Should You Exercise Outdoors When the AQI Is High? A Practical India Guide

The 6 AM Shoelace Moment

It is a winter morning. Your walking group is already at the park gate.

You bend down to tie your shoes. The sky is the colour of weak tea.

Your phone says the AQI is 186. A friend’s app says 290.

Do you go?

Here is the short answer: before exercising in polluted air, first make sure you are reading the Indian AQI scale for a station near you. Then match the session to the category and to your health. Moderate air may mean a normal walk for you, but a shorter, easier one for a friend with asthma. Very Poor or Severe air usually means an indoor session.

1. First, Which AQI Are You Reading?

Here is a surprise for many people: the same AQI number can mean different things.

India’s National Air Quality Index (NAQI), published by the Central Pollution Control Board, has six bands. Many international apps and some purifier displays show the US AQI instead, which uses different bands for the same numbers.

So your friend’s 290 may be a US reading, or a different station, or both.

Location matters too. CPCB’s own city bulletin notes that averaging stations across a city “is not a scientifically sound approach”, even though it is used for simplicity. Use the nearest station’s reading, through the CPCB website or its SAMEER app.

2. Why Exercise in Polluted Air Changes the Equation

At rest, you breathe a modest volume of air each minute. During a brisk walk, that rises. During a run, it rises much further, and more of it comes through your mouth, bypassing some of your nose’s filtering.

More air per minute means more particles per minute. That is why the same smog matters more on a run than on a stroll.

But exercise is also one of the most powerful things you can do for your health. So the question is not “Is polluted air harmful?” It is “When does the dose outweigh the benefit?”

A 2016 modelling study by Tainio and colleagues estimated exactly that for long-term mortality. At typical urban pollution levels, the benefits of walking and cycling far outweighed the harm from air pollution. Even at a background PM2.5 level of 100 µg/m³, harms only exceeded benefits after about 90 minutes of cycling a day, or more than 10 hours of walking.

Two cautions keep that finding honest:

• It is a population model of long-term outcomes. It does not predict an asthma attack or chest symptoms on a given morning.
• PM2.5 in µg/m³ is a concentration, not an AQI number. Do not read “100” on your app as the same thing.

The Verdict: for most healthy adults, a daily walk is still worthwhile on many polluted days. The real decisions are intensity, duration, route and who you are.

3. A Decision Guide by Indian AQI Category

CPCB attaches a health statement to each category. The right-hand column is our practical reading of that wording. It is not an official activity guideline.

Who counts as sensitive? People with asthma, COPD or other lung disease, heart disease, older adults, children and teenagers, pregnant women and outdoor workers are commonly listed. If you are in one of these groups, move one row down the table.

4. Where You Exercise Matters as Much as When

Pollution is not spread evenly across a city.

The Delhi advisory recommends avoiding slow, heavy-traffic roads, areas near polluting industries, and construction or demolition sites. A park in the middle of a residential area is usually a better choice than a walk along a busy arterial road.

Timing helps too, but use real data, not folklore. The Delhi advisory specifically names early-morning and late-evening sessions for severe-AQI days. On other days, remember that CPCB’s AQI is a running 24-hour average, so it barely changes from hour to hour. To compare times of day, watch your nearest station’s PM2.5 concentration over a few days. Your own station’s pattern is the best guide.

5. Masks: What an N95 Can and Cannot Do

A good respirator can help when you have to be outside. It is not a licence to run a half-marathon through smog.

According to US EPA guidance on smoke:

• A well-fitted N95 significantly reduces exposure to fine particles. Leaks around the edges let unfiltered air in.
• Choose two head straps. Masks with ear loops are not designed to seal tightly to the face.
• Facial hair breaks the seal. The skin under the edge should be clean-shaven.
• It filters particles, not gases. It does not protect against gases such as carbon monoxide.
• Young children are hard to fit. Approved respirators are not made in small children’s sizes.

Cloth masks and loose surgical masks do not seal the way a fitted respirator does.

Exercising hard in an N95 is also uncomfortable. The mask resists breathing, gets damp and may slip, and a mask that has slipped no longer seals. For a commute or an unavoidable errand, wear a fitted respirator. For a workout, an indoor session is usually the simpler answer.

6. A Good Indoor Session When the Air Outside Is Polluted

Skipping exercise for weeks of winter smog has its own cost. The WHO notes that any amount of physical activity is better than none.

Indoor options that work in most homes:

• brisk walking in place, or on a walking pad or treadmill
• a 20–30 minute circuit of squats, step-ups, wall push-ups and lunges
• skipping, if your floor and neighbours allow
• yoga or a mobility routine

Close the windows, run a purifier sized for the room (our guide on choosing the right purifier size explains how), and skip agarbatti or dry sweeping before your session.

Building stairwells and basement gyms may not have cleaner air than outdoors. Indoor air is only better when it is actually being filtered or is well away from the source.

Which Choice Fits Today?

• Good to Moderate, and you feel well: go out. Pick a quieter route.
• Poor: keep it short and easy outdoors, or bring the session indoors. Sensitive groups should choose indoors.
• Very Poor or Severe: indoors, almost always.
• Any day you feel unwell: rest or go gentle, whatever the number says.