Delhi Air Pollution Season Begins: AQI Health Guide, Masks and Asthma Tips
Delhi's air usually worsens sharply as October progresses. Here is what AQI actually means, who faces greater health risk, when an N95 may help, how to reduce indoor exposure, and when respiratory symptoms need medical attention
Editorial illustration representing Delhi air pollution season, AQI monitoring and respiratory health precautions
Table of Contents (18 sections)
Delhi does not need to be under a blanket of severe smog for residents to start thinking about air pollution.
October is historically the month when the capital's air quality begins a marked seasonal deterioration. Government data for the five years from 2021 through 2025 show Delhi's average Air Quality Index, or AQI, was about 100 in September but roughly 212 in October.
That does not mean every October day is polluted, or that the AQI immediately becomes dangerous at the start of the month. Air quality can improve sharply after rain or stronger winds and deteriorate again when weather and emissions combine unfavourably.
It does mean that October is a useful time for families — particularly those with asthma, other respiratory illness, cardiovascular disease, young children or older relatives — to start checking the AQI before deciding how much time to spend outdoors.
Delhi and NCR have also entered the 2026 winter-control period with new regulatory measures. A Commission for Air Quality Management direction requires a valid Pollution Under Control Certificate, or PUCC, for vehicles to obtain fuel across NCR from October 1.
Delhi has separately notified seasonal pollution controls that become relevant as winter progresses, while CAQM's revised Graded Response Action Plan, or GRAP, can activate stronger measures when air quality reaches specified levels.
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For an individual resident, however, the immediate question is simpler:
What should you actually do when the AQI rises?
Key Takeaways
Historical October AQI average ~212 (vs ~100 in September).
Properly fitted N95 may help on high-pollution days; cloth masks do not.
Reduce indoor smoke sources; seek medical care for worsening symptoms.
First, Understand What Delhi's AQI Number Means
India's National Air Quality Index converts concentrations of major pollutants into a single number and category.
CPCB divides the index into six broad categories:
Good: 0–50
Satisfactory: 51–100
Moderate: 101–200
Poor: 201–300
Very Poor: 301–400
Severe: 401–500
The number is useful because a pollution concentration measured in micrograms per cubic metre is difficult for most people to interpret during everyday decisions.
AQI is not, however, a personal medical diagnosis.
Two people exposed to the same outdoor air can react differently depending on their health, age, level of physical activity, duration of exposure and other factors.
CPCB says people with lung or heart disease, children and older adults may experience breathing discomfort even in the moderate range. At poor levels, prolonged exposure can cause breathing discomfort more broadly, while very poor and severe conditions carry progressively greater health concern.
That is why someone with asthma may reasonably change plans before a healthy adult who has no respiratory symptoms.
Why October Is Such an Important Turning Point
Delhi's October deterioration is visible in official historical figures.
The monthly average AQI values for September from 2021 to 2025 were:
2021: 78
2022: 104
2023: 108
2024: 105
2025: 105
That gives a five-year September average of exactly 100.
For October, the corresponding readings were:
2021: 173
2022: 210
2023: 219
2024: 234
2025: 223
The five-year October average works out to about 212.
In other words, the historical monthly average more than doubled between September and October across that period.
But it is important not to reduce Delhi's pollution problem to one source.
CAQM's 2026 expert review of Delhi-NCR source-apportionment studies identified a mixture of contributors to winter PM2.5. These include secondary particles formed from gaseous emissions, transport, biomass burning, dust and industrial sources.
Weather then determines how efficiently those pollutants disperse.
As the post-monsoon period advances, weaker ventilation, lower temperatures and other unfavourable meteorological conditions can allow pollutants to remain closer to the ground for longer.
Regional pollution movement also matters because Delhi is part of a much larger airshed.
This is why statements such as "stubble burning causes Delhi pollution" or "traffic alone causes Delhi pollution" are incomplete. Different sources contribute at different times, and their relative importance varies with weather and location.
PM2.5 Matters More Than the Haze You Can See
A grey sky can be an obvious warning sign, but visibility is not a reliable measurement of health risk.
One of the pollutants of greatest concern is PM2.5 — particulate matter measuring 2.5 micrometres or less in aerodynamic diameter.
These particles are small enough to penetrate deeply into the respiratory system.
WHO's current health guidance links air-pollution exposure with respiratory and cardiovascular harm, among other health effects. Its 2026 technical brief identifies children, pregnant women, older adults and people living with chronic disease among groups facing greater risk.
That does not mean every day of moderately polluted air will make someone ill.
Health risk depends on concentration, exposure time and individual susceptibility.
The useful principle is therefore exposure reduction, not panic.
Who Should Be Especially Careful?
Some residents should pay closer attention to rising AQI because they may be more vulnerable to pollution-related symptoms or worsening of an existing condition.
These include:
Children, particularly younger children
Older adults
Pregnant women
People with asthma
People with chronic obstructive pulmonary disease or other chronic lung conditions
People with cardiovascular disease
People whose work keeps them outdoors for long periods
People undertaking strenuous outdoor exercise
A person with an existing heart or lung condition should follow the treatment plan already prescribed by their doctor rather than changing medication because the AQI has increased.
