UV photons split CFC molecules, releasing chlorine (Cl) radicals in the stratosphere. Each Cl radical then runs a catalytic chain: it strips an oxygen from ozone (making chlorine monoxide, ClO), and ClO reacts with a free oxygen atom to regenerate Cl — meaning a single chlorine atom can destroy tens of thousands of ozone molecules before it is removed from the cycle.
Cl + O3 → ClO + O2
ClO + O → Cl + O2 (net: O3 + O → 2 O2, Cl unconsumed)
Rate = k(T) · [Cl] · [O3]
- CFC emission rate — how many CFC molecules are released, the ultimate source of chlorine radicals.
- UV intensity — drives CFC photolysis; more UV photons split more CFCs into Cl.
- Temperature — colder stratospheric temperatures (as in the Antarctic polar vortex) favor polar stratospheric clouds that accelerate the catalytic cycle.
- Reaction speed — a visualization time-scale control speeding up or slowing the catalytic cycle animation.
This exact mechanism caused the Antarctic ozone hole, prompting the 1987 Montreal Protocol that phased out CFCs worldwide.