Have you ever opened the AirCasting map, seen those brightly colored dots, and wondered what they mean? Each dot shows the local air quality, scored on the Air Quality Index (AQI). Once you can read the colors, you can make smarter, healthier choices about the air around you.

The short version: the colored dots on the AirCasting map show how clean or polluted the air is at each sensor, in real time. Green means clean air. As the colors shift to yellow, orange, and red, pollution rises and so does the risk to your health. Here is how to read them.

What is the Air Quality Index (AQI)?

The Air Quality Index turns air pollution measurements into a single, easy number and color. In the United States it runs from 0 to 500 across six categories. The higher the number, the more polluted the air and the greater the health risk.

The U.S. Environmental Protection Agency (EPA) created the AQI in the 1970s to make air pollution easier to understand. It translates common pollutants, like car exhaust and smog, into health-based categories.

Not every country uses the same system. AQIs vary from country to country, with different scales and colors.

The EPA’s AQI also guides sensitive groups, such as people with asthma and older adults, on when to adjust outdoor activity as pollution climbs.

What do the AQI colors and numbers mean?

Each AQI color maps to a range of numbers and a level of health concern. Green is good. Maroon is hazardous. Here is the full scale.

Why does the AirCasting map use different colors than the official AQI?

The AirCasting map focuses on one pollutant, PM2.5, and shows its actual concentration rather than an index score. So its colors track micrograms of particles per cubic meter of air (µg/m³), not the 0 to 500 AQI number.

The AirCasting app maps PM2.5 concentrations to colors like this: 0–9 µg/m³ is green, 10–35 is yellow, 36–55 is orange, and 56–150 is red. You can adjust these ranges in the app.

The colors line up roughly with the AQI, but they measure different things. The AQI blends several pollutants into an index. AirCasting shows you the real concentration of the particles you are breathing.

Why show concentrations at all? Because actual numbers give a more precise, nuanced picture of what is in the air than a single index can.

Here is a number that surprises most people: the World Health Organization estimates that 99% of the world’s population breathes air that exceeds its recommended limits. Air pollution is not a distant problem. It is almost everywhere, which is exactly why being able to read it matters.

What are the major air pollutants?

The AQI is built from five major pollutants. The AirCasting map focuses on one of them, particle pollution, because it is among the most harmful to human health.

• Ground-level ozone
• Particle pollution (PM2.5 and PM10)
• Carbon monoxide
• Sulfur dioxide
• Nitrogen dioxide

Each one can affect your health, especially for children, older adults, and people with asthma or heart disease.

Particle pollution deserves special attention. These tiny particles come from traffic, wildfire smoke, power plants, and everyday sources like cooking and burning candles indoors. They are small enough to reach deep into your lungs and enter your bloodstream. Short-term exposure can cause headaches and worsen breathing problems. Long-term exposure is linked to heart attacks, stroke, and lung disease.

What the AQI gets right, and where it falls short

The AQI is a powerful public tool, but it has real limits. Knowing both helps you use it wisely.

What it does well

• The simple, color-coded design makes air quality easy for anyone to read and act on.
• It warns the public when pollution is high enough to harm health, especially for children, the elderly, and people with breathing problems.
• It helps local governments track air quality against safety standards.

Where it falls short

• It can hide which specific pollutant is driving poor air, so you lose sight of the distinct risks.
• It is based on longer, often 24-hour, exposures, so it can miss the short, sharp pollution spikes you actually breathe during the day.
• It covers only the five criteria air pollutants. It leaves out hundreds of hazardous air pollutants like formaldehyde and benzene from petrochemical plants and urban fires.
• Research shows health effects can occur well below current regulatory thresholds, especially for the most toxic particles, like those in diesel exhaust.

How do you check the air right where you are?

Official monitors are few and far between, and the AQI averages pollution over time. But the air you breathe changes by the minute and by the block. To see your air, right where you are, you need to measure it yourself.

That is what a personal monitor does. The AirBeam Mini is a small, portable sensor that tracks PM2.5 in real time and feeds it straight to the AirCasting map. You can watch how your air changes as you cook, commute, or move between neighborhoods, and share what you find with your community.

Communities are already doing this. In New York City, neighborhood groups used AirBeams to map air pollution block by block and found levels far higher than official readings suggested.

Making air quality easy to understand

Air quality data used to require a scientist to interpret. Tools like AirCasting and the AirBeam Mini put it in everyone’s hands, in real time.

With a quick glance at the map, you can decide:

• Whether it is a good day for a run
• If your child should wear a mask today
• Where in your city the air is cleanest

The bigger picture

Clean air is not just a concern for researchers or policymakers. It is a basic human right. Knowing what is in the air you breathe is the first step toward protecting yourself, your family, and your neighborhood.

Frequently asked questions

What do the colors on the AirCasting map mean? Green means the air is clean, and the risk rises as the colors move through yellow, orange, and red. Each color reflects how much PM2.5 pollution is in the air at that sensor.

What is a good AQI number? An AQI of 0 to 50 (green) is good, meaning air quality is satisfactory for everyone. Above 100, the air starts to affect sensitive groups.

What is the difference between the AQI and PM2.5? The AQI is an index from 0 to 500 that blends several pollutants into one score. PM2.5 is a single pollutant, fine particles, measured in micrograms per cubic meter. The AirCasting map focuses on PM2.5.

Why is the air near me different from the nearest official reading? Official monitors are sparse and average pollution over time, so they miss the block-by-block changes you actually breathe. A personal monitor like the AirBeam Mini shows the air right where you are.