PRANA
Air quality basics
What PM2.5 is, what the limits are, how to read the AQI, and what helps at home.
4 min read
What PM2.5 is
PM2.5 means airborne particles 2.5 micrometres across or smaller. They’re small enough to get deep into the lungs and pass into the bloodstream, and exposure is linked to stroke, lung cancer and chronic lung disease.
It’s also everywhere: in 2019, 99% of the world’s population lived in places that didn’t meet WHO’s air quality guidelines.
- Human hair
- about 70 µm
- PM10
- 10 µm or less
- PM2.5
- 2.5 µm or less
How much is too much
WHO’s guideline for PM2.5 is 5 µg/m³ as a yearly average and 15 µg/m³ over 24 hours. India’s national standard allows 40 and 60.
Yearly average
24-hour average
Reading India’s AQI
The AQI turns pollution readings into one number from 0 to 500, split into six bands. Here’s what each band means, and the PM2.5 level behind it.
| Band | AQI | PM2.5, 24-hour (µg/m³) | Possible health impact |
|---|---|---|---|
| Good | 0–50 | 0–30 | Minimal impact |
| Satisfactory | 51–100 | 31–60 | Minor breathing discomfort to sensitive people |
| Moderate | 101–200 | 61–90 | Breathing discomfort to people with lung disease, asthma and heart disease |
| Poor | 201–300 | 91–120 | Breathing discomfort to most people on prolonged exposure |
| Very poor | 301–400 | 121–250 | Respiratory illness on prolonged exposure |
| Severe | 401–500 | Above 250 | Affects healthy people and seriously impacts those with existing diseases |
Indoor air isn’t automatically cleaner
Shutting the windows doesn’t shut pollution out. Monitors in more than 3,000 Delhi homes found winter indoor PM2.5 many times above WHO guidelines, in richer and poorer homes alike.
Homes make their own pollution too. Cooking, mosquito coils, incense sticks, tobacco smoke, wood or charcoal burning, and dust are all common indoor sources, and outdoor particles find their way in.
cigarettes’ worth of PM2.5 came from burning a single mosquito coil, in a laboratory test.
What a purifier’s filters do
A purifier pulls room air through a stack of filters, over and over. Each layer has its own job.
- Pre-filterCatches hair, lint and larger dust, and protects the finer layers behind it.
- HEPA filterThe US standard is at least 99.97% of particles at 0.3 µm, the size hardest to catch; bigger and smaller ones are caught more easily. In Europe’s EN 1822 grades, H13 means at least 99.95% and H14 at least 99.995%.
- Activated carbonTakes out some gases and odours, not particles. It works best with plenty of carbon.
Six habits that help
- Shut windows on bad-air days
Keep doors and windows closed in the morning and late evening. If you need to air the house, do it between 12 pm and 4 pm.
- Keep the purifier running
Run it continuously, on the highest setting you can live with, when the air is bad.
- Close the room
A purifier cleans the room it’s in. Shut the door and windows so it isn’t trying to clean the whole house.
- Change filters on time
Every filter fills up. Follow the maker’s replacement schedule.
- Air out when it’s cleaner outside
Cutting indoor sources and letting in clean outdoor air are the most effective steps. Always ventilate while cooking.
- Skip smoke indoors
Don’t burn mosquito coils or incense in closed rooms, and don’t smoke indoors. Wet-mop rather than sweep.
HUSH
Quiet, and how to get it
How quiet a bedroom should be, what acoustic panels do, and what we know about white noise.
1 min read
For good sleep, steady background noise in a bedroom should stay below 30 dB(A), and single noises, like a door or a horn, below 45 dB.
Steady noise in the bedroom, for good sleep.
The loudest single noise at night.
Panels absorb, walls block
Acoustic panels soak up sound inside a room, so it echoes less and voices carry less. How much they absorb is rated by NRC, on a scale from 0 to 1. Panels don’t stop noise travelling between rooms; that takes sound insulation, which is a different job.
White noise
A steady sound can mask sudden ones. But the evidence that continuous noise improves sleep is still weak, so treat it as something to try rather than a cure.
TERRA
Plants, honestly
What plants can and can’t do for a room.
1 min read
Plants famously removed some chemicals in small sealed test chambers. In a real room the effect is tiny: you’d need between 10 and 1,000 plants per square metre of floor to match the air an ordinary building already exchanges through ventilation.
plants per square metre of floor to match normal ventilation. Plants won’t replace a purifier.
Where plants do help is how a room feels. Research links indoor plants to modest benefits, such as slightly lower blood pressure.
LUMA
Light that keeps time
Light sets your body clock. Bright days and dim evenings help it keep time.
1 min read
Ordinary room light in the evening can delay melatonin, the hormone that tells your body it’s night, and shorten its release by about 90 minutes. Colour matters too: blue light suppresses melatonin about twice as long as green light.
Here’s what a well-lit day looks like, in numbers.
Brightness matters at least as much as colour. In the evening, choose dim, warm-white light: bulbs sold as warm white are around 2,200–3,000 K.
SOMNUS
Better sleep starts with the bedroom
How much sleep adults need, and what the room can do.
1 min read
Adults should sleep 7 or more hours a night, regularly. Keep the bedroom quiet, relaxing and cool.
hours a night, on a regular basis, for adults.
On mattresses, medium-firm ones, especially those you can adjust yourself, come out best for comfort, sleep quality and spine alignment.
Coming soon.
This guide is general information, not medical advice. If you have a health condition, talk to your doctor.