Disclaimer: This content is provided for informational and educational purposes only and is not intended as medical advice or a substitute for professional medical evaluation, diagnosis, or treatment. Reading this content does not establish a provider-patient relationship. Always seek the advice of your physician or other qualified healthcare provider regarding any medical concerns or conditions. Never disregard professional medical advice or delay seeking care because of something you have read here.

The AQI scale has six colored bands, from good air at 50 and below to hazardous above 300. Orange, 101 to 150, is the first point where some people should change their plans.

Those bands are not arbitrary. The breakpoints were set from the health-effects evidence reviewed for the national air quality standards, and a value of 100 roughly matches the short-term health-based standard for the pollutant being reported. Between 101 and 150 the air is unhealthy for sensitive groups; above 150 both sensitive groups and the general population are at risk (Communicating Air Quality Conditions: The Air Quality Index).

In Pasadena the question is rarely academic. After a fire season, two apps can show different numbers for the same block within the same hour, and a parent standing at the front door with a stroller needs an answer rather than a range.

Hand holding a phone showing a colored air quality dial against a bright sky with foothills behind

What Do the AQI Colors and Numbers Actually Mean?

Six categories, each with a color, a number range, and a level of health concern. A value at or below 50 is good air; anything over 300 is hazardous, and the higher the number the greater the health concern (Air Quality Index (AQI) Basics).

The color is the part worth memorizing, because it is what a weather app shows at a glance. Green and yellow are ordinary days. Orange is the first decision point. Red, purple, and maroon all mean the same thing in practice, which is that outdoor time should be short and light for everyone.

Color and category	AQI values	What it means for you
Green - Good	0 to 50	Air quality is satisfactory and poses little or no risk. Normal outdoor plans.
Yellow - Moderate	51 to 100	Acceptable, but there may be a risk for people who are unusually sensitive to air pollution.
Orange - Unhealthy for Sensitive Groups	101 to 150	Sensitive groups may feel effects. Move workouts indoors, shorten time outside, keep windows shut.
Red - Unhealthy	151 to 200	Some of the general public may feel effects; sensitive groups may feel more serious ones. Everyone cuts outdoor time.
Purple - Very Unhealthy	201 to 300	Health alert: the risk of health effects is increased for everyone. Stay inside with filtered air.
Maroon - Hazardous	301 and higher	Health warning of emergency conditions: everyone is more likely to be affected. Stay inside and follow local alerts.

One number on that chart does not describe the whole day. The AQI reports the worst of the measured pollutants at that moment, so a reading can climb through the afternoon and fall again by evening, which is why checking before you go out beats checking once in the morning.

At What AQI Should You Stay Inside?

It depends on who is going outside, and that is the honest answer rather than a dodge. The scale is built around sensitive groups first, so the same reading calls for different behavior from a healthy adult and from a child with asthma.

If You Are in a Sensitive Group

Orange is your line. On a Code Orange day the practical advice is to reschedule outdoor activity to a better time or place, or make it less intense: walk instead of running, shorten the session, or move it indoors entirely (About Air Quality). Above 150 the recommendation applies to everyone, not only to sensitive groups.

If Nobody in the House Is in a Sensitive Group

Red, 151 to 200, is where healthy adults should start cutting back. Keep activity levels low outdoors and skip the vigorous things first, which means yard work and running rather than a walk to the mailbox. At purple and above, plan on staying in.

When the Smoke Is Visible

Trust your eyes and nose alongside the number. During a smoke event the guidance is to stay indoors or limit time outside, keep activity light when you do go out, and spend time somewhere with cleaner and cooler air if your own home cannot stay cool.

Who Is at Higher Risk from Bad Air?

Children, older adults, pregnant women, people with heart or lung disease, and people with higher exposure such as outdoor workers. Most healthy people recover quickly from smoke exposure without lasting effects, which is exactly why the groups that do not deserve the attention (Wildfire Smoke and Health).

Children and teens matter here for a physical reason: they breathe more air for their body size and spend more time outdoors, and children with asthma may be more sensitive than adults to the same air. Heart disease belongs on the list too, because particle pollution has been linked to heart attacks and strokes in that group.

Older adults often sit in two or three of these categories at once, which changes the math at home. An 80-year-old with a heart condition on an orange day is not in the same position as a healthy neighbor the same age, and the plan should reflect that rather than the forecast alone.

Keeping someone indoors for several days only works if the days are manageable. Home care agencies that handle personal care and post-discharge support, such as A Better Solution In Home Care, cover the shopping, meals, and company that make a closed-window week possible. What to check before signing with any agency is its own topic (Hiring a Caregiver in Pasadena).

Why Is PM2.5 the Number That Matters Most?

Because the particles are small enough to reach places in the body that larger dust cannot. PM2.5 means fine inhalable particles generally 2.5 micrometers across or smaller, and the average human hair is about 70 micrometers wide, making it roughly 30 times larger than the largest fine particle (Particulate Matter (PM) Basics).

Size decides where particles end up. Some particles under 10 micrometers get deep into the lungs, and some of those may pass into the bloodstream. Of all the measured pollutants, PM2.5 is the one that poses the greatest risk to health, which is why it drives the AQI on smoky days.

