Air pollution and the AQI
Air pollution is dirt in the air: smoke from vehicles, factories, burning of waste and crop stubble, and dust. The most worrying are tiny particles called PM2.5 (smaller than 2.5 micrometres, much thinner than a hair) and PM10, and gases such as ozone and nitrogen dioxide.
The Air Quality Index (AQI) turns these amounts into one number, usually from 0 to 500. Low is clean. The bands are named and coloured: good (green), moderate (yellow), unhealthy for sensitive people (orange), unhealthy (red), very unhealthy (purple) and hazardous (maroon). Countries use slightly different scales, so use the one from your local weather or environment service.
Why exercise and dirty air is a double hit
At rest you breathe about 6 litres of air a minute. When you run, it can be 5 times more or even higher, and you start to breathe through your mouth, which does not filter the dust. So on a dirty-air day, hard exercise brings several times more dust into your lungs.
Fine dust can irritate the airways and cause coughing, a sore throat and a tight chest. It can make asthma worse. Over years it raises the risk of lung and heart problems. Children are affected more because they breathe faster for their size and their lungs are still growing.
Smart choices on bad-air days
- Check first: look at the AQI before outdoor play.
- Move indoors: skipping, yoga, stairs, dance or stretching at home or in a hall.
- Lighter and shorter: a gentle walk instead of a hard run, and shorter sessions.
- Time and place: choose a park away from busy roads, and a time when the AQI is lower (often afternoon).
- Mask: a well-fitting N95, KN95 or FFP2 mask filters most fine dust. Cloth masks and loose surgical masks help much less. A mask can make breathing harder, so do not do hard exercise in it.
- Indoor air: keep windows closed on very bad days, use a purifier if you have one, and do not burn incense, coal or wood indoors.
- Listen to your body: stop if you cough, wheeze, feel dizzy or have chest pain. Children with asthma follow their doctor's plan.
Outbreaks and how infections spread
An outbreak is a sudden rise in cases of a disease. If it spreads over a country it is an epidemic, and across the world a pandemic. A public-health emergency is when such a threat is serious enough that special action is needed.
Germs spread along a chain:
- Source: a sick person or animal, or dirty water.
- Way of travelling: breathing droplets in the air, touching surfaces, dirty food or water, or insects such as mosquitoes.
- New person: someone who is not protected.
Break one link and the spread slows. Isolate the sick, wash hands, cough into your elbow, drink clean water, wear a mask in crowds when advised, and get vaccines.
Responding to a public-health emergency
- Notice and report: doctors and schools report unusual illness to the health department.
- Check: tests confirm the disease, and health workers find people who were in close contact (contact tracing).
- Tell the facts: officials give clear, honest advice. Trust official sources, not rumours or chain messages.
- Act: isolate the sick, treat them, keep contacts under watch (quarantine when advised), vaccinate where a vaccine exists, and clean water and spaces.
- Review: learn what worked, restore services and care for people's mental health.
What you can do: stay home when ill, follow school and health rules, wash hands, get vaccines on time, keep calm, and never share unchecked news. Help neighbours who may be alone, from a safe distance if the disease is infectious.
Try it: your emergency kit and AQI diary
For a week, note the local AQI each morning and decide what exercise is right that day. Prepare a small home health kit: thermometer, soap, a few masks, an emergency phone list, basic medicines your doctor approved. Then use the free-play step of the 3D to see how contacts and protection change the spread.
Key formulas and definitions
- AQI: low = clean; high = polluted (bands 0-50, 51-100, 101-150, 151-200, 201-300, 300+).
- Hard exercise: about 3 to 5 times more air breathed than at rest.
- Chain of infection: source → way of travelling → new person.
- Break any link to stop the spread.
- Outbreak steps: notice → check → tell → act → review.
- Spread factor R = contacts × chance × (1 − protection). R below 1: outbreak fades.
Worked examples
1. Today's AQI is 180. Which band is it and what exercise would you choose?
180 lies in 151-200: unhealthy (red). Do not run hard outdoors. Choose indoor exercise such as skipping, yoga or stairs, or a short gentle walk away from traffic.
2. A child at rest breathes 6 litres of air a minute and breathes 4 times as much while running. How much air does she breathe in a 15-minute run?
While running: 6 × 4 = 24 litres a minute. In 15 minutes: 24 × 15 = 360 litres. This is 4 times the dust she would breathe at rest in the same dirty air.
3. Name one way to break each link of the chain of infection for flu.
Source: the sick person stays home or isolates. Way of travelling: wash hands, cough into the elbow, wear a mask in crowds, ventilate rooms. New person: get vaccinated and stay away from those who are ill.
Common mistakes
- Thinking a thin cloth mask stops PM2.5. Only well-fitting N95, KN95 or FFP2 type masks filter most fine dust.
- Doing hard exercise outdoors on a hazardous-AQI day because it is 'only dust'. Breathing hard means breathing in more dust.
- Thinking indoor air is always clean. Indoor smoke, incense and cooking fumes also pollute the air.
- Forwarding unchecked health messages in an emergency. Rumours spread faster than the disease; use official sources.