AQI 300 is good or bad? What Delhi's AQI levels 300, 400 and 500 mean, and what to do

Every winter the app says 300, then 412. AQI 300 is good or bad? What does AQI 400 mean for the school run, or Dadi's morning walk?

This guide explains, in plain language, what each AQI level means on India's official scale, what to do at each one, and what you can do inside your home.

What is AQI? The meaning of AQI in one paragraph

AQI stands for Air Quality Index. India's National AQI, run by the Central Pollution Control Board (CPCB), takes measurements of eight pollutants (PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃ and lead) and turns them into one number and one colour. The pollutant in the worst state decides the overall AQI (PIB). In a Delhi winter, that pollutant is very often PM2.5 or PM10. If terms like PM2.5 or sub-index are new to you, our page on AQI and PM2.5 terms explains them.

The six CPCB AQI bands

AQI	Category	Possible health impact (CPCB)	PM2.5, 24-hour average (µg/m³)
0–50	Good	Minimal impact	0–30
51–100	Satisfactory	Minor breathing discomfort to sensitive people	31–60
101–200	Moderate	Breathing discomfort to people with lung disease such as asthma, heart disease, children and older adults	61–90
201–300	Poor	Breathing discomfort to most people on prolonged exposure	91–120
301–400	Very Poor	Respiratory illness on prolonged exposure	121–250
401–500	Severe	Affects healthy people and seriously impacts those with existing diseases	250+

Sources: CPCB AQI portal and the PIB release on the launch of the National AQI (2014).

India's six CPCB AQI bands at a glance, with one simple action for each.

AQI level kitna hona chahiye? (How low should AQI be?)

On India's scale, the honest answer is 50 or below ("Good"), and up to 100 ("Satisfactory") is acceptable for most healthy people. Anything above 100 starts to matter for people with asthma, heart disease, children and older adults, according to CPCB's own description of the bands above.

AQI 300 is good or bad?

AQI 300 is bad. It sits at the top of the "Poor" band (201–300), one point below "Very Poor". CPCB says air in this band causes breathing discomfort to most people on prolonged exposure, not just sensitive groups. If PM2.5 is the main pollutant, an AQI near 300 means the 24-hour PM2.5 average is around 120 µg/m³ (PIB, 2014).

AQI 300 is common in a Delhi winter, but common isn't safe. It also triggers official action: at a Delhi AQI of 201 and above, the Commission for Air Quality Management (CAQM) invokes Stage I of GRAP (see below).

AQI 300: what to do

The Ministry of Health and Family Welfare's National Programme on Climate Change and Human Health (NPCCHH) gives clear advice for days when AQI is above 200 (NCDC/MoHFW Health Advisory, 2022):

• Avoid outdoor walks in the morning and late evening.
• Avoid jogging, running or other strenuous exercise outdoors.
• Keep external doors and windows closed in the morning and late evening.
• Pregnant women, young children and older people should restrict outdoor movement as far as possible.
• See a doctor if anyone has breathlessness, cough, chest discomfort, giddiness or red, watery eyes.

AQI 400 meaning: health effects at "Very Poor" and "Severe"

An AQI of 301–400 is "Very Poor". CPCB links it to respiratory illness on prolonged exposure. Cross 400 and you are in "Severe", which CPCB says affects healthy people and seriously impacts those with existing diseases (CPCB). Driven by PM2.5, an AQI above 400 means a 24-hour average above 250 µg/m³ (PIB, 2014).

Why fine particles matter: WHO estimates that outdoor air pollution caused 4.2 million premature deaths worldwide in 2019, mainly from fine particulate matter that leads to heart and lung disease and cancers (WHO).

At 400 and above, follow all the AQI 300 steps more strictly. MoHFW's advisory also asks people with chronic heart or lung problems to avoid any strenuous activity, keep their medicines at hand, and seek medical advice quickly if symptoms get worse (NCDC/MoHFW). If you choose to wear a mask, the same advisory says a disposable N95 or N99 is useful when it fits well over the nose and mouth and exposure is short.

And AQI 500?

500 is the top of India's AQI scale. Readings at the cap mean the air is at least as bad as the "Severe" band describes, and possibly worse. Treat it as a stay-indoors day for everyone who can.

When to open windows: the MoHFW 12–4 pm advice

People often ask whether they should never open a window in winter. MoHFW's advice is more practical. On days with poor to severe AQI, it says not to open external doors and windows in the morning and late evening, and to ventilate if necessary between 12 pm and 4 pm (NCDC/MoHFW Health Advisory, 2022; repeated in the NPCCHH chest clinic guidance note, November 2025).

