In atmospheric chemistry, the Leighton relationship is an equation that determines the concentration of tropospheric ozone in areas polluted by the presence of nitrogen oxides.
Ozone in the troposphere is primarily produced through the photolysis of nitrogen dioxide by photons with wavelengths (λ) less than 420 nanometers,[1] which are able to reach the lowest levels of the atmosphere, through the following mechanism:[2]: pg.
22 The symbol M represents a "third body", an unspecified molecular species that must interact with the reactants in order to carry away energy from the exothermic reaction.
Since O(3P) is very reactive and O2 is abundant, O(3P) can be assumed to be in steady state, and thus an equation linking the concentrations of the species involved can be derived, giving the Leighton relationship:[2][3] This equation shows how production of ozone is directly related to the solar intensity, and hence to the zenith angle, due to the reliance on photolysis of NO2.
This relationship is named after Philip Leighton, author of the 1961 book Photochemistry of Air Pollution, in recognition of his contributions in the understanding of tropospheric chemistry.[2]: pg.