How Much Air Pollution Is Too Much? | AQI Cutoffs

Air that looks “fine” can still irritate lungs, eyes, and the throat. Air that smells sharp might be harmless, or it might be a sign to stay indoors. So instead of guessing, use a simple yardstick that’s made for day-to-day decisions: the Air Quality Index (AQI).

The AQI rolls several pollutant readings into one scale from 0 to 500. Higher numbers mean dirtier air and a higher chance of symptoms. Use it to choose the lighter option on rough days.

How Much Air Pollution Is Too Much? AQI Cutoffs That Matter

If you want one rule you can apply in seconds, start here: once the AQI is over 100, some people should change plans. Over 150, most people should scale back outdoor time, especially anything that raises your breathing rate.

The table below uses the U.S. color categories and ranges, as shown on AirNow’s AQI basics. Treat these as action triggers, not a moral scorecard.

AQI Range	Color And Label	What It Means For A Typical Day
0–50	Green (Good)	Normal outdoor plans usually feel fine. Great time for long walks and open windows.
51–100	Yellow (Moderate)	Most people feel okay. If you’re unusually sensitive, keep hard workouts shorter.
101–150	Orange (Unhealthy For Sensitive Groups)	Kids, older adults, pregnant people, and those with heart or lung disease should dial back prolonged outdoor effort.
151–200	Red (Unhealthy)	Many people notice irritation. Swap intense outdoor exercise for an indoor option.
201–300	Purple (Health Alert)	Air is harsh for most people. Stay inside as much as you can and keep activity light.
301–400	Maroon (Hazardous)	Skip outdoor time unless it’s necessary. If you must go out, keep it brief and protect your breathing.
401–500	Maroon (Hazardous)	Emergency conditions. Avoid being outside. Watch for symptoms and follow local alerts.

Why 100 And 150 Feel Like Turning Points

AQI 0–100 often lines up with normal days for many people. Past 100, at least one pollutant has crossed a health-based level. Past 150, longer outdoor time starts to feel rough for many.

Still, your body is the final judge. If your eyes burn, your chest feels tight, or you’re coughing after a short time outside, treat that as your signal to step back even if the AQI looks lower.

What The AQI Measures And What It Misses

The AQI is a public messaging tool, not a lab report. It can tell you when the air is likely to bother you, and it helps you compare days. It won’t explain the exact mix you breathed at your doorstep, minute by minute.

Pollutants That Often Drive The Number

• Fine particles (PM2.5): Tiny bits from smoke, traffic, and burning. These are a common driver during wildfire smoke.
• Coarse particles (PM10): Larger dust and dirt that can rise in dry, windy weather.
• Ozone at ground level: A gas that can sting airways, often higher on hot, sunny afternoons.
• Nitrogen dioxide and sulfur dioxide: Gases tied to combustion and industrial sources, sometimes spiking near busy roads or facilities.
• Carbon monoxide: A gas from incomplete combustion that can rise near fires or heavy traffic.

What Can Make The AQI Feel Wrong

Three things trip people up: monitor distance, update lag, and the “worst pollutant wins” rule. A moderate ozone day can still have a smoky pocket nearby.

Quick Ways To Check Air Quality Before You Step Outside

You don’t need a fancy setup. You need a habit. Check air quality the same way you check rain.

1. Look up today’s AQI on a trusted map or app, then tap into the hourly view. A single daily number can hide a nasty afternoon spike.
2. Watch the pollutant name next to the AQI. PM2.5-driven days call for different moves than ozone-driven days.
3. Check nearby monitors if your app shows them. If numbers vary a lot across town, trust the one closest to you.
4. Use your symptoms as a cross-check. If your body reacts, treat that as your warning, even if the index looks mild.

What To Do When The AQI Is High

“Stay inside” is blunt advice. Real life still happens. The goal is to cut dose: less time in bad air, less heavy breathing, and cleaner air where you spend most hours.

Dial Back Outdoor Effort First

• Shift workouts to early morning or later evening if ozone is the driver.
• Swap runs for a lighter walk when the AQI rises, or choose an indoor session.

