THE OZONE DEPLETION POTENTIAL DEFINITION AND VERY SHORT- LIVED SUBSTANCES (CF3I And HCFOs)
The ozone depletion potential (ODP) concept was initially developed to measure the potential impact of long‐lived gases, those with multi-year atmosphere lifetimes, on stratospheric ozone.
For very short-lived substances (VSLSs) with atmospheric lifetimes less than a few months, such as the HCFOs and CF3I (iodotrifluoromethane), most of their effect occur in the troposphere. A recent paper [1] reconsiders the concept of ozone depletion potentials (ODPs) for such short‐lived chemicals to properly account for their impact on stratospheric and tropospheric ozone, noting that it is important to recognize that tropospheric ozone has increased substantially over the last century, largely as the result of emissions from human activities.
The ODP concept uses the decline in total ozone column (troposphere and stratosphere) because it is the total column decrease that is of concern to protecting humans and the biosphere from
increases in ultraviolet radiation. Analyses of potential effects of ozone for VSLSs such as CF3I showed 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. The paper concludes that the stratospheric ozone column ozone decrease due to CF3I emissions was essentially zero (within statistical error), while producing significant changes in tropospheric ozone.
The paper suggests that policy considerations for VSLSs not only consider the traditional total column values for ODP but should also account for the ODP due to stratospheric ozone loss only, termed Stratospheric ODP (SODP), to help the ODP concept satisfy its primary requirement of protecting stratospheric ozone. For long‐lived species, ODP and SODP values should be nearly the same because almost all the ozone depletion occurs in the stratosphere. However, for many VSLSs, especially those with very short atmospheric lifetimes, ODP and SODP values can be quite different.
To further investigate the SODP concept, the paper examined the most recent published literature for ODPs determined for other VSLSs, including HCFO-1233zd(E). For this HCFO the paper concluded that most of the total ozone column decrease occurred in the troposphere (~ 53%), reducing the already extremely small potential effect on stratospheric ozone even further.
[1] Revising the Ozone Depletion Potentials Metric for Short‐Lived Chemicals Such as CF3I and CH3I
Jun Zhang, Donald J. Wuebbles, Douglas E. Kinnison, and Alfonso Saiz‐Lopez, JGR Atmospheres, Volume 125, Issue9 , 16 May 2020, https://doi.org/10.1029/2020JD032414
Additional Information
• See HCFOs, HBFOs, Stratospheric Ozone and Climate Change on the EFCTC website.
• CF3I, iodotrifluoromethane is being considered for use as a component in refrigerants such as R-466A for use in air conditioning and refrigeration. It is a very short-lived substance with a globally averaged atmospheric lifetime of about 6 days. It photolyzes rapidly to form reactive iodine atoms under a sunlit atmosphere and its lifetime and fate of decomposition products depends largely on location of the emissions.