Potential impacts of CF<sub>3</sub>I on ozone as a replacement for CF<sub>3</sub>Br in aircraft applications

Abstract

Abstract. Iodotrifluoromethane (CF 3 I) has been considered to be a candidate replacement for bromotrifluoromethane (CF 3 Br), which is used in aircraft for fuel inerting and for fire fighting. In this study, the chemical effects of aircraftreleased CF 3 I 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 CF 3 I were in the range of 0.07 to 0.25. As a sensitivity study, we also analyzed CF 3 I 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 CF 3 I 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 CF 3 I is released from aircraft is a dominant factor in its ozone depletion effects. On the assumption that the CF 3 I emission profile is representative of actual release characteristics, aircraftreleased CF 3 I has much lower impacts than CF 3 Br.

Potential impact of iodinated replacement compounds CF<sub>3</sub>I and CH<sub>3</sub>I on atmospheric ozone: a three-dimensional modeling study

“…The MOZART-3 CTM of the global atmosphere is one of the leading tools for the study and prediction of current and future atmospheric composition and of possible effects from anthropogenic emissions into the atmosphere. The model was updated to incorporate the complete set of iodine chemistry used in the previous 2-D modeling study by Li et al (2006). Major chemistry reactions and rates that could impact effects of CF 3 I and CH 3 I on atmospheric ozone concentrations relative to earlier studies (e.g., Solomon et al, 1994) include: CF 3 I, CH 3 I, IO, HOI, INO, INO 2 , IONO 2 , OIO, ICl, IBr, and I 2 absorption cross-sections for photochemical reactions (Sander et al, 2003(Sander et al, , 2007, thermal reaction-rate coefficients of CH 3 I + OH → I + H 2 O + CH 2 O, and catalytic cycles involving reactions of IO with ClO or BrO and I with O 3 , HO 2 or O (see Li et al, 2006).…”

“…A thorough understanding of the potential effects of the iodine compounds on stratospheric ozone builds upon the previous twodimensional studies (Li et al, 2006). Using the available analyses of global source emissions for CH 3 I (Lee-Taylor and Redeker, 2005;Bell et al, 2002), background CH 3 I concentrations in the atmosphere are also evaluated and compared with observational data towards determining the capabilities of 3-D models towards accounting for CH 3 I chemistry.…”

“…Although current atmospheric concentrations of iodine-containing gases are very small, CF 3 I and CH 3 I are both a potentially significant source of atmospheric iodine despite being very short-lived and are of interest in the upper troposphere and lower stratosphere as a source of iodine radicals for ozone destruction (WMO, 2007). Ozone destruction in the lower stratosphere due to catalytic cycles involving iodine was not well understood, but recent laboratory studies have improved the understanding of atmospheric chemical processes of iodine species including their photochemistry (WMO, 2007;Li et al, 2006;Bösch et al, 2003).…”

“…As the next stage for further potential impact analysis of the compounds on ozone beyond the previous studies using 2-D models (Li et al 2006;Solomon et al, 1994), ODPs of the two iodinated VSL replacement compounds CF 3 I and CH 3 I are evaluated using the National Center for Atmospheric Research (NCAR) Model for OZone And Related Tracers version 3 (MOZART-3) 3-D chemistry-transport model (we also update the ODP using the latest version of the University of Illinois at Urbana-Champaign (UIUC) 2-D chemical-radiative-transport (CRT) model). A thorough understanding of the potential effects of the iodine compounds on stratospheric ozone builds upon the previous twodimensional studies (Li et al, 2006).…”

Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br, and CF3I

“…3 This property increases the potential for CF 3 I applications, for example, as a plasma etching gas 4 and as a possible replacement for CF 3 Br in fire extinguishing systems. 5 This series of CF 3 X molecules have C 3V symmetry, and the main effect of a change in the substituent X is the elongation and subsequent weakening of the C-X bond. The effect on the overall electronic structure of the molecule on changing X is not dramatic, since the orbitals of the X atom show little mixing with the CF 3 orbitals.…”