What's in my air
Carbon monoxide — the one where an air purifier is the wrong purchase entirely
Carbon monoxide is a colourless, odourless gas produced by incomplete combustion, which binds haemoglobin far more strongly than oxygen does and can be fatal at concentrations that give no sensory warning.
Limits and standards
India's NAAQS are ambient (outdoor) standards, and there is no statutory Indian indoor air quality standard for homes. WHO's guideline values are health-based targets rather than regulatory limits, and are consistently stricter.
| Standard | Limit | What it means |
|---|---|---|
| India NAAQS — 8-hour average | 2 mg/m³ | — |
| India NAAQS — 1-hour average | 4 mg/m³ | — |
| WHO 2021 guideline — 24-hour | 4 mg/m³ | — |
| WHO — short-term | 35 mg/m³ (1 hour); 100 mg/m³ (15 minutes) | The short averaging times exist because CO poisoning is an acute event. Exposure is measured in minutes, not years. |
Where it comes from
Gas water heaters (instant geysers) in bathrooms
The most common cause of Indian residential CO fatalities. An LPG geyser in a small, closed bathroom consumes the available oxygen and shifts to incomplete combustion, producing CO rapidly.
Generators run indoors or in attached spaces
A petrol or diesel generator in a garage, stairwell or covered balcony can raise indoor CO to fatal levels within minutes.
Charcoal and biomass burning indoors
Angeethi and charcoal braziers used for heating in closed rooms are a documented winter cause of deaths in north India.
Blocked or poorly maintained flues
Any combustion appliance whose exhaust path is obstructed will vent products of combustion into the room.
Vehicle exhaust
An engine idling in an attached garage, or exhaust drawn in from a parking area below.
Why it matters
- CO binds to haemoglobin with an affinity over 200 times that of oxygen, so it displaces oxygen from the blood at low concentrations.
- Early symptoms — headache, dizziness, nausea, confusion — are easily mistaken for something ordinary, and the confusion itself impairs the ability to recognise the problem and leave.
- It kills people who are asleep, because there is nothing to wake them.
- Unlike every other entry in this library, the intervention is a detector rather than a filter — and that difference is the entire point of this page.
Note
Can you detect it yourself?
Consumer air quality monitors are genuinely useful for tracking change and poor at absolute measurement. Knowing which of the two you are looking at prevents most of the disappointment in this category.
| Question | Answer |
|---|---|
| Can you sense it? | None. This is the defining characteristic of carbon monoxide and the reason it is dangerous. Any claim to smell 'gas' relates to the odorant added to LPG, not to CO. |
| What a consumer monitor shows | A certified CO alarm, not an air quality monitor. Look for EN 50291 or UL 2034 certification, an end-of-life indicator and a digital display showing ppm. Many general air quality monitors do not measure CO at all despite a busy display. |
| Field test | None applicable — this is a continuous-alarm situation, not a spot-test one. |
What removes it
Effectiveness ratings below describe the technology working correctly, within its service life, on water or air that suits it. “Depends” means there is a condition in the caveat that decides the outcome — read it before buying.
- CO alarm (EN 50291 or UL 2034 certified)Effective
The correct and only appropriate device. Fit one in or adjacent to any room with a gas appliance, and near sleeping areas.
Caveat: Sensors have a service life, typically 7–10 years. Note the replacement date on installation — an expired alarm is a decoration.
- VentilationEffective
Permanent ventilation in any room with a combustion appliance. A gas geyser bathroom needs a permanently open vent, not just an openable window.
- Correct appliance installationEffective
Relocating an instant geyser outside the bathroom, or converting to an electric storage heater, removes the hazard rather than managing it.
- Never running generators in enclosed spacesEffective
Not a technology, an operating rule. Generators belong outdoors, well away from windows and vents.
What does not work
Each of these is commonly assumed — or actively marketed — to help with carbon monoxide. None of them do.
HEPA air purifiers
HEPA filters particles. CO is a gas and passes through without interaction. Every purifier sold in India for household use is irrelevant to carbon monoxide.
Activated carbon filters
Activated carbon has negligible capacity for carbon monoxide. Adsorbing it requires specialised catalytic media used in industrial and respirator applications, not in room purifiers.
Ionisers and ozone generators
No removal, and they introduce their own problems.
Opening a window after symptoms begin
By the time symptoms are recognised, judgement may already be impaired. Leave the building first and ventilate afterwards.
Source control that beats filtration
For most indoor pollutants the highest-leverage intervention is not a device. These are the changes worth making before, or instead of, buying anything.
- Never install or operate an LPG instant geyser inside a closed bathroom. If one is already installed, ensure permanent ventilation and consider relocating or replacing it.
- Fit a certified CO alarm near sleeping areas and near any gas appliance. It is the cheapest meaningful safety device in the house.
- Never run a generator indoors, in a stairwell, in a garage or on a covered balcony, even with a door open.
- Never use charcoal, angeethi or biomass for indoor heating in a closed room.
- Have gas appliances serviced and flues checked annually.
Why this page exists on an air purifier site
Because people search for 'air purifier for carbon monoxide', and the correct answer is that there is not one, and that they should buy something else instead.
It would be straightforward to write this page around a purifier recommendation. It would also be dangerous, because someone would buy the purifier, believe the problem was addressed, and still have an unventilated gas geyser in the bathroom.
The intervention that saves lives here costs under ₹3,500 and takes ten minutes to install. If you take one thing from this library, take this one.
Important
Frequently asked questions
Does an air purifier remove carbon monoxide?
Can you smell carbon monoxide?
Why are gas geysers dangerous in bathrooms?
What CO detector should I buy in India?
Sources
Every limit and standard quoted on this page comes from one of the documents below. Where a figure is not in one of these, we have not published it.
National Ambient Air Quality Standards (NAAQS), notification dated 18 November 2009
Central Pollution Control Board, Ministry of Environment, Forest and Climate Change · published 2009-11-18 · checked 2026-08-01
India's legally applicable ambient air standards. They are ambient (outdoor) standards — India has no equivalent statutory indoor air quality standard for homes.
World Health Organization · published 2021-09-22 · checked 2026-08-01
The 2021 revision tightened most values substantially. WHO guideline values are health-based targets, not regulatory limits, and are considerably stricter than India's NAAQS.
WHO Guidelines for Indoor Air Quality: Selected Pollutants
World Health Organization · published 2010-01-01 · checked 2026-08-01
Covers formaldehyde, benzene, carbon monoxide, naphthalene, nitrogen dioxide, PAHs, radon, trichloroethylene and tetrachloroethylene specifically as indoor pollutants.
This page states what published standards say and what the physics of each technology allows. It does not state what is in your supply — no page can. Where the two questions meet is a test result, and every entry in this library says which test to ask for.