Often visible as smog, ozone is formed in the atmosphere from hydrocarbons and nitrogen oxides, two major pollutants emitted by automobiles, react with sunlight.
                    
                
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                Aozone is formed in the atmosphere from
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                Bozone is formed in the atmosphere when
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                Cozone is formed in the atmosphere, and when
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                Dozone, formed in the atmosphere when
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                Eozone, formed in the atmosphere from
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