Errands still happen. If you have to drive in smog or smoke, set the car vents to recirculate, keep windows shut, and avoid idling behind buses. Parking a block away from a road can lower what you breathe. When you get home, wash hands and face to clear grit. Change clothes if you were outside long.

Make A Clean-Air Room At Home

If the air outside is rough, your home can be your relief zone. Pick one room where you spend a lot of time and make it the cleanest air you can manage.

• Close windows and doors.
• Run a HEPA air cleaner sized for the room, or use a box-fan filter setup with a high-rated HVAC filter.
• Avoid indoor sources like candles, incense, and frying that can add particles.

Use Masks The Right Way For Smoke

Cloth masks don’t block fine smoke particles well. If you need to be outside during PM2.5 days, a well-fitted respirator like an N95 can cut what you breathe. Fit matters more than brand. Gaps around the nose or cheeks waste the effort.

Numbers That Help When You Want More Than One Index

You might also see pollutant numbers like “PM2.5: 28 µg/m³” in apps. For a reference point, the WHO global air quality guidelines (2021) list levels used by many researchers and agencies.

Pollutant	WHO Guideline Level	Averaging Time
PM2.5	15 µg/m³	24-hour mean
PM10	45 µg/m³	24-hour mean
Ozone (O₃)	100 µg/m³	8-hour mean
Ozone (O₃)	60 µg/m³	Peak-season mean of daily max 8-hour values
Nitrogen dioxide (NO₂)	25 µg/m³	24-hour mean
Sulfur dioxide (SO₂)	40 µg/m³	24-hour mean
Carbon monoxide (CO)	4 mg/m³	24-hour mean

A Practical Way To Combine AQI And Pollutant Numbers

If an app shows both, let the AQI drive your decision and use the pollutant number to explain the “why.” When PM2.5 is high, put your energy into filtration and masks. When ozone is high, put your energy into timing and intensity, since ozone tends to peak later in the day.

Indoor Air Steps That Pay Off On Bad Days

Bad outdoor air often turns into bad indoor air through leaks, door openings, and HVAC intake. You can shrink that leak without turning your house into a sealed bunker.

Quick Setup Checklist

• Pick one main room and run your filter there all day.
• Keep doors to that room closed if the rest of the home is drafty.
• If you have a gas stove, use the vent hood while cooking.

What About Opening Windows At Night?

Sometimes night air is cleaner. Sometimes it’s worse, especially during smoke events or when pollution settles close to the ground. Check the hourly AQI first. If the number drops and stays down, a short airing-out can feel good. If it rises again, close up and return to filtration.

Who Should Be Extra Careful

Some bodies react faster. Kids breathe more air per pound than adults. Older adults may have less reserve. People with asthma, COPD, heart disease, or who are pregnant often feel bad-air days sooner.

If you fit one of these groups, treat AQI over 100 as your cue to cut outdoor exertion. Keep rescue inhalers and meds where you can reach them, and stick to the plan your clinician has already given you.

When To Treat Symptoms As A Medical Problem

A scratchy throat after a short walk can be a normal response to dirty air. Signs that call for medical care are stronger and persistent.

• Shortness of breath at rest
• Chest pain, pressure, or a racing heartbeat that won’t settle
• Wheezing that doesn’t improve with your usual medicine
• Confusion, fainting, or severe headache
• Blue lips or face

If any of these show up, seek urgent care. If symptoms are mild but keep returning on polluted days, bring it up at your next visit and ask for a plan you can follow when the AQI spikes.

A One-Page Outdoor Plan For Any AQI

Use this as a quick routine. It keeps your choices steady, even when the numbers change hour by hour.

1. Check AQI and the main pollutant. If it’s PM2.5, prep masks and filtration. If it’s ozone, plan around afternoon peaks.
2. Match activity to the range. Under 100: normal. 101–150: lighter effort for sensitive groups. 151+: shift indoors.
3. Cut exposure time. Short trips beat long hangs when air is rough.
4. Pick cleaner routes. Step away from traffic corridors when you can.
5. Protect your clean-air room. Keep it closed, filtered, and free of smoke from cooking or candles.
6. Watch your body. If you’re coughing or tight-chested, step back. Your comfort is data.

Most days, if you ask “how much air pollution is too much?”, let the AQI be your trigger and keep one clean room ready.