Calm nights and early mornings trap pollution near the ground, while afternoon air is usually better mixed, so a short afternoon airing is a sensible middle path.

GRAP stage in Delhi: what Stages 1 to 4 mean

The Graded Response Action Plan (GRAP) is the emergency plan CAQM uses across the National Capital Region. Under the revision of 21 November 2025, it has four stages based on Delhi's AQI (CAQM GRAP schedule; PIB, 22 November 2025):

GRAP stage	Delhi AQI	Examples of actions
Stage I – "Poor"	201–300	Dust control at construction sites, traffic management, uninterrupted power to discourage diesel generator sets, more public transport, public alerts
Stage II – "Very Poor"	301–400	Stage I actions plus staggered timings for public offices in Delhi and nearby districts
Stage III – "Severe"	401–450	Strict restrictions on dust-generating construction and demolition work, curbs on older BS-III petrol and BS-IV diesel vehicles, hybrid classes for children up to Class V, and decisions on 50% office attendance
Stage IV – "Severe+"	Above 450	Truck entry into Delhi stopped except essential, CNG, electric and BS-VI diesel trucks; construction bans extended to linear public projects; hybrid classes for higher classes; possible further emergency measures

Two points are worth knowing. First, each stage adds to the ones before it: Stage III actions apply on top of Stages I and II. Second, CAQM can invoke a stage in advance, based on IMD and IITM forecasts, before the AQI actually reaches it (CAQM).

GRAP stages as revised by CAQM on 21 November 2025: the higher the AQI, the stricter the curbs.

Why the AQI level in Delhi climbs every winter

The short version: more smoke, and weather that traps it.

• Temperature inversion. On cold, calm nights a layer of warmer air sits above colder air near the ground and acts like a lid. A peer-reviewed study describes how this "results in the cold and polluted air trapped close to the surface" (Heliyon, 2023, via PMC).
• Stubble burning, with nuance. A 2025 study reported by The Hindu put the overall contribution at about 14% of PM2.5 in Delhi-NCR, and AQI often stays "Very Poor" to "Severe" from December to February after the burning stops (The Hindu).
• Local sources all year round. Vehicles, industry, construction dust, waste burning and household burning keep going. Winter weather just gives the pollution nowhere to go.

Indoor vs outdoor AQI: is your home actually cleaner?

Closed windows don't guarantee clean air indoors; a monitor tells you for sure.

The AQI on the news is an outdoor number, usually averaged over 24 hours and, for Delhi, across many monitoring stations.

Indoors is a different picture. The US EPA explains that indoor particle levels depend on outdoor levels, how much air leaks in, ventilation and filtration, and indoor sources such as cooking, candles and burning (US EPA, Indoor Particulate Matter). So closing the windows doesn't automatically make your home's air "Good". A tadka, a mosquito coil or an incense stick can raise PM2.5 indoors even when outdoor AQI improves. MoHFW specifically advises avoiding mosquito coils and incense sticks in closed rooms (NCDC/MoHFW).

The only way to know is to measure. A home monitor lets you measure PM2.5 indoors and see whether your steps are working. For a wider look at the sources, read our guide to indoor air pollution in India.

Is breathing Delhi air like smoking cigarettes?

You may have seen headlines saying Delhi air is "like smoking 20 cigarettes a day". Here is where that idea comes from, and its limits.

The comparison comes from a rule of thumb published by Berkeley Earth, an independent research group: one cigarette a day is roughly equal, in health impact, to breathing PM2.5 at 22 µg/m³ for a day (Berkeley Earth). By that rule, a day near the top of "Poor" (PM2.5 about 120 µg/m³) works out to around five cigarettes, and a "Severe" day above 250 µg/m³ to more than eleven.

Treat those numbers carefully. It is a rough estimate of mortality risk from outdoor PM2.5, not a medical measurement, and time spent in cleaner indoor air changes your real exposure. The takeaway: on "Very Poor" and "Severe" days, cut your exposure where you can.

