Tag: pm2.5

PM2.5 vs PM10: What Is the Difference and Which Matters More Indoors?

PM10 is particulate matter 10 microns across or smaller; PM2.5 is the finer fraction, 2.5 microns or smaller. PM10 is mostly dust and mostly lodges in the nose and throat, while PM2.5 is mostly smoke and combustion particles and can travel deep into the lungs. Indoors, PM2.5 is the number that matters more, and a HEPA purifier captures both.

What the Numbers Mean

“PM” stands for particulate matter: tiny solid or liquid particles floating in air. The number is a size cut-off in microns (a micron is a thousandth of a millimetre).

PM10 includes every particle 10 microns or smaller.
PM2.5 includes every particle 2.5 microns or smaller.
PM1.0 includes every particle 1 micron or smaller.

These are nested, not separate. All of PM2.5 is also counted inside PM10, and all of PM1.0 is inside PM2.5. So when a monitor shows PM10 higher than PM2.5, that is expected: the PM10 figure includes the fine particles plus the coarser ones between 2.5 and 10 microns. Both are far too small to see individually; a human hair is many times wider than either.

Where Each Comes From in Indian Cities

	Coarser particles (PM10 side)	Fine particles (PM2.5 side)
Main outdoor sources	Road dust, construction and demolition, unpaved ground, wind-blown soil	Vehicle exhaust, stubble and crop-residue burning, wood and waste burning, industry, firecrackers
Main indoor sources	Sweeping, dusting, shaking bedding, fans lifting settled dust	Frying and tadka, agarbatti and dhoop, mosquito coils, smoking, candles
How they behave	Settle out of the air relatively quickly; come back up when disturbed	Stay suspended for a long time; travel far and slip through gaps
When they peak	Dry, windy days; near construction; summer dust	Still, cold evenings and nights; October to January in north India

This is why a dusty house in summer and a smoky winter evening feel different. Dust you can often see on surfaces; our guide on why your house gets so dusty covers that side. Winter smog is mostly the fine fraction, which you cannot see settling anywhere.

Why PM2.5 Does More Harm

The body’s airways act like a series of filters. Larger particles are mostly caught in the nose and throat and cleared by mucus, sneezing and coughing. The smaller the particle, the further it gets:

Coarse particles in PM10 mostly irritate the nose, throat and upper airways. That is the sneezing, itchy throat and dust-allergy side of air pollution.
PM2.5 can reach the small airways and air sacs deep in the lungs, where the body’s clearing mechanisms are slower.
Fine particles from combustion also tend to carry the products of burning with them, which is part of why smoke is treated as more harmful than plain dust.

That is why the health limits for PM2.5 are much stricter than for PM10, and why public health agencies focus on PM2.5. If smog season brings on throat burning or watery eyes, see our page on throat irritation and burning eyes in smog; for anything that persists or affects breathing, see a doctor.

In one line: PM10 is mostly the dust you can sweep; PM2.5 is mostly the smoke you cannot see. Indoors in winter, watch PM2.5 first.

PM1.0: The Smallest Number on Your Monitor

Some monitors and purifiers also report PM1.0. It is the finest slice of PM2.5 and is dominated by fresh combustion particles: vehicle exhaust, burning, incense and cooking smoke. There is no Indian standard for PM1.0, so it is best used as a trend signal. If PM1.0 jumps while you are cooking or lighting dhoop, the source is in the room; if it climbs slowly in the evening with the windows shut, it is likely seeping in from outside.

What Each Kind of Sensor Can See

Most home air-quality monitors and purifier sensors use a laser particle sensor. A small fan draws air past a laser beam, the sensor counts the flashes of scattered light, and software estimates the mass in each size range.

Laser particle sensors report PM1.0, PM2.5 and PM10. They measure particle size, not what the particle is. They cannot tell pollen from smoke from dust.
Gas sensors (TVOC, eCO₂, NO₂) measure different things altogether: volatile chemicals, an estimate of carbon dioxide build-up, and a traffic-related gas. They do not see particles.
Older or very cheap “dust” sensors often report a single vague number and struggle with the finest particles. A monitor that shows only one unlabelled number is not telling you much.

