Air pollution in a city in China was studied to see where it comes from. The study used a computer model to look at how pollution moves and where it comes from. They found that most of the pollution in the city comes from nearby sources like factories and cars. When the weather is bad, the pollution gets worse. Factories that make glass are a big source of pollution in the city. If emissions from these sources are reduced, the pollution levels in the city could go down by a significant amount.