= Solution
Prefer a replacement that releases little reactive <chlorine> or <bromine> into the <stratosphere>: ideally omit those elements, or give the parent gas a short <troposphere> removal time compared with transport to the <stratosphere>. A carbon–hydrogen bond can permit rapid attack by the <hydroxyl radical>; other readily oxidized functionality can also shorten the atmospheric residence time. The degradation products must themselves avoid transporting long-lived reactive halogen to altitude. Merely retaining fewer <chlorine> atoms is less effective than preventing their delivery altogether.
Both <chlorine> and <bromine> participate in catalytic <ozone> destruction. <Bromine> is much more effective per delivered atom, by a factor of roughly 60 in the usual lower-stratospheric comparison; the precise effectiveness depends on chemical partitioning and location. <Fluorine> is largely trapped in very stable <hydrogen fluoride> and does not sustain an analogous ozone-destroying cycle. Thus \b[short-lived gases without <chlorine> or <bromine> have the smallest direct <ozone-depletion potential>]. Fluorination alone does not ensure a small climate impact.<Scientific Assessment of Ozone Depletion 2022 executive summary>[Tropospheric <bromine> and <fluorine> assessments: per-atom effectiveness and the absence of direct fluorine-driven <ozone> depletion]{ref}
Back to article page
