The Air Quality Index, or AQI, is a scale that tells how clean or polluted the air is in a specific place. Students need this cheat sheet to connect daily air quality reports to real health and environmental decisions. It helps explain why some days are safe for outdoor activity while others require caution.
Understanding AQI also supports learning about pollution, weather, and public health.
Key Facts
- The AQI scale usually runs from 0 to 500, and higher numbers mean more air pollution and greater health risk.
- AQI 0-50 is Good, which means air quality is satisfactory and air pollution poses little or no risk.
- AQI 51-100 is Moderate, which means air quality is acceptable but may affect a small number of unusually sensitive people.
- AQI 101-150 is Unhealthy for Sensitive Groups, which means children, older adults, and people with heart or lung disease should reduce long outdoor activity.
- AQI 151-200 is Unhealthy, which means everyone may begin to feel health effects and sensitive groups may feel more serious effects.
- AQI 201-300 is Very Unhealthy, and AQI 301-500 is Hazardous, which means outdoor exposure should be greatly reduced or avoided.
- Major pollutants used in AQI reporting include ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.
- To reduce exposure on high-AQI days, check local AQI, limit intense outdoor exercise, close windows, and use filtered indoor air when possible.
Vocabulary
- Air Quality Index
- The Air Quality Index is a number and color scale that reports how polluted the air is and how it may affect health.
- Particulate Matter
- Particulate matter is a mixture of tiny solid particles and liquid droplets in the air that can be breathed into the lungs.
- Ground-Level Ozone
- Ground-level ozone is a harmful gas formed when pollutants from vehicles, factories, or other sources react in sunlight.
- Sensitive Groups
- Sensitive groups are people who are more likely to be harmed by air pollution, including children, older adults, and people with asthma or heart disease.
- Pollutant
- A pollutant is any substance in the environment that can harm living things, damage materials, or reduce air, water, or soil quality.
- Exposure
- Exposure is the amount of contact a person has with a pollutant over a period of time.
Common Mistakes to Avoid
- Thinking a low AQI means there is no pollution is wrong because AQI 0-50 still means some pollutants may be present, just at levels considered low risk.
- Ignoring sensitive groups is wrong because an AQI that seems acceptable for most people can still affect children, older adults, and people with asthma.
- Assuming all air pollution is visible is wrong because harmful gases like ozone and carbon monoxide cannot always be seen or smelled.
- Using only temperature to decide if air is safe is wrong because a cool or comfortable day can still have high particle pollution or ozone.
- Exercising hard outdoors on high-AQI days is wrong because faster breathing can pull more pollutants deeper into the lungs.
Practice Questions
- 1 A city reports an AQI of 42. What AQI category is this, and what does it mean for outdoor activity?
- 2 A school checks the AQI before recess and sees a value of 132. Which groups should be most careful, and what activity change would be reasonable?
- 3 During a wildfire, the AQI rises from 85 to 190. By how many points did the AQI increase, and which category does 190 fall into?
- 4 Explain why a sunny day with clear skies can still have unhealthy air quality.
Understanding Air Quality Index (AQI) Reference
An AQI report is built from measurements of separate pollutants, not from one sample called pollution. Scientists measure each pollutant over a set time period, compare the result with health-based standards, then convert it to an index value. The reported AQI is usually based on the pollutant with the highest index value.
This matters because a day can have low particle pollution but high ozone, or the reverse. Looking at the main pollutant helps explain the warning. It tells students which source and condition may be causing the problem.
Ground-level ozone forms when gases from vehicles, power plants, and industrial equipment react in sunlight. It often becomes worse on hot, bright afternoons. Ozone can irritate airways and make breathing during running or sports feel harder.
Particle pollution is made of tiny solid or liquid bits in the air. Smoke from wildfires, wood burning, diesel engines, construction, and dust can raise particle levels. The smallest particles can travel deep into the lungs.
Carbon monoxide comes from incomplete burning of fuel, while nitrogen dioxide is strongly linked to traffic and combustion. Sulfur dioxide can come from burning sulfur-containing fuels, especially near some industrial sources.
Weather changes pollution levels from hour to hour. Wind can spread pollutants away from their source, while still air lets them build up. Rain can remove some particles from the atmosphere.
A temperature inversion can trap cooler air near the ground under warmer air. When this happens, vehicle exhaust and smoke may remain close to where people breathe. Wildfire smoke can travel hundreds of miles, so a community may have poor air even when there is no nearby fire.
AQI can therefore differ between neighborhoods, especially near busy roads, factories, valleys, or fires. A regional reading is useful, but it cannot describe every street perfectly.
Students meet AQI information in weather apps, school activity decisions, sports practices, and wildfire alerts. The best response depends on the person and the activity. Hard exercise makes people breathe faster and take in more air, so moving a workout indoors can reduce the amount of pollution inhaled.
People with asthma should follow their health plan and keep prescribed medicine available. Closing windows helps only when indoor air is cleaner than outdoor air. A well-fitted filter can reduce particles, but ordinary fans do not remove pollution by themselves.
Pay attention to the report time, forecast, main pollutant, and any local health guidance. These details turn one number into a practical decision about where, when, and how long to be active.