For a full comparison of monitors, apps and what each can measure, read how to check air quality at home.

Boon Airvana’s AtmoScan sensor reads PM1.0, PM2.5 and PM10 with a laser, plus TVOC, eCO₂ and NO₂, every second, so you can see which kind of pollution is in your room.

See Boon Airvana →

How a HEPA Purifier Handles Both

A HEPA filter is a dense mat of fine fibres. It does not work like a sieve with holes of a fixed size; particles are caught by several mechanisms at once. Large particles slam into fibres, mid-sized ones are intercepted as they pass close to a fibre, and the very smallest ones zig-zag randomly and stick when they touch a fibre. There is a size in between, around 0.3 microns, that is hardest to catch, and HEPA filters are rated at that hardest size.

PM10: the pre-filter catches the largest dust and hair; the HEPA layer catches the rest of the coarse fraction easily.
PM2.5 and PM1.0: captured by the HEPA layer. An H13 grade filter captures 99.95% of particles in a single pass at its rated test size.
Gases and smells: not captured by HEPA at all. That is the job of an activated carbon layer, and even carbon only helps with some gases. Our guide on HEPA vs ionizer vs UV purifiers explains why HEPA is the technology to rely on for particles.

The filter grade is only half the story. How much air passes through the filter each hour (the CADR) decides how quickly the room’s particle level actually falls.

Indian Limits and Which Number to Watch

Standard	PM2.5	PM10
India NAAQS, 24-hour	60 µg/m³	100 µg/m³
India NAAQS, annual	40 µg/m³	60 µg/m³
WHO 2021 guideline, 24-hour	15 µg/m³	Not covered here
WHO 2021 guideline, annual	5 µg/m³	Not covered here

For daily decisions in an Indian home: in winter, watch PM2.5 and keep it under 60 µg/m³ at the very least, as close to 15 as you can manage in the bedroom. In dusty months, PM10 tells you when to close up and when the sweeping has stirred things up. PM1.0 tells you when something in the room is burning.

Frequently Asked Questions

What is the difference between PM2.5 and PM10?

PM10 is all particulate matter 10 microns or smaller; PM2.5 is the finer part, 2.5 microns or smaller. PM2.5 is counted inside PM10. PM10 in Indian cities is dominated by road dust and construction, while PM2.5 comes mostly from combustion: vehicles, stubble and waste burning, firecrackers, and indoor smoke from cooking and incense.

Which is more harmful, PM2.5 or PM10?

PM2.5 is generally considered more harmful because the particles are small enough to reach deep into the lungs, where they are cleared more slowly. Coarser PM10 particles are mostly trapped in the nose and throat. That is why PM2.5 limits are much stricter. Both are worth reducing, but indoors in winter PM2.5 is the number to watch first.

Why is my PM10 reading always higher than PM2.5?

Because PM10 includes PM2.5. The PM10 figure counts all the fine particles plus the coarser ones between 2.5 and 10 microns, so it is always equal to or higher than PM2.5. A big gap between the two means a lot of coarse dust; readings close together mean the air is mostly fine particles, typical of smoke and winter smog.

Does a HEPA air purifier remove both PM2.5 and PM10?

Yes. A HEPA filter captures both coarse and fine particles, and an H13 grade filter captures 99.95% of particles in a single pass at its rated size. How quickly the room clears depends on the purifier’s CADR relative to the room size and on keeping the door closed. HEPA does not capture gases or odours.

What is PM1.0 and should I worry about it?

PM1.0 is particles 1 micron or smaller, the finest part of PM2.5. It mostly comes from fresh combustion such as vehicle exhaust, incense and cooking smoke. India has no separate standard for it, so treat it as a signal: a sudden PM1.0 spike usually means something is burning in or near the room.

Can an air quality sensor tell if particles are pollen or smoke?

No. Laser particle sensors measure particle size and estimate mass in each size range; they cannot identify what a particle is made of. You can make reasonable guesses from patterns, for example a PM1.0 spike while cooking, but a home sensor cannot confirm pollen, mould spores or smoke specifically.

