Delhi Air Quality by Month: When the Smog Starts and When to Visit

Quick answer: Delhi’s air is usually worst from late October to January, and November is the peak: a 15-year study of city monitors found average PM2.5 of 227 µg/m³ in November against 39 in August. The monsoon months are the cleanest. If you have asthma or heart disease, avoid November and December.

Last verified October 2026. Air quality, official orders and guidance change, so confirm live readings and the official links in Sources before you travel.

Delhi’s air is not bad all year. It is bad in a pattern, and the pattern is regular enough to plan around. A visitor who lands in August meets a different city from one who lands in the first week of November, and most first-time visitors only find that out at the airport.

This guide puts numbers on the difference, explains what Indian AQI readings mean (they are not the same as the US scale), covers the government’s emergency alert system called GRAP, and says what a visitor can realistically do about it. Our general India safety guide has a short air quality section, and the health preparation guide covers the rest of your medical checklist. This page goes deeper on the one problem that can actually change a Delhi trip.

What do Indian AQI numbers actually mean?

India’s official Air Quality Index comes from the Central Pollution Control Board (CPCB), the national pollution regulator. The scheme was developed with IIT Kanpur and an expert group, and the environment ministry launched it in 2014. It runs from 0 to 500 in six bands. Eight pollutants feed into it, and the worst single pollutant sets the overall number, so one bad reading is enough to push the whole index up.

Category	AQI range	Official health statement
Good	0 to 50	Minimal impact
Satisfactory	51 to 100	May cause minor breathing discomfort to sensitive people
Moderately polluted	101 to 200	May cause breathing discomfort to people with lung disease such as asthma, and discomfort to people with heart disease, children and older adults
Poor	201 to 300	May cause breathing discomfort on prolonged exposure, and discomfort to people with heart disease
Very poor	301 to 400	May cause respiratory illness on prolonged exposure, more pronounced in people with lung and heart disease
Severe	401 to 500	May cause respiratory impact even in healthy people, and serious impact in people with lung or heart disease, even during light physical activity

Do not compare these bands with the US scale. The air quality table printed in the CDC Yellow Book calls 151 to 200 Unhealthy and starts Hazardous at 300. India’s bands are labelled differently and the breakpoints differ, so a number from an Indian source and a number from a US app can describe different levels of pollution. Whichever app you use, note which scale it follows and read the label as well as the digits.

Delhi air quality month by month

No agency publishes a tidy official chart of safe and unsafe months. The table below combines a long-term study of Delhi monitors with the dates this year when the air quality commission triggered its emergency measures. Read it as a pattern, not a forecast.

When	What the evidence shows	What it means for a visitor
June to September	The monsoon-season average was 66 µg/m³ of PM2.5 in a study covering 2007 to 2021, and August had the lowest monthly average of the year, 39 µg/m³	The cleanest stretch. Heat, humidity and rain bring their own problems, covered in the monsoon travel guide
October	Air quality starts to deteriorate and PM2.5 climbs through the month as rain stops and winds slow	Early October is the safer end. Start checking live readings from mid-month
Late October to mid-November	Crop burning in neighbouring states is blamed for 15 to 20 days of worsening air in this window, and 24-hour PM2.5 reached about 500 µg/m³ in some recent years	The highest-risk window, and Diwali often falls inside it
November	The highest monthly average in the 15-year study, 227 µg/m³	Avoid if you have a lung or heart condition
December and January	The winter average was 174 µg/m³, and these were the only two months without a falling trend in the study. The commission invoked its Stage III measures on 16 January 2026 and Stage IV on 17 January	Expect more bad days than good, and check every morning
February and March	I could not verify month-level figures. The commission revoked Stage II on 18 February 2026 and Stage I on 16 March 2026	Usually easing, but confirm with live data
April and May	Stage I (Poor, AQI 201 to 300) was invoked on 16 April and again on 19 May 2026, and the summer average was 101 µg/m³	Poor days still happen in the hot season, so leaving winter does not guarantee clean air

You can translate those averages into CPCB language using the PM2.5 breakpoints from the official table. This is a rough conversion, not a daily AQI, because averages hide the very bad days. It still shows the shape of the year.

