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| city smog |
The brownish haze seen mostly in the summer and especially around big cities is smog. The main ingredient in smog is ozone. When ozone is high up in the atmosphere, it helps protects us from the Sun’s stronger rays. But near the ground, ozone forms smog when sunlight and heat interact with oxygen and particles produced by the burning of fossil fuels. Smog makes it hard for some people to breathe, especially those with asthma. "Ozone alerts" are not just for Los Angeles (famous for its smog). Many cities in the U.S. issue them through newspapers, TV, and radio stations to let people know when the air can be unhealthy for outdoor activities.
