On potential effects from the aviation and refrigeration sectors on ozone and climate

Global aviation operations and refrigeration sectors contribute to the global ozone budget and to climate change via emissions of relevant gases and particles, subsequently followed by a complex set of chemical and physical processes. For the refrigeration sector, iodotrifluoromethane (CF3I) and methyl iodide (CH3I) are two very short‐lived substances (VSLSs) with potential commercial applications in refrigeration to replace long-lived hydrofluorocarbons (HFCs), which are of concern for climate. Iodine atoms from CF3I and CH3I, once released into the atmosphere, can react catalytically to destroy ozone and potentially add to stratospheric ozone depletion if the iodine gets into the stratosphere. This study evaluates their potential impact on atmospheric ozone based on recent advances in the understanding of atmospheric iodine chemistry. It also reconsiders the policy-relevant metric of ozone depletion potentials (ODPs) for such short‐lived chemicals. Analyses of potential effects of ozone for some of these chemicals show very small effects on the total ozone column and almost all ozone loss occurring in the lower troposphere, where these VSLSs would essentially reduce the overall human‐produced ozone pollution. A new metric is introduced to help clarify the effects of these very short‐lived chemicals on the global atmosphere for policy considerations. For the aviation sector, after a hiatus of more than 20 years, the possibility of commercial and business supersonic aircraft that fly in the lower stratosphere is being discussed and specific designs are under consideration. The impact on stratospheric ozone from potential fleets of supersonic aircraft have raised concerns and is of interest for evaluation of possible new aircraft designs. The first part of this dissertation revisits the ozone and climate impacts from a potential fleet of supersonic aircraft that were examined in scientific assessments over 20 years ago. This study uses an advanced global atmospheric model to provide a modern baseline relative to the prior analyses. The results show that the derived impact on the distribution of atmospheric ozone is similar to the models used in the earlier analyses. The results also indicate that the effects on ozone and radiative forcing show a strong sensitivity to the particular levels of nitrogen oxides (NOx) and water vapor (H2O) emissions, and a stronger ozone sensitivity to NOx emission is found in new analyses compared to prior studies. To investigate the sensitivity of atmospheric responses of ozone and radiative forcing from supersonic aircraft emissions of NOx and H2O at varying altitudes, the second part of this analysis conducts a series of sensitivity studies as a function of cruise altitude using the same model used in the first part. The effects on total column ozone and radiative forcing show a strong dependence from cruise altitude, especially for flights above 17 km. Impacts on stratospheric ozone can be reduced by either flying at lower cruise altitudes or by the development of low NOx emitting combustors. This study can potentially help facilitate technological development and optimize aircraft operations towards making supersonic travel environmentally friendly.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste