Potential impacts of supersonic aircraft emissions on ozone and resulting forcing on climate: An update on historical analysis

Commercial aircraft flying at supersonic speeds in the lower stratosphere are being discussed once again after a hiatus of almost 20 years. Potential environmental effects from fleets of such aircraft need to be understood for their possible impacts on stratospheric ozone; levels of stratospheric ozone determine the amount of biologically harmful ultraviolet radiation from the Sun reaching the Earth's surface. Changes in the distribution and concentrations of ozone also have implications on climate. This study evaluates the potential impact on stratospheric ozone and on climate forcing from different levels of nitrogen oxides (NOx) and water vapor (H2O) emissions from supersonic transport. Toward establishing a baseline relative to prior studies, we also compare these new analyses with results from the 1999 aviation assessments, using the same aviation emissions. Despite the understanding of atmospheric processes used in studying chemistry-climate interactions have been greatly enhanced over the last 20 years, this study finds that, for the baseline scenario, the resulting effects on stratospheric ozone are similar to those from many of the models in the prior assessment, although with a stronger ozone sensitivity to NOx emissions. We show that the resulting ozone effects largely depend on the NOx and H2O emission levels and the net changes in stratospheric ozone are determined by the chemical interactions between different ozone production and depletion cycles. We also calculate the radiative forcing impact for the resulting changes in the distributions of ozone and H2O, and confirm that stratospheric H2O emissions are an important factor in potential climate impacts from supersonic aircraft emissions.