Event

The Montreal Protocol

A class of materials identified as harmful and removed from world production by treaty — and the only environmental agreement that has plainly worked.

Agreed in 1987 and in force from 1989, the Montreal Protocol phased out the chlorofluorocarbons and related compounds that were depleting stratospheric ozone. It is the only treaty ever ratified by every member state of the United Nations, and the ozone layer is measurably recovering.

As a materials story it is unusually clean. CFCs were a triumph of materials chemistry — non-toxic, non-flammable, stable, and developed in the 1930s specifically to replace refrigerants that killed people when they leaked. Their stability is exactly what made them harmful: unreactive enough to reach the stratosphere intact, where ultraviolet light breaks them and the released chlorine catalyses ozone destruction.

History

Molina and Rowland published the mechanism in 1974 and were widely disbelieved. The Antarctic ozone hole was reported by Farman, Gardiner and Shanklin in 1985 — an observation so far outside the expected range that satellite data had been discarding comparable readings as instrument error.

The substitution ran in stages, and each stage created the next problem. HCFCs deplete less ozone and were an interim answer; HFCs deplete none and are potent greenhouse gases, which the 2016 Kigali Amendment addresses; hydrofluoroolefins and hydrocarbons are the current direction.

Economic significance

It is the standing counter-example to the claim that material substitution at global scale is impossible. An entire class of industrial chemicals was identified, regulated and replaced within about a decade, across refrigeration, air conditioning, foam blowing, aerosols and solvent cleaning.

It is also the standing warning about substitution done in stages. Three decades of rigid insulation foam in existing buildings still contains the earlier blowing agents and releases them at demolition, so the emissions of a solved problem are still arriving.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

involved

Polyurethane — material · rigid foam blowing agents moved from CFCs to HCFCs to HFCs to hydrocarbons, and each stage solved one problem and created the next
Chlorine — element · the element the mechanism turns on: released in the stratosphere, it catalyses ozone destruction and is not consumed doing it
Fluorine — element · in the replacements as much as in the originals, which is why the argument moved from ozone to global warming potential rather than ending

Sources

Wikidata
Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
Material World
Our own writing

Where it comes from, and what it becomes

Follow The Montreal Protocol back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

The Montreal Protocol → involved (the element the mechanism turns on: released in the stratosphere, it catalyses ozone destruction and is not consumed doing it) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation → takes as input (the feedstock for solar salt and, in the salars, for the far stronger brines that lithium comes from) → Seawater
The Montreal Protocol → involved (rigid foam blowing agents moved from CFCs to HCFCs to HFCs to hydrocarbons, and each stage solved one problem and created the next) → Polyurethane → is produced by (a diisocyanate and a polyol reacting as they are mixed, so the polymer and the finished part are made in the same moment) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
The Montreal Protocol → involved (in the replacements as much as in the originals, which is why the argument moved from ozone to global warming potential rather than ending) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
The Montreal Protocol → involved (the element the mechanism turns on: released in the stratosphere, it catalyses ozone destruction and is not consumed doing it) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
The Montreal Protocol → involved (in the replacements as much as in the originals, which is why the argument moved from ozone to global warming potential rather than ending) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite
The Montreal Protocol → involved (rigid foam blowing agents moved from CFCs to HCFCs to HFCs to hydrocarbons, and each stage solved one problem and created the next) → Polyurethane → is produced by (a diisocyanate and a polyol reacting as they are mixed, so the polymer and the finished part are made in the same moment) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite

These are the most distinct paths back. The Montreal Protocol can be traced through others besides.