Air Quality & Health Guides

Air pollution is one of the largest environmental risks to health, and yet it is invisible, which makes it easy to ignore until a season of smog forces the issue. This guide is a plain, evidence-based introduction to air quality and health: what the pollutants are, why they matter, who is most at risk, and — most usefully — the practical things you can do to reduce your exposure day to day. It is also the doorway to the wider DailyAQI guide library, where each of these topics is explored in depth.

What air pollution is made of

"Air pollution" is a mixture, not a single substance, and the components behave differently. The one most closely tied to health harm is fine particulate matter, PM2.5 — particles small enough to travel deep into the lungs and pass into the bloodstream. Coarser PM10 (dust, pollen, construction and road grit) irritates the airways, while gases such as nitrogen dioxide, ozone, sulphur dioxide and carbon monoxide arise from traffic, industry and combustion. The Air Quality Index bundles these into one number so you do not have to track each pollutant yourself; if you want to know exactly what that number means, start there.

Why air quality matters for health

The World Health Organization and national bodies link both short-term and long-term exposure to air pollution with a range of effects. In the short term, high pollution can irritate the eyes, nose and throat, trigger coughing and breathlessness, and set off asthma attacks. Over years, sustained exposure is associated with reduced lung function, respiratory and cardiovascular disease, and other serious conditions. The risk rises with both the level of pollution and the length of exposure, which is why reducing the hours you spend breathing bad air — not just the peak you experience — is what counts. This is general information and not a substitute for medical advice.

Who is most at risk

Everyone breathes the same air, but not everyone is affected equally. Some groups should take precautions at lower AQI levels than the general population:

• Children, whose lungs are still developing and who breathe faster relative to their size.
• Older adults, who are more likely to have underlying heart or lung conditions.
• Pregnant people, because exposure can affect both parent and baby.
• People with asthma, COPD or other lung disease, for whom pollution is a direct trigger.
• People with heart disease, since fine particles are linked to cardiovascular events.

If you or someone you care for is in one of these groups, the guidance below matters more, and acting a category earlier than everyone else is sensible.

Using the AQI day to day

The simplest habit that protects your health is to check the live AQI before you plan outdoor time, the way you check the weather. A quick look at your city's live reading tells you whether a run is a good idea, whether a child's sports practice should move indoors, and whether it is a day for a mask. Below 100, normal activity is fine. Between 101 and 200, sensitive groups should pace themselves. Above 200, most people should limit strenuous outdoor exertion, and above 300 everyone should. Turning the number into a decision is the whole point of the index.

Practical ways to reduce your exposure

You cannot personally clean a city's air, but you can substantially cut how much of it you breathe. The most effective steps are unglamorous and cheap.

• Time it. On bad days, shift outdoor exercise to cleaner hours and lower the intensity.
• Mask well. A properly fitted N95 or FFP2 filters most fine particles; a loose cloth mask does little.
• Filter indoor air. A HEPA air purifier sized to the room meaningfully lowers indoor PM2.5.
• Ventilate wisely. Air out rooms when outdoor air is cleaner, and keep windows closed during peaks.
• Cut indoor sources. Reduce indoor smoke, use extraction while cooking, and avoid burning incense or candles on high-pollution days.

None of these requires a large budget, and together they can turn a severe-air day into a manageable one for the people in your home.

Reading your body as well as the number

The AQI is the best single guide to outdoor conditions, but your own symptoms are useful information too, especially if you are in a sensitive group. Scratchy eyes, a dry or irritated throat, coughing, a tight chest or unusual breathlessness during activity can all appear when pollution is high, and for someone with asthma they can be an early warning to get indoors and follow their treatment plan. The sensible approach is to let the number set your expectations and your body confirm them: if the AQI is high, take precautions before symptoms start; if you notice symptoms even at a moderate reading, treat yourself as more sensitive than average and act accordingly. None of this replaces medical advice — anyone with a diagnosed condition should follow the plan their doctor has given them — but paying attention to how you feel is a reasonable complement to checking the index.

The seasonal picture in India

Air quality in much of India follows a strong yearly rhythm. Winter is the hard season: cool, still air and temperature inversions trap emissions from traffic, industry, heating and cooking close to the ground, and in the north this coincides with seasonal crop-residue burning, producing the smog that blankets cities from roughly October to February. The monsoon, by contrast, washes particles out of the air and usually brings the cleanest months of the year. Knowing this rhythm helps you plan — building indoor-air defences before winter, and making the most of the cleaner season for outdoor activity.

Indoor air matters too

People spend most of their time indoors, so indoor air quality is not a footnote. Outdoor pollution seeps inside, and indoor activities — cooking, cleaning, burning fuel or candles, and simple dust — add their own load. On a high-pollution day, a closed room with a running HEPA purifier can be dramatically cleaner than the street; on a clean day, opening the windows refreshes stale indoor air. The goal is not to seal yourself in, but to match your ventilation to whichever air, indoors or out, is cleaner at the time.

Masks: what actually helps

When outdoor air is genuinely bad and you cannot avoid being out in it, a mask is the most portable protection you have — but only the right one. A well-fitted N95 or FFP2 respirator is designed to filter the majority of fine particles, and fit is everything: gaps around the nose and cheeks let unfiltered air bypass the filter entirely. A loose surgical mask or a cloth face covering does comparatively little against PM2.5, because the particles are small enough to slip through and around them. On severe days, a properly sealed N95 worn for the duration of your exposure is a sensible precaution, especially for those at higher risk. It is a supplement to reducing exposure, not a licence to ignore it.

Air purifiers and cleaner indoor air

Because most people spend most of their time indoors, cleaning indoor air is often the highest-impact step available. A HEPA air purifier sized appropriately for the room can substantially lower indoor fine-particulate levels, and on a high-pollution day a closed room with a purifier running is frequently far cleaner than the street outside. The essentials are matching the unit's rated capacity to the room, running it continuously during pollution peaks rather than in short bursts, and keeping the windows closed while it works. Combined with reducing indoor sources — venting cooking smoke, avoiding indoor burning — a purifier turns your home into a reliable refuge during the worst of the season.

Building a plan for the high-pollution season

Because India's bad-air months are predictable, the smartest approach is to prepare before they arrive rather than react once the smog sets in. That means sorting out indoor-air defences ahead of winter, having well-fitting masks on hand, identifying the cleaner hours and cleaner routes for any unavoidable outdoor activity, and agreeing a simple household rule for the most vulnerable — a threshold at which children's outdoor sports move indoors, or an elderly relative stays in. A plan made in advance is far easier to follow than a decision made in the moment, and it removes the daily debate about what to do.

How the DailyAQI guide library is organised

This overview is a starting point; the detail lives in the individual guides. There are explainers on the pollutants themselves and how they differ, practical guides to masks and air purifiers, health-focused pieces on asthma and protecting children, and context pieces on why particular cities and seasons are so polluted. Each is written to be honest and useful rather than alarmist, grounded in CPCB and WHO guidance, and free of invented statistics. Browse them alongside your city's live data, and the number on the screen turns into knowledge you can act on. And because the guidance is only as good as the reading it is paired with, keep the air quality near you to hand as you read.

Key takeaways

• Air pollution is a mixture; fine particulate matter (PM2.5) is the component most tied to health harm.
• Both short- and long-term exposure carry risks that rise with level and duration — reduce hours in bad air, not just peaks.
• Children, older adults, pregnant people, and those with lung or heart conditions should take precautions earlier.
• Check the live AQI daily, then time activity, mask well, filter indoor air and cut indoor sources.
• In India, winter is the high-pollution season and the monsoon the cleanest; plan your defences accordingly.