See PM1.0, PM2.5 and PM10 in your room separately, every second. Boon Airvana pairs a laser particle sensor with an H13 HEPA filter.

See Boon Airvana →

October 16, 2026

What Is a Safe AQI Level Indoors? A Plain Guide for Indian Homes

A safe indoor AQI is 50 or below, the CPCB “Good” band. Anything up to 100 (“Satisfactory”) is acceptable for most healthy people, but children, older family members and anyone with asthma or heart disease do better when the room stays under 50. Above 100 indoors, it is time to close up, filter the air and cut indoor sources of smoke.

If you have searched “AQI kitna hona chahiye”, that is the answer in one line: aim for under 50 inside your home, treat 51 to 100 as fine for a short while, and act once it crosses 100.

The Short Answer

The AQI (Air Quality Index) turns several pollutants into one number on a 0 to 500 scale. Lower is better. In Indian cities during October and November, the number that drives the AQI is almost always fine particulate matter (PM2.5), so in practice “a safe AQI” means “a low level of fine particles”.

India’s AQI and its air-quality standards are written for outdoor air. There is no separate household number that you are required to meet, so the sensible approach is to borrow the outdoor bands and the health-based limits, and hold the air in the rooms where you spend most time, especially the bedroom, to the stricter end of them.

Rule of thumb: under 50 is the goal, under 100 is acceptable, over 100 indoors means you need to act, and over 200 indoors means the room is not protecting you at all.

The CPCB Bands and What to Do Indoors

These are the Central Pollution Control Board’s National AQI bands. The right-hand column is practical guidance for the inside of a home, not an official instruction.

AQI	Band	What to do indoors
0-50	Good	Ventilate freely. Open windows for fresh air, especially after cooking.
51-100	Satisfactory	Fine for most people. Sensitive family members may notice symptoms; a purifier on low or Auto keeps the bedroom in the Good band.
101-200	Moderate	Keep windows mostly closed during the worst hours, ventilate briefly when outdoor air is cleaner, run a purifier in occupied rooms.
201-300	Poor	Windows closed, purifier running continuously in the bedroom and living room, avoid incense and frying without the chimney or exhaust on.
301-400	Very Poor	Treat the bedroom as a clean room: door shut, purifier sized for the room, gaps under doors reduced. Limit outdoor exercise.
401-500	Severe	Same as above, with everyone who is vulnerable kept in the cleanest room. If anyone has breathing difficulty, contact a doctor.

When outdoor AQI goes past 400 or “500+”, the useful question is no longer what the city reads but what your sealed bedroom reads. A correctly sized purifier in a closed room can pull a room far below the outdoor number; an undersized one in a room with an open door cannot. The GRAP stages explained guide covers what the city restrictions at each level mean.

AQI Number vs PM2.5 in µg/m³

This is the most common source of confusion. AQI and PM2.5 are two different scales. PM2.5 is a concentration: micrograms of fine particles in a cubic metre of air (µg/m³). AQI is an index: a 0 to 500 number calculated from that concentration (and from other pollutants), designed so that people can read it at a glance.

A monitor that shows “PM2.5: 60” and one that shows “AQI: 100” may be describing similar air. The numbers are not interchangeable.
India’s AQI is built so that an index of 100 lines up with the 24-hour national standard for each pollutant. For PM2.5, that standard is 60 µg/m³.
Some devices and apps use another country’s AQI formula. The same air can show a different AQI number on two screens, so check which scale your monitor or app uses before comparing.

When in doubt, look at the raw PM2.5 in µg/m³. It is the figure the health limits below are written in.

WHO and Indian Limits for PM2.5 and PM10

Pollutant	WHO 2021 guideline	India NAAQS
PM2.5, 24-hour	15 µg/m³	60 µg/m³
PM2.5, annual	5 µg/m³	40 µg/m³
PM10, 24-hour	Not used in this guide	100 µg/m³
PM10, annual	Not used in this guide	60 µg/m³

The WHO guideline is a health target: the level below which the evidence of harm is weakest. The Indian National Ambient Air Quality Standards (NAAQS) are the legal outdoor limits. The gap between the two is large, which is why an outdoor reading can be “within the national standard” and still be well above what the WHO recommends.

