travel past those defences, reach deep into the lungs, and the smallest can cross into the bloodstream. The WHO describes air pollution as a major public-health threat, with fine particulate matter linked to cardiovascular and respiratory disease and lung cancer.
- Larger dustMostly caught earlyReaches: Nose & throat.
- Fine particles (PM2.5)Pass the body's first defencesReaches: Nose & throat, Deep in the lungs.
- The smallest particlesCan cross into the bloodReaches: Nose & throat, Deep in the lungs, Into the bloodstream.
A clear sky is not clean air
Haze is not a reliable signal. Your eyes and nose are poor instruments for this.
This is why a clear-looking day can still be an unhealthy one. Haze is not a reliable signal. A bright morning can carry high PM2.5, and a grey one can be cleaner than it looks. Your eyes and nose are poor instruments for this.
Who feels it first
Some people feel the effects sooner.
- 01
Children
They breathe faster relative to their body size and their lungs are still developing.
- 02
Older adults
They often have less physiological reserve.
- 03
Asthma, COPD and heart conditions
Symptoms can worsen when levels rise.
Reading the AQI
The Air Quality Index is a useful starting point. It turns complex measurements into a single number you can act on. But it comes from fixed monitoring stations, reflects outdoor air, and is averaged over time.
What the AQI gives you
- A single number that sums up complex measurements
- A quick, shared reference you can act on
What it may not capture
- A busy road near your home
- A short spike during the evening
- The air inside your rooms
That's the problem in a single breath. Next, we look at the city where it is most visible every winter.