That also explains why haze and the AQI usually move together in the fire season. Fine particles are the main cause of reduced visibility, so an orange sky over the San Gabriels and a rising number in your app are two views of the same thing.

Does an N95 Mask or an Air Purifier Help?

Both help, and they do different jobs. A respirator protects you on the way to the car; a filter protects the room you sleep in.

Masks for Going Outside

The guidance is specific about the type. Wear a NIOSH Approved respirator such as an N95 to protect your lungs if you need to go out when smoke levels are high. A cloth or surgical mask is not built to filter fine particles, so it is reassurance rather than protection, and a loose N95 is not much better than none.

Filtering the Air Indoors

Indoor air filtration is the other half. Ask a heating and cooling technician which filters your system can take, and use a high-efficiency filter rated MERV 13 or higher if the system can safely handle one. A portable air cleaner works for a single room, and a do-it-yourself air cleaner is an option when stores are sold out.

Making One Clean Room

Creating a cleaner air room at home is often the realistic version of staying inside. Pick the room where the household sleeps or spends the day, keep its windows and doors shut, run the filtration there, and stop worrying about the whole house during the worst two or three days.

Why Do Two Apps Show Different AQI Numbers?

Because they are not measuring the same thing in the same place. The AQI translates pollutant concentrations into one normalized number, and the reading depends on which monitor or sensor feeds it, how recent that reading is, and whether the value shown is current, an hourly average, or a forecast for the day.

Three habits settle most of the confusion. Use the official map rather than a general weather widget during a smoke event, note whether you are looking at a forecast or a current reading, and check the time stamp, because a two-hour-old number is a different claim from a live one.

The bands are wide enough that small differences between apps rarely change what you should do. A reading of 96 in one app and 104 in another sits on the Yellow and Orange boundary, and the sensible response to either is the one you would take at Orange.

What If Symptoms Linger After the Air Clears?

Then the AQI has stopped being a useful measurement and the symptoms are. Short-term smoke exposure can cause headaches, eye irritation, coughing, increased phlegm, wheezing, chest tightness, and difficulty breathing, and most of it fades within days.

What does not fade is worth a visit. A cough and phlegm that continue for weeks after the smoke has gone are a common question in this area and have their own answer (Coughing Up Phlegm Weeks After the Smoke), as does the question of which symptoms can wait and which cannot (After a Wildfire: Which Smoke Inhalation Symptoms Can Wait and Which Can’t).

A cough that started with a fire and never left belongs with a lung specialist rather than another round of waiting (Coughing That Started After the Fire and Never Left). For someone who cannot easily get to an office, a doctor who visits at home can listen to the chest and check oxygen without the trip.

Eyes are the symptom people put up with longest. Smoke causes eye irritation directly, and weeks of dryness and redness after a fire season are worth an exam rather than more drops; mobile optometry services such as Rad Mobile Eye Care cover Pasadena and handle dry eye and red eye at home.

What Else Changes After a Fire Nearby?

The air is the first worry and not the only one. Once a fire has moved through structures rather than only brush, the ash that settles on soil, decks, and play areas becomes its own question, separate from anything the AQI measures.

That matters most for households with small children, who put hands and toys in their mouths. Lead in soil after a wildfire, and how families get it tested, is covered separately (Lead in the Soil After a Wildfire).

The practical version for the next smoky week is short. Check the number before each trip outside, treat Orange as the line for anyone sensitive and Red as the line for everyone, keep one room filtered, wear a fitted N95 when you must be out, and treat symptoms that outlast the smoke as a reason to be seen.

Frequently Asked Questions

Does the AQI cover anything besides smoke?

Yes. EPA sets an AQI for five pollutants regulated under the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. On hot, still summer days in the valleys the number is often driven by ozone rather than by particles.

Can indoor air be worse than the AQI suggests?

It can. The AQI describes outdoor air, so indoor levels depend on how much outside air gets in and what happens inside. Cooking, candles, and vacuuming add particles of their own, which is worth remembering during a week spent with the windows closed.

Is exercise outdoors ever worth it on a moderate day?

For most people, yes, and the trade-off is the point. Moderate air is acceptable for the general public, and the benefits of regular activity are real. If you are unusually sensitive to air pollution, a yellow day is the one to move indoors or keep easy.

How long should windows stay closed after smoke clears?

There is no fixed number of hours. Use the readings rather than the calendar, and open up once values are back in the green or low yellow range and the air outside no longer smells of smoke.

Do air quality alerts come to a phone automatically?

Only if you set them up. Free email alerts and the official app can notify you when levels change in your area, which is more reliable than remembering to look during a busy week.

Does an orange day mean schools should cancel outdoor activity?

Not automatically, and schools work from their own guidance. Published advice for schools leans on adjusting intensity and duration rather than canceling, which is the same logic families use at home.

Sources Used

About Air Quality – Centers for Disease Control and Prevention (2026)
Air Quality Index (AQI) Basics – AirNow, U.S. Environmental Protection Agency
Communicating Air Quality Conditions: The Air Quality Index – U.S. Environmental Protection Agency (2026)
Particulate Matter (PM) Basics – U.S. Environmental Protection Agency (2026)
Wildfire Smoke and Health – U.S. Environmental Protection Agency (2026)

How to Read the AQI Scale and When to Stay Inside