Smog City West is a tool that shows you how air pollution builds up in your area

Smog City West is an interactive simulation created by the University of Illinois that lets you see how different pollution sources create smog in a city. You adjust factors like car traffic, power plant emissions, and sunlight, then watch how ground-level ozone forms in real time. It is designed to help you understand why some days have worse air quality than others, and what actually causes the haze you see on the horizon.

The tool focuses on ground-level ozone, which is different from the ozone layer high in the atmosphere. Ground-level ozone forms when sunlight hits nitrogen oxides and volatile organic compounds — gases that come from cars, factories, and other sources. On hot, sunny days with little wind, these chemicals react and create smog. Smog City West lets you experiment with turning down each source to see which ones matter most.

This is not a real-time air quality monitor for your specific location. Instead, it is an educational tool that teaches the science behind why air quality changes. If you want to know today's actual air quality in your area, you would use the EPA's AirNow website or your local air quality agency's data.

Key Takeaways

  • Smog City West shows how nitrogen oxides, volatile organic compounds, and sunlight combine to form ground-level ozone on hot days.
  • The simulation lets you adjust pollution sources like traffic and power plants to see which ones have the biggest effect on smog formation.
  • Ground-level ozone is different from the ozone layer; it forms near the ground and is the main ingredient in smog you can see.
  • The tool is educational and does not show real-time air quality for your location — use AirNow or your local agency for current conditions.

How the simulation works and what you can change

When you open Smog City West, you see a simplified city with a few main pollution sources: cars on the road, a power plant, and a factory. You also see a sun that moves across the sky and a wind indicator. The interface gives you sliders to adjust each source up or down, and a clock so you can speed up or slow down time.

As you change the sliders, you watch the air quality meter and the visual smog in the city change in response. If you turn down car traffic, you see fewer nitrogen oxides being released. If you reduce the power plant output, emissions drop. The simulation shows you the chemical reactions happening — how nitrogen oxides and volatile organic compounds interact with sunlight to create ozone. On a cloudy day or with low traffic, the air stays clearer. On a hot, sunny day with heavy traffic, smog builds up fast.

The point is to build intuition about cause and effect. Many people think smog just happens on hot days, but the simulation shows you that it requires a specific combination: pollution sources, sunlight, and stagnant air. If any one of those is missing or reduced, smog formation slows down.

Why ground-level ozone is different from the ozone layer

The ozone layer is a natural part of the upper atmosphere that protects us from ultraviolet radiation. Ground-level ozone is a pollutant that forms near the ground when sunlight triggers a chemical reaction between nitrogen oxides and volatile organic compounds. They are the same molecule, but in different places and with very different effects on human health.

Ground-level ozone is harmful to breathe. It irritates your lungs and airways, especially during exercise or outdoor activity. People with asthma, children, and older adults are more sensitive to it. On days when the EPA issues an air quality alert, ground-level ozone is usually the main reason. Smog City West helps you see why those alerts happen — it is not random, but the result of specific pollution sources reacting with weather conditions.

What pollution sources create the most smog

In Smog City West, you can experiment with turning down each source to see which one makes the biggest difference. In real cities, the answer varies by location and season. In urban areas with heavy traffic, cars and trucks are often the largest source of nitrogen oxides. In areas with coal or natural gas power plants, those facilities can be major contributors. Refineries, chemical plants, and other industrial sources add volatile organic compounds.

The simulation shows that reducing any single source helps, but the effect is not always equal. On a day with strong wind and clouds, even high pollution levels do not create much smog because the chemicals do not have time to react. On a still, hot, sunny day, even moderate pollution levels create visible haze. This is why air quality forecasts focus on weather as much as pollution levels — the same amount of emissions creates different smog depending on the conditions.

How to use Smog City West to understand your local air quality

Start by running the simulation on a typical summer day — hot, sunny, and still. Watch how smog builds up over the course of the day. Then try turning down one pollution source at a time and see what changes. This gives you a mental model of how your local air quality actually works.

When you see an air quality alert in your area, think back to what you learned in the simulation. Was it a hot, sunny day? Were there pollution sources nearby? Did the wind die down? The simulation does not predict your specific location's air quality, but it teaches you the logic behind why certain days are worse than others. That understanding helps you decide when to limit outdoor activity, especially if you have asthma or heart disease.

You can also use the simulation to understand why air quality regulations target specific sources. If the simulation shows that reducing car traffic makes a big difference, that explains why cities implement congestion pricing or promote electric vehicles. If power plants are the main source, that explains why regulations focus on those facilities.

Finding real air quality data for your location

Smog City West teaches the science, but it does not show you today's actual air quality. To find that information, visit AirNow.gov, which is run by the EPA and shows current air quality conditions for your zip code. You can also check your local air quality agency's website — most cities and counties have one that updates hourly or daily.

AirNow uses the Air Quality Index, or AQI, which ranges from 0 to 500. An AQI below 50 is good. Between 50 and 100 is moderate — sensitive groups should consider limiting outdoor activity. Above 100 is unhealthy for sensitive groups. Above 150 is unhealthy for everyone. The index tells you not just whether the air is bad, but how bad it is and who should be concerned.

Why air quality matters for your health

Ground-level ozone and other air pollutants enter your lungs when you breathe. Ozone irritates the lining of your airways, causing coughing, wheezing, and shortness of breath. Repeated exposure over time can reduce lung function and increase the risk of respiratory disease. People with asthma are more sensitive because their airways are already inflamed.

Air pollution also affects your heart. Fine particles can enter the bloodstream and trigger inflammation, which increases the risk of heart attack and stroke. Children are at higher risk because their lungs are still developing. Older adults are at higher risk because their bodies are less able to repair damage. Even healthy people can feel the effects on a bad air day — difficulty exercising, chest tightness, or a scratchy throat.

On days when the AQI is high, limit strenuous outdoor activity, especially for children and older adults. Keep windows closed if the air outside is worse than inside. If you have asthma or heart disease, follow your doctor's information about when to stay indoors and whether to use your rescue inhaler.

Frequently Asked Questions

Can I use Smog City West to predict tomorrow's air quality?

No. Smog City West is a teaching tool that shows how smog forms, not a forecast model. To predict air quality, you need real weather data, real pollution measurements, and complex computer models. Use AirNow.gov or your local air quality agency for forecasts and current conditions.

Why does smog form more on hot days?

Heat provides the energy that drives the chemical reaction between nitrogen oxides and volatile organic compounds. On cool days, even with the same pollution levels, the reaction happens much more slowly. Smog City West lets you adjust the sun's intensity to see this effect in action.

If I reduce car traffic in the simulation, does that mean banning cars will solve air pollution?

Reducing car traffic helps, but it is not a complete solution. The simulation shows that power plants and factories also contribute. Real air quality improvement usually requires action on multiple sources — cleaner vehicles, cleaner power plants, and industrial controls. Smog City West helps you see why regulations target different sectors.

Is the ozone in smog the same as the ozone layer?

It is the same molecule, but in different places. The ozone layer is high in the atmosphere and protects us from ultraviolet radiation. Ground-level ozone forms near the ground and is a pollutant that harms your lungs. Smog City West focuses on ground-level ozone because that is what affects your health on bad air days.

What should I do on a day when the air quality is bad?

Check the AQI on AirNow.gov. If it is above 100, limit strenuous outdoor activity, especially if you have asthma, heart disease, or are very young or old. Keep windows closed and use air conditioning with a clean filter if you have it. If you must go outside, consider wearing an N95 mask, which filters out fine particles and ozone.