Period	Average PM2.5 (2007 to 2021)	Roughly falls in this CPCB PM2.5 band
August	39 µg/m³	Satisfactory (31 to 60)
Monsoon season	66 µg/m³	Moderately polluted (61 to 90)
Summer	101 µg/m³	Poor (91 to 120)
Winter	174 µg/m³	Very poor (121 to 250)
Post-monsoon	192 µg/m³	Very poor (121 to 250)
November	227 µg/m³	Very poor (121 to 250)

One caution on dates. The study ends in 2021 and found a small downward trend of about 1.35 µg/m³ a year across the whole period, so recent years may sit a little lower. The seasonal shape has not changed. If you are weighing a few alternative months for the whole of India, the best time to visit India tool shows how Delhi’s season fits against the rest of the country.

Why does Delhi’s air get so bad in late autumn?

Several things stack up at once. In October and November the wind shifts from south-easterly to north-westerly, rain stops, winds slow down and the layer of air near the ground gets shallower, so pollution has nowhere to go. The rice harvest also falls in this window, and farmers in Punjab and Haryana burn leftover crop stubble to clear fields quickly. Researchers at the Centre for Research on Energy and Clean Air also list vehicles, industry, power stations and firecrackers around Diwali as contributors.

How much of Delhi’s smog comes from stubble fires is argued over. Modelling studies have put the share of PM2.5 in the Delhi region that comes from non-local fires at 20 to 40 percent in October and November, while a 2025 measurement study in a Nature Portfolio journal concluded that the link between crop burning and Delhi readings is not clearly established. For a visitor the argument matters less than the outcome: the same weeks are bad most years, and rain is the thing that clears them. In that study a rain event on 10 November 2023 pulled readings down to 50 to 60 µg/m³ almost at once, and they climbed again within days.

Does Diwali make it worse?

Firecrackers are named as a source around Diwali, and the same measurement study recorded PM2.5 rising sharply on Diwali night in 2023, only two days after rain had cleaned the air. In 2026 published calendars list Diwali on 8 November, which lands inside the worst window. Check the date on our India festival calendar before you book. For closures, regional customs and where to base yourself that week, see our Diwali travel guide for tourists.

The trade-off is real. Diwali week gives you lights, markets and a lively atmosphere, but it also brings crowded trains, higher hotel prices and the worst odds for air quality in the year. If you have a respiratory condition, skip Delhi that week. If you are healthy and want the festival, plan your outdoor time around the live readings and keep a spare day in the schedule. I did not verify the current firecracker restrictions, which change by authority and by year, so do not assume a ban is in force or being followed.

What is GRAP, and will it change your plans?

GRAP, the Graded Response Action Plan, is the emergency playbook run by the Commission for Air Quality Management (CAQM) for Delhi and the surrounding National Capital Region. Its stages are tied to Delhi’s AQI: Stage I is Poor (201 to 300), Stage II is Very poor (301 to 400), Stage III is Severe (401 to 450) and Stage IV is Severe plus (above 450).

The commission revised the schedule on 21 November 2025. The government’s press summary of that revision lists measures such as uninterrupted power supply so that diesel generators are used less, traffic management at congestion points, public alerts, and extra metro and electric or CNG bus services at Stage I. Stage II adds staggered office timings, and Stage III lets authorities move offices to half strength with the rest working from home. That summary says nothing about tourist sites, and it does not set out the Stage IV measures, so read the full schedule on the commission’s website if it matters to you.

For a traveller, GRAP works best as a warning light. When the commission invokes Stage III or IV, readings are already in the Severe band and you should treat that day as an indoor or low-exertion day. The commission posts each order, with its date, on its home page.

How do you check Delhi’s air quality before and during a trip?

Before booking, use the monthly pattern above and the Delhi destination guide to decide whether your dates fall in the risky window.
From about a week out, start looking at live readings. The CDC Yellow Book points travellers to AirNow, to the World Air Quality Index project (real-time data from more than 10,000 stations in over 80 countries) and to WHO historical data. CPCB publishes the official Indian readings.
Read the category and the scale, not just the number. See the table earlier on this page.
Check for the time you will actually be outside. In the Delhi-NCR measurements from autumn 2022 and 2023, day and night PM2.5 differed by roughly 20 percent or less, so an early start will not reliably get you ahead of the haze.
Look at the commission’s website for current GRAP orders.
Repeat the check for each city on your route. I have not verified city-by-city comparisons, so do not assume the next stop is cleaner or dirtier.

