Potential impacts of CF₃I on ozone as a replacement for CF₃Br in aircraft applications

Abstract. Iodotrifluoromethane (CF₃I) has been considered to be a candidate replacement for bromotrifluoromethane (CF₃Br), which is used in aircraft for fuel inerting and for fire fighting. In this study, the chemical effects of aircraft-released CF₃I on atmospheric ozone were examined with the University of Illinois at Urbana-Champaign two-dimensional chemical-radiative-transport (UIUC 2-D CRT) model. Using an earlier estimate of the aircraft emission profile for tank inerting in military aircraft, the resulting equivalent Ozone Depletion Potentials (ODPs) for CF₃I were in the range of 0.07 to 0.25. As a sensitivity study, we also analyzed CF₃I emissions associated with fuel inerting if it were to occur at lower altitudes using an alternative estimate. The model calculations of resulting effects on ozone for this case gave ODPs≤0.05. Furthermore, through interactions with the National Institute of Standards and Technology (NIST), we analyzed the potential effects on ozone resulting from using CF₃I in fire fighting connected with engine nacelle and auxiliary power unit applications. The scenarios evaluated using the NIST estimate suggested that the ODPs obtained by assuming aircraft flights occurring in several different latitude regions of the Northern Hemisphere are extremely low. According to the model calculation, the altitude where CF₃I is released from aircraft is a dominant factor in its ozone depletion effects. On the assumption that the CF₃I emission profile is representative of actual release characteristics, aircraft-released CF₃I has much lower impacts than CF₃Br.