In atmospheres that receive hydrocarbon and NO pollution accompanied by intensesunlight and stagnant air masses, oxidantstend to form.❑ Gross photochemical oxidant (GHO) is a substance in the atmosphere capable ofoxidizing iodide ion to elemental iodine and is used to indicate the presence ofphotochemical smog and its severity.❑ The primary oxidant in the atmosphere is ozone. Other atmospheric oxidants includeH2O2, organic peroxides (ROOR'), organic hydroperoxides (ROOH), andperoxyacyl nitrates such as peroxyacetyl nitrate (PAN).