How to learn about there is smog near you right now

The fastest way to check smog in your area is to visit AirNow.gov, which shows real-time air quality for your zip code. Type in your location and you will see the current Air Quality Index (AQI) — a number from 0 to 500 that tells you how polluted the air is. Green means good air, yellow means moderate, orange means unhealthy for sensitive groups, red means unhealthy for everyone, and purple means hazardous. The map updates every hour.

Your phone can also tell you. Most weather apps include an air quality tab — check Apple Weather, Google Weather, or your phone's built-in weather app. If you use an iPhone, swipe to the air quality card. On Android, tap the air quality button in Google Weather. These apps pull data from the same government monitors as AirNow, so the numbers match.

If you want alerts sent to you automatically, read the AirNow app (free on iOS and Android) and set your location. You can choose to get notified when air quality hits orange, red, or purple. Text alerts are also available through some state environmental agencies — search "[your state] air quality alerts" to find the signup page for your specific state.

Key Takeaways

  • AirNow.gov and most weather apps show your current Air Quality Index updated hourly, with color codes from green (good) to purple (hazardous).
  • Smog is usually worst in the afternoon and early evening, when heat and traffic combine, and improves overnight as temperatures drop.
  • People with asthma, heart disease, or lung conditions should limit outdoor activity when the AQI is orange or higher, even if they feel fine.
  • Children and older adults are more sensitive to smog than healthy adults, so watch air quality forecasts if you have family in those groups.
  • Closing windows and running an indoor air filter can reduce smog indoors, but the most effective protection is staying inside during high pollution events.

What the Air Quality Index numbers actually mean

The AQI is a single number that combines five pollutants: ozone, particulate matter (PM2.5 and PM10), nitrogen dioxide, sulfur dioxide, and carbon monoxide. Each pollutant gets its own mini-score, and the highest one becomes your AQI. This matters because different people react to different pollutants — someone with asthma might be hit hard by ozone, while someone with heart disease might react more to particulate matter.

Here is what each range means for your day:

  • 0–50 (Green): Air quality is satisfactory. Everyone can be outdoors normally.
  • 51–100 (Yellow): Air quality is moderate. Unusually sensitive people might notice symptoms, but most people are fine.
  • 101–150 (Orange): Air quality is unhealthy for sensitive groups — children, older adults, and people with heart or lung disease should limit outdoor activity.
  • 151–200 (Red): Air quality is unhealthy for everyone. The general public should reduce outdoor activity; sensitive groups should avoid it.
  • 201–300 (Purple): Air quality is very unhealthy. Everyone should avoid outdoor activity.
  • 301+ (Maroon): Air quality is hazardous. Stay indoors with windows closed.

The number itself is less important than your personal risk. If you have asthma or heart disease, you should take action at orange. If you are healthy, you can usually wait until red. Check your own health history and talk to your doctor about what AQI level means you should stay inside.

When smog is worst and why it happens

Smog is usually worst in the afternoon and early evening, between 2 p.m. and 7 p.m. This is when the sun is strongest and ground-level ozone forms from reactions between car exhaust and sunlight. The heat also traps pollutants close to the ground instead of letting them rise and disperse. By evening, as the sun sets and temperatures drop, the air usually clears.

Smog gets worse in summer and early fall, when temperatures are high and the sun is strong. It also gets worse during heat waves, when stagnant air sits over a region for days without wind to push it away. Some areas — like valleys or cities surrounded by mountains — trap smog more easily because wind cannot blow it out.

Traffic is the biggest source of smog in most cities. Rush hour (7–9 a.m. and 4–6 p.m.) produces more pollution, but the worst smog does not hit until a few hours later, after the sun has had time to cook the exhaust into ozone. Industrial facilities, power plants, and wildfires also contribute, especially if they are upwind of your location.

What to do when smog is orange or higher

If you have asthma, heart disease, or lung disease, stay indoors when the AQI is orange or higher. Close your windows and doors, and run an air conditioner or HEPA filter if you have one. If you must go outside, wear an N95 or P100 mask — surgical masks do not filter smog. Avoid strenuous activity like running or heavy yard work, which makes you breathe harder and pull more polluted air into your lungs.

