GHO measurement interference❑ Nitrogen dioxide, NO2, is not regarded as a gross photochemical oxidant. However, it isapproximately 15% as efficient as O3in oxidizing iodide to iodine(0), and acorrection is made in measurements for the positive interference of NO2.❑ Sulfur dioxide, SO2, is oxidized by O3and produces a negative interference forwhich a measurement correction must also be made.