Why Indoor and Outdoor AQI Differ

Many people assume that closing the windows makes indoor air clean. It helps, but fine particles are small enough to travel through gaps around doors, windows, AC ducts and exhaust openings. Without filtration, indoor PM2.5 in a polluted city usually follows the outdoor level, with a lag.

Indoor air can also be worse than outdoor air for short spells, because a home has its own sources:

Cooking, especially frying and tadka, without a chimney or exhaust running. See how Indian cooking affects indoor air.
Agarbatti, dhoop, camphor and mosquito coils.
Dust stirred up by sweeping, dusting and fans.
Firecracker smoke drifting in around Diwali, covered in our Diwali smoke and indoor air guide.

And there is one thing a sealed room gets worse at: carbon dioxide from breathing builds up when windows stay shut. That is not a particle problem and a purifier does not fix it; a short airing when the outdoor air is at its cleanest does.

A Realistic Indoor Target

The WHO 24-hour figure of 15 µg/m³ is hard to hold through a north Indian winter, but it is the right direction. A practical ladder:

Minimum: keep indoor PM2.5 below the 24-hour NAAQS of 60 µg/m³ in every room people use. On the Indian AQI that means staying at or under 100.
Better: keep the bedroom in the Good band (AQI 50 or below) through the night, because that is where most hours of breathing happen.
Best you can practically do: get the bedroom as close to the WHO 24-hour guideline of 15 µg/m³ as your room and purifier allow, especially for children, older relatives and anyone with a lung or heart condition.

Getting there is mostly a matter of sizing. A purifier needs enough Clean Air Delivery Rate (CADR) for the room’s volume, and the door needs to stay shut while it works. The air purifier size calculator gives you the CADR your room needs.

Boon Airvana shows a live AQI on its display and reads PM1.0, PM2.5 and PM10 every second, so you can see whether your bedroom is actually under 50, not just guess.

See Boon Airvana →

How to Know Your Room’s Number

You cannot see or smell PM2.5 reliably, so a number is the only way to know. Two sources together give you the full picture:

Outdoor: the AQI for your city tells you what is pressing on your windows today and whether a short airing makes sense.
Indoor: a laser particle monitor or a purifier with a built-in PM sensor tells you what is in the room. Our guide on how to check air quality at home compares monitors, apps and what each can and cannot measure.

Check the reading at three moments: after cooking, late in the evening when outdoor pollution tends to settle low over cities, and first thing in the morning in the bedroom. If the morning bedroom reading is under 50, your setup is working.

If someone at home has persistent cough, wheezing or breathlessness during smog season, a low indoor AQI helps but it is not a treatment. See a doctor, and tell them about the air at home.

Frequently Asked Questions

What AQI level is safe inside a home?

An indoor AQI of 50 or below, the CPCB Good band, is the target. Between 51 and 100 is acceptable for most healthy people for short periods. Above 100, close windows during the worst hours, cut indoor smoke sources and run a correctly sized air purifier, especially in the bedroom. Children, older people and anyone with asthma or heart disease benefit most from keeping rooms under 50.

AQI kitna hona chahiye ghar ke andar?

Inside the home, AQI should ideally be 50 or less. Up to 100 is acceptable for a short time for healthy adults. If it is above 100 indoors, keep doors and windows shut during peak pollution, avoid incense and smoky cooking without the exhaust on, and run an air purifier sized for the room.

Is AQI the same as PM2.5?

No. PM2.5 is a concentration measured in micrograms per cubic metre. AQI is an index from 0 to 500 calculated from that concentration and other pollutants. On India’s AQI, an index of 100 lines up with the 24-hour PM2.5 standard of 60 µg/m³. Different apps may use different AQI formulas, so compare raw PM2.5 when you can.

Can indoor AQI be worse than outdoor AQI?

Yes, for short spells. Frying or tadka without an exhaust, agarbatti or dhoop, mosquito coils and sweeping can push indoor particle levels above the outdoor reading. In smog season, fine particles also seep in through gaps, so a closed home without filtration usually follows the outdoor level rather than staying clean.

What should I do if my room AQI is above 300?

