Still Open
Seven things are unfinished. Each is written so you can act on it: a number to check, a rule to follow, or a question with no good source yet. Two of them are gases nobody regulates at all.
Not Covered by Any Rules
These two are not loopholes in the treaty. They were never in it.
Nitrous oxide is now the biggest ozone-damaging gas we emit, and the Montreal Protocol does not cover it at all. No other treaty does either. It mostly comes from farm fertiliser. [14]
Short-lived chlorine gases, mainly dichloromethane, are uncontrolled and rising. Their chlorine in the stratosphere went from 69 ppt in 2000 to 111 ppt in 2017. [15] [16]
Gaps in the Rules We Have
These are inside the treaty and could be closed by the countries that wrote it.
Feedstock and by-product exemptions are still uncontrolled, and are thought to cost about seven years of recovery. Watch whether any meeting of the parties moves to close them. [17]
Kigali rules and HFC smuggling. Industry put illegal refrigerants at up to 30% of the EU market in 2022. No similar figure exists for most other regions. [18]
Questions With No Good Answer Yet
These need someone to find or produce a source.
Monitoring does not cover the world evenly. CFC-11 was caught because eastern Asia has many stations. Large areas have far fewer. This needs a sourced coverage map, which does not exist here yet. [10] [11]
Rocket launches and satellites burning up on re-entry put alumina and chlorine straight into the ozone layer. Human-made alumina could reach ten times natural levels by 2040. The size of the effect is not settled. [19] [22]
The 2026 WMO and UNEP report is being written and is not out as of August 2026. When it lands, every recovery date on this slate needs checking against it, starting with the 2040 and 2066 figures on the home page. [23]
Two smaller gaps in the sources themselves. Source [7] needs a primary reference for the Canadian, Swedish and Norwegian spray can bans. Source [9] needs a dated count of how many countries have ratified Kigali. 160 of 198 had done so by October 2024, and more than 170 by early 2026, but this slate does not yet cite a current figure. Both are good first contributions.
Notice that this page has more entries than the what worked page. The ozone layer is the clearest environmental success we have, and it still has seven open items and two completely unregulated gases. That is what a solved problem actually looks like up close.