If you are healthy but the AQI is red or higher, reduce outdoor activity. This means no running, no sports practice, no long walks. Short trips outside are usually okay, but do not spend hours outdoors. Children and older adults should follow the same rules as people with chronic illness — they are more vulnerable even if they feel fine.

Indoors, close windows and doors to keep smog out. Run an air conditioner on recirculate mode (not fresh air mode) if you have one. A HEPA filter or air purifier can help, but it works best in a single room with the door closed — it cannot clean an entire house. Do not use a gas stove or fireplace, which adds more pollution inside. If you have a rescue inhaler, keep it with you.

How to prepare for smog season in your area

If you live in an area with regular summer smog, prepare before the season starts. Check the air quality forecast on AirNow.gov — it shows predicted AQI for the next few days. If your area typically has orange or red days in summer, talk to your doctor now about what you should do. Ask whether you need a rescue inhaler, whether your current medications are enough, and what symptoms mean you should call.

Stock up on N95 masks before smog season if you have a chronic lung or heart condition. They are cheaper and easier to find in spring than during a smog event. Make sure your air conditioner is serviced and working — a broken AC during a heat wave and smog event is dangerous. If you do not have AC, look into cooling centers in your area now; most cities open them during heat waves and they have filtered air.

Sign up for air quality alerts through your state environmental agency or the AirNow app. This way you will know when smog is coming before you make plans. If you exercise outdoors, move your routine to early morning when ozone levels are lowest, or switch to indoor workouts during smog season.

Understanding the difference between smog and other air pollution

Smog is not the same as all air pollution. Ozone smog (also called photochemical smog) is what you see on hazy summer days — it forms when sunlight cooks car exhaust and industrial emissions. Particulate matter (PM2.5 and PM10) is tiny dust, soot, and chemical particles that come from traffic, factories, wildfires, and construction. Both are tracked in the AQI, but they behave differently.

Ozone smog is worst in the afternoon when the sun is strongest. Particulate matter can be bad any time, and it does not clear as quickly — it can linger for days if there is no wind. Wildfires produce massive amounts of particulate matter, which is why air quality can be terrible even in areas far from the fire.

The AQI combines all pollutants into one number, so you do not need to track them separately. Just check the AQI and follow the color code. If you want to know which pollutant is causing the problem, AirNow.gov shows a breakdown — tap "Details" on the map to see which pollutant has the highest score.

Frequently Asked Questions

Can I exercise outdoors when the AQI is yellow?

If you are healthy, yes. Yellow means moderate air quality, and most people can exercise normally. If you have asthma, heart disease, or lung disease, avoid strenuous outdoor activity at yellow — stick to light activity like walking. If you feel symptoms like chest pain or shortness of breath, stop and go inside.

Does a regular face mask protect me from smog?

No. Surgical masks and cloth masks do not filter smog. You need an N95 or P100 mask, which has a tight seal and filters 95% or 99% of particles. Make sure it fits your face properly — if air leaks around the edges, it does not work. Masks do not filter ozone, only particulate matter, so they are most useful during wildfire smoke or dust events.

Why is air quality worse in my neighborhood than the next town over?

Air quality varies by location because pollution sources are not evenly spread. A busy highway, industrial facility, or power plant upwind of your area will make your air worse. Valleys and areas surrounded by mountains trap smog more easily. AirNow.gov shows monitors throughout your region, so you can see which neighborhoods have better air and plan outdoor activity accordingly.

Does rain clean the air of smog?

Yes, rain removes particulate matter and some gases from the air, so air quality usually improves during and after rain. Ozone smog also breaks down faster in cooler, wetter conditions. However, rain does not always clear the air completely — if pollution sources are still active, smog can return within hours after the rain stops.

What should I do if I do not have an air conditioner during a smog event?

Close all windows and doors to keep smog out. Use a HEPA air purifier in one room with the door closed, or go to a cooling center — most cities open them during heat waves and they have filtered air. If you have a fan, point it out a window to push indoor air outside rather than pulling smog in. Avoid strenuous activity that makes you breathe harder.