Shut the door and windows of the room you are using, run an air purifier sized for that room on a high setting or Auto, and avoid any indoor smoke. Keep vulnerable family members in the cleanest room. If anyone has breathlessness, chest tightness or wheezing that does not settle, contact a doctor rather than relying on the purifier.

What PM2.5 level should I aim for indoors?

At minimum, keep indoor PM2.5 below 60 µg/m³, the Indian 24-hour standard. A better goal for the bedroom is the Good AQI band. The health-based target is the WHO 24-hour guideline of 15 µg/m³; it is hard to hold all winter, but getting the bedroom close to it is a reasonable aim with a correctly sized purifier and a closed door.

Want to see your bedroom’s AQI every second instead of guessing? Boon Airvana reads PM1.0, PM2.5 and PM10 and shows a live AQI on its display.

See Boon Airvana →

October 16, 2026

Do Indoor Plants Purify Air? What the Research Actually Shows

Not in any way you would notice. Indoor plants do absorb small amounts of some gases, but in a normal home the effect is tiny compared with opening a window, and plants do nothing meaningful for PM2.5, the fine particles behind India’s winter smog. Keep plants for how they make a room feel; use ventilation and a HEPA filter for the air.

The Short Answer

Lists of “air purifying plants” are among the most shared home tips in India, usually with the snake plant, money plant, areca palm and peace lily at the top. The claim is not completely invented: plants and the microbes in their soil can take up some volatile chemicals. The problem is scale. A few pots in a living room process a very small volume of air compared with the air that leaks in and out of the room every hour, let alone the air a purifier moves.

Bottom line: plants are good for wellbeing, not for air cleaning. For smog season, the useful tools are ventilation when outdoor air is cleaner, and HEPA filtration when it is not.

Where the Idea Came From: the NASA Study

Almost every “plants clean the air” article traces back to a 1989 NASA study, often called the Clean Air Study. It looked at how houseplants might help clean air in sealed spaces, with a future space station in mind.

The key detail is how it was done. Plants were placed in small, sealed test chambers, a known amount of a chemical was injected, and researchers measured how the level fell over time. In a small sealed box with no fresh air coming in, even a slow removal process shows up clearly.

A home is the opposite of a sealed chamber. Air constantly leaks in and out through doors, windows, gaps and exhausts, and new pollution keeps arriving. The chamber result was real, but it does not transfer to a living room.

What Later Research Found

Researchers have since gone back over the chamber studies and asked the obvious question: how many plants would a real home need to match what ordinary ventilation already does?

A widely cited review by Cummings and Waring, published in 2019, converted the chamber results into a form that can be compared with real buildings. Their conclusion was that you would need an impractically large number of plants per square metre of floor, far more than anyone could fit in a home, to equal the air cleaning that normal air exchange through a building already provides.

In other words, the gas removal plants offer is swamped by the air that moves through a room anyway. Adding a few more pots does not change that.

Why Plants Do Nothing for PM2.5

Even the NASA study was about gases (volatile organic compounds), not particles. That matters in India, because the pollution that sends the AQI into Poor, Very Poor and Severe from October to January is mostly PM2.5: fine particles from vehicles, stubble burning, waste burning and firecrackers.

To remove particles, air has to be pushed through a filter. A plant has no fan and no filter. A few particles land on leaves, but the room’s air is not being drawn past them in any meaningful volume.
Dusty leaves do not mean the plant is “cleaning” the air; settled dust would have settled on the floor or shelf anyway.
No plant reduces carbon monoxide or adds a meaningful amount of oxygen to a room. Neither does an air purifier, for that matter: see what air purifiers cannot remove.

There is also a downside worth knowing. Overwatered pots and constantly damp soil can grow mould, and mould releases spores into the air. For anyone with allergies or asthma, a crowd of wet pots in a bedroom can make the air worse, not better. Let the top of the soil dry between waterings, use pots with drainage, and keep heavily watered plants out of the bedroom of anyone sensitive.

A filter only works if it moves enough air for your room. Find the CADR your room needs before you buy any purifier.

