4. belongs to a class of similar problems which are all solved in the similar way The pollutants were easily identified and could be banned by law. Governments ban identifiable pollutants from the marketplace all the time. 5. has solutions which can be easily tried and abandoned The Vienna conference in 1985 was a small group of countries which agreed to experiment with a ban as the solution. After it became evident this was workable, a formal Protocol was signed. When it became clear this worked, the schedule was speeded up. Success bred more success. The consumer boycott was voluntary, so there were no political consequences if it failed. When people saw it working they got on the bandwagon. 6. comes with a limited set of alternative solutions. Everybody agreed there was no practical alternative to a global ban. And the ban was practical: industry had substitutes for the banned spray cans that consumers could buy.