What can you do about it: masks, medication and your hotel room?

The CDC’s advice is blunt. Dust masks, surgical masks and bandanas offer limited protection against severely polluted air, and the best strategy is to avoid prolonged time outdoors. A NIOSH-approved particulate respirator, such as an N95 or P100, can filter very small particles because it is designed to seal against the face. The CDC also notes that NIOSH does not currently approve respirators for children. Travellers with asthma, COPD or heart disease are advised to limit strenuous or prolonged outdoor activity when the AQI is poor.

Indoor air counts too. The same CDC chapter lists smoke from cooking fires, tobacco, incense and candles as indoor pollutants that can aggravate asthma, which is worth remembering in temples and small restaurants. If you have a lung or heart condition, talk to your doctor or a travel clinic well before departure, carry enough regular medication and any rescue inhaler for the whole trip plus delays, and ask what to do on a bad day. This is general information, not medical advice.

How should you plan if your dates fall in smog season?

If your dates are flexible and you have a respiratory or heart condition, move them. The monsoon months have the cleanest air in the data, though they bring heavy rain, so weigh that against the monsoon guide. If your dates are fixed, shorten the Delhi portion, keep a spare day so you can shift outdoor sightseeing, and book hotels with good indoor space rather than a packed outdoor itinerary.

Delhi is also where most international flights land, so it is hard to avoid completely. Our Delhi airport arrival guide covers the first hours, and the Golden Triangle itinerary shows how to keep Delhi days to a minimum while still seeing Agra and Jaipur. The India itinerary planner helps you build the rest of the route around your dates. Finally, check your policy wording. Some policies cover cancellation for named causes only, so air quality is not automatically a covered reason to cancel, a point our India travel insurance guide raises. This is general guidance, so read your own policy.

Common mistakes, and who should skip Delhi in winter

Judging by one reading. Air quality changes hour by hour and day by day, so check the live number for the day you will be outside.
Trusting a surgical mask. The CDC says surgical masks and bandanas give limited protection in severely polluted air.
Comparing scales. A US app and an Indian source may use different bands, so look at the label.
Assuming mornings are clean. Delhi-NCR measurements showed small day and night differences in autumn.
Leaving the check until you land. By then your flights and hotels are already paid for.

Skip Delhi from late October to January if you have asthma, COPD or heart disease, if you are travelling with a baby or small child, or if your plans depend on long outdoor days. For everyone else, a few bad days are survivable with a plan.

Frequently asked questions

Which month is the worst for air quality in Delhi?

November. A study of Delhi monitors covering 2007 to 2021 found it had the highest monthly average PM2.5, 227 µg/m³. The wider risky window runs from late October to January.

Which month has the cleanest air in Delhi?

August had the lowest monthly average PM2.5 in the same study, 39 µg/m³, and the monsoon season as a whole was the cleanest part of the year.

Is it safe to visit Delhi in November?

Many healthy adults visit without trouble, but the official CPCB scale says Severe readings can affect even healthy people. People with lung or heart conditions should speak to a doctor first, and the CDC advises limiting strenuous outdoor activity when the AQI is poor. This is not medical advice.

Do I need an N95 mask in Delhi?

The CDC suggests a NIOSH-approved particulate respirator, such as an N95 or P100, for travellers exposed to poor outdoor air, and says surgical masks and bandanas offer limited protection. It adds that NIOSH does not currently approve respirators for children.

What does a Delhi AQI of 400 mean?

On the CPCB scale 400 is the top of the Very poor band (301 to 400), which may cause respiratory illness on prolonged exposure. Above 400 the Severe band begins, where even healthy people may be affected and GRAP Stage III applies.

What is GRAP and does it close tourist sites?

GRAP is the Graded Response Action Plan, an emergency schedule run by the Commission for Air Quality Management with four stages tied to Delhi’s AQI. The government summary of the November 2025 schedule lists measures aimed at traffic, power and office hours, and does not mention tourist sites. Check the commission’s site and the attraction’s own page for current orders.