How to reduce AQI at home in Delhi

You can't change the city's AQI by yourself, but you can lower the PM2.5 you breathe indoors:

1. Check the AQI before planning your day, and move walks and exercise away from early mornings on bad days.
2. Keep windows shut in the morning and late evening, and ventilate briefly between 12 pm and 4 pm if you need to, as MoHFW advises.
3. Cut indoor sources. Skip incense, candles and mosquito coils on bad days, use the kitchen exhaust while cooking, and never burn an angithi in a closed room, which MoHFW warns can cause fatal carbon monoxide build-up.
4. Wet-mop instead of sweeping. MoHFW recommends wet mopping, or a vacuum with a HEPA filter if you vacuum (NCDC/MoHFW).
5. Use a HEPA air purifier sized for the room you spend most time in, usually the bedroom. The US EPA recommends choosing one whose Clean Air Delivery Rate (CADR) suits the room size (US EPA, Guide to Air Cleaners in the Home). Our guide on how to choose an air purifier explains how. Festival nights need extra planning: here's how to keep Diwali smoke out of your home.
6. Avoid air cleaners that intentionally produce ozone, which the EPA calls a lung irritant (US EPA). Room fresheners and fragrance don't clean the air.
7. Measure. A monitor shows whether the bedroom is actually cleaner than outside.

Not sure which size fits your bedroom? Our bedroom purifier checklist for budgets under ₹5,000 covers CADR, noise and filter costs. When you're ready, you can shop air purifiers built for Indian homes.

Frequently asked questions

AQI 300 is good or bad?

Bad. AQI 300 is the top of CPCB's "Poor" band, which causes breathing discomfort to most people on prolonged exposure. Limit time outdoors and avoid outdoor exercise.

What is AQI 400 meaning?

AQI 301–400 is "Very Poor" and 401–500 is "Severe". Above 400, CPCB says the air affects healthy people too and seriously affects those with existing disease.

AQI level kitna hona chahiye?

Ideally 0–50 ("Good"). Up to 100 ("Satisfactory") is acceptable for most healthy people. Above 100, sensitive groups start to feel the effects.

What time should I open windows in Delhi winter?

On poor to severe AQI days, MoHFW advises keeping them shut in the morning and late evening and ventilating, if needed, between 12 pm and 4 pm.

Which GRAP stage is in force in Delhi now?

It changes with the AQI forecast. CAQM announces each stage on caqm.nic.in. Stage I starts at AQI 201, Stage II at 301, Stage III at 401 and Stage IV above 450.

Is indoor air cleaner than outdoor air?

Not necessarily. Outdoor PM2.5 leaks in, and cooking, incense and burning add more. Measuring indoors is the only way to know.

Sources

1. Central Pollution Control Board, National Air Quality Index portal: https://airquality.cpcb.gov.in/AQI_All_India/
2. Press Information Bureau (2014), National Air Quality Index launch release (bands and breakpoints): https://www.pib.gov.in/newsite/printrelease.aspx?lang=2&reg=3&relid=110654
3. Press Information Bureau, press note on AQI pollutants: https://www.pib.gov.in/PressNoteDetails.aspx?ModuleId=3&NoteId=159871&id=159871&lang=1&reg=20
4. NCDC / MoHFW, NPCCHH Health Advisory on Air Pollution (September 2022): https://ncdc.mohfw.gov.in/uploads/pdf/air4.pdf
5. NCDC / MoHFW, NPCCHH guidance note on chest clinics (November 2025): https://ncdc.mohfw.gov.in/uploads/pdf/Guidance%20note%20on%20CHEST%20Clinic%20NPCCHH%20November%202025.pdf
6. CAQM, GRAP schedule for NCR (revision 21.11.2025): https://caqm.nic.in/FileUploadDomain/WebsiteDocument/Home/News/GRAP%20Schedule7e3bd726-7308-484f-995f-7cb3fa705b8d.pdf
7. PIB, CAQM revises GRAP (22 November 2025): https://www.pib.gov.in/PressReleasePage.aspx?PRID=2192852&lang=2&reg=3
8. WHO, Ambient (outdoor) air pollution fact sheet: https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health
9. Berkeley Earth, "Air Pollution and Cigarette Equivalence": https://berkeleyearth.org/air-pollution-and-cigarette-equivalence/
10. US EPA, Indoor Particulate Matter: https://www.epa.gov/indoor-air-quality-iaq/indoor-particulate-matter
11. US EPA, Guide to Air Cleaners in the Home: https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home
12. "Stubble-burning activities in north-western India in 2021", Heliyon (2023), via PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC10275965/
13. The Hindu, stubble burning contributes about 14% of PM2.5 in Delhi-NCR: https://www.thehindu.com/sci-tech/energy-and-environment/stubble-burning-in-punjab-haryana-contributes-only-14-of-pm25-in-delhi-ncr-study/article69219780.ece