Revising the Ozone Depletion Potentials Metric for Short-Lived Chemicals such as CF3I and CH3I

Ozone Depletion Potentials (ODPs) are an important metric in national and international policy for evaluating the relative importance of different gases to affecting global ozone, especially stratospheric ozone. In evaluating the ODPs of iodotrifluoromethane (CF₃I) and methyl iodide (CH₃I) using the recently updated understanding of atmospheric iodine chemistry, only extremely minor ozone loss would be expected to occur in the stratosphere from a reasonable level of potential use and emissions of the very short -lived (lifetime of ~6 days) CF₃I, with slightly larger destruction of stratospheric ozone from the slightly longer-lived (lifetime of ~12 days) CH­₃I. We find larger ODPs than prior studies because of the inclusion of additional chemistry and from new analyses for where those emissions would occur. In addition, most of the ozone destruction would likely occur in the lower troposphere over continental surfaces, reducing anthropogenicozone pollution. The traditional ODP concept uses total column ozone change, which is useful for evaluating the effects on ultraviolet radiation reaching the Earth’s surface, but this does not account for the large increase from past human activities on tropospheric ozone. As a result, the traditional ODP approach does not provide entirely an accurate representation of the effects of very short-lived substances (VSLSs) on stratosphere ozone and the resulting ODPs may overly emphasize changes in tropospheric ozone. An examination of the literature finds similar very small loss rates in the stratosphere for other VSLSs. A new metric, Stratospheric ODP (or SODP), is defined that only accounts for stratospheric ozone loss, providing a useful additional tool for policy considerations of very short-lived substances on stratospheric ozone.