Air Quality
Air Quality Monitors: What to Measure, and What Actually Works
An air purifier without a monitor is an act of faith. You assume it is working, you assume the filter is still good, and you have no idea whether the biggest source of indoor pollution in your home is the street outside or your own kitchen.
A monitor answers those questions, and the answers are frequently surprising. Most households discover that cooking, not traffic, produces their highest indoor PM2.5 readings of the day — and that the extractor fan they rarely use is the most effective air-quality device they own.
That behavioural effect is the real value. The monitor does not clean anything; it tells you what to change.
Which parameters are worth paying for
| Parameter | Priority | Why |
|---|---|---|
| PM2.5 | Essential | The pollutant most linked to health effects, and the one a purifier removes. Insist on a laser scattering sensor. |
| PM10 | Useful | Coarser dust. Usually comes free with a PM2.5 sensor. |
| CO2 | High and under-rated | A direct proxy for ventilation. Above 1,000 ppm indicates stale air and documented cognitive effects; above 1,500 ppm, ventilate. |
| Temperature & humidity | Useful | Drives comfort and mould risk. Aim for 40–60% RH. |
| TVOC | Indicative only | Consumer sensors report a broad, uncalibrated index. Useful for spotting a spike after painting or new furniture; not a precise measurement. |
| HCHO (formaldehyde) | Weak on consumer units | Genuinely hard to measure cheaply. Treat consumer readings with scepticism. |
| CO (carbon monoxide) | Safety, not air quality | Worth having if you burn gas indoors — but a dedicated CO alarm is the correct safety device. |
Sensor quality, and why cheap monitors mislead
PM sensors come in two broad classes. Laser scattering sensors shine a laser through an air stream and count the light scattered by individual particles; they are reasonably accurate down to low concentrations. Infrared sensors are far cheaper and lose accuracy badly below about 50 µg/m³ — which is precisely the range you care about once a purifier is running.
CO2 has the same split. Genuine NDIR (non-dispersive infrared) sensors measure CO2 directly. Cheap 'eCO2' readings are estimated from a VOC sensor and are not a CO2 measurement at all — they will happily show a rise because you opened a bottle of nail polish. If CO2 matters to you, require NDIR explicitly.
Important
Calibration, drift and sanity-checking your monitor
- All optical PM sensors drift as dust accumulates on the optics. Clean the intake per the manual every couple of months.
- Sanity-check against a nearby CPCB or SAFAR reference station: take your monitor outdoors, wait ten minutes and compare. You are looking for the same ballpark, not an exact match.
- NDIR CO2 sensors self-calibrate against fresh air. If yours never sees outdoor air it can drift high — put it near an open window for an hour occasionally.
- High humidity inflates PM readings on optical sensors, because water droplets scatter light like particles. A reading spike during heavy monsoon rain is often an artefact.
- Do not compare two different monitors and assume the more alarming one is right. Compare each against a reference instead.
What to actually do with the data
- Establish a baseline: what is your bedroom at 3 am with the purifier off?
- Test your purifier: close the room, run on high for 40 minutes, and confirm PM2.5 falls substantially. This is how you detect an exhausted filter.
- Find your own sources: watch what happens when you fry, light incense, use a mosquito coil, or run a vacuum without a HEPA bag.
- Time your ventilation: on a good AQI day, open windows and watch CO2 fall. That is free air quality.
- Decide where the next purifier goes based on which room is consistently worst, not on which room is largest.
Prices and options
| Budget | What you get | Caveats |
|---|---|---|
| Under ₹3,000 | Basic PM2.5, often infrared sensor | Poor accuracy at low concentrations; treat as a rough indicator |
| ₹3,000 – ₹8,000 | Laser PM2.5/PM10, temp, humidity | The sensible consumer choice for verifying a purifier |
| ₹8,000 – ₹15,000 | Adds TVOC, logging, app history | VOC index is indicative, not calibrated |
| ₹15,000 – ₹25,000 | Genuine NDIR CO2 plus PM | The tier worth buying if ventilation matters to you |
| ₹25,000+ | Reference-grade sensors, calibration certificates | For offices, schools and compliance reporting |
Indicative Indian market ranges for budgeting, not quotations. Prices move frequently — always confirm on the marketplace or with a supplier before purchasing.
Where to buy
We have not individually tested products in this category, so we are not going to rank them as though we had. Use the buying criteria above to judge listings yourself, and these searches as a starting point.
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