Every winter in Delhi NCR, the same number takes over conversations, news headlines, and phone notifications: AQI. But even though most of us have learned to associate a high AQI with "bad day, stay indoors," fewer people actually know what the number measures, or why the difference between an AQI of 20 and an AQI of 300 is so much larger than it sounds.
What AQI actually measures
The Air Quality Index is a standardised scale that converts the concentration of pollutants in the air — mainly fine particulate matter (PM2.5 and PM10), along with gases like ozone and nitrogen dioxide — into a single number. The idea is to make a complex mix of pollutants easy to understand at a glance, rather than requiring everyone to interpret raw micrograms-per-cubic-metre readings.
Why the scale isn't linear
Here's the part that trips most people up: AQI doesn't rise in a straight line with pollution levels. It's a stepped scale, and the health impact accelerates sharply as you move into higher bands. The jump from "Good" to "Moderate" is nowhere near as harmful as the jump from "Very Poor" to "Severe" — even though both look like similarly sized jumps on paper.
This is why Delhi's typical winter AQI readings of 300, 400, or higher aren't just "worse" than a good day — they represent exposure levels associated with measurably higher risk of respiratory and cardiovascular strain, especially with sustained exposure over weeks.
Why "under 20" is the real target, not just "better than outside"
Many indoor solutions are marketed on relative improvement — "reduces indoor pollution by X%" — without stating what that improvement actually adds up to. An AQI under 20 sits solidly within the "Good" category on the national scale, which matters because it's not just "less bad" than outdoor air during Delhi's winter — it's a genuinely healthy air quality reading, full stop.
- 0–50 (Good): Minimal health impact
- 51–200 (Satisfactory to Moderate): Manageable for most, but can affect sensitive groups
- 201+ (Poor to Severe): Increasing risk for everyone, serious risk for children, seniors, and those with respiratory conditions
Understanding this scale is really the first step in understanding why whole-home air quality management matters — it's not about making bad air "somewhat better." It's about holding a home consistently in the one band where air quality stops being a health concern at all.
See how Kair holds AQI under 20 indoors.
Explore how the 5-stage filtration process works, whatever the outdoor AQI looks like.