Mr. SMOG is California's tool for tracking air pollution in real time

Mr. SMOG is a website and mobile app run by the South Coast Air Quality Management District (SCAQMD), which covers Los Angeles, Orange County, San Diego, and Ventura County in California. It shows you the current air quality where you are, updated hourly, so you can decide whether to exercise outdoors, keep windows closed, or stay inside.

The tool displays the Air Quality Index (AQI), a number that tells you how polluted the air is right now. The higher the number, the worse the air. Mr. SMOG also breaks down which pollutants are present — ozone, nitrogen dioxide, particulate matter — and explains what each one means for your health.

You do not need to create an account or pay anything. You can check conditions for your zip code, a specific address, or any location in the four-county region. The app sends push notifications if air quality drops below a level you choose, so you do not have to check manually.

Key Takeaways

  • Mr. SMOG shows hourly air quality readings for Los Angeles, Orange, San Diego, and Ventura counties, updated from monitoring stations across the region.
  • The Air Quality Index number ranges from 0 to 500, with higher numbers meaning worse air and greater health risk.
  • You can set alerts to notify you when air quality reaches a level that matters to you — for example, when it becomes unhealthy for sensitive groups.
  • The tool identifies which pollutant is the main problem on any given day, so you know whether to worry about ozone, smoke, or dust.

How the Air Quality Index works

The AQI is a single number that summarizes how clean or dirty the air is. It ranges from 0 to 500. A reading of 0 to 50 is green and means air quality is good. A reading of 51 to 100 is yellow and means it is moderate — most people are fine, but people with asthma or heart disease should limit outdoor activity. A reading of 101 to 150 is orange and means it is unhealthy for sensitive groups. A reading of 151 to 200 is red and means it is unhealthy for everyone. A reading above 200 is purple or maroon and means it is very unhealthy or hazardous.

Mr. SMOG calculates the AQI by measuring five main pollutants: ground-level ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and particulate matter (PM2.5 and PM10). The pollutant with the worst reading becomes the "primary pollutant" for that hour, and its reading becomes the AQI for your location.

The readings come from air monitoring stations operated by SCAQMD. These stations are placed across the four-county region and measure pollution continuously. Mr. SMOG updates the data every hour, so the number you see reflects conditions from the most recent hour, not a prediction of what will happen later.

Where to find Mr. SMOG and how to use it

You can access Mr. SMOG through the SCAQMD website at www.aqmd.gov or by downloading the Mr. SMOG mobile app from the Apple App Store or Google Play Store. The website and app work the same way.

When you open Mr. SMOG, it will ask for your location. You can allow it to use your phone's GPS, or you can type in a zip code or street address. Once you enter a location, the app shows you the current AQI, the primary pollutant, and a color-coded map of the region showing air quality in different areas.

You can also set up alerts. Tap the settings or notification icon and choose the AQI threshold that matters to you. For example, if you have asthma, you might set an alert for when the AQI reaches 101 (unhealthy for sensitive groups). When air quality hits that level, your phone will send you a notification so you can plan your day accordingly.

What different AQI levels mean for your health

The AQI number tells you not just how polluted the air is, but what you should do about it. At 0 to 50 (green), air quality is good and you can exercise and spend time outdoors normally. At 51 to 100 (yellow), air quality is moderate. People without lung or heart disease are usually fine, but people with asthma, emphysema, or heart conditions should limit strenuous outdoor activity.

At 101 to 150 (orange), air quality is unhealthy for sensitive groups. Children, older adults, and anyone with asthma, COPD, or heart disease should avoid outdoor activity. At 151 to 200 (red), air quality is unhealthy for everyone. Most people should avoid outdoor activity, and sensitive groups should stay indoors. At 201 and above (purple or maroon), air quality is very unhealthy or hazardous. Everyone should avoid outdoor activity, and sensitive groups should remain indoors and keep windows closed.

Mr. SMOG includes these health recommendations on the app itself, so you do not have to memorize the ranges. The color and the description tell you what to do.

Why air quality varies by location and time

Air quality is not the same everywhere in the four-county region. A monitoring station in downtown Los Angeles might show a different AQI than one in San Diego or in the inland valleys. This happens because pollution sources are not evenly distributed — some areas have more traffic, more industry, or more wildfire smoke depending on wind patterns.

Air quality also changes throughout the day. Ozone, the most common pollutant in Southern California, typically builds up during the afternoon and early evening as the sun heats the air. In the morning, air quality is often better. In winter, air quality can worsen because cooler air traps pollution closer to the ground. In summer, wildfire smoke can arrive suddenly and make air quality worse across a wide area.

Mr. SMOG shows you the conditions at the monitoring station closest to your location, so the reading reflects your neighborhood rather than the entire region. If you are planning to travel to another part of the four counties, you can check the air quality there by entering a different zip code.

Understanding the pollutants Mr. SMOG measures

Mr. SMOG tracks five main pollutants, and understanding what they are helps you know what you are breathing. Ground-level ozone is the most common problem in Southern California. It forms when sunlight reacts with pollution from cars and industry. It irritates your lungs and makes breathing harder, especially during exercise. Nitrogen dioxide comes mainly from vehicle exhaust and power plants. It can trigger asthma and reduce lung function over time.

Particulate matter (PM2.5 and PM10) is tiny dust, soot, and smoke particles. PM2.5 particles are so small they can lodge deep in your lungs and enter your bloodstream. They come from vehicle exhaust, wildfires, dust, and industrial sources. Sulfur dioxide comes from burning coal and oil, and it irritates airways. Carbon monoxide is a colorless, odorless gas from vehicle exhaust that reduces the oxygen your blood can carry.

On the Mr. SMOG app, you can see which of these pollutants is the primary one on any given day. This tells you what is causing the poor air quality and helps you understand what you are being exposed to.

Frequently Asked Questions

Does Mr. SMOG predict future air quality?

No. Mr. SMOG shows current conditions updated hourly, not forecasts. SCAQMD does publish air quality forecasts on its website, but Mr. SMOG itself displays only the most recent measurements from monitoring stations.

Can I use Mr. SMOG outside the four-county region?

Mr. SMOG covers only Los Angeles, Orange, San Diego, and Ventura counties. If you live elsewhere in California or the United States, you can check air quality through the EPA's AirNow website (www.airnow.gov), which covers the entire country.

Why does the AQI sometimes jump from one hour to the next?

Air quality can change quickly because wind patterns shift, traffic increases, or wildfire smoke arrives. Mr. SMOG updates hourly, so you may see a noticeable change between readings. This is normal and reflects real changes in pollution levels, not an error.

What should I do if the AQI is unhealthy?

If the AQI is 101 or higher, limit outdoor activity, especially strenuous exercise. Keep windows closed, use air conditioning with a clean filter if you have it, and consider wearing an N95 mask if you must go outside. People with asthma or heart disease should take extra precautions and may want to stay indoors.