Ozone is formed secondarily by a chemical reaction between nitrogen oxides, volatile organic compounds, and carbon monoxide in the presence of sunlight. Produced by vehicle exhaust, industrial emissions, gasoline vapors, and chemical solvents, ozone is one component of photochemical smog. Health effects include chest pain, coughing, nausea, throat irritation and congestion, irritations of the respiratory system, reduced lung function, aggravated asthma, inflamed and damaged cells that line the lungs, aggravated chronic lung diseases, and permanent lung damage.

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