The molecule has a bent structure. The superoxide anion, , and the hydroperoxyl radical exist in
equilibrium in
aqueous solution: : + + The
pKa of HO2 is 4.88. Therefore, about 0.3% of any superoxide present in the cytosol of a typical cell is in the protonated form. It oxidizes
nitric oxide to nitrogen dioxide: Gaseous hydroperoxyl is involved in reactions that influence both
stratospheric and
tropospheric ozone. In the stratosphere and in low-
NOx regions of the troposphere, the hydroperoxyl radical can react directly with
ozone, forming
OH• and contributing to ozone depletion: + O3 → OH• + 2O2In these low-NOx regions of the troposphere, the hydroperoxyl radical also reacts with itself to form
hydrogen peroxide. This process serves as a major source of hydrogen peroxide in the troposphere: + → H2O2 + O2Conversely, in high-NOx regions of the troposphere, the hydroperoxyl radical reacts with NO to produce OH• and : + NO → OH• + Subsequent photolysis of the resulting leads to ozone formation. ==References==