Air-pollution advice should complement medical care, not replace it.
What People With Asthma Should Do
Air pollution can act as a trigger for asthma symptoms in susceptible people.
WHO describes common asthma symptoms as cough, wheezing, shortness of breath and chest tightness.
For someone with diagnosed asthma, the practical priority during higher-pollution periods is preparation.
Check the local AQI before prolonged outdoor activity.
Keep prescribed medication available as instructed by your doctor.
Do not stop preventive or controller medication because symptoms happen to be mild on a particular day.
If the AQI is poor or worse, consider reducing strenuous outdoor activity, particularly close to heavy traffic or other obvious pollution sources.
If pollution repeatedly appears to worsen your symptoms, discuss your personal asthma action plan with your treating doctor.
Parents of children with asthma should make sure the child's school, caregiver or other responsible adult knows what medication has been prescribed and what the child's usual warning signs are.
The same principle applies to adults with chronic lung or cardiovascular disease: follow the existing medical plan and seek professional advice if symptoms change.
N95 vs Cloth Mask: What Actually Helps With Pollution?
This is one of the most common questions during Delhi's pollution season.
A cloth face covering and a certified particulate respirator are not equivalent.
Cloth masks are primarily designed as face coverings and should not be relied upon as protection from fine particulate air pollution.
A properly certified, close-fitting particulate respirator such as an N95 is designed to filter a high proportion of airborne particles when it fits correctly and is worn properly.
N95 is the US certification terminology. Comparable certified respirators include FFP2 under European standards and certain properly certified KN95 products under Chinese standards.
But several qualifications matter.
First, fit is critical. Air leaking around the sides reduces protection.
Second, a respirator should cover both the nose and mouth.
Third, an N95 is primarily a particulate filter. It is not a complete barrier against every gaseous pollutant in polluted urban air.
Fourth, buying something labelled "N95" is not enough. WHO advises consumers to look for recognised certification because the terminology can be used on products that may not have undergone appropriate testing.
Fifth, respirators are not a substitute for avoiding unnecessary exposure.
India's NCDC 2025 air-pollution advisory says people may consider a close-fitting N95 or N99 on poor-to-severe-plus days, defined in that advisory as AQI above 200.
WHO is more cautious about recommending respirators as a population-wide health measure because evidence for real-world health outcomes among the general public remains limited.
Those positions are not necessarily contradictory.
A certified, correctly fitted respirator can reduce inhaled particulate exposure, but wearing one does not make heavily polluted air harmless.
Someone who experiences difficulty breathing while wearing a respirator, particularly a person with an underlying respiratory or cardiovascular condition, should seek individual medical advice rather than forcing prolonged use.
Should Children Wear N95 Masks?
Parents should be especially cautious about assuming an adult respirator will work properly for a child.
The effectiveness of a respirator depends heavily on fit, and adult-sized masks may leave significant gaps on a child's face.
Children also vary greatly in face size, tolerance and ability to use a respirator correctly.
For a child with asthma or another medical condition, individual advice from the child's doctor is preferable to relying on a generic mask recommendation.
Reducing unnecessary outdoor exposure on very polluted days may be more practical than depending entirely on a face covering.
Outdoor Exercise: When Should You Change Your Routine?
Exercise increases the amount of air a person breathes, meaning strenuous outdoor activity can increase the amount of pollution inhaled during the same period.
That does not mean Delhi residents should stop exercising for the entire winter.
Instead, adjust activity to conditions.
Check the AQI before running, cycling or playing outdoor sport.
On days when pollution is high, consider moving strenuous exercise indoors or reducing intensity and duration.
Avoid busy traffic corridors where pollution exposure may be higher.
NCDC advises avoiding outdoor morning and late-evening exercise on poor-to-severe-plus days.
Timing matters because pollution can vary substantially during the same day.
How to Reduce Pollution Exposure Indoors
Going indoors does not automatically mean the air is clean.
Outdoor particles can enter buildings, while indoor sources can add further pollution.
Simple measures can help reduce exposure.
When outdoor pollution is high, limit unnecessary opening of doors and windows during the worst periods. When outdoor air improves, ventilation can be useful.
Avoid cigarette and bidi smoke indoors.
Avoid unnecessary burning of incense, mosquito coils, candles or other materials that produce smoke in closed rooms.
Use kitchen exhaust and ventilation appropriately when cooking.
Wet cleaning can reduce the amount of dust that becomes airborne compared with dry sweeping.
If driving through heavy pollution, keeping windows closed and using the vehicle's recirculation setting can reduce direct intake of outside air for short periods.
Does an Air Purifier Help?
Air purifiers require more nuance than advertisements sometimes suggest.
A correctly sized unit with an effective particulate filter can reduce airborne particles in the room in which it is operating.
But performance depends on the filter, room size, airflow, maintenance, building leakage and how frequently doors and windows are opened.
WHO has said the evidence does not support treating portable air cleaners as a blanket population-wide public-health solution.
Its guidance notes that they may nevertheless be considered for some people with pre-existing conditions who need to remain at home during pollution episodes.
