PM2.5
Highest risk
Fine particulate matter
Particles 2.5 micrometres or smaller — about 30 times thinner than a human hair. They travel deep into the lungs, and some can even pass into the bloodstream.
Indoor Air Awareness
You take 20,000 breaths a day. Do you know what you're breathing?
Air quality isn't just about smog outside. It's about the invisible particles inside your home and office.
Facts sourced from US EPA & WHO
3-minute read
Breaths today
0
Live estimate
Estimated from your local time at 14 breaths per minute. A typical adult breathes 12–20 times a minute at rest.
90%
of the average person's time is spent indoors.
US EPA
2–5×
Indoor levels of some pollutants are often 2 to 5 times higher than outdoors.
US EPA
99%
of the world's population breathes air that exceeds WHO guideline limits.
WHO, 2022
01 · The Basics
What is AQI?
Think of the Air Quality Index as a thermometer for air pollution. It turns complex pollutant measurements into one simple number from 0 to 500.
- Higher number, dirtier air. The higher the AQI, the greater the level of pollution and the greater the health concern.
- Colour coded. Each range has a colour, so you can judge the air at a glance — green is good, red means act.
- Worst pollutant wins. AQI is calculated for each pollutant, and the highest one becomes the headline number.
Good to know: India's CPCB and the US EPA both use a 0–500 scale, but their category bands differ. This page uses the US EPA scale — the same one shown on O2IAQ monitoring dashboards.
The AQI thermometerUS EPA
500Hazardous
300Very Unhealthy
200Unhealthy
150Sensitive Groups
100Moderate
50Good
0Clean air
02 · The Invisible Enemies
Three things worth knowing by name
You can't see them, but they shape how you feel, focus and sleep — especially indoors.
PM10
Dust · Pollen · Mould
Coarse inhalable particles
Particles 10 micrometres or smaller — larger dust, pollen and mould. They can irritate the eyes, nose and throat, and aggravate asthma and allergies.
CO2
Ventilation signal
Carbon dioxide
Not part of the AQI, but the clearest sign of stale indoor air. Outdoors it sits around 420 ppm; in a closed, crowded room it can climb past 1,000 ppm — levels linked to drowsiness and poorer focus.
Drawn to scale
A single strand of human hair is roughly 50–70 micrometres wide. A PM2.5 particle is so small that nearly 30 of them could line up across it — far too small to see, and small enough to slip past your body's natural filters.
- Human hair ≈ 70 µm
- PM10 ≤ 10 µm
- PM2.5 ≤ 2.5 µm
Scale: 4 px = 1 µm. Source: US EPA, Particulate Matter Basics.
03 · The Colour Scale
Read the air like a traffic light
The standard US EPA colours, simplified into what they mean for your day.
0 – 50
Good
Fresh air
Air quality is satisfactory, and air pollution poses little or no risk. Open the windows and breathe easy.
51 – 100
Moderate
Acceptable
Acceptable for most people, though those who are unusually sensitive to air pollution may feel some effects.
101 +
Unhealthy
Time to take action
From 101, children, older adults and people with heart or lung conditions are affected first. Above 150, everyone may start to feel it.
Try it — drag to explore the full scale
All six official US EPA categories, from 0 to 500.
Good
42
Air quality is satisfactory, and air pollution poses little or no risk. Health guidance: US EPA / AirNow
Step 1 · Know the problem
Step 2 · Fix it
Knowing the problem is step one. Fixing it is step two.
That's why we built O2Cure. We provide military-grade air purification and monitoring to ensure every breath you take indoors is safe, verified, and pristine.
O2IAQ Monitor
Sample
Indoor
32
Good
Outdoor
168
Unhealthy
Indoor air is 81% cleaner than outside
PM2.5
7
µg/m³
PM10
18
µg/m³
CO₂
612
ppm
Illustrative values for demonstration.