Ozone

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Ozone is a colorless and odorless gas. Ozone is a secondary pollutant, rather than one directly emitted, formed when hydrocarbons (commonly known as VOCs) and nitrogen oxides combine in the presence of sunlight. High concentrations of tropospheric ozone are the result of smog or haze conditions caused principally by human activity. The stratospheric ozone layer protects life on Earth from dangerous levels of ultraviolet light from the Sun.