We check the weather before we leave the house, but how often do we check the air?
The Air Quality Index (AQI) is a simple, color-coded system that helps us understand how clean or polluted the air is – and what it means for our health. There are six levels of air quality ranging on a scale from 0 to 500. Whether you’re looking out for vulnerable loved ones, planning an outdoor run, or wondering whether today’s the day to crack the windows open, knowing the AQI can help you make smarter, safer choices.
Let’s break it down.
🌿 GREEN = GOOD
AQI 0–50
✅ Air quality is considered satisfactory, and air pollution poses little or no risk.
What to do:
- Enjoy the outdoors freely – go for a walk, bike ride, or run.
- A perfect day to air out your home or workspace by opening the windows.
- Safe for everyone, including babies, seniors, and people with chronic health conditions.
🌤️ YELLOW = MODERATE
AQI 51–100
🟡 Air quality is acceptable, but there may be a mild risk for unusually sensitive individuals.
What to do:
- Sensitive individuals (e.g., those with asthma, allergies, COPD or lung disease) should consider lowering the intensity or duration of outdoor activities.
- Everyone else can enjoy normal outdoor activities.
- Opening windows is okay but consider checking back later in the day if levels rise.
🍊 ORANGE = UNHEALTHY FOR SENSITIVE GROUPS
AQI 101–150
🟠 People with heart or lung disease, older adults, children, pregnant individuals, and outdoor workers or athletes are at increased risk.
What to do:
- Sensitive populations should reduce outdoor exertion – take more breaks, move slower, and consider shifting activities indoors.
- Even healthy people may start to feel minor symptoms with extended exposure.
- Avoid airing out your home; outdoor air isn’t clean enough for ventilation.
🔴 RED = UNHEALTHY
AQI 151–200
🔴 Everyone may begin to experience adverse health effects, especially after prolonged or intense exposure.
What to do:
- Sensitive individuals: stay indoors and avoid physical activity.
- Everyone else should avoid long or strenuous outdoor exercise.
- Keep doors and windows closed. Use a high-performance air purifier, like the Austin Air HealthMate, to maintain safe indoor air quality.
- Children and teens should avoid outdoor sports or gym classes.
🟣 PURPLE = VERY UNHEALTHY
AQI 201–300
🟣 Health alert: The risk of health effects is increased for everyone. Even short exposure can be harmful.
What to do:
- All physical outdoor activity should be limited or moved indoors.
- Use caution with ventilation—this is not the day to bring outdoor air inside.
- If you must be outside, wear a properly fitted N95 mask to reduce exposure to fine particles.
- Keep air purifiers running continuously indoors.
🟤 MAROON = HAZARDOUS
AQI 301–500
🟤 This is the highest alert level. The air is dangerous. Emergency conditions are in effect.
What to do:
- Everyone should stay indoors as much as possible.
- Do not exercise outdoors – even light activity like walking the dog can put strain on your lungs.
- Sensitive populations should avoid indoor exercise too.
If your area is under a hazardous air warning, treat it like an emergency:
- Run your air purifier(s) nonstop.
- Seal leaks around doors and windows.
- Avoid using fans that draw outdoor air in.
- Keep activity levels low – even indoors.
- Check in on neighbors who may not have access to clean air solutions.
Why AQI Matters Indoors, Too
It’s tempting to think you can avoid poor air quality by staying inside, but that’s only part of the story.
An efficient ventilation system is essential for good Indoor Air Quality (IAQ) to exchange stagnant, carbon dioxide-laden indoor air with fresh, oxygen-rich outdoor air. But it’s not as simple as cracking open a window when outdoor air is polluted.
Pollutants from outside – like pollen, mold spores, car exhaust, and industrial emissions—can enter your home through open windows, doors, and HVAC systems. Once inside, these pollutants can linger and even become more harmful due to interactions with indoor conditions.
Indoor pollution levels can be 2 to 5 times higher than outdoor levels – and sometimes up to 100 times higher, according to the CDC’s Agency for Toxic Substances and Disease Registry. This applies in both rural and urban settings.
Monitoring AQI in Real Time
Outdoor air quality fluctuates throughout the day due to temperature, wind, sun, and other environmental factors.
The best way to stay informed is to visit AirNow.gov, the official source of AQI updates in the United States. Their interactive map shows live data on particulate matter (PM2.5 and PM10) and ground-level ozone – the most common and harmful pollutants.
Real-world events and pollutants can cause dramatic shifts in the Air Quality Index, sometimes within hours. Here’s a rundown of some key examples across AQI categories – from mild to severe:
🟡🟠 Mild Impact (Often YELLOW or ORANGE AQI)
As outlined above, these situations typically affect sensitive individuals the most but can become widespread under the right (or wrong!) conditions.
- Pollen surges – Spring and fall bring spikes in tree, grass, or ragweed pollen, which can irritate the respiratory system and contribute to moderate AQI readings.
- Vehicle traffic – Rush hour in urban areas can temporarily raise AQI, especially near highways.
- Hot, sunny days – Lead to the formation of ground-level ozone, a common pollutant in cities.
- Fireworks displays – Short-term spike in PM2.5 due to chemical and smoke release.
- Lawn mowing or yard equipment – Gas-powered tools emit volatile organic compounds (VOCs) and fine particles.
🟠🔴 Moderate to Severe Impact (Often ORANGE to RED AQI)
These events tend to elevate AQI for entire communities and can pose health risks to everyone – not just those with existing conditions.
- Construction and demolition – Stir up dust (PM10) and release diesel exhaust.
- Agricultural activity – Fertilizer and tilling release ammonia and particulate matter, particularly in rural areas.
- Industrial emissions – Power plants, factories, and refineries can release sulfur dioxide, nitrogen oxides, and heavy metals.
- Temperature inversions – A weather phenomenon that traps pollutants close to the ground, often causing AQI to spike quickly.
🟣🟤 Extreme Impact (RED, PURPLE, or MAROON AQI)
These are usually regional or large-scale events that can push AQI into “very unhealthy” or “hazardous” territory for days or weeks.
- Wildfires – The number one cause of hazardous AQI in the U.S. in recent years. Smoke contains PM2.5, carbon monoxide, and toxic gases.
- Dust storms – Common in arid regions; raise PM10 and PM2.5 to dangerous levels.
- Volcanic eruptions – Ash and sulfur dioxide can degrade air quality hundreds of miles away.
- Chemical plant explosions or industrial accidents – Release highly toxic gases like chlorine or benzene, which can spike AQI and prompt shelter-in-place orders.
- Major transportation disasters – Oil spills, train derailments, or cargo fires can release pollutants into the air and water supply.
- Climate-related events – Increasingly common heat waves, droughts, and stagnant air conditions worsen air quality by intensifying existing pollution.
Bottom Line
Understanding the AQI gives you the power to make informed choices about your health and your home. From when to exercise to when to seal up your windows and turn on your air purifier, a quick check of the AQI can help protect your lungs, your loved ones, and your peace of mind.
Breathe easy. Stay safe. And remember – clean air is essential, not optional.
Need help choosing an Austin Air Purifier that can handle hazardous conditions? We can help you find the right fit.