India's NCDC advisory also says air purifiers may be beneficial on poor-to-severe-plus pollution days.
If using one, avoid devices that intentionally generate ozone or produce harmful by-products.
A purifier should also not be used as justification for smoking, burning incense or creating other avoidable indoor pollution.
What Delhi's 2026 Pollution Rules Change
The policy response is also changing this winter.
From October 1, CAQM's Direction No. 101 provides for fuel to be dispensed across NCR only when a vehicle has a valid Pollution Under Control Certificate.
That measure targets vehicular emissions and applies across the National Capital Region rather than only within Delhi.
Construction rules need slightly more explanation.
CAQM's revised 2026 GRAP framework includes dust-mitigation requirements for construction and demolition sites at Stage I, while stronger restrictions or bans on specified C&D activities can apply at Stage III.
Delhi has also notified scheduled winter pollution-control measures beginning in November, including restrictions affecting certain dust-generating construction and demolition work, subject to the notification's conditions and exemptions.
Rajatheertha has separately explained Delhi's November work-from-home, parking and seasonal pollution measures in its guide to the 50% office-attendance rule.
The important distinction is that there is not a universal "all construction banned from October 1" rule.
Some controls are standing requirements. Others are scheduled seasonal measures. Still others depend on the GRAP stage in force.
Check AQI, Not Just the Sky
One of the simplest protections is also one of the most useful: check the official AQI before planning prolonged outdoor exposure.
CPCB's Sameer system and official government air-quality platforms provide local information.
Do not assume that a bright-looking morning means pollution is low, and do not assume every hazy-looking day is severe.
Station readings can also vary across Delhi, so neighbourhood conditions may differ from the citywide figure.
AQI is best treated as a practical planning tool.
When Should You See a Doctor?
Pollution can produce irritation or respiratory symptoms, but readers should not try to diagnose a serious condition based on AQI alone.
India's NCDC advises seeking medical attention when symptoms such as breathlessness, cough, chest discomfort or pain, wheezing, or worsening symptoms occur during high-pollution periods.
For people with chronic pulmonary or cardiovascular disease, worsening of usual symptoms is particularly important.
Seek prompt medical advice if:
Breathlessness is new, worsening or unusual for you.
Wheezing or chest tightness becomes significant.
An existing asthma or respiratory condition is becoming harder to control.
You develop chest discomfort or chest pain.
Symptoms persist despite following your prescribed treatment plan.
A child, older adult or other vulnerable person appears to be having increasing breathing difficulty.
Severe breathing difficulty, severe chest pain, confusion, collapse, bluish lips or face, or another potentially life-threatening symptom requires urgent medical attention rather than waiting for the AQI to improve.
What Not to Do
There is no supplement, home remedy, juice or food that can make polluted air safe to breathe.
A healthy diet and adequate hydration are sensible parts of general health, but they should not be marketed as a detoxification treatment for PM2.5 exposure.
Do not start inhalers, steroids, antibiotics or other medication simply because the AQI is high unless a qualified medical professional has advised their use.
Do not assume that an expensive mask automatically provides better protection.
Do not buy an air purifier solely on marketing claims without checking the filtration method, appropriate room size and maintenance requirements.
And do not treat an N95 as permission to spend unnecessary hours outdoors during a severe pollution episode.
The Practical Delhi Pollution Checklist
For most residents, the useful approach is straightforward.
Check the official AQI before prolonged outdoor plans.
Reduce strenuous outdoor activity when pollution is high.
People with asthma, heart disease or chronic lung conditions should keep prescribed medicines available and follow their doctor's plan.
If a respirator is needed on a polluted day, use a genuine, well-fitting certified particulate respirator rather than a cloth face covering.
Reduce indoor smoke sources.
Use an air purifier carefully if appropriate for your household, and avoid ozone-producing devices.
Watch children, older adults and people with chronic illness more closely.
Seek medical advice when respiratory or cardiac symptoms appear or worsen.
The Bigger Picture
Personal precautions can reduce exposure, but they cannot solve Delhi's pollution problem.
That distinction matters.
WHO's approach to air pollution emphasises reducing emissions and population exposure rather than shifting responsibility entirely to individuals through masks and air cleaners.
CAQM's own expert work shows why: winter pollution comes from a mixture of transport, secondary particulate formation, biomass burning, dust, industrial sources and regional pollution movement.
Delhi's October history tells residents when to start paying closer attention.
It does not tell us that every October day will be dangerous.
The best strategy is therefore neither complacency nor panic: follow verified AQI information, reduce avoidable exposure when levels worsen, follow medical advice for existing conditions, and treat pollution-control measures as a public-health issue rather than a seasonal inconvenience.
Medical note: This article provides general public-health information and does not replace diagnosis or treatment from a qualified medical professional.
Key Takeaway
October historically marks Delhi’s sharp AQI rise. Check AQI, protect vulnerable people, use well-fitted N95 if needed, reduce indoor smoke and seek care for worsening symptoms.
The Rajatheertha Team publishes news, explainers, guides and updates across India and the world. Our coverage follows Rajatheertha's editorial, verification and corrections standards.
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