Size Your Room →

Plants vs Ventilation vs a HEPA Purifier

	Indoor plants	Opening windows	HEPA air purifier
PM2.5 and PM10	No meaningful effect	Lowers indoor PM only when outdoor air is cleaner; raises it on smog days	Captures both; how fast depends on CADR vs room size
Gases and odours (VOCs)	Very small effect in a real home	Effective, by diluting with outdoor air	Some, if it has activated carbon; not every gas
Carbon dioxide from breathing	No meaningful effect	Effective	No effect
Works in Severe AQI?	No	No, it brings the smog in	Yes, in a closed room sized correctly
Downsides	Mould risk from wet soil	Lets in dust, noise and smog	Running cost and filter replacement

To the question “do plants clean air better than a budget HEPA purifier?”, the answer is no. Even a modest HEPA purifier sized for the room removes far more particles than any number of plants you could fit in it. Our guide on whether air purifiers actually work covers what a purifier can and cannot be expected to do.

The best combination for most Indian homes: air the house briefly when the AQI for your city is at its lowest point in the day, run a HEPA purifier in the rooms you use when it is high, and control indoor sources such as frying without an exhaust and burning incense in closed rooms.

Keep Your Plants, for the Right Reasons

None of this means you should give your plants away. Greenery at home is widely associated with feeling calmer and more pleasant surroundings, and looking after plants is a good habit. Just do not count them as air-cleaning equipment, especially not for a child, an older parent, or anyone with asthma during smog season.

A few habits keep plants and clean air working together:

Pick hardy, low-water plants that suit your light, so the soil is not wet all the time.
Wipe dusty leaves with a damp cloth rather than dusting them dry, which only puts the dust back into the air.
Keep pots on the balcony or in the living room rather than crowding a bedroom, and check the soil surface and saucers for mould or a musty smell.
Do not let a plant shelf block the intake or outlet of your air purifier; it needs clear space around it to move air.

If the reason you were buying plants was a family member’s cough or wheezing in winter, the plants will not fix it. Get the room’s PM2.5 measured, filter the air properly, and see a doctor if symptoms continue.

Frequently Asked Questions

Do indoor plants really purify the air?

Only very slightly. Plants and their soil microbes can take up small amounts of some gases, but in a normal home that effect is tiny compared with ordinary air exchange through doors and windows. Plants do nothing meaningful for PM2.5, the fine particles behind winter smog in Indian cities. Keep them for wellbeing, not as air cleaners.

What did the NASA plant study actually prove?

The 1989 NASA study found that plants could reduce some volatile chemicals inside small, sealed test chambers. A home is not sealed: air keeps leaking in and out and new pollution keeps arriving. Later analysis, including Cummings and Waring in 2019, concluded you would need an impractically large number of plants per square metre to match normal ventilation.

Do snake plants or money plants remove PM2.5?

No. Removing particles needs air to be pushed through a filter, and plants have neither a fan nor a filter. Some dust settles on leaves, but it would have settled somewhere else anyway. For PM2.5 during smog season, a HEPA air purifier sized for the room is the tool that works.

Are indoor plants better than a budget HEPA air purifier?

No. A HEPA purifier with a CADR suited to the room removes far more particles than any number of plants you could fit in it, and plants do almost nothing for PM2.5. Plants also cannot react when pollution spikes. The budget purifier needs to be sized correctly and have its filter replaced on time to do its job.

Can indoor plants make air quality worse?

They can. Overwatered pots and soil that stays damp can grow mould, which releases spores into the air. That can bother people with allergies or asthma. Use pots with drainage, let the top of the soil dry between waterings, and keep heavily watered plants out of the bedroom of anyone who is sensitive.

Which plants are best for indoor air quality in India?

No plant meaningfully improves indoor air quality in a real home, so choose plants for how easy they are to care for in your light and climate, not for air-cleaning claims. Hardy, low-water plants reduce the mould risk from damp soil. For cleaner air, rely on ventilation when outdoor AQI is low and a HEPA purifier when it is high.

For particles that plants cannot touch, Boon Airvana pushes air through an H13 HEPA filter and shows you the PM2.5 level in the room as it falls.

See Boon